Glaucoma screening by optometrists: Positive predictive value of visual field testing

Purpose Visual field testing is increasingly being performed by optometrists in order to improve glaucoma detection. The aim of this study was to assess the positive predictive value (PPV) of visual field testing as currently practised by optometrists. Methods A retrospective study was performed of referrals for suspected glaucoma to an ophthalmology department during a 3 month period. The PPV for glaucoma was determined according to the reason for referral. Results There were 86 referrals for suspected glaucoma. Isolated field loss accounted for 12% of these referrals but no cases of glaucoma detection. These subjects were either false positive referrals or had field defects of non-glaucomatous aetiology (tilted optic disc and porencephalic cyst). The PPV for glaucoma among referrals with isolated field loss was significantly less than that among referrals with field loss in association with corroborative abnormalities (0 vs 60%, p=0.005). No such difference was found for referrals with raised intraocular pressure (43% vs 57%, p = 0.38) or suspicious discs (25% vs 53%, p = 0.60). Conclusions Visual field testing is currently leading to unnecessary referrals to the hospital eye service with no detectable improvement in the accuracy of glaucoma suspect referrals. It is important that optometrists perform visual field testing in accordance with validated screening methodology.