New approaches to visualize the anterior chamber angle

5.The superior and inferior mirrors are usually easier to use for visualizing the CBP and should be assessed first.

6.While narrowing the slit and reducing the light intensity, the examiner should look not only at the angle but also through the lens, especially behind the lens equator. The focus should be relatively posterior.

7.To examine the angle structures, the gonioscopic mirror should be tilted towards the angle of interest or the patient should be asked to look towards the gonioscopic mirror. Attention should be given to visualizing the pigmented trabecular meshwork (TM), both with the dim light and when the light is intensified. The examiner could judge an angle to be opened, closed, or occludable by the dynamics of visualization of the pigmented TM.

–If the pigmented TM could not be seen with both normal and dim light, the angle is ‘closed’.

–If the pigmented TM could be seen with both normal and dim light, the angle is ‘opened’.

–If the pigmented TM could be seen with normal light but not with dim light, the angle is ‘occludable’.

8.If the lens is situated at a relatively anterior position, the CBP could be seen through the lens equator.1 This may be facilitated by tilting the gonioscopic mirror away from the angle of interest or by asking the patient to look away from the mirror. Dimming the light and narrowing the slit beam will also aid in visualization of the CBP, since the pupil will become larger (Fig. 1).

Fig. 1. A: Visualization of ciliary body processes (arrows) by dim light slit-lamp gonioscopy. With small pupil size, the intensity of light should be reduced and the slit is narrowed. B: When the pupil is larger, the ciliary body processes can be demonstrated with higher intensity of light.

The problem with this technique is that angle structures can be difficult to see with dim light. The pupil also can be too small for examiners to look through the structures behind the lens. These problems can be eliminated by using infrared light or gonioscopy with ‘no light’.

Dark-room infrared gonioscopy (DIG)

With infrared light, gonioscopy can be performed without ‘light’. This means that we can eliminate all of the bright light of the slit-lamp, and will make it possible to

look at the angle and its dynamics in the dark, as well as its response during light or accommodative stimulation. For example, an occludable angle may be opened using normal gonioscopy with a slit-lamp, but it is closed in the dark when using infrared gonioscopy. This may be used as objective evidence to determine whether the angle is occludable. At present, there is no commercial instrument available for infrared gonioscopy. By modifying existing instruments, infrared gonioscopy is possible. Two techniques can be used for DIG: an infrared video camera and the IR mode of HRA (Heidelberg Retinal Angiograph).

DIG with infrared video camera

Infrared gonioscopy can be performed using a cheap, commercially-available infrared video camera. Any infrared video camera that is capable of focusing close-up can be used. The camera that we used was manufactured by Fujiko (model FK-308), and incorporated a Samsung 1/3 inches B/W (0 lux) CCD and a f 3.6 mm/F 2.0

Fig. 2. A: Setting for dark-room infrared gonioscopy with an infrared video camera. B: A Koeppe lens is placed on the eye and the examiner holds the camera close to the lens. C: The examiner looks at the image from the monitor.

lens (Fig. 2). For this procedure, the camera is connected to a TV monitor. The patient has to be in a supine position, and direct gonioscopy with a Koeppe lens is performed. Before the examination, all of the lights in the room are turned off. The examiner holds the camera close to the Koeppe lens, and is adjusted to a position in which the angle structure can be visualized by looking at the monitor (Fig. 2). The examiner can move the focus to different areas around the eye to view all angle positions. During the examination, an assistant can turn a flashlight on and

Fig. 3. Dark-room infrared gonioscopy with an infrared video camera and Koeppe lens in an ‘occludable angle’ eye prior to laser iridotomy. With light stimulation, the pigmented trabecular meshwork can be seen (A). When the light is turned off, the pigmented trabecular meshwork is obscured.

Fig. 4. Dark-room infrared gonioscopy with an infrared video camera and Koeppe lens in a ‘nonoccludable angle’ eye after laser iridotomy and iridoplasty. The pigmented trabecular meshwork can be seen either with (A) or without light stimulation (B).

off in front of the patient’s fellow eye to stimulate pupillary constriction and accommodation. The dynamics of the visibility of the angle structure can be studied in dark (with widely dilated pupil) and light (with constricted pupil) conditions.

An example of an eye with an occludable angle is shown in Figure 3. In a light condition, the pupil was constricted and the pigmented trabecular meshwork could be seen. In a dark condition, the pupil was dilated and no trabecular meshwork could be seen. This demonstrated that this eye was occludable and, thus, laser iridotomy and/or iridoplasty were justified. After laser iridotomy and iridoplasty, the pigmented trabecular meshwork could be seen both in light and dark conditions (Fig. 4). This eye is considered non-occludable.

