Test-retest variability for standard automated perimetry and short-wavelength automated perimetry in diabetic patients.

PURPOSE

To assess limits for significant improvement or deterioration of visual fields in diabetic patients based on short-term test-retest variability in subjects with different degrees of retinopathy.

METHODS

Fifty patients with diabetic retinopathy ranging from level 10 to 75 [according to the Early Treatment Diabetic Retinopathy Study (ETDRS) severity scale] were tested repeatedly with both standard automated perimetry (SAP) and short-wavelength automated perimetry (SWAP) with short intervals. The association between visual field loss and degree of retinopathy outside fovea was analysed. Test-retest variability of global and local visual field indices and prediction limits for significant change were calculated.

RESULTS

The amount of visual field loss was significantly associated to the degree of retinopathy, with a correlation coefficient of -0.51 for SAP (P = 0.0003) and -0.45 for SWAP (P = 0.002). Global test-retest variability was smaller with SAP than with SWAP (P < 0.0001). For both SAP and SWAP, local test-retest variability was considerably smaller at test points with normal sensitivity than at test points with reduced sensitivity (P < 0.0001). Paracentral test points within 10 degrees of eccentricity had less variability than peripheral points (P < 0.0001), implying that smaller change is required to reach statistically significant improvement or deterioration at initially normal and paracentral points than at depressed points and peripherally located test points.

CONCLUSION

Our results propose that SAP, as well as SWAP, can be useful for monitoring visual function outside fovea in diabetic patients with various degrees of retinopathy. We report a preference for SAP because of less variability generally. Limits for significant improvement or deterioration have been assessed but need future validation in a longitudinal study.