Repeatability of foveal thresholds measured using adaptive optics microperimetry

Abstract

Purpose : To evaluate the repeatability of threshold measurements at the fovea using adaptive optics (AO) based microperimetry in normal sighted controls.

Methods : The foveal cone mosaics of five normal sighted controls were imaged at two time points separated by two months with a custom-built, multi-modal AO scanning light ophthalmoscope equipped with microperimetry. Circular stimuli of 550Δ30 nm light subtending 3.6 arcmin² and 29 arcmin² were presented to the fovea for 187.5 msec. Stimulus irradiance was chosen trial-by-trial using both the QUick ESTimation of threshold (QUEST) and method of constant stimulus (MOCS) paradigms. Following 120 training trials, QUEST (44 trials) and MOCS (100 trials) experiments were performed alternately with both stimulus sizes in random order four times each for a total of 1272 trials per session. For each trial, the subject responded yes/no to perceiving the stimulus. Trials were pooled by stimulus size and session for QUEST and MOCS methods separately, were corrected for guessing, and fit with a logistic psychometric function (Palamedes toolbox) allowing a lapse rate. For each subject, thresholds were converted from normalized device settings to irradiances using the average stimulus light source measurement from that subject’s two sessions. This implicitly assumes Weber law threshold behavior with respect to session-to-session variation in the irradiance of the stimulus light source. Threshold irradiance, defined as the stimulus yielding 78% frequency seen, was compared across stimulus sizes, testing paradigms and sessions using paired sample two-tailed t tests.

Results : Foveal thresholds expressed as light power were lower for the 29 arcmin² stimuli in comparison to the 3.6 arcmin² stimuli for all sessions and testing paradigms (29 arcmin²: 80 ± 8 pW/deg², 3.6 arcmin²: 400 ± 81 pW/deg²; p<0.0001). Thresholds for 29 arcmin² were not significantly different when measured with QUEST compared to MOCS (p=0.66), but for 3.6 arcmin² were lower when using QUEST (p=0.001). Across sessions, thresholds were not significantly different for 29 arcmin² stimuli (MOCS: p=0.87, QUEST: p=0.33) or for 3.6 arcmin² QUEST (p=0.07) but were lower in session 2 by 11.7 ± 6.3% for 3.6 arcmin² MOCS (p=0.03).

Conclusions : Foveal thresholds are generally repeatable across testing paradigms and sessions in normal-sighted subjects. QUEST provided results at least as repeatable as MOCS, but required fewer trials.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.