Diagnosis

Acute primary angle closure

The diagnosis of APAC is mainly clinical. There is a sudden, usually symptomatic rise in IOP. This is usually unilateral, but bilateral simultaneous attacks can occur. Patients complain of periocular or ocular pain, headache, nausea, and/or vomiting. The patients also complain of blurring of vision with haloes. Slit lamp examination will reveal conjunctival injection, corneal epithelial edema with a mid dilated sluggish/nonreacting pupil. The IOP is likely to be greater than 30 mmHg. The anterior chamber will be shallow and gonioscopy will show occludable or occluded drainage angles in both eyes. In some instances, if there is a severe anterior chamber reaction, with hypopyon, the IOP maybe normal or low due to ciliary body shutdown. It is important that these episodes of APAC are not misdiagnosed as uveitis. Also, certain types of open angle glaucoma can be

Table 3. Gonioscopy grading systems

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associated with an acute rise in IOP with ocular pain, conjunctival injection, and corneal edema. These include phacolytic glaucoma, Posner– Schlossman syndrome, pseudoexfoliative glaucoma, and neovascular glaucoma.

Angle assessment in angle closure

In angle closure, the drainage angle is occludable and there are features indicating that trabecular obstruction has occurred like PAS. The gold standard technique to diagnose angle closure is gonioscopy. There are three widely used grading systems. The Scheie scheme is based on the angle structures seen during gonioscopy (Scheie, 1957). The Shaffer system requires the assessment of the angular distance between the iris and cornea (Becker and Shaffer, 1965). The Spaeth scheme allows for more detailed recording of the angle characteristics (geometric angle, iris profile, true and apparent level of insertion) (Spaeth, 1971). Table 3 gives a summary of the grading systems (Scheie,

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1957; Becker and Shaffer, 1965; Spaeth, 1971; South East Asia Glaucoma Interest Group, 2008). The Goldmann lens gives a stable, clear view of the important landmarks but indentation of appositionally closed angles using this lens has not been validated, and is difficult as the curvature of the lens is more than the corneal curvature. Therefore, the use of a four-mirror, like the Zeiss four-mirror is necessary. This lens has the same radius of curvature as the cornea so the patient’s own tear film functions as a coupling agent. The Goldmann-type lenses require an optical coupling agent.

Gonioscopy technique

Gonioscopy should be carried out in a darkened room. The patient should have adequate topical anasthesia and should be looking in the primary position. The slit lamp beam should be 1 mm high and narrow. The light must be kept away from the pupil, at the lowest illumination that will allow angle visualization. The lens can be moved minimally along the cornea to see over the convexity of the iris, however, care must be taken not to apply pressure and cause indentation. Using high magnification, the termination of the corneal wedge (which marks the anterior edge of the trabecular meshwork) can be identified. Additionally, it is important to locate the scleral spur as the trabecular meshwork is directly anterior to this structure. Assessment of whether the iris is in contact with the trabecular meshwork is done. If it is not, the angle between the trabecular meshwork and adjacent peripheral iris is estimated and the level of the most anterior point of contact between the iris and angle structures is described. This is carried out for all four quadrants, then dynamic gonioscopy can be carried out.

If Goldmann-style lenses are being used, the patient should be instructed to look toward the mirror, the examiner should then press on the rim of the lens overlying the mirror, so as to indent the central cornea. The accuracy of indentation using this method has not been validated. The ideal technique involves using another goniolens with a diameter smaller than the corneal diameter, e.g. a four-mirror Zeiss lens. Pressure should be applied over the cornea, so as to displace aqueous from the centre of the anterior chamber into the periphery,

pushing the iris posteriorly, falsely opening the drainage angle. This allows one to assess whether the iridotrabecular contact is appositional or synechial (i.e. permanent). The extent of the synechial closure should be assessed. Once it is determined that the angle is indeed occludable, the slit beam height and illumination and room lights should be turned up ideally prior to indentation gonioscopy to look for PAS. Any pseudo-PAS would open up with bright light besides the pressure applied on the cornea. Iris processes should not be confused with PAS. Iris processes are uveal extensions from the iris on to the trabecular meshwork and occur in normal angles. Figure 1 shows the normal angle anatomy.

Ultrasound biomicroscopy (UBM)

UBM gives good qualitative information about the drainage angle including visualization of the ciliary body. However, highly reproducible quantitative information is dependent on examiner technique and experience. UBM is usually performed with the patient in the supine position. A suitably sized eye cup (around 20 mm) is inserted between the eyelids and the coupling medium (e.g. methylcellulose and/or normal saline) is inserted into it. The probe is then inserted into the medium and real time images are displayed on a video monitor. These can be stored and/or printed out for analysis. It should be noted that room illumination and accommodation must be kept constant. Also the configuration of the anterior segment and the proportions of the structures seen depends on the plane of the section and any degree of tilt in the scanning probe (Liebmann, 2006). Figure 2 shows an UBM scan of narrow angles.

Kumar et al. (2008) have used the UBM to define plateau iris. The features of UBM are defined in each quadrant, and include the presence of an anteriorly directed ciliary body, an absent ciliary sulcus, a steep iris root from its point of insertion followed by a downward angulation from the corneoscleral wall, presence of a central flat iris plane, and irido-angle contact. At least two quadrants have to fulfill the above criteria for plateau iris to be defined (Kumar et al., 2008). Figure 3 shows the features.

imaging, which is objective and reproducible. Research comparing UBM, AS-OCT, and gonioscopy shows the AS-OCT is good at identifying narrow angles; however, the device does identify more subjects as having closed angles than gonioscopy (Radhakrishnan et al., 2005, 2007). Figure 4 shows an AS-OCT scan of an eye with narrow angles.

Scanning peripheral anterior chamber depth analyzer (SPAC)

The SPAC does not image the angle per se but takes rapid slit images of the central and peripheral anterior chamber using an optical method and creates an iris anterior surface contour using these measurements. This is then graded and compared to the normative database and the resultant grade gives a risk assessment for the patient (Kashiwagi et al., 2004). The SPAC correlates well with the modified van Herick system in grading peripheral ACD. However, it overestimates the proportion of

narrow angles relative to gonioscopy and the modified van Herick grading system (Baskaran et al., 2007).

Visual-field loss

It has been observed that the pattern of visual-field loss in PACG is different from that of POAG. Gazzard et al. showed that subjects with POAG had greater superior hemifield loss than in the inferior hemifield. This difference between the two hemifields was less pronounced in the PACG patients. However, the PACG group exhibited more severe visual-field loss compared to the POAG group. The authors postulated that POAG is thought to be due to a combination of pressure dependent and independent mechanisms whereas PACG is predominantly pressure related. This may be why there is less of a difference between the two hemifields in PACG patients. The reason for the more severe field loss is less clear and maybe due to the tendency of PACG patients to present later (Gazzard et al., 2002).