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Glaucoma Dialogue IGR 15-2

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Comment by George Spaeth on:

53737 Do findings on routine examination identify patients at risk for primary open-angle glaucoma? The rational clinical examination systematic review, Hollands H; Johnson D; Hollands S et al., JAMA (Journal of the American Medical Association), 2013; 309: 2035-2042

Find related abstracts

The authors attempted to quantify the value of risk factors associated with the development of primary open-angle glaucoma (POAG) for the purpose of developing screening techniques for use by the general physician. The authors employed an extensive review of the literature extending as far back as 1950.

The authors define glaucoma as “an optic neuropathy characterized by irreversible loss of retinal ganglion cells, resulting in progressive thinning of the retinal nerve fiber layer […] often associated with higher IOP.”

High myopia was identified as the single strongest risk factor based on an odds ratio extracted from a single study. Four other studies identified a glaucoma prevalence of 6.0% in patients with greater than three diopters of myopia. Age is identified as an independent risk factor for POAG with threshold value 80 years associated with a prevalence of 7.8%.

The examination findings of cup-to-disc ratio (CDR) and cup-to-disc asymmetry were also evaluated. A CDR of 0.7 had a likelihood ratio of 14 and CDR asymmetry of 0.3 or greater of LR of 7.3. However, while disc assessment is vitally important in evaluation of glaucoma, CDR is not satisfactory as it does not account for position of the cup or overall size of the disc.¹ A 'normal' CDR does not rule out POAG.

While disc assessment is vitally important in evaluation of glaucoma, CDR is not satisfactory as it does not account for position of the cup or overall size of the disc.1 A "normal" CDR does not rule out POAG

Intraocular pressure (IOP) was found to have a LR of 13 at a threshold value of 22 mmHg or greater. However, there was much heterogeneity among studies. Low IOP does not rule out glaucoma. AGIS showed that many patients with an average IOP of 12 mmHg for six years had minimal loss in visual field. However, 14% of this group experienced a worsening of four or more AGIS units of visual field (4/21 units).²

This study addresses the complexity of glaucoma and the variability between trained observers. Thus, effective screening by untrained observers is challenging. The study identifies isolated risk factors and exam findings but does not address the impact of these findings on the patient or their level of functioning. It is important to consider the patient's disability and life expectancy when evaluating for initiation of treatment, both for the ophthalmologist and the general practitioner. As our knowledge of the disease process expands, more effective screening may be plausible. At this juncture, general practitioners should have a low threshold for prompt referral to a specialist, and be aware that the absence of risk factors or specific examination findings does not exclude the possibility of glaucoma.

At this juncture, general practitioners should have a low threshold for prompt referral to a specialist, and be aware that the absence of risk factors or specific examination findings does not exclude the possibility of glaucoma

The major value of this report is to remind practitioners that findings in the 'normal range' do NOT rule out glaucoma. The major concern about this report is the authors' failure to point out that values in the abnormal range do not rule in glaucoma. It is not possible validly to generalize from a population finding (such as a CDR of 0.7) to an individual. Thus, for example, one should not conclude that a person has glaucoma just because she is elderly, say 80 years of age, because NO age is always associated with the presence of glaucoma. Likelihood ratios less than 100 do not rule a condition in. Thus high myopia, a CDR of 0.7, and an age of 100 years are findings of no value in establishing that a particular person with those findings actually has glaucoma, even though they are significant risk factors, because a person can have all those findings and yet still not have glaucoma, and because there is no way to distinguish the non-glaucomatous person with those findings from the glaucomatous person with exactly the same findings. However, when a finding is ALWAYS associated with glaucoma then and only then can that finding be applied to all individuals. An example would be an IOP of 80 mmHg.

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