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Normal Intersubject Threshold Variability and Normal Limits of the SITA SWAP and Full Threshold SWAP Perimetric Programs

From the Department of Ophthalmology, Malmö University Hospital, Lund University, Lund, Sweden.

PURPOSE. To compare intersubject variability and normal limits of threshold values between the new Swedish interactive test algorithm short wavelength automated perimetry (SITA SWAP) and the older Full Threshold SWAP programs (Carl Zeiss Meditec, Dublin, CA).

METHODS. Normal reduction of differential light sensitivity with age, age-corrected thresholds, intersubject variability, and normal limits of sensitivity were calculated from SITA SWAP and Full Threshold SWAP fields obtained in 53 normal subjects between 20 and 72 years of age.

RESULTS. Age influence on threshold sensitivity was the same with the two SWAP programs. On average, sensitivity decreased by 0.13 dB per year of age. Age-corrected normal threshold sensitivity was significantly higher (P < 0.0001) for SITA SWAP than for Full Threshold SWAP. The means for a subject 45.4 years of age were 28.8 dB with SITA SWAP and 24.4 dB with Full Threshold SWAP. Intersubject variance was 22% smaller with SITA SWAP than with Full Threshold SWAP. Normal limits at the P < 5% significance level were, on average, 14% narrower with SITA SWAP than with Full Threshold SWAP using Total Deviations from age-corrected normal thresholds and 11% narrower when applying Pattern Deviation, which is intended to adjust for general depression or elevation of the field.

CONCLUSIONS. SITA SWAP test results from normal eyes showed higher sensitivities than results from the older Full Threshold SWAP. This represents an increase of the dynamic range, which implies that more patients can be tested with SWAP. The smaller intersubject variability with SITA SWAP means narrower normal limits and may be associated with more sensitive probability maps.