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GLAUCOMA SCREENING

UPDATE YOUR CONSENSUS KNOWLEDGE

Selected from: Weinreb RN, Healy PR, Topouzis F (eds.). Glaucoma Screening. Amsterdam: Kugler Publications 2008.

Is glaucoma an important public health problem?

• Glaucoma is the leading cause of preventable irreversible blindness.
• Primary angle-closure glaucoma (PACG) accounts for approximately 25% of all glaucomatous optic neuropathy worldwide, but 50% of bilateral glaucoma blindness.
• PACG is predominantly asymptomatic.
• Some Asian populations have a high prevalence of advanced angle-closure glaucoma.
• Long-term data show substantial frequency of open-angle glaucoma blindness in some populations

Comment: Additional population-based data are needed on the rates and risks of vision loss.

Is there an accepted and effective treatment?

• High-quality randomized trials (treatment vs no treatment) and meta-analyses have shown that topical ocular hypotensive medication is effective in delaying onset and progression of OAG.
• Patients' perceived vision-related quality of life (VRQOL) and visual function is correlated with visual field loss, especially binocular visual field loss, in OAG.

Comment: The greater the visual field loss, or the later the stage of the disease, the more symptomatic the disease.

• There is good evidence that preventive iridectomy/otomy will eliminate the risk of acute angle closure when performed on the fellow eye of patients who have experienced acute angle closure.

Are facilities for diagnosis and treatment available?

• The resources for diagnosis and treatment of glaucoma vary worldwide.

Comment: Many countries have insufficient facilities to provide care at present practice standards relative to developed countries.

Comment: There is a need to identify areas without facilities to help plan resource allocation

Is there an appropriate screening test?

• The tests available and effective for case-finding are not necessarily the same as those for population- based glaucoma screening which requires a very high specificity to be cost-effective.

Comment: Screening requires a test with a high specificity. Diagnosis requires a test with a high sensitivity.

• There is evidence that limbal anterior chamber depth (LCD) may be an appropriate screening test for angle closure.

Comment: Using a LCD of 25% corneal thickness as a cut-off all those cases falling below this level would require gonioscopy. Approximately 4% of occludable angles may be missed by this method.

Comment: More research is required concerning alternative screening tests.

Is the natural history adequately understood?

• OAG-incidence rates are known for untreated and treated patients with ocular hypertension.
• Progression event rates for patients (in clinical trials, under clinical care or observation) in terms of percent of patients/eyes progressing per year are available both for OAG and ocular hypertension.
• Asymptomatic angle closure is associated with later presentation and more advanced loss of vision than symptomatic angle closure where facilities for treatment are readily available.
• The current best estimate for progression from PACS to PAC or PAC to PACG is approximately 20-30% over five years.

Comment: The data on the natural history of PACS/PAC/PACG are sparse and would benefit from confirmation in further studies.

Is the cost of case finding economically balanced?

• The best evidence to date, based on two modeling studies, suggests:
1. Screening of high-risk subgroups could be more cost-effective than screening the entire population;
2. Screening may be more cost-effective as glaucoma prevalence increases;
3. The optimal screening interval is not yet known;
4. Screening may be more cost-effective when initial assessment is a simple strategy that could be supervised by non medical technicians.

Comment: Expert consensus is required on how cost data should be collected and reported in glaucoma care. This includes reporting visually relevant outcomes on a per-patient basis.

Comment: Additional data are required to develop a glaucoma disease staging system based on disability.