Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

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•The classic Goldmann lens consists of three mirrors, one of which is specifically for gonioscopy (Fig. 10.9A); some goniolenses have one (Fig. 10.9B), two or four mirrors (Fig. 10.9C).

•Lenses of similar basic structure but with modifications include the Magna View, Ritch trabeculoplasty, Thorpe four-mirror and the Khaw direct view.

•Because the curvature of the contact surface of the lens is steeper than that of the cornea, a viscous coupling substance of refractive index similar to the cornea is required to bridge the gap between cornea and lens.

2Technique

aIt is essential that the examination takes place in a room in which the ambient illumination is very low – completely dark if possible.

bThe size and intensity of the slit beam should be reduced to the absolute minimum compatible with an adequate view, in particular avoiding any of the beam being directed through the pupil.

c The patient is seated at the slit-lamp and advised that the lens will touch the eye but will not usually cause discomfort.

dA drop of local anaesthetic such as proxymetacaine 0.5% is instilled.

eThe forehead must be kept against the headband and both eyes should remain open.

fA drop or two of coupling fluid (an artificial tear preparation such as hypromellose 0.3%) is placed on the contact surface of the lens.

gThe patient is asked to look upwards and the lens is inserted rapidly so as to avoid loss of the coupling fluid. The patient then looks straight ahead.

hIndirect gonioscopy gives an inverted view of the angle opposite to the mirror.

iOnce the initial examination has been performed and the findings noted, increasing the level of illumination may help in defining the angle structures.

jWhen the view of the angle is obscured by a convex iris, it is possible to see ‘over the hill’ by asking the patient to look in the direction of the mirror. Only slight movement is permissible, otherwise the structures will be distorted and a closed angle may appear open.

kExcessive pressure with a non-indentation lens narrows the angle appearance (in contrast to the effect of pressure during indentation gonioscopy – see below). Excessive pressure also causes folds in the cornea which compromise the clarity of the view.

lIn some eyes, suction on the cornea from the lens may artificially open the angle; awareness of the need to avoid retrograde as well as anterograde pressure on the lens will help to avoid.

Fig. 10.9 Goldmann goniolens. (A) Three mirror; (B) single mirror; (C) four mirror

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Indentation gonioscopy

1Goniolenses include the Zeiss (generally used along with the detachable Unger fork handle – Fig. 10.10), Posner (modified Zeiss with fitted handle) and Sussman (no handle), all of which have four-mirror gonioprisms.

•The contact surface of the lenses has a curvature flatter than that of the cornea, negating the need for a coupling substance.

•The lenses do not stabilize the globe and are not suitable for laser trabeculoplasty.

2Technique

aThe first stages are as set out above for non-indentation gonioscopy.

bIndentation is performed by gently pressing the lens posteriorly against the cornea (Fig. 10.11A); this forces aqueous into the angle, pushing the peripheral iris posteriorly.

cIf the angle is closed only by apposition between the iris and cornea it will be forced open, allowing visualization of the angle recess (Figs. 10.11B).

dIf the angle is closed by adhesions between the peripheral iris and cornea – peripheral anterior synechiae (PAS – Fig. 10.12A) it will remain closed (Fig. 10.12B).

eDynamic gonioscopy can be invaluable in helping to define the structures in angles which are difficult to assess, such as in distinguishing an extensive or double highly-pigmented Schwalbe line from the pigmented trabecular meshwork.

Fig. 10.10 (A) Zeiss goniolens; (B) lens in place

Fig. 10.11 Indentation gonioscopy in appositional angle closure. (A) Total angle closure prior to indentation; (B) during indentation the entire angle becomes visible (arrow) and the cornea develops folds

(Courtesy of W Alward, from Color Atlas of Gonioscopy, Wolfe 1994)

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Fig. 10.12 Indentation gonioscopy in partial synechial angle closure. (A) Total angle closure prior to indentation; (B) during indentation part of the angle becomes open (small arrow) and the remainder remains closed (large arrow) due to PAS

(Courtesy of W Alward, from Color Atlas of Gonioscopy, Wolfe 1994)

Direct gonioscopy

Direct goniolenses work by constructing the viewing surface of the lens in a domed or slanted configuration such that exiting light rays strike the contact lens/air interface at a steeper than critical angle so that they will pass through to the observer. This approach is called ‘direct’ because light rays from the angle are viewed directly, without reflection inside the lens. They do not require a slit-lamp and are used with the patient in the supine position, typically under general anaesthesia in the evaluation and surgical treatment of infantile glaucoma.