DIG with HRA-IR mode

The IR mode for viewing the retina in the HRA can be used for infrared gonioscopy. The HRA requires an ‘iris adapter lens’ to focus on the iris (Fig. 5A). The

lens is available from Heidelberg Engineering, GmbH. This lens is designed to cover the built-in HRA lens (Fig. 5B). The lens has a power of +25 diopters (focal length 40 mm) with a working distance of 34 mm. Prior to examination, the iris adapter lens is put on the HRA lens and the HRA mode is turned to IR mode. A Goldmann-type 3-mirror lens is inserted and the HRA is focused on the iris. The examiner views the image of the eye from the computer monitor (Fig. 5C). The angle structure and the structure behind the lens equator can also be visualized by changing the focusing knob. The dynamic of the angle can be observed in dark and light conditions in the same manner as described above.

An example of an ‘occludable angle’ eye from the anterior lens position is shown in Figure 6. On slit-lamp examination, the anterior chamber was shallow and a mild cataract was observed (Figure 6A). On routine gonioscopy with the slit-lamp, the trabecular meshwork could not be seen, especially when the light was dimmed. The iris configuration was markedly convex. Using the dim light slit-lamp gonioscopy

Fig. 5. Setting for dark-room infrared gonioscopy with HRA IR mode. Iris adapter lens (A). HRA with iris adapter lens in place (B). During the examination, the light in the room is turned off. The examiner views the angle structure from the computer monitor (C).

technique, the ciliary body processes (CBP) could be visualized through the lens when the gonioscopic mirror was tilted and the light was reduced with a narrow slit beam (Figure 6B). The CBP could be demonstrated only from the superior mirror. There was no peripheral anterior synechiae (PAS), but some appositional closure could be demonstrated using indentation gonioscopy. When using HRA infrared gonioscopy, the CBP could be demonstrated clearly, even with a small pupil size, but only from the superior mirror (Figure 6C). With a larger pupil size (light turned off), the CBP could be demonstrated in every quadrant (Fig. 7). The trabecular meshwork was obscured only when in the dark. This demonstrated that HRA infrared gonioscopy can facilitate the visualization of CBP in the case of anterior lens position. The visualization of CBP behind the lens is evidence that

Fig. 6. An eye with anterior lens position and occludable angle. The anterior chamber is shallow

(A). Using the dim light slit-lamp gonioscopy technique, the ciliary body processes can be seen behind the lens from the superior mirror (B). With dark-room infrared gonioscopy with HRA, more ciliary body processes can be seen even with a small pupil size (C).

Fig. 7. Dark-room infrared gonioscopy with HRA in an eye with anterior lens position (the same eye as in Fig. 6), the ciliary body processes can be clearly demonstrated in all quadrants. Note that the pupil is dilated in the dark.

the lens is located in an abnormal anterior position, which has been referred to as ‘lens forward movement’.

Figure 8 shows another example of an occludable eye in a patient that had already undergone patent iridotomy in both eyes. The anterior chamber was mildly shallow. On routine gonioscopy, the iris configuration was found to be markedly

Fig. 8. Right eye of a patient with anterior lens position. Patent iridotomy with shallow anterior chamber (A). Dim light slit-lamp gonioscopy reveals no ciliary body processes (B). However, using dark-room gonioscopy with HRA, ciliary body processes can be demonstrated from the nasal and inferior mirror (C).

Fig. 9. Left eye of a patient with anterior lens position (the same patient as in Fig. 8). Using darkroom gonioscopy with HRA, ciliary body processes can be demonstrated in all quadrants.

convex, and the trabecular meshwork could not be seen, especially with dim light. Using the dim light slit-lamp gonioscopy technique, the CBP could not be observed in all quadrants (Figure 8B). Using HRA infrared gonioscopy, the CBP could be demonstrated clearly in two quadrants in the right eye (Figure 8C) and all four

quadrants in the left eye (Fig. 9). This is another case of lens forward movement that persisted after laser iridotomy, and the CBP could only be visualized using infrared gonioscopy.

The significance of CBP visualization in angle-closure glaucoma

Normally, the CBP cannot be seen through the lens in an eye with a deep anterior chamber, normal lens thickness, and normal CBP because the light from the CBP could not ‘escape’ from the eye. In a deep anterior chamber, according to Snell’s law,2 the ‘incident angle’ of light from CBP that refracted at the lens surface around the pupillary border is larger than the ‘critical angle’ of the lens-aqueous interface, which causes ‘total internal reflection’ (Fig. 10). Using figures from the Gullstrand

Fig. 10. Snell’s law and critical angle. For the anterior lens cortex-aqueous interface, the critical angle for total internal reflection is 74.6º.

