Diagnostic methods in PAC 11

DIAGNOSTIC METHODS IN PAC

AXIAL CHAMBER DEPTH MEASUREMENT (ACD)

As mentioned in the introduction and appears in the chapters concerning the Main Classification as well as the Main Groups and subclassification of PAC, almost as much attention will be paid to axial chamber depth measurement as to gonioscopy.

In the most recent guidance manuals on PAC treatment28,29 this stress on the routine clinical application of ACD measurement is not to be found, even though it now is well recognised that a small ACD is a significant predictor of PAS42.

In this book there are, however, several explanations as to why the use of ACD measurement is so strongly recommended. The examination may be used as a reasonably reliable and rapid supplement to the somewhat more complicated gonioscopy, especially with regard to early PAC diagnosis and the indication for preventive treatment. In such a situation, gonioscopy is often difficult, whereas ACD measurement is easy to perform. Apart from that, ACD assessment is particularly valuable with respect to proper main classification of PAC and thus for the specific treatment, which, as mentioned in the introduction, represents the second purpose of this book.

Finally, the increasing use of ultrasonic examinations inclinics means that more and more ophthalmologists are able to perform ultrasonic ACD determination instead of optical pachymetry; though the latter is our primary recommendation in this book. The new laser scanning pachymetry further seems to be one of the preferred instruments in the future to measure ACD37 .

Both ACD measurement and LCD determination are linked to relative pupil block (ref: Group I: PAC with pupil block, p. 55). These two measurements show a positive correlation without significant difference between the two eyes, both among healthy people and patients with PAC. According to Tørnquist3, the average ACD value with unilateral acute PAC is 1.61 mm in the acute eye and 1.77 mm in the healthy eye, whereas both values vary significantly from ACD in normal eyes (≥ 2.5 mm).

12 Diagnostic methods in PAC

On the other hand, in the case of unilateral secondary forms of angle-closure (SAC), there is a marked difference between the ACD measurements and the LCD assessments in the two eyes.

The advantage of the ACD method as opposed to the LCD assessment is that it provides an accurate quantitative estimate of the chamber depth and that this measurement does not change even after YAG-laser iridotomy, which is not the case with LCD3. Especially following preventive laser treatment, it is desirable to have case notes which include an objective and reasonably reliable indication criterion for the YAG iridotomy.

As previously stated, ACD determination is of great importance in the main classification of PAC with respect to differential diagnosis between pupil block conditioned PAC and the plateau iris form. This is illustrated in the section concerning main classification of PAC and in the flow chart for specific treatment of primary angle-closure (fig. 19).

As a general rule, pupil block conditioned PAC only occurs with values below 2.5 mm ACD (internal measurement) and predominantly with values ≤ 2.0 mm. Furthermore, the prevalence rate rises significantly with lower ACD values – up to 85% below 1.5 mm31. This clear, inverse relationship to the prevalence of PAC with pupil block and thereby the degree of angle narrowness means that ACD measurement is the only method that enables a quantitative, indirect estimation of the size of the chamber angle. This makes the measurement a rational supplement to the subjective gonioscopic assessment of the narrowness of the chamber angle with the pupil block form of PAC (ref: Main classification and classification methods). The relationship between the axial chamber depth and the prevalence of angle-closure does not, however, exist with purely plateau iris PAC where the angle is narrow in spite of normal ACD (≥ 2.5 mm)12. This is used in the differential diagnosis between pupil block and plateau iris PAC.

As stated, the differential diagnosis between primary and secondary angle-closure forms (PAC and SAC) is further assisted by combined use of both LCD and ACD measurements. In the case of post-inflammatory absolute pupil block with iris bombé, there is a significant difference between the two eyes of the patient as regards LCD, whereas the ACD measurements are equal, i.e. there is a lack of correlation between LCD and ACD in the eye in question. In the case of ciliary block (formerly known as malignant

Diagnostic methods in PAC 13

glaucoma), choriodal detachment and “uveal effusion” (cyclitis annularis pseudotumerosa), forward sub-luxated lens with increased relative pupil block as well as with SAC following a central vein thrombosis, both LCD and ACD are reduced in the eye in question, i.e. there is correlation between LCD and ACD, however with a difference between the two eyes for both parameters.

With this in mind, the significance of a full examination, including ACD of the “healthy” eye with regard to a difference between the eyes will be stressed many times in the following pages.

Methodology

Optical pachymetry

The ACD measurement itself is carried out using a special attachment on a Haag-Streit slit lamp (fig. 3). The chamber depth measuring device (pachymeter II) is mounted on two steel pins on top of the microscope. The right eyepiece is exchanged for a special measuring eyepiece, and the refraction is adjusted to +6. The microscope arm is locked in place on the microscope pillar, leaving the right eyepiece at a 40 degree angle from the sagital light beam. The slit lamp light must be placed directly in front of the eye which is to be examined, and the patient must fixate the light slit (i.e. a perpendicular light beam onto the cornea) and maintain gaze at a horizontal level. A vertical aperture on an anterior flange on the ACD measurer keeps the angle at 40 degrees and furthermore ensures that the examiner uses his right eye only. A narrow light beam passing through the anterior chamber can now be estimated monocularly (right eye). The section of light must be in the vertical-axial plane (i.e. edge of the pupil at 6 and 12 o’clock), and the section must be divided horizontally at 3 and 9 o’clock position. By moving the measuring arch to the left, the image in the single ocular is seen to divide; this is gradually increased until the optical section of the anterior lens capsule is aligned with the optical section of the corneal endothelium in the lower half (fig. 4). The best way to achieve this position is to use the next lowest magnification on the Haag-Streit slit lamp.

This procedure directly determines the “internal ACD value” (excluding corneal thickness). We prefer this efficient and simple

14 Diagnostic methods in PAC

methodology instead of using the “external ACD value” (including cornea thickness), measuring from the anterior surface of the lens to the corneal surface. When using this last method, it is subsequently necessary to measure the corneal thickness with a similar measuring device (pachymeter I), and subtract this value from the “external ACD value” in order to calculate the accurate internal value. Recently it was documented that the directly measured “internal ACD value” using the pachymeter II alone was about 6% too high compared to the real ACD value measured by the more complicated “external” ACD method using pachymeter I + II46. As an example: An “internal” value of

Fig. 3. Axial chamber depth (ACD) measurement by means of optical pachymetry. Photo: The Glaucoma Clinic, Copenhagen University Hospital.

2.0 mm should then be reduced with 0.12 mm and an “internal” value of 2.5 mm with 0.15 mm.

