Effectiveness of optometrist screening for diabetic retinopathy using slit-lamp biomicroscopy

Purpose To assess the effectiveness of optometrists as screeners for diabet ic retinopathy using slit-lamp binocular indirect ophthalmoscopy through di lated pupils. Methods Prospective study of a screening scheme. Screening was performed by 27 locally accredited optometrists in their practice. The referral protoco l used a new simple grading system of retinopathy, especially designed for use in an optometrist screening programme. All positive referrals and 10% o f negative referrals were reexamined by an ophthalmologist. Sensitivity, sp ecificity, likelihood ratios and technical failure rates were calculated. Results The optometrists screened 4904 people with diabetes in 18 months. ' Subthreshold' (screen negative) reports accounted for 4438 (90.5% of 4904); 429 (9.67%) of these were re-examined at secondary screening. There was di sagreement regarding grading in 13 patients, of whom 5 (1.16% of 429) had s ight-threatening retinopathy (STDR); this extrapolates to 52 patients if al l the 4438 test-negatives had been examined. Of the 371 'threshold' patient s, 112 (30.18%) were false positives; the commonest cause for false positiv e referral was drusen in patients with background diabetic retinopathy. The sensitivity for identification of STDR was 76% (95% CI 70% to 81%) and spe cificity 95% (95% CI 95% to 96%). The likelihood ratio of a positive test i ndicating STDR was 16.54 (93% CI 14.17 to 19.23) and that of a negative tes t 0.25 (95% CI 0.20 to 0.32). The technical failure rate was 0.2%. Conclusions Suitably trained and accredited community optometrists performe d well when screening for diabetic retinopathy using slit-lamp biomicroscop y through a dilated pupil. This was facilitated by the use of simple gradin g and referral criteria. The sensitivity, positive likelihood ratio and spe cificity were high.