How accurate are optometrist referrals for glaucoma in the NICE era?

Abstract

PurposeTo determine if the reason(s) stated by the optometrist affect the positive predictive value (PPV) of referrals for suspected glaucoma.MethodsOptometrist referrals in Portsmouth are streamlined though the Glaucoma Referral Refinement Scheme (GRRS). We retrospectively analysed 100 ‘positive’ and 100 ‘negative’ referrals to the GRRS. Positives: those referred on to a secondary care glaucoma clinic; negatives: those discharged from the GRRS. Reason(s) for referral were determined and classified: intraocular pressure (IOP) optic disc changes (OD), visual field defect (VF), shallow anterior chamber depth (ACD). Since negative referrals to GRRS are four times more prevalent than positives, we calculated a ‘corrected’ PPV for each reason by multiplying the number of negatives by 4.ResultsThe overall PPV was 0.16. 70.4% cases were referred for a single reason (47.2% IOP, 12.2% OD, 8.8% VF, 2.4% ACD); the PPV was 0.11 for IOP and for OD, 0.05 for VF, 0.17 for ACD. 26.2% were referred for two reasons; the PPV was 0.47 for IOP + OD, 0.21 for OD + VF and 0.14 for IOP + VF. 4.2% were referred for IOP + OD + VF with a PPV of 0.62. Positive family history of glaucoma (21.4% referrals) did not increase PPV. The GRRS increased the PPV to 0.8.ConclusionsThe majority of patients are referred for a single reason, yet the chance of a positive diagnosis is low. Accuracy is increased when IOP is reported in combination with OD, but VF adds little value as a second parameter. The highest PPV is found when all three reasons are stated (IOP + OD + VF). The proportion of referrals for IOP alone is similar to that found prior to the NICE guidelines. However, the PPV is considerably lower; 0.11 compared to 0.3–0.4 found in previous studies. In the NICE era, refinement schemes play an important role in reducing false positive referrals.