Ultrasonic or laser based chamber depth measurement

ACD measurement may also be carried out using the ultrasonic A- scanning equipment normally used for cataract surgery biometry. It should, however, be stressed that an ultrasonic measurement determines the external value (including cornea). The “internal value” may then be found by subtracting the average cornea thickness of 0.5 mm, remembering that only one decimal is used with ACD measurement by the optical method. Therefore, it is impor-

Diagnostic methods in PAC 15

tant to specify whether the given measurement either includes or excludes the corneal thickness.

When using ultrasonic determination, the ultrasonic head must be in contact with cornea, which may lead to corneal indentation with the risk of underestimating the chamber depth. This may be avoided by using the new laser-based non-contact biometrical technique, precisely as with optical pachymetry. Thus, these two methods are the most precise. It should, however, be noted that the laser-based biometry also measures the “external

Fig. 4. Methodology with optical pachymetry

ACD”, and that the corneal thickness must be subtracted, just as is the case with the ultrasonic method.

Laser scanning pachymetry (Visante OCT system)

This very new, versatile system provides high-resolution, noncontact optical coherence tomography, customized for the anterior chamber37. As the Visante OCT, apart from performing pachymetry, has also been designed to image and evaluate anterior chamber angles, this new unit might possess the necessary qualities for being one of the most essential tools in the diagnosis and clas-

16 Diagnostic methods in PAC

sification of PAC44. It is a disadvantage that the ciliary body is not visualized.

Sources of error

The average value of the normal axial chamber depth changes throughout life due to the growth of the lens. The axial chamber depth varies from approx. 3.2 mm (internal measurement) at puberty to 3 mm at the age of 40 and finally 2.7 mm at the age of 70. This pronounced age difference means that the importance of the ACD parameter in respect of a possible pupil-block conditioned risk of PAC is not as reliable among the 40-50-years old as it is among the elderly population when using the mentioned limit values. Therefore, it is important to stress that the required pathoanatomical PAC classification – as the condition is found among the younger population – is to a great extent dependent on an adequate gonioscopy.

Apart from this, the biological ACD variation is marked and reaches ± 0.35 mm (corresponding to ± SD), increasing at a high age. On average, the values among women are 0.15 mm lower than those of men. If the mentioned limit values (2.0 and 2.5 mm) are found when examining a patient, the importance of these values as classification criteria should be subject to reservation, and it must be stressed that the final classification, especially in situations such as these, must, first and foremost, be determined by gonioscopy.

Finally, ethnic variation is significant with low values among Inuits and East Asian people. In the case of cataract, the ACD value will in some cases decrease and in others increase.

GONIOSCOPY

Introduction

Gonioscopy should be carried out on a routine basis at the slightest suspicion of a glaucoma diagnosis. This examination is vital for the proper diagnosis and classification of glaucoma and hence for the specific treatment of the condition.

Unfortunately, gonioscopy is riddled with problems when compared to other forms of glaucoma examinations as there are numerous

Diagnostic methods in PAC 17

possibilities for methodology errors connected to the gonioscopy procedure itself. Furthermore, interpretation of the gonioscopic view is difficult owing to the extensive biological variation of the normal anatomy of the chamber angle. Gonioscopy is very much an acquired art, and optimal utilisation of the procedure requires considerable personal experience. However, awareness of the sources of error and of the proper interpretation of the findings will result in a shorter learning phase. With this in mind, the following section therefore contains a thorough review of gonioscopy, including guidelines based on personal clinical experience over a considerable period of time. The aim is not only to provide an adequate, objective foundation for specific PAC treatment (ref: Introduction), but also to demonstrate a simple and purely practical standard procedure.

The gonioscopy methodology described in this book (fig. 11) has, through decades of use by the authors, been proven both effective and reliable.

Gonioscopy requires the use of goniolenses due to the fact that it is not possible to visualise the chamber angle directly through cornea at an angle as the light beam radiating from the chamber angle will be totally internally reflected. Furthermore, observation of Schlemm’s canal via the slit lamp is obstructed by the superficial scleral lip which covers the chamber angle (ref: Limbal chamber depth measurement (LCD), Sources of error).

Goniolenses and their uses

Gonioscopy requires the use of two different types of lenses for indirect gonioscopy of the individual eye; first a lens for a quick routine check – as well as an indentation gonioscopy (Posner’s)

– then a more stable lens (Goldmann’s) for a detailed assessment without any real possibilities for indentation (fig. 5).

It is particularly important to observe this requirement if the examiner is inexperienced. Also, optimum benefit from gonioscopy is dependent on good patient co-operation, which is only obtained through a thorough explanation of the procedure to the patient and a gentle technique without undue movements of the gonioscopy lens.

18 Diagnostic methods in PAC

Posner’s 4-mirror indentation lens

There are several modifications of the Zeiss 4-mirror lens, however we recommend the Posner model (Zeiss lens with an angulated handle), which is the one used by the authors.

The corneal contact area of the lens has a diameter of only 8 mm (fig. 5a). This is considerably less than the normal adult cornea (average diameter 11.5 mm) and provides a good basis for corneal indentation.

a

b

Fig. 5. Contact lenses for gonioscopy. a: The Goldmann lens on the left, the Posner lens on the right. b: Technique for gentle application of the Posner lens. Photo: P. Kock Jensen and Lars Solander, the Glaucoma Clinic, Copenhagen University Hospital

Diagnostic methods in PAC 19

At the same time, the smaller lens size makes it is easier to place the lens on the cornea. The gentlest way of placing the lens on the cornea is, following local anaesthesia, to catch the upper eyelid while the patient looks up with both eyes open and then place the lens centrally on the cornea while the patient looks straight ahead with both eyes open. The lower eyelid is fixed with the fingers holding the lens itself (fig. 5b). When examining the right eye of the patient, the Posner lens is held in the left hand, and the right hand is used for the left eye. The examiner should observe the eye through the slit lamp while placing the Posner lens on the eye.

The contact area of the lens has a radius of curvature of 7.85 mm, i.e. the same radius of curvature as the surface of the cornea (average 7.8 mm). This has the advantage that a contact medium such as methylcellulose is unnecessary, as the tear film is quite adequate. In this way, it is easy to change between the two eyes for the necessary comparison. If the lens is not held completely parallel with the surface of cornea, air bubbles will enter between the lens and cornea in part of the contact area. The easiest way of eliminating any air is by rotating the round handle of the lens carefully between the thumb and index finger until the contact area is freed from air. Use of methylcellulose cannot be recommended as a contact medium will only make the examination more unstable.

Posner gonioscopy should therefore be performed before Goldmann gonioscopy using methylcellulose!

