An Analysis of Scotopic Microperimetry in Healthy Adults

Scotopic microperimetry measures retinal sensitivity under very low light and may be useful in conditions characterized by nyctalopia, such as retinitis pigmentosa and age-related macular degeneration. The Scotopic Macular Integrity Assessment device enables two-color perimetry to isolate rod and cone responses. This study assesses the reliability, test-retest repeatability, and sensitivity in healthy participants aiming to establish normative values.

Scotopic microperimetry was performed using cyan and red stimuli on a 37-point radial grid after dark adaptation on control participants with no history of eye disease and visual acuity of 0.1 logarithm of the minimum angle of resolution or better. Fixation stability, fixation losses, and identification of the rod-free zone were used as reliability metrics. A subset underwent repeat testing within 4 weeks.

Thirty-nine participants (19 male and 20 female), median age 24 years (interquartile range, 9.5 years) and 23 years (interquartile range, 9 years) for the right and left eyes, respectively, completed testing. Overall 77 eyes underwent scotopic testing, with 82% meeting reliability criteria. Mean cyan and red sensitivities were 19.9 ± 1.1 dB and 20.9 ± 1.2 dB in right eyes, and 20.1 ± 1.4 dB and 21.3 ± 1.4 dB in left eyes, respectively. Volumetric cyan and red sensitivities were 2868 ± 157 dB.deg2 and 3077 ± 176 dB.deg2 in the right eyes, respectively, and 2892 ± 205 dB.deg2 and 3126 ± 207 dB.deg2 in the left eyes, respectively. Mean sensitivity coefficients of repeatability (CoR) were ± 1.4 dB (cyan) and ± 2.1 dB (red) while pointwise coefficients of repeatability were ± 7.2 dB (95% confidence interval, 6.5-7.6 dB) for cyan and ± 7.9 dB (95% confidence interval, 7.3-8.4 dB) for red, with no significant differences between eyes or genders. Fixation stability assessed using the 95% bivariate contour ellipse area for cyan was 2.9 ± 5.9 deg2 and 2.3 ± 2.2 deg2 for the right and left eyes, respectively, and for red were 0.7 ± 0.6 deg2 and 0.9 ± 0.8 deg2 for the right and left eyes, respectively. Again, there were no significant differences between cyan and red tests (Friedman test, bivariate contour ellipse area 63%, P = 0.455; bivariate contour ellipse area 95%, P = 0.432).

Scotopic microperimetry using the Scotopic Macular Integrity Assessment device was feasible and well-tolerated. Repeatability metrics demonstrated limitations in fine spatial mapping of scotopic retinal sensitivity.

This study highlights potential areas for future improvements in scotopic microperimetry before its use as an outcome measure in clinical trials for retinal disease.