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P.R. Healey, P. Mitchell, Blue Mountains Eye Study, Centre for Vision Research; Glaucoma Case Detection: A Population–Based Assessment . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3442.
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Glaucoma is an important cause of blindness. Yet recent statements in the US and UK have recommended against screening in part on the basis of the poor predictive value of tonometry, poor reliability of visual field screening and mild nature of the vision loss. This study assessed the severity of visual loss and predictive value of case detection methods in a well–defined older population.
Subjects were drawn from The Blue Mountains Eye Study, which examined 3654 participants aged 49+ years during 1992–4. Goldmann applanation tonometry could be performed in 99%, optic disc photographs in 98% and 76–point suprathreshold visual field testing in 89% of participants. Open–angle glaucoma (OAG) diagnosis required matching optic disc and full threshold (Humphrey 30–2) visual field appearance without regard to intraocular pressure (IOP). Subsequently optic disc stereo–photographs were assessed by trained, masked, non–clinician graders for focal notching of the optic disc rim.
The prevalence of OAG was 3.0%. Twenty–five percent of participants with OAG had serious bilateral visual field loss; including 19 with congruous hemifield or full field visual loss and 6 with advanced bilateral loss. Fifty percent of glaucoma cases were previously undiagnosed. A disc rim notch was found in at least one eye of 205 participants (5.72%) with a strong age–related increase in prevalence. After adjusting for other glaucoma risk factors, a notch in either eye was associated with 21.2–fold increase in the odds of diagnosis of OAG (95CI 8.8–50.8). The sensitivity of a disc rim notch for OAG was 90.3% and specificity 96.8%. Positive predictive value (PPV) was 45.4% and the negative predictive value 99.7%. In contrast, the positive predictive value of suprathreshold visual field screening and intraocular pressure >21mmHg in this population was 15.2% and 15%. All PPV’s increased with age but a notch retained the highest PPV for all age groups.
In this population, open angle glaucoma was frequently undiagnosed and caused serious vision loss in a substantial proportion of participants. In contrast to tonometry and visual field screening, optic disc examination detected these cases relatively efficiently.
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