The lens may be held in two ways (fig. 6a-b). When initially assessing the lower and upper chamber angle area (see below), the lens handle is held directly (fig. 6a) since this will create an upper and lower horizontally positioned mirror. If a subsequent examination of nasal and temporal angle areas is desired, the examiner should hold the lens with his fingers indirectly around the horizontally positioned handle (fig. 6b), thus placing all the mirrors at an angle. By positioning the lens in this way, it is possible to have an overview of almost the entire angle without having to rotate the slit lamp light (see below). The rest of the angle may be seen by turning the lens a mere 11 degrees.

Diagnostic methods in PAC 21

impressed only slightly until no air remains (7a). A certain amount of experience is required in order to achieve a stable position for the examination.

a

b

Fig. 7. Posner lens application. a: Without indentation. b: With indentation.

In order to ease the use of the technique, we can recommend the following (fig. 8). Adjust the chin rest on the slit lamp so that you may rest your elbow on the slit lamp table. If your arm is too short, you may use an “elbow block”. Hold the handle of the lens close to the edge of the lens so that you may rest your hand on the chin of the patient. This will give a better control of the lens as the lens moves freely on the cornea. Make sure that the lens is placed in an axial position by then looking directly at the patient instead of through the slit lamp and check that the patient has both eyes open and is looking straight ahead. This is the primary examination position. It is important to note that the patient will often close the other eye spontaneously, resulting in an unstable examination situation.

22 Diagnostic methods in PAC

Fig. 8. Position of hand and arm when working with Posner lens gonioscopy (the elbow is placed on the slit lamp table!). Photo: Lars Solander, the Glaucoma Clinic, Copenhagen University Hospital.

2.Examination in the primary position with indentation with regard to peripheral anterior synechiae (PAS-closed angle)

The next step is the axial indentation in the primary position (fig. 7b) with simultaneous observation of the chamber angle anatomy, especially with regard to any peripheral anterior synechiae (PAS) as well as having iris contour and mobility in mind. If the space is very narrow the visualisation of the angle anatomy does, however, require the patient to look towards the angular mirror used in order to observe the peripheral side of the iris convexity instead of maintaining the primary position. But this procedure is difficult due to the instability of the lens. Indentation on a very soft eye may easily lead to indistinct folds of MD when the indentation is excessive, which is yet another reason why the Posner lens should be used before the Goldmann lens. When tension rises above 30 mmHg, indentation becomes increasingly difficult, mainly due to

Diagnostic methods in PAC 23

pain reaction. Adequate indentation gonioscopy is therefore very difficult to perform with untreated acute PAC at high pressures. However, the possibility of carrying out indentation is improved if the patient is well informed beforehand.

The lens is therefore ideal for routine gonioscopy with the aim of initially assessing the situation in both eyes. It is essential not only in connection with indentation gonioscopy with respect to PAS (fig. 7b) but also in the assessment of iris contour and mobility (ref: Normal anatomy of the chamber angle). The lens is however, especially in the hands of the inexperienced, too unstable for evaluation of small chamber details under high power magnification (e.g. occludable angle? due to PAC). It is therefore recommended to combine its use with the Goldmann gonioscopy lens, especially in the learning phase.

It is important to note that apart from the mentioned advantages, the Posner lens is absolutely essential for carrying out adequate examination of very narrow angles. In such situations, it is only possible to visualise peripheral synechiae by using the Posner lens. This fact has aroused increasing international support during the last decade, and it must be strongly advised that one should use the lens on a routine basis

Goldmann’s gonioscopy lens

There are two types of Goldmann lenses: The 1-mirror and the more efficient 2-mirror model. The contact surface on the lens has a diameter of 15 mm with a larger curvature than that of the cornea (fig. 5a). This means that the lens in the primary position rests mainly on the sclera and requires the use of a contact medium in order to avoid air seeping into the space between the lens and the cornea. Therefore, the lens is not suitable for corneal indentation, but it is more stable once it has been placed on the eye, which means that it is not necessary to use an elbow rest and the left hand for examination of the patient’s right eye as is the case with the Posner lens. A Goldmann lens is easier to use with higher magnification when observation of small details is required and where corneal indentation is not needed (e.g. nar- row-occludable angle?).

24 Diagnostic methods in PAC

Because the Goldmann lens is larger than the Posner lens, it is more difficult to place it on the eye and more irritating for the patient than the smaller Posner lens, especially if the patient has a tendency to squeeze the eyelids together. The easiest way to place the lens on the eye is to observe the eye directly and not through the slit lamp.

Examination with the Goldmann lens is carried out in two stages:

1.Examination in the primary position for open or narrow angle.

2.Examination while the patient looks into the angular mirror with regard to an occludable or appositional-closed angle.

When small peripheral anterior synechiae (PAS) are diagnosed following indentation gonioscopy with the Posner lens, it is possible to verify their presence when the patient looks directly into the angular Goldmann mirror.

However, because of its size and the use of a contact medium, the Goldmann lens will irritate the patient more than the Posner lens, and if only the Goldmann lens is used, the examiner will most likely be tempted only to examine one eye, also in order to avoid bilateral blurring of vision, which follows the use of methylcellulose. For adequate examination of both nasal and temporal angle sectors it is furthermore necessary to rotate the slit lamp light away from the usual vertical position to a more horizontal level when using the Goldmann lens. As mentioned above, this is not necessary with the Posner lens.

In this connection, it should be stressed that gonioscopy should always be carried out bilaterally in order to avoid misinterpretation due to the considerable inter-individual variation of the normal anatomy. The reason why this important possibility exists is to be found in the fact that the normal chamber angle anatomy is almost always identical in the two eyes. In case of PAC suspicion the unaffected or less pathologic eye should also be used as a control eye, because the PAC predisposition is bilateral (ref: ACD measurement). The initial examination with the Posner lens makes it possible to repeat “back and forth” assessments between the two eyes without excessive irritation and usually means that

Diagnostic methods in PAC 25

a subsequent Goldmann gonioscopy examination need only be performed on the one eye. This combined use of the two lenses is recommended, especially in the learning phase.

Goldmann’s 3-mirror lens is not recommended for gonioscopy for several reasons. Firstly, because the contact surface of the lens has a diameter of 18 mm, which makes it more difficult for the patient to look into the angular mirror. Secondly, the degree of slope on the 3-mirror lens gonioscopy mirror is slightly different from that of the Goldmann lens, which means that the occludability of the angle will be assessed differently. However, we recommend use of Goldmann’s 3-mirror lens for inducing blood flow into Schlemm’s canal with the intent of identifying the canal, because the large lens diameter makes it possible to compress the aqueous veins (ref: Normal anatomy of the chamber angle, The uveal meshwork (iris processes)).

Gonioscopy methods with PAC

The necessary basis for adequate gonioscopy methodology requires not only a clear and practically applicable chamber angle classification based on carefully defined definitions but also the application of standardised examination techniques.

