Glaucoma affects approximately 65 million people around the world and an expected 7.5 million are blind due to the disease. It is the second most common cause of blindness worldwide.¹ It is estimated that perhaps half the blindness from glaucoma in the world is caused by angle closure.² Accordingly, in order to be effective, any case detection has to include methods to detect angle closure.

A clinic examination is different from a screening programme in the community. In the clinic the patient has sought us out and the responsibility is ours to detect and treat any pathology, including glaucoma. Some short cuts that may be satisfactory in screening programmes are not acceptable in a clinic. The best method to detect (and assess) glaucoma is to perform a comprehensive eye examination for all patients who attend the clinic, irrespective of the complaints they present with.³

Five components of the comprehensive eye examination are specifically relevant to assess glaucoma.

It is important to remember that the Goldmann applanation tonometer may record falsely high IOP if corneal thickness (not corneal oedema) is increased. This message is reiterated by the OHTS finding that in a thick cornea the risk of progression is minimal for patients with ocular hypertension. There is no consensus about which correction formula to use to adjust for corneal thickness; we use Elher's formula, which applies a 5 mm Hg correction for every 70 μ of corneal thickness. Routine central corneal thickness (CCT) measurement is ideal; it should at least be measured in all patients with ocular hypertension and suspected normotensive glaucoma (NTG). As far as management is concerned, IOP is the only known causal factor and the only factor that we can alter therapeutically.

Figure 1 Gonioscopy showing peripheral anterior synechia

The ideal technique is dynamic gonioscopy with an indentation-type lens like the 4-mirror Susmann gonioscope. The anterior chamber angle is a dynamic structure and it can change over a periodof time due to changes in lens thickness, position, and other factors. It is therefore essential to perform gonioscopy on a routine basis, even in a ‘known’ caseof POAG.

The flashlight and van Herrick tests are sometimes suggested as surrogates for gonioscopy. On its own, the flashlight test is close to useless.⁵ The van Herrick test may be of some use in screening programmes, but is of little help in the clinic where gonioscopy is the gold standard.⁵

The numerous signs that need to be sought during disc assessment are beyond the scope of this article; they include rim thinning or notch, disc haemorrhage, wedge-shaped RNFL, etc. (Figures 2 & 3).

Figure 2 Optic disc photograph with inferior notch

Figure 3 Optic disc photograph with disc haemorrhage

Newer imaging techniques are now available for documentation of the optic disc. These include the Heidelberg retinal tomogram (HRT), scanning laser polarimetry (GDX), and optical coherence tomography (OCT). The Association of International Glaucoma Societies (AIGS) consensus meeting concluded that at present there was insufficient evidence to validate the routine use of these instruments. The meeting also concluded that, in the hands of a specialist, imaging techniques can provide valuable information. We concur with these conclusions. We also feel that these instruments have a great potential for follow-up.

We first need to obtain baseline fields, both for diagnosis and for comparison on follow-up. The first few fields usually demonstrate a learning curve and cannotbe used as a baseline. To determine progression, we currently use the overview programme (Figure 4) and the glaucoma progression analysis (GPA). The GPA provides statistical help to determine progression (Figure 5).

Figure 4 Overview print-out

Figure 5 Glaucoma progression analysis: single field print-out

Frequency Doubling Perimetry (FDP) is a rapid and relatively inexpensive test that can accurately detect established field defects. FDP has a high sensitivity and specificity. It can fulfill the objective of confirming a field defect prior to surgery, but does not have the programmes for follow-up.

The Bjerrum Screen is good enough for documenting a defect, and, if it correlates with the other findings, is enough to go to surgery. The demonstration of a functional defect becomes especially important in the areas where we would go for primary surgery. The Bjerrum Screen, however, is not good for follow-up.

Tonometry will only detect angle closure in a patient with raised IOP. The structural and functional tests described for POAG (optic disc examination, perimetry) will only detect angle closure that has damaged the disc or visual field. As approximately 75 per cent of subjects with PACG in Asia have optic nerve damage, strategies that detect functional damage in POAG may also be suitable for PACG. However, such tests will not detect eyes without functional damage or eyes at risk for angle closure. Such eyes at risk, and those with early disease, are the ones we need to detect. In these cases, an iridotomy can be curative.

Figure 6 Van Herrick test showing shallow peripheral anterior chamber

It is also important to remember that the flashlight and van Herrick tests do not detect angle closure but occludable angles, which are only a risk factor for angle closure. This distinction is important because only a minority of occludable angles progress to angle closure. Using the van Herrick test for screening will result in too many false positives.

In summary, the clinical assessment of a patient for glaucoma requires a complete comprehensive examination (including gonioscopy) on all adult patients seen in the clinic, followed by appropriate investigations (visual fields) to document damage and follow up patients with suspected glaucoma as well as confirmed cases.

Ravi Thomas, Director, LV Prasad Eye Institute, and Dr Kallam Anji Reddy Distinguished, Chair of Ophthalmology, LV Prasad Eye Institute, Banjara Marg, Banjara Hills, Hyderabad, 500 034, Andhra Pradesh, India.

Rajul S Parikh, Consultant, VST Centre for Glaucoma Care, LV Prasad Eye Institute, Banjara Marg, Banjara Hills, Hyderabad, 500 034, Andhra Pradesh, India.