1 Goniolenses

aDiagnostic lenses include the Koeppe, a dome-shaped direct diagnostic goniolens which comes in several sizes (Fig. 10.13).

bSurgical lenses (Fig. 10.14) used for angle surgery include the Medical Workshop, Barkan and Swan-Jacob.

2Technique

aGonioscopy is performed with the patient in the supine position (note that this may deepen the angle appearance) in conjunction with an operating or hand-held microscope (or magnifying loupes) and an additional illumination source if necessary.

bThe technique cannot be used with a desktop slit-lamp so clarity, illumination and variable magnification are not comparable with indirect lenses.

Fig. 10.13 Koeppe goniolenses

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Fig. 10.14 Surgical goniolenses. (A) Medical Workshop; (B) Barkan; (C) Swan-Jacob

Identification of angle structures

Figure 10.15 shows the anatomy of angle structures.

1Schwalbe line is the most anterior structure, appearing as an irregular opaque line. Anatomically it demarcates the peripheral termination of Descemet membrane and the anterior limit of the trabeculum. It may be barely discernible, particularly in younger patients. In contrast, there may be pigment deposits on or anterior to Schwalbe line (Sampaolesi line) that may make interpretation of the angle structures difficult.

2The corneal wedge is useful in locating an inconspicuous Schwalbe line. Using a narrow slit beam, two distinct linear corneal reflections can be identified (see Fig. 10.15), one on the inner and one on the outer corneal surface; the outer reflection will arc round across the corneoscleral interface – due to the sclera being opaque – to meet the inner reflection at the apex of the corneal wedge which coincides with the Schwalbe line.

3The trabeculum extends from Schwalbe line to the scleral spur and has an average width of 600 µm. In younger people it has a ground-glass appearance and appears to have depth. The anterior non-functional part lies adjacent to Schwalbe line and has a whitish colour. The posterior, pigmented functional part lies adjacent to the scleral spur and has a greyish-blue translucent appearance in the young. Trabecular pigmentation is rare prior to puberty, but in older eyes involves the posterior trabeculum to a variable extent, most marked inferiorly. Patchy trabecular pigmentation in a suspiciously narrow angle raises the possibility of intermittent iris contact.

4Schlemm canal may be identified in the non-pigmented angle as a slightly darker line deep to the posterior trabeculum. Blood can sometimes be seen in the canal (Fig. 10.16), either physiologically (sometimes due to excessive pressure on the episcleral veins with a goniolens), or in the presence of low intraocular or raised episcleral venous pressure.

5The scleral spur is the most anterior projection of the sclera and the site of attachment of the longitudinal muscle of the ciliary body. Gonioscopically it is situated immediately posterior to the trabeculum and appears as a narrow, dense, often shiny, whitish band.

6The ciliary body stands out just behind the scleral spur as a pink to dull-brown to slate-grey band. Its width depends on the position of iris insertion and it tends to be narrower in hypermetropic eyes and wider in myopic eyes. The angle recess represents the posterior dipping of the iris as it inserts into the ciliary body.

7Iris processes are small extensions of the anterior surface of the iris which insert at the level of the scleral spur and cover the ciliary body to a varying extent (see Fig. 10.16). They are present in about one-third of normal eyes and are most prominent during childhood and in brown eyes. The processes should not be confused with PAS which are generally broader.

8Blood vessels running in a radial pattern at the base of the angle recess are often seen in normal eyes. Pathological blood vessels run randomly in various directions. As a general principle, any blood vessel that crosses the scleral spur onto the trabecular

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meshwork is abnormal.