Chamber angle: Classification and definitions

1. Open or primary narrow angle

The size of the chamber angle is the most important and often most difficult gonioscopy assessment that has to be made. The reason for this is partly the previously mentioned considerable inter-in- dividual normal variation of the angle structures and partly the normal intra-individual variation in the degree of opening within the different angle sectors.

Under normal circumstances the angle is more open in the lower sector than in the upper sector. This is specially the case at 6 o’clock (the physiological “angle coloboma”). In eyes with narrow angles the degree of narrowness is also more pronounced in the upper sector than in the lower which again is narrower than the temporal and nasal sectors38. Furthermore, the iris root usually has an undulating configuration, and the final conclusion as to

26 Diagnostic methods in PAC

the degree of narrowness has to be based on a judgement of the upper and lower halves of the angle separately.

The problem is further complicated by the fact that different angle classification methods are recommended. Scheie4 uses the identification of the individual angle structures as a basis for his assessment, and if the pigmented trabecular meshwork (Schlemm’s canal) is not visible, the angle is described as narrow. Schaffer5, on the other hand, uses the geometric angle between the trabecular meshwork and the anterior surface of the iris for classification, and an angle of 10 degrees is described as a narrow angle. Spaeth’s methodology6 is a somewhat complicated development of Schaffer’s methodology.

Since the chamber angle may not be directly measured via the slit lamp, the geometric angle specification will hint an unrealistic objectivity. Therefore, throughout the last decades, we have used a classification system based on a simplification of Scheie’s identification technique concerning an open or narrow angle.

However, the uncertainty of this principle is that it is necessary to carefully observe the standardised examination techniques in order to avoid misinterpretations. For instance, if one is unaware that the contact lens has been placed at an angle and not on the optical axis in the centre of cornea, the pigmented trabecular meshwork may be visualised, and the angle may then incorrectly be perceived as being open. Furthermore, the above situation will often result in lens indentation and thereby affect the degree of opening.

In order to avoid these problems, a standardised examination technique is aimed at as described in the previous section: Examination in the primary position for open or narrow angle (Posner and Goldmann lens).

Based on the above principles: An open angle is defined as an angle in which all of the pigmented trabecular meshwork or Schlemm’s canal (in case of unpigmented trabecular meshwork) can be identified over the entire circumference when carrying out the examination in the primary position without indentation. (see fig. 9).

A primary narrow angle may be defined as an angle in which the pigmented trabecular meshwork or Schlemm’s canal, using the same examination techniques, by and large

Diagnostic methods in PAC 27

Fig. 9. Varying degrees of open/narrow angle: The two drawings on the left: Pigmented trabecular meshwork is visible, implying open angle. The two drawings on the right: Pigmented trabecular meshwork is not visible, implying narrow angle. The drawing in the middle: Pigmented trabecular meshwork is partly visible, implying, for instance suspect PAC, as appears in the lower angle sector. a: Sampaolesis’ line. b: Pigmented trabecular meshwork. c: Scleral spur. d: Ciliary band. e: Iris knee.

cannot be identified either in the upper half or in the lower half of the chamber angle (see fig. 9). The use of the Posner lens for diagnosing narrow angle demands a certain amount of experience with the lens, which is why beginners are advised to verify the diagnosis by subsequently performing gonioscopy with a Goldmann lens.

This, however, does not conclude the examination. The primary narrow angle is now either occludable or closed, and the closed angle is either closed due to iris/cornea apposition (appositionalclosed”) or due to synechiae (“PAS-closed”) as shown in fig. 10.

Therefore, it should be noted that the term narrow angle is not in itself satisfactory, but always demands a further adjective for adequate objective description of the existing PAC possibilities.

2. Narrow-occludable angle or narrow appositional-closed angle

These classification terms are used when the initial Posner gonioscopy reveals a narrow angle without PAS.

Using the Posner lens, this is only a diagnosis of exclusion since it is only really possible to carry out this classification for certain with a subsequent Goldmann gonioscopy without any indentation. When the patient, with this more stable examination, looks into the angular mirror (fig. 11) and the pigmented trabecular meshwork is

28 Diagnostic methods in PAC

Fig. 10. Terminology with gonioscopy examination.

visible, a narrow-occludable angle is present, whereas a meshwork that is not visible implies an appositional-closed angle.

3. Narrow synechiae-closed angle

As mentioned previously, the diagnosis of PAS is best undertaken using indentation gonioscopy with the Posner lens. The identification of trabecular meshwork is the requirement for a reliable PAS diagnosis since PAS formation is often adherent to the meshwork. The identification requires an evaluation of the amount of pigment in the meshwork of the individual patient, which is best gained in the lower part of the angle at around 6 o’clock (“angle coloboma”). This particular area is hardly ever closed with synechiae (ref: The normal anatomy of the chamber angle, the corneoscleral trabecular meshwork). Following this, it is possible to verify synechiae contact to trabecular meshwork. Moreover, in order to verify PAS, careful observation of the transition zones between PAS free angle areas and synechiae areas is to be recommended since trabecular meshwork contact is best observed here.

4. Abnormal iris contour and iris mobility

When diagnosing a narrow angle, it is important to be aware of the fact that the gonioscopy examination is not complete until the iris contour and mobility have been assessed since this assessment is necessary for the differential diagnosis between pupil block and plateau conditioned PAC36 (ref: Chamber angle – normal anatomy). The examination can only be carried out by using the Posner lens.

Diagnostic methods in PAC 29

It should be stressed that the above mentioned gonioscopic classification (1-2-3-4) is of vital importance for the specific PAC treatment (ref: Introduction).

Standardised PAC gonioscopy methodology

As stated in the previous section concerning chamber angle classification, gonioscopy requires standardised examination techniques in order to avoid misinterpretations.

Apart from the above-mentioned guidelines, the following should be noted:

–The examination should always be carried out under dimmed illumination and using as small a slit lamp light as possible, i.e. the aperture of light should be narrow and set low.

–If a strong light is shone through the pupil the miosis obtained may open the angle to such a degree that one might misinterpret the angle as being open.

–For the same reason and especially if threatening (imminent) PAC is suspected, pilocarpine should not be used for at least six hours before gonioscopy!

–Always start the gonioscopy procedure by examining the lower sector of the angle around 6 o’clock (the physiological “angle coloboma”). The first task is always to identify the pigmented trabecular meshwork (Schlemm’s canal) and, if possible, also the scleral spur and ciliary band. Since the angle is always most open around 6 o’clock, it is nearly almost always possible to see the pigmented trabecular meshwork in the “angle coloboma”, even if synechiae have spread to the remainder of the angle. When the degree of trabecular meshwork pigmentation has been estimated as well as the appearance of other identifiable angle structures at 6 o’clock there will be a basis for identifying the angle structures in the rest of the circumference. We therefore recommend: Start with the lower sector of the angle and work upwards to the point at which the synechiae start. The examination of the sides should be left to last since this is where the examination is most difficult.

