Long-term variability in short-wavelength automated perimetry compared to standard perimetry in glaucoma patients and normal subjects

AIMS: To compare long-term variability (LTV) in short-wavelength automated perimetry (SWAP) with that of standard white-on-white (W-W) perimetry, in primary open angle glaucoma (POAG) patients and normal subjects and to determine its clinical significance. PATIENTS AND METHODS: The sample comprised 30 patients of stable POAG (group 1) and 20 age-matched normal controls (group2) who performed both SWAP and W-W perimetry thrice at monthly intervals. Long-term variability at each location in the visual field was calculated as the standard deviation of three threshold decibel values taken from the three visual fields performed. Mean LTV was then calculated for the entire field for each subgroup and compared. RESULTS: Mean LTV in SWAP and W-W perimetry in glaucoma patients was 3.01 ± 0.74 dB and 2.73 ± 1.07dB respectively. In normal subjects mean LTV of SWAP and W-W perimetry was 2.69 ± 0.91 db and 1.97 ± 1.34 dB respectively. Intra group analysis revealed that mean LTV of SWAP was greater compared to W-W perimetry in normal subjects and glaucoma patients. In the latter, the difference did not reach statistical significance. Inter group analysis showed that mean LTV in both SWAP and W-W perimetry was greater in glaucoma patients than in normal subjects. Factors other than POAG that could influence LTV, including progression of cataract and change in pupil size due to use of pilocarpine were excluded. Mean examination time for SWAP per sitting was 7.65% longer than that for W-W perimetry. CONCLUSIONS: Higher mean LTV of SWAP as compared to W-W perimetry needs to be taken into consideration when evaluating serial visual fields for change. Use of rapid threshold algorithms e.g. SITA (Swedish interactive test algorithm) SWAP should be encouraged as these will reduce the patient fatigue and increase the reliability of the test.