Fig. 10.15 Normal angle structures

(Courtesy of W Alward, from Color Atlas of Gonioscopy, Wolfe 1994)

Fig. 10.16 Blood in Schlemmcanal (arrow), and iris processes

(Courtesy of J Schuman, V Christopoulos, D Dhaliwal, M Kahook and R Noecker, from Lens and Glaucoma, in Rapid Diagnosis in Ophthalmology, Mosby 2008)

Grading of angle width

Shaffer system

The Shaffer system records the angle in degrees between two imaginary lines tangential to the inner surface of the trabeculum and the anterior surface of the iris about one-third of the distance from its periphery. In practice, the angle is graded by many according to the visibility of various structures. The system assigns a numerical grade to each quadrant of the angle as below (Fig. 10.17); it should be borne in mind that most angles are narrowest superiorly.

1 Grade 4 (35–45°) is the widest angle, characteristic of myopia and aphakia, in which the ciliary body can be visualized with ease.

2Grade 3 (25–35°) is an open angle in which at least the scleral spur can be identified.

3Grade 2 (20°) is a moderately narrow angle in which only the trabeculum can be identified.

4 Grade 1 (10°) is a very narrow angle in which only Schwalbe line, and perhaps also the top of the trabeculum, can be identified.

5Slit angle is one in which there is no obvious iridocorneal contact but no angle structures can be identified.

6Grade 0 (0°) is a closed angle due to iridocorneal contact and is recognized by the inability to identify the apex of the corneal wedge. Indentation gonioscopy will distinguish ‘appositional’ from ‘synechial’ angle closure (see Fig. 10.20).

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Fig. 10.17 Grading of angle width

Other systems

1Spaeth system is detailed but underused. It describes consideration of the position of the iris insertion, the angular approach and curvature of the peripheral iris.

2Scheie classification refers to the angle structures visible and allocates a Roman numeral accordingly. In contrast to common clinical use, in the original system a higher numeral (e.g. IV) actually signifies a narrower angle.

3The van Herick method (Table 10.1) uses the slit-lamp alone to estimate the anterior chamber angle width:

•A thin bright slit beam is set approximately perpendicularly to the corneal surface (offset from the optics by about 60°) to the patient's temporal side for each eye.

•The beam is used to estimate the ratio of the corneal thickness to the most peripheral part of the anterior chamber (see Figs 10.40B and 10.41B).

•This method provides a useful approximation in a majority of patients and has utility as a screening tool and as an aid to assessment in angles which are difficult to interpret on gonioscopy. However, it overestimates angle width in a proportion of patients, particularly those with a ‘plateau iris’ conformation.

Table 10.1 -- Van Herick method for anterior chamber angle assessment

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Fig. 10.41 Primary angle-closure. (A) Closed angle; (B) van Herick grade 1

(Courtesy of L MacKeen fig. A; J Schuman, V Christopoulos, D Dhaliwal, M Kahook and R Noecker, from Lens and Glaucoma, in Rapid Diagnosis in Ophthalmology, Mosby 2008 – fig. B)

Pathological findings

1Peripheral anterior synechiae

•Primary angle-closure glaucoma.

•Anterior uveitis.

•Iridocorneal endothelial (ICE) syndrome.

2Neovascularization

•Neovascular glaucoma.

•Fuchs heterochromic cyclitis.

•Chronic anterior uveitis.

3Hyperpigmentation

•Pigment dispersion syndrome.

•Pseudophakic pigment dispersion.

•Pseudoexfoliation syndrome.

•Blunt ocular trauma.

•Anterior uveitis.

•Following acute angle-closure glaucoma.

•Following YAG laser iridotomy.

•Iris melanoma.

•Iris pigment epithelial cysts.

•Naevus of Ota.

4Trauma

•Angle recession.

•Trabecular dialysis.

•Cyclodialysis.

•Foreign bodies.

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5Blood in the Schlemm canal

•Carotid-cavernous fistula and dural shunt.

•Sturge–Weber syndrome.

•Obstruction of the superior vena cava.

•Physiological variant.