–Always start by comparing the angle anatomy in the two eyes, i.e. start with the Posner 4-mirror lens as this lens may be easily moved back and forth between the two eyes.

30 Diagnostic methods in PAC

Start the examination with the Posner lens 4-mirror lens

1. Examination in the primary position without active indentation

The primary position is the position in which the patient looks straight ahead (make sure that the patient keeps the other eye open!!) and the lens is placed centrally on cornea in an axial position with as little pressure as possible; enough, however, to avoid air entering between the lens and cornea. With respect to “user tips”, ref: Goniolenses and their uses.

In order to ensure that the examination is carried out in the primary position, it is necessary from time to time to look directly at the patient instead of through the slit lamp.

Drawing 1A, fig. 11 shows that pigmented trabecular meshwork may be identified by examining the patient in the primary position, both in the upper and lower sectors of the angle (objectively), and according to the definition of an open chamber angle given earlier (ref: Chamber angle: Classification and definitions) the final conclusion is that here we have an open angle.

Drawing 1B, fig. 11 shows, according to previous definition, that it is a narrow angle as the pigmented trabecular meshwork cannot be identified on examination in the primary position due to a prominent convex iris contour. It will be necessary to continue the gonioscopy in this situation.

2. Drawing 2, fig. 11 also shows an examination in the primary position with the Posner lens, only now with indentation. From the drawing it appears that the pigmented trabecular meshwork is not visible in the upper sector due to PAS, but now visible in the lower sector and without PAS, i.e. the angle is PAS-closed in the upper sector and presumably occludable or appositional closed in the lower

However, as mentioned earlier, the Posner lens is often too unstable for determining whether the angle is occludable or appositional closed as such a determination will require stable inspection under high magnification. Therefore, it is necessary to use the Goldmann lens for a subsequent examination of the lower sector, especially if the examiner is inexperienced with using the Posner lens.

If the acute angle-closure has not been treated and the IOP is high (> 30 mmHg), it is difficult to adequately indent with the Posner

32 Diagnostic methods in PAC

lens, not least due to the patient’s reaction to the pain. Furthermore, the cornea is usually oedamatous, which means that, at best, the examiner is able to make the diagnosis of closed angle due to PAC, but is not able to determine if the angle is appositional closed or PAS-closed. In this situation, it is therefore necessary to instigate acute medical treatment in order to lower the pressure

(ref: Treatment of acute PAC) and to apply local treatment with 50% glucose eye drops in order to clear the cornea before attempting a further Posner indentation.

In the event of suspicion of appositional angle closure with a patient who does not react to the pain, a good tip for lowering the pressure is to perform an intensified, but gentle cornea indentation with the detached plastic cone from the Goldmann applanation (ref: Treatment of acute PAC).

Continuation with Goldmann’s gonioscopy lens

3.As shown in drawing 3, fig. 11, the examination of the lower sector is initially performed using the Goldmann lens in the primary position with a high slit lamp enlargement, and if the trabecular meshwork is not visible, it can be concluded that there is a narrow angle in the lower sector.

4.The next step is the examination with the Goldmann lens with the patient looking directly into the angular mirror of the lens as shown in drawing 4, fig. 11. If Pigmented trabecular meshwork is visible when using this procedure, the examiner may conclude that the angle is occludable in the lower sector. We recommend this procedure rather than having the examiner move the lens lower down on the eye and thereby risking an indentation with the lower edge of the lens, which may induce pain. This will make it difficult to obtain an optimal result from the gonioscopy.

Gonioscopy findings

Normal anatomy of the chamber angle

The normal anatomy of the chamber angle shows a considerable inter-individual variation, but little intraindividual difference

Diagnostic methods in PAC 33

between the two eyes. This is why one eye may normally be used as a control eye with respect to the pathoanatomy in the other eye. However, this is only possible if the examiner has a thorough knowledge of normal variations of the angle anatomy.

Seven different angle structures should be assessed in connection with gonioscopy (fig. 12):

1.Iris contour and iris mobility

2.The uveal meshwork (iris processes)

3.The ciliary band

4.The scleral spur

5.The corneoscleral trabecular meshwork

6.Schwalbe’s line

7.Normal blood vessels in the angle

Fig. 12. The four structures of the normal chamber angle.

1. Iris contour and iris mobility

The best way to assess the iris contour (fig. 13) is to use the Posner lens (ref: Goniolenses and their uses) since this lens will show the entire radial iris contour from pupil edge to periphery, whereas the Goldmann lens only shows the peripheral part of the iris.

In the normal emmetropic adult eye, the iris is slightly anteriorly convex due to a slight physiological pupil block, which makes the pressure in posterior chamber slightly higher than in anterior chamber.

In the case of hypermetropia, the iris contour is typically more anteriorly convex, while the iris contour of myopic eyes is either flat or concave (fig. 13). These conditions are accentuated with eye pathology. Hypermetropic PAC eyes with pupil block as well as eyes with secondary angle-closure (SAC) due to axial lens ad-

34 Diagnostic methods in PAC

vancement will have an extreme iris convexity (see below). In the case of plateau conditioned PAC, on the other hand, the iris is abnormally flat, whereas the myopic pigment glaucoma eye often has an extreme iris concavity.

Fig. 13. Iris contours.

The iris mobility is examined by applying indentation with the Posner lens in the primary position (fig. 7b). Mobility assessment is based on two factors; partly on the change of the entire radial iris contour and partly on the change of the degree of narrowness in the chamber angle. The latter may be quantified by the degree of visibility of the main angle structures. (fig. 12).

Among healthy people, the iris is so mobile that with a slight indentation the iris can concave from the pupil border up to the iris root. At the same time, this will open the angle and make the tip of the angle visible, enabling identification of all of the structures of the angle, including the ciliary band. The latter is due to the fact that the iris root or “the iris knee” (the last roll of iris) can almost be levelled out completely among healthy people.

In connection with glaucoma pathology, the mobility may either be considerably increased (PAC with pupil block and pigment glaucoma) or extremely decreased (PAC with plateau iris and SAC due to axial lens advancement). As will be described in greater detail later, the two main groups of PAC have quite a different anatomical pathogenesis: Abnormal pupil block or plateau iris. The assessment of iris mobility remains one of the most important methods available for separating these two important clinical entities36.