Table 1. Conditions in which ciliary body processes may be seen with gonioscopy.

1.Aphakia

2.Anterior lens dislocation

3.Posterior lens dislocation

4.Anterior lens position

5.Increased in anterior lens thickness

6.Combination of increased in anterior lens thickness and anterior lens position

Schematic eye,3 this critical angle at the lens-aqueous interface is calculated to be 74.6º. For an eye with a deep anterior chamber, light from the tip of the CBP strikes an anterior lens surface that is always larger than the critical angle, so the CBP cannot be visualized regardless of pupil size. However, in some abnormal conditions, the CBP may be seen through the pupil during gonioscopy (Table 1).

Compared to Asian eyes, Western eyes have deeper anterior chamber depth.

Fig. 11. A: In an eye with a deep anterio chamber, light from the tip of ciliary body processes cannot “escape” from the eye because the incident angle (76°, 80°) at the anterior lens surface is more than the critical angle (74.6°). B: In an eye with a mild shallow anterior chamber from anterior lens position, light from the tip of ciliary body processes can “escape“ from the eye because the incident angle (73°) at the anterior lens surface is less than the critical angle (74.6°). By tilting the gonioscopic mirror away from the angle of interest, the tip of ciliary body processes can be demonstrated. C: In an eye with a very shallow anterior chamber from anterior lens position, the ciliary body processes can be demonstrated more easily because light from the ciliary body processes “escape” from the eye with a more acute angle (the incident angle is now 68°).

With aging, the axial thickness of the lens increases and the depth of the anterior chamber is reduced. This may be due to the movement of the lens to a more anterior position, the increased anterior lens thickness, or a combination of both. In a deep anterior chamber, light from the CBP can not escape the eye due to total internal reflection at the lens-aqueous interface (Fig. 11A). When the anterior chamber is shallow due to the anterior lens position and/or increased anterior lens thickness, the amount of incident light from the CBP that strikes an anterior lens surface that is smaller than the critical angle so that light can ‘escape’ from the eye (Figure 11B). By tilting the gonioscopic mirror in the opposite direction of the angle of interest, the CBP can be visualized. When the anterior chamber is very shallow, the visualization of the CBP is much easier to accomplish and a smaller tilt of the gonioscopic mirror is required (Figure 11C). The same is true for a large pupil (occurring when the patient is in a dark room) compared to a small pupil

Fig. 12. In an eye with anterior lens position, a dilated pupil (when the patient is in a dark room) will aid in the visualization of the ciliary body processes and marked tilting of the gonioscopic mirror is not required. Note that the incident angle of light at the anterior lens surface when the eye is a in a dark condition (lower) is more acute (68°) than when the eye is in a light condition (73°) (upper). The red line is the incident light that strikes the anterior lens surface at the critical angle (74.6°).

Table 2. Biometry (ultrasound, immersion technique) of eyes that showed acute angle closure and their fellow eyes

(Not all eyes had biometry data. Numbers in parentheses are standard deviations. PI = peripheral iridotomy; AACGC = acute angle-closure glaucoma; ACD = anterior chamber depth; LT = lens thickness; AL = lens thickness)

(occurring when there is light or accommodative stimulation) (Fig. 12).

In our consecutive series of 16 acute angle closure eyes (15 cases, one case had acute angle closure in both eyes), the CBP could be demonstrated in all eyes with DSG. All of the eyes had patent iridotomies at the time of examination. Of the 15 fellow eyes, one eye was blind and could not be examined. In the remaining 14 fellow eyes, CBP could be demonstrated with DSG in all but one eye. In the only eye in which CBP could not be seen, it could be demonstrated with DIG. The biometry (ultrasound, immersion technique) of some eyes had been done (table 2).

Fig. 13. Diagram showing the clinical categories and stepwise approach for eyes with ‘anterior lens position’ or ‘forward lens movement’. See text for detail discussion.

It can be seen that all eyes had a true anterior chamber depth of less than 2 mm (ACD minus corneal thickness) and a lens thickness of less than 5 mm.

