Comparison of clinical optic disc assessment with tests of early visual field loss

Clinical optic disc assessment may identify glaucomatous optic neuropathy prior to a patient developing visual field abnormalities on achromatic automated peri-metry (AAP). Tests targeting axons that are selectively damaged or whose redundancy is low, such as short wavelength automated perimetry (SWAP) and frequency doubling perimetry (FDP), may detect visual field loss before it is seen on AAP. This study investigated whether patients in whom characteristic glaucomatous optic disc damage was present without AAP abnormalities had visual field abnormalities with SWAP and FDP.

A sample of patients (n = 50) with ocular hypertension (normal AAP) were selected, who had SWAP, FDP and stereofundus photography performed. The photographs were then analysed by two glaucoma subspecialists who were masked to the assessments of the other and to the patients' SWAP and FDP results. A categorization of the optic discs was made as either normal or abnormal and this was compared with their SWAP and FDP findings.

On comparing SWAP and FDP with clinical optic disc assessment as the 'gold standard', the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were 33%, 92%, 57% and 81%, respectively, for SWAP and 25%, 89%, 49% and 79%, respectively, for FDP.

In glaucoma suspects, the study suggests that SWAP and FDP identify subjects with early glaucomatous optic neuropathy missed by AAP.