In connection with abnormal pupil block, the narrow angle is conditioned by aqueous accumulation in the posterior chamber resulting in an anteriorly convex iris, whereas the narrow angle

Diagnostic methods in PAC 35

in the case of plateau iris is caused by an abnormal anterior positioning of the ciliary body7 and thereby the iris root (“the iris knee”), which will then be levelled with the trabecular meshwork (see the UBM pictures: fig. 14 and fig. 23). This pathoanatomy is also the reason why the iris contour is flat.

Pupillary

block

Plateau

iris

Fig. 14. UBM iris contour and mobility before and after indentation. Top: Pupil block conditioned PAC. Bottom: Plateau iris conditioned PAC. Photo: P. Kock Jensen and Svend V. Kessing, the Glaucoma Clinic, Copenhagen University Hospital.

The different forms of pathogenesis result in two different types of iris mobility:

In the case of pupil block, on indentation gonioscopy the iris becomes anteriorly concave over its entire radius (fig. 14, top). In connection with early cases without synechiae and increrased IOP, even the most peripheral angle anatomy, including the ciliary band, will usually be visualised.

In the case of plateau iris, on the other hand, indentation will only produce a small intermediary located iris concavity, and “the iris knee” will barely alter (fig. 14, bottom). In this situation, the identification possibilities of the angle structures change very little, maybe with a slightly better visualisation of the trabecular meshwork while the ciliary band remains invisible. This is due to the fact that the ciliary body functions as a “chock” for contour changes of the peripheral iris8 (fig. 14 and 23).

36 Diagnostic methods in PAC

Consequently, assessment of iris mobility represents an important part of gonioscopy with special differential diagnostic consequences within the area of PAC.

2. The uveal meshwork (iris processes)

The uveal meshwork is probably the angle structure that shows the highest degree of normal variation. This may well result in a misinterpretation, and a normal anatomy be considered as pathological with the consequent risk of providing improper therapy. Therefore, it is particularly important to be familiar with the uveal meshwork.

During the formation of the anterior chamber in the embryonic period, the chamber is filled with loose fibrous tissue, which is covered by a homogeneous layer of glittering endothelium cells towards the chamber. The remainder of this tissue comprises the uveal meshwork. In newborn babies the uveal meshwork still has a colourless, homogeneous, pellucid structure, extending from the root of iris across the angle to the anterior part of the underlying corneoscleral trabecular meshwork. Visualisation is difficult and requires high enlargement. After this, an increasing regression of the tissue with fenestration of the endothelial surface and the fibril development is usually seen. Among adults the uveal meshwork is thus more or less pigmented, depending on the colour of the eye, and always has a lace-like porous structure stretching from the root of iris to the scleral spur. In some cases, coarser fibrillary structures are seen, the so-called iris processes (fig. 12), which are situated in front of the underlying more flattened fenestrated uveal meshwork. Sometimes, the iris processes stretch right up to the corneoscleral trabecular meshwork.

The uveal meshwork is usually most well-developed nasally in the angle and least-developed at 6 o’clock (the physiological “angle coloboma”).

When regression of the endothelium-covered uveal meshwork does not occur, goniodysgenesis will arise, which is most likely the reason for congenital and infantile glaucoma and possibly also for juvenile glaucoma.

At times, the uveal meshwork containing the many iris processes will be misinterpreted as representing goniosynechiae, and the

Diagnostic methods in PAC 37

examiner may misdiagnose the patient as having a chronic angleclosure and consequently may even perform a YAG iridotomy!! (See 2nd case report). This situation is especially seen among younger people with brown eyes where the corneoscleral trabecular meshwork still remains unpigmented, whereas the uveal meshwork and the iris processes are heavily pigmented and therefore especially clear. The examiner does not acknowledge the actual location of Schlemm’s canal in front of the scleral spur, but instead regards the slightly pigmented ciliary band (fig. 9) as representing the corneoscleral pigmented trabecular meshwork. The risk of making this misinterpretation is especially high among patients with juvenile glaucoma.

In order to avoid this misinterpretation, we recommend the following: Using the Goldmann 3-mirror lens in the primary position, carry out compression until the eye is soft. Then decompress while applying a slight scleral pressure with the edge of the lens in the opposite direction of the angular mirror; in most cases, this will produce a retrograde filling of blood into the observed part of Schlemm’s canal (fig. 15a). The large contact surface of the 3-mirror lens (18 mm) is usually necessary for adequate scleral compression of the aqueous veins and thereby retrograde filling of blood into the canal. This procedure helps identify the position of the canal and the true facts of the case. In order to avoid misinterpretation, it is important to be aware of the gracile lace-like structure of the uveal meshwork and the iris processes as opposed to the more solid genuine goniosynechiae (fig. 15b).

3. The ciliary band

The ciliary band is formed by the longitudinal fibres of the ciliary muscle on their way to the scleral spur. Gonioscopically, the ciliary band stretches from the root of iris to the scleral spur (fig. 9). As mentioned in point 2 above, the ciliary band is partly hidden under the uveal meshwork, especially among people with brown eyes (fig. 12), but it is always seen in the “the angle coloboma” at 6 o’clock. Usually, the colour is slightly grey – a little greyer than the unpigmented corneoscleral trabecular meshwork. However, among dark-eyed people the colour is slightly pigmented and may therefore easily be confused with the pigmented trabecular meshwork.

38 Diagnostic methods in PAC

The width of the ciliary band depends on the iris insertion on ciliary body and varies considerably from person to person. In the

a

b

Fig. 15. Differential diagnosis between iris processes and PAS.

a:Visualisation of the position of trabecular meshwork with blood filling of Schlemm’s canal.

b:Left: Lace-like iris processes. Right: Solid PAS up to the scleral spur.

case of myopia, the ciliary band is wide, but in connection with plateau conditioned PAC it is mostly invisible where the iris is inserted right behind the scleral spur (see below).

4. The scleral spur

The scleral spur forms the posterior edge of the corneoscleral trabecular meshwork directly in front of the ciliary band (fig. 12),

Diagnostic methods in PAC 39

and is, as such, often covered by the uveal meshwork except in the lower part in “the angle coloboma”. The scleral spur has the same white colour as the unpigmented trabecular meshwork, but is usually easily seen in connection with averagely pronounced pigmentation of the meshwork since it will then lie in between two darker and wider lines (fig. 9). When the scleral spur has been identified at 6 o’clock, it can usually be found under the uveal meshwork in the rest of the angle.

5. The corneoscleral trabecular meshwork

The corneoscleral trabecular meshwork stretches from the scleral spur to Schwalbe’s line (fig. 12), and Schlemm’s canal lies deeper in relation to the middle and posterior 1/3 of the meshwork. Among adults, this filtering part of the meshwork is usually slightly pigmented and as such is easy to identify since the degree of pigmentation is always least temporally around the horizontal line and largest nasally in the lower quadrant, where the uveal meshwork is also most pronounced.