Anterior lens position or ‘forward lens movement’ as described by Ritch1 is one of the important causes of angle-closure glaucoma. Although it has been described in the literature, evidence about its clinical course and management were limited. In our experience, patients with anterior lens position can be presented in four categories (Fig. 13): (1) occludable angle (in which ≥ 270º of the posterior TM cannot be seen4) without any apposition of the peripheral iris and the posterior (pigmented) TM; (2) apposition of the peripheral iris and the posterior TM with or without some amount of PAS, but with normal IOP; (3) category 2 with a large amount of PAS that causes increased IOP; (4) acute angle closure with signs and symptoms of acute attack angle-closure glaucoma. According to the present classification of angle closure,4 category 1 can be classified as ‘primary angle closure suspect’ (PACS), category 2 as ‘primary angle closure’ (PAC) and category 3 as ‘primary angle-closure glaucoma’ (PACG). Patients in category 1 can progress to category 2 and 3. The factors that cause patients to develop acute attack angle closure (category 4) are not known.

We recommend a stepwise approach for patients with anterior lens position according to the category of the disease that one encounters (Fig. 13). All categories of anterior lens position have some degree of relative pupillary block, and laser iridotomy with or without iridoplasty should be done in all eyes.5 After iridotomy, management will be different for each category depending on the amount of appositional closure, PAS and cataract. Patients in category 1 will only need to be followed-up gonioscopically for signs of apposition and/or PAS. Patients in category 2 who have a clear lens should also be closely observed for progression of PAS. Once there is evidence of progressive PAS, removal of the lens by phacoemulsification with intraocular lens implantation (PE IOL), combined with mechanical goniosynechialysis6 (GSL) is recommended. Although the IOP is normal in this

category, performing GSL will ensure a wide open angle that will not be compromised if there is further PAS in the future. If patients in category 2 have significant cataract, PE IOL with GSL is recommended. Patients in category 3 have PAS that causes high IOP. The duration of PAS is important in these cases. Campbell and Vela6 reported success of GSL for PAS for up to one year. Teekhasaenee and Ritch7 reported success of PE IOL with GSL for uncontrolled chronic angle closure glaucoma after acute angle-closure glaucoma with PAS for up to six months. From this evidence, PE IOL with GSL is recommended for patients in category 3 with PAS of six months to one year. If the lens is clear, the risks and benefits of the procedures should be thoroughly discussed with the patients. If the patients have longstanding PAS of more than one year, combined PE IOL with trabeculectomy should be considered instead.

In patients presented with acute angle closure (category 4), iridotomy and/or iridoplasty should be performed.5 If there is significant cataract, PE IOL with GSL is recommended after the inflammation is controlled. For patients with a clear lens, PE IOL with GSL is recommended if there is a large amount of residual PAS. If there is only a small amount of PAS, close follow-up for progressive PAS and increased IOP is recommended. Once there is evidence of progressive PAS, PE IOL with GSL should be done.

In our case series, PE IOL with GSL were successful in controlling IOP without medication in half of the eyes (eight eyes). One eye required extracapsular cataract extraction with IOL implantation combined with trabeculectomy. The remaining eyes were adequately treated with medication or they were observed. These data suggest that the crystalline lens is an etiology of acute angle closure. Removal of the lens combined with GSL can cure most of the eyes. It should be emphasized that performing only PE IOL without GSL will not work in these cases,8 because the aqueous outflow is still blocked by PAS.

We would like to emphasize that causes of angle closure should be identified in every case of ‘primary’ angle closure glaucoma. Since most cases have some degree of relative pupillary block, other causes of angle closure and PAS should be thoroughly evaluated. In our case series, all 16 eyes had been shown to have anterior lens position as a cause of angle closure. This emphasizes that the crystalline lens is an important etiologic factor of ‘primary’ acute angle closure.

Conclusions

Visualization of CBP is an important, but easily overlooked sign of anterior lens position and/or increased anterior lens thickness. This may be the most common cause of acute angle-closure in Asian eyes. The CBP can be visualized by modifying the technique used in routine slit-lamp gonioscopy, with the dimming of the light and narrowing of the slit beam. Attention should be also paid to regions beyond the angle and into the back of the lens. In some cases with mild anterior lens position, gonioscopy may be performed in a dark room with an infrared light using either a video camera or HRA in IR mode to reveal the CBP more easily.

Removal of the lens by PE IOL combined with GSL is the treatment of choice and can cure most of the affected eyes. For fellow eyes, to prevent the development of angle-closure, appropriate examination and intervention should be done according to the presence of appositional closure, PAS, and cataract.

References

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3.Katz M, Kruger PB. The Human Eye as an Optical System. In: Tasman W, Jaeger EA (eds) Duane’s Clinical Ophthalmology [CD-ROM]. Philadelphia: Lippincott Williams & Wilkins 2005.

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