Comparative Measurements of Rod Function in Retinal Degenerations with Two-color Dark-adapted Perimetry

Abstract

Purpose : Novel treatment strategies for inherited retinal degenerations (IRD) are directed at either improving rod function or arresting its progressive loss. Rod function can be measured with two-color dark-adapted perimetry (TCDP). Modified Humphrey Field Analyzers (mHFA) developed for TCDP (Jacobson et al., 1986; Roman et al., 2005) have been established as the ‘standard’ with a long-standing track record of published results in dozens of IRDs. More recently, Nidek MP1-S and Medmont DAC systems have become available for TCDP but their comparison to mHFA remains unknown to date.

Methods : We performed TCDP with the MP1-S in 10 RP patients and with the DAC in 10 RP patients; each patient also had TCDP with mHFA. mHFA projects stimuli into a white bowl; DAC has LEDs placed at specific loci within a black bowl. Both perimeters perform under free viewing conditions. MP1-S presents filtered LCD display to the central visual field under infrared retinal tracking. The shorter wavelength stimuli were 500, 505, <505 nm, and longer wavelength stimuli were 650, 620, >605 nm for the mHFA, DAC and MP1-S, respectively. All stimuli were Goldman V sized (1.7deg in diameter) and 200 ms in duration.

Results : MP1-S and mHFA comparison were performed along the horizontal and vertical meridians between 4 and 14 deg eccentricity with 2 deg spacing. Loci with rod-mediation based on previously established mHFA criteria, demonstrated sensitivity difference (blue minus red) for MP1-S stimuli of 16.7+/-3.9 dB (mean+/-sd; when adjusted for ND filters used to extend the dynamic range of the instrument). DAC and mHFA comparison were performed in retina-wide testing extending to 72 deg eccentricity in temporal and nasal fields on a 12 deg grid. Loci with mHFA-defined rod mediation showed a sensitivity difference for DAC stimuli of 22.0+/-6.6 dB. Available dynamic ranges for the shorter wavelength stimuli were 65 dB, 75 dB and 50 dB for the mHFA, DAC and MP1-S, respectively.

Conclusions : Rod function using TCDP can be measured with the mHFA, Nidek MP1-S and Medmont DAC. The blue-red difference cutoff corresponding to underlying rod function for both colors of TCDP were 9 and 8.8 dB for MP1-S and DAC, respectively. Strengths, weaknesses and availability should be considered carefully in the decision to use a specific equipment for studies of natural history and clinical trials involving measurement of rod function in IRDs.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.