Among children and younger people the trabecular meshwork is unpigmented. The unpigmented meshwork may be identified via its typically greyish, slightly granulated pellucid surface; this becomes slightly clearer when applying indentation with the Posner lens. If the trabecular meshwork is difficult to identify, its position between the scleral spur and Schwalbe’s line can be used as a guideline as these two structures are easier to locate, especially in the “angle coloboma” at 6 o’clock (see below). Finally, as mentioned earlier, a positive identification of Schlemm’s canal is possible if the canal is filled with blood by using the Goldmann 3-mirror lens (fig. 15a).

6. Schwalbe’s line

Schwalbe’s line is formed by the peripheral edge of Descemet´s membrane with direct contact to the anterior part of the corneoscleral trabecular meshwork (fig. 12). The line may be more or less prominent, but in most eyes it is usually most easily visualised in the lower direction, mainly because it is considerably more pigmented at around 6 o’clock (Sampaolesis’ line, fig. 9). This makes it easier to identify the right location of the corneoscleral trabecular meshwork in this sector, but may also give rise to misinterpretation. On examination with the Goldmann lens, the

40 Diagnostic methods in PAC

pigmented line in the lower angle sector shown in fig. 16a was thought to be the pigmented trabecular meshwork, and the angle was therefore considered as being open, not occludable. However, later examinations with the Goldmann lens with the patient looking into the mirror showed that the pigmented trabecular meshwork was situated further back, partly covered by goniosynechia (fig. 16b). This was therefore an eye with chronic angle-closure and with a most pronounced Sampaolesis’ line.

Sometimes, Schwalbe’s line is very thickened and prominent and may even be seen both on direct slit lamp examination and with gonioscopy. This condition is called posterior embryotoxon and is, as a solitary finding, an insignificant normal variation of Schwalbe’s line. If there are further developmental defects in the chamber angle (Axenfeld’s and Rieger’s syndrome), marked iris attachments will be connected to the embryotoxon formation with a subsequent risk of glaucoma.

7. Normal blood vessels in the angle

Normal blood vessels in the chamber angle are seen with considerable inter-individual variation; however in spite of this, they do have certain characteristics, which do make it possible to distinguish them from neovascularisation (angle rubeosis).

Normally, the main ciliary arterial circle runs parallel to the limbus in the anterior part of the ciliary body and is invisible on gonioscopy. Sometimes, part of the main ciliary arterial circle is visible in a sector of the ciliary band where its curved course, with only a part of each loop being visible, resembles a sea serpent. The radial iris vessels run from the arterial circle and through to the iris root in the iris pigment layer and from there onwards into the iris stroma with a radially visible course towards the pupil covered by a thin layer of iris stroma and with only a few diagonal anastomoses. The veins from the pupil border also run in a straight radial line towards the iris root. Finally, in slightly pigmented eyes it is sometimes possible to see a radially situated artery deep within the ciliary band, presumably an anterior ciliary artery after the scleral passage on its way to the main ciliary arterial circle.

Diagnostic methods in PAC 41

a

b

Fig. 16. Differentiation between Sampaolesis’ line and the pigmented trabecular meshwork. a: Examination of the lower angle in the primary position with the Goldmann lens – visible pigmented trabecular meshwork? b: Examination of the same eye with the patient looking into the mirror in the Goldmann lens –pigmented trabecular meshwork and PAS + Sampaolesis’ line. Photo: Svend V. Kessing, the Glaucoma Clinic, Copenhagen University Hospital.

Glaucoma pathology in the chamber angle

After a diagnosis of narrow angle, gonioscopic identification of peripheral anterior synechiae (PAS) is the most important observation, partly in order to verify the PAC diagnosis and partly as a way of correctly PAC staging of each individual case with regard to specific treatment. PAS develop insidiously from the most narrow, upper angle sector and downwards39.

42 Diagnostic methods in PAC

As mentioned under “Normal anatomy of the chamber angle” (2: The uveal meshwork (iris processes)), it may be difficult to distinguish between PAS and a physiologically pronounced uveal meshwork with iris processes (see fig. 15a-b). PAS with PAC are more solid when compared to the porous lace-like uveal meshwork, and furthermore they are clearly formed by the iris stroma. Most often the synechiae emanate from the deepest part of the angle and have a continuous adhesion to the angle wall, in some cases right up to Schwalbe’s line, though never centrally to it. However, in case of very small PAS they sometimes emanate from the trabecular meshwork.

The duration of appositional angle-closure necessary to form PAS is not known, but is probably dependent on the degree of inflammation in the angle area, pressureor only apposition-con- ditioned. The latter seems to be the most frequent as up to 2/3 of all cases of PAC develop asymptomatically as “creeping” angle closure17, 34, 35.

In the case of suspect narrow angles, the PAC diagnosis may be verified by the occurrence of a single, but well-defined PAS in the upper narrowest sector of the angle. Based on a semi-quantitative estimate, the occurrence and spreading of PAS form the basis for the subclassification (staging) of PAC, opening up the possibilities for specific treatment. With a PAS involvement of < 50% of the angle circumference the remainder of the outflow function will normally be sufficient to maintain a normal IOP without treatment, whereas without medical treatment the eye pressure will permanently be increased when PAS comprises > 50% of the circumference. Finally, involvement of > 80-90% often signifies a manifest glaucoma with indication for maximum drug administration/fistulating operation (see flow chart for specific treatment of primary angle-closure, fig. 19).

As is well known PAS are not pathognomic for PAC as they are found following uveitic inflammation, after a post-operative flattened anterior chamber, neovascular glaucoma, iridocorneal endothelium syndrome (ICE syndrome) and in congenital defects with development arrest (Axenfeld, Rieger). Whereas PAS are frequently seen after iris bombé, they are seldom seen following acute iritis and then presumably only in connection with a concurrent narrow angle. The development of synechiae is far more common in cyclitis with “fat” precipitates. As is clearly seen in

Diagnostic methods in PAC 43

the cyclitic trabeculitis (Boeck´s disease), the likely explanation is that the “fat” precipitates are mainly deposited on the trabecular meshwork in the lower part of the chamber as prominating pellucid “jelly-fish”; in extreme cases they are continuous with and in contact with the iris. When these precipitates become organised, large tent-shaped synechiae are formed in the lower area of the angle; therefore, apart from by the degree of the opening of the chamber angle, it is possible to distinguish them from PAS with PAC by their morphology and localisation. As in PAC, the synechiae are never central to Schwalbe’s line as opposed to neovascular glaucoma where the synechiae do sometimes extend centrally to Scwalbe’s line. This is also the case in the ICE-syndrome and with congenital defects.

