Repeatability of Retinal Sensitivity Measurements Using a Medmont Dark-Adapted Chromatic Perimeter in Healthy and Age-Related Macular Degeneration Cases

Abstract

Purpose: To determine the intrasession and intersession test-retest repeatability of retinal sensitivity measurements using a dark-adapted chromatic perimeter (DACP).

Methods: For intrasession testing, retinal sensitivity within the central 24° for the 505-nm stimulus was measured after 20, 30, and 40 minutes of dark adaptation (DA) and for the 625-nm stimulus was measured after the first and second 505-nm tests. For intersession testing, retinal sensitivity for both stimuli was measured after 30 minutes of DA at baseline and 1 month. The point-wise sensitivity (PWS) difference and coefficient of repeatability (CoR) of each stimulus and group were determined.

Results: For intrasession testing, 10 age-related macular degeneration (AMD) and eight control subjects were recruited. The overall CoR for the 505-nm stimulus was 8.4 dB for control subjects and 9.1 dB for AMD cases, and for the 625-nm stimulus was 6.7 dB for control subjects and 9.5 dB for AMD cases. For intersession testing, seven AMD cases and 13 control subjects returned an overall CoR for the 505-nm stimulus of 8.2 dB for the control and 11.7 dB for the AMD group. For the 625-nm stimulus the CoR was 6.2 dB for the control group and 8.4 dB for the AMD group. Approximately 80% of all test points had a PWS difference of ±5 dB between the two intrasession or intersession measurements for both stimuli.

Conclusions: The CoR for the DACP is larger than that reported for scotopic perimeters; however, the majority of test points had a PWS difference of ±5 dB between tests.

Translational relevance: The DACP offers an opportunity to measure static and dynamic rod function at multiple locations with an acceptable reproducibility level.

Keywords: age-related macular degeneration; dark-adapted chromatic perimeter; scotopic perimeter; test-retest repeatability.

Figure 1

(A) Dark-adaptation curve from a healthy eye and the dynamic ranges of various scotopic perimeters. The DACP (505 nm, cyan stimulus) has the greatest dynamic range compared with the S-MAIA (505 nm, cyan stimulus) and the MP-1S (white stimulus). For the MP-1S, the dynamic range without a neutral density filter is shown. When neutral density filters were applied the minimum stimulus intensity could be further reduced and the dynamic range can be extended. Note that the minimum stimulus intensity of the S-MAIA is around the rod–cone break of the dark-adaptation curve in a healthy eye. (B) The Medmont DACP.

Figure 2

Average PWS of each test for the 505- and 625-nm stimuli. Note that for the 505-nm stimulus, there was a significant increase in the average PWS between test 1 (20 minutes after dark-adaptation) and 2 (30 minutes after dark-adaptation) but not between test 2 and 3 (40 minutes after dark adaptation) in the AMD group. Error bars: 95% confidence interval.

Figure 3

Bland-Altman plots of PWS for the 505- and 625-nm stimuli (A). There was no association between the difference and magnitude of PWS in any of the examination pairs. The AMD group had a greater limit of agreement compared with the control group for both stimuli. Note that the larger dots represent greater overlapping of test points. Cumulative percentage of PWS difference (B) showed that approximately 80% of all test points had a PWS difference of ±5 dB between the two tests.

Figure 4

Coefficient of repeatability of each test point for the 505- and 625-nm stimuli. Plots are presented in retinal view and referenced to the right eye. Note that central test points (<10°) are more repeatable than the peripheral test points.

Figure 5

Average PWS of each visit for the 505- and 625-nm stimuli. No significant change in average PWS between the visits was detected for both the 505- and 625-nm stimuli. Error bars: 95% confidence interval.

Figure 6

Bland-Altman plots of PWS for the 505- and 625-nm stimuli (A). The AMD group had a greater limit of agreement compared with the control group for both stimuli. Cumulative percentage of PWS difference (B) showed that approximately 80% of all test points had a PWS difference of ±5 dB between the two visits.

Figure 7

Coefficient of repeatability of each test point for the 505- and 625-nm stimuli. Plots are presented in retinal view and referenced to the right eye. In general, central test points (<10°) are more repeatable than the peripheral test points.