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Evaluation of the optic nerve head

Normal optic nerve head

Neuroretinal rim

The neuroretinal rim (NRR) is the tissue between the outer edge of the cup and the optic disc margin. The normal rim has an orange or pink colour and a characteristic configuration in most healthy eyes: the inferior rim is the broadest followed by the superior, nasal and temporal (the ‘ISNT’ rule).

Optic disc size

Optic disc size is important in deciding if a cup-disc (C/D) ratio is normal. Normal median vertical diameter for non-glaucomatous discs is 1.50 mm in a Caucasian population. It can be assessed clinically as follows:

aA narrow slit beam is focussed on the disc using a fundus biomicroscopy lens.

bThe height of the beam is adjusted until it matches the distance between the superior and inferior limits of the NRR (not the scleral rim surrounding the neural tissue), and the diameter in millimetres read from the slit-lamp graticule.

cA correction factor may be necessary, dependent on the lens used (Table 10.2). Refractive error affects measurement only minimally, although myopia above −8 dioptres may distort the result.

Table 10.2 -- Correction factors for estimating optic disc diameter

Cup–disc ratio

The C/D ratio indicates the diameter of the cup expressed as a fraction of the diameter of the disc; the vertical rather than the horizontal ratio is generally used in clinical practice. The NRR occupies a relatively similar cross-sectional area in different eyes.

•Small discs have small cups with a median C/D ratio of about 0.35 (Fig. 10.18A)

•Large discs have large cups with a median C/D ratio of about 0.55 (Fig. 10.18B).

•Only 2% of the population have a C/D ratio greater than 0.7.

•In any individual, asymmetry of 0.2 or more between the eyes should also be regarded with suspicion, though it is critical to exclude a difference in overall disc size.

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Fig. 10.18 Normal discs. (A) Small disc with a low C/Dratio; (B) large disc with a higher C/Dratio

(Courtesy of S Farley, T Cole and L Rimmer)

Changes in glaucoma

In many cases, it is not possible to decide with certainty whether an individual optic disc is glaucomatous. The clinical findings and results of investigation should be considered together to guide management. Glaucomatous damage results in characteristic signs involving (a) the optic nerve head, (b) the peripapillary area and (c) the retinal nerve fibre layer.

Optic nerve head

The spectrum of disc damage in glaucoma ranges from highly localized tissue loss with notching of the NRR to diffuse concentric enlargement of the cup, as well as changes in vasculature. Pathological cupping is caused by an irreversible decrease in the number of nerve fibres, glial cells and blood vessels. A documented increase in cup size is always significant. If an eye with a small optic disc and correspondingly small cup develops glaucoma, the cup will increase in size, but even in the presence of substantial damage may still be smaller than that of a large physiological cup, so overall disc diameter must be taken into account as discussed above. Assessment of the thickness, symmetry and colour of the NRR is of substantial importance (see ‘ISNT’ rule above).

Subtypes of glaucomatous damage

The appearance and pattern of disc damage may correlate with subtypes of glaucoma and provide clues as to the pathogenic mechanisms involved. Four ‘pure’ glaucomatous disc appearances have been described, although the majority of discs are unclassifiable.

1Focal ischaemic discs are characterized by focal superior and/or inferior polar notching (Fig. 10.19A) which may be associated with localized field defects with early threat to fixation.

2Myopic disc with glaucoma refers to a tilted (obliquely inserted), shallow disc with a temporal crescent of parapapillary atrophy, together with features glaucomatous damage (Fig. 10.19B). Discs with degenerative myopia are excluded. Dense superior or inferior scotomas threatening fixation are common. These discs tend to occur in younger male patients.

3Senile sclerotic discs are characterized by a shallow, saucerized cup and a gently sloping NRR, variable peripapillary atrophy and peripheral visual field loss (Fig. 10.19C). Patients are older (both genders equally), and the disc type is associated with ischaemic heart disease and hypertension.

4Concentrically enlarging discs (verified by serial monitoring) are characterized by uniform NRR thinning (Fig. 10.19D) and are frequently associated with diffuse visual field loss. At presentation IOP is often significantly elevated.

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