Neovasularisation in the anterior segment of the eye is, especially in the initial fase, limited to the chamber angle (angle rubeosis) and can therefore only be diagnosed by means of gonioscopy. In any condition where there is a risk of neovascularisation in the anterior segment, it is advisable to perform a gonioscopy.

Angle rubeosis is seen secondary to two different groups of diseases:

1.Vascular retinopathies (central artery or vein occlusion, diabetes, carotid artery stenosis, possibly with normal pressure glaucoma, Eales disease).

2.Chronic inflammations (chronic iridocyclitis, chronic anterior uveitis, Fuchs’ heterochromic cyclitis). In both groups of diseases the new vessels arise from the main arterial circle in the ciliary body and from there run radially onto the anterior iris and the posterior cornea.

The new iris vessels have an irregular, curved course on the surface of the iris as opposed to the normal iris vessels (ref: Normal blood vessels in the chamber angle). The new vessels on the posterior surface of the cornea appear on the ciliary band and from here run radially and superficially across the scleral spur up to the trabecular meshwork where the vessels branch out circumferentially in the filtrating part of the meshwork. The new vessels are accompanied by a transparent layer of fibrotic tissue, which occludes the meshwork and causes secondary glaucoma.

44 Diagnostic methods in PAC

In vascular retinopathies, the fibrovascular activity is considerably more pronounced than in inflammatory conditions. In the course of weeks the new vessels will, in these conditions, lead to the formation of broad solid PAS leading to further increase in pressure. The synechiae formation is caused by shrinkage of the accompanying fibrotic tissue along the new radial vessels. The concurrent shrinkage of the fibrovascular formation on the iris results in uveal ectropion of the pupil.

It should therefore be emphasised that the angle rubeosis in inflammatory conditions does not usually cause PAS formation and is on the whole less harmful with thinner angle vessels. However, in heterochromic uveitis the thinner vessels show a tendency to bleed, both spontaneously and in connection with an operation.

Abnormal chamber angle pigmentation localised only in the trabecular meshwork is seen among younger patients with pigment dispersion and among elderly patients with pseudoexfoliation. In both these cases, the temporal meshwork sector becomes just as pigmented as the remaining circumference, which is not found under normal conditions. In pseudoexfoliation, pigmentation as well as pseudoexfoliation material can be found on the trabecular meshwork in the lower angle sector in addition to the typical material on the pupilliary margin and the anterior surface of the lens.

Coarser, diffuse pigmentation, most pronounced on Schwalbe’s line in the lower angle (Sampaolesi´s line), is seen following inflammatory conditions, for example after acute PAC. Diffuse pigmentation of the chamber angle in connection with other signs of previous acute PAC (“glaukomphlecken” and sector shaped grey iris atrophy, ref: acute/subacute PAC with pupil block) may thus have a differential diagnostic importance.

Black, coarse pigmentation in the lower angle, possibly with some rounded pigmentation, is typical for previous hyphaema, often arising in connection with a contusion trauma. In the latter case, apart from this coarse angle pigmentation, other post-traumatic chamber angle changes can be found such as limbus-concentric clefts in the uveal meshwork, in the ciliary band (cyclodialysis) or in the corneoscleral trabecular meshwork (traumatic trabeculotomy). In connection with traumatic trabeculotomy, even a long time after the trauma, it is possible to cause bleeding into the

Diagnostic methods in PAC 45

chamber through the damaged trabecular meshwork (elimination of the meshwork’s unidirectional valve effect) by retrograde filling of blood into Schlemm’s canal (ref: Normal anatomy of the chamber angle:The uveal meshwork). A similar situation exists with a post-inflammatory meshwork lesion following an iritis. Moreover, especially after a contusion, a sector shaped inadequacy of blood filling of the canal can be seen. This probably represents a traumatic, cicatricial collapse of the canal, which may lead to post-traumatic glaucoma. Iris dialyses and PAS are also part of the post-traumatic angle morphology.

PROVOCATION TEST

Due to poor sensitivity and specificity, provocation tests with PAC are only recommended for patients with subjective prodromal symptoms or with heredity where the objective examination by means of the other methods has not clarified the situation adequately. Apart from this, the provocation test is recommended for diagnostic assessment if imminent pure plateau iris conditioned PAC is suspected as in this situation, where the ACD is normal, gonioscopy remains the only method available for diagnosis (see also: Group II: Detection and diagnosis).

Dark-room test – prone position

With the dark-room test an introductory applanation pressure measurement is performed, and the patient is then placed in a prone position in a dark-room for at least 45 minutes. The patient is supported by the forehead, which must be pointed directly downwards. The patient must not sleep, close or press on the eyes. If a relative is not present to ensure this, another person must be present to check this, and music may be played. At the end of the test, with closed eyes, the patient is assisted to the slit lamp where a final pressure measurement is undertaken. When there is an increase in pressure of at least 8 mm, the test is regarded as positive. At the time of the test, the patient should not be receiving any form of anti-glaucomatous treatment. The provocation test in the form of dark-room test – prone position was, however, only positive in 24% of the eyes which later developed manifest PAC. Therefore it

46 Diagnostic methods in PAC

was concluded that the method cannot generally be recommended as a predicative test for performing an iridotomy17.

ULTRASOUND BIOMICROSCOPY (UBM)

UBM is a high frequency ultrasound examination of the anterior segment of the eye as the enlargement is sufficient for assessing details in the anterior and posterior chambers (fig. 17). The resolution is 40 micron, i.e. it is possible to visualise the zonula threads. The penetration depth is only 4 mm, and therefore the examination does not reveal any retrolenticular details. A large eye cup has to be used and unintended indentation with risk of misinterpretation of the results must be avoided.

Fig. 17. UBM of chamber angle area in a normal person. P. Kock Jensen and Svend V. Kessing, The Glaucoma Clinic, Copenhagen University Hospital.

The method has created possibilities for a better pathogenitical understanding of several diseases localised in the anterior segment of the eye, not least within the field of glaucoma disorders (primary and secondary angle closure, pigmentation glaucoma, ciliary block (malignant glaucoma)).

Diagnostic methods in PAC 47

The UBM method has proved to be ideal for the examination and interpretation of the pathoanatomy that exists in primary angle-closure and especially in plateau iris conditioned PAC.

Fig. 23 shows an example of this (UBM with typical plateau iris anatomy).

UBM is thus suitable for determining the pathogenesis in difficult angle-closure cases.

However, it must be emphasized that the examination is difficult to carry out in the proper manner (at right angles to the ocular surface) and it is not without some discomfort for the patient.

48 Diagnostic methods in PAC