Pattern ERG as an objective measure of contrast senitivity function

Abstract

Purpose : Contrast sensitivity is difficult to objectively quantify. The pattern ERG (pERG) is an objective measure of retinal ganglion cell functionality. The purpose of this study is to determine if pERG can be used to objectively measure contrast sensitivity function at different spatial frequencies in healthy eyes.

Methods : The right eye of 5 normal subjects with a mean age of 25 years were tested for this study. All subjects had no ocular disease, and had best corrected visual acuity of at least 20/20. The pERGs were recorded using an ISCEV compliant Espion E3 system (Diagnosys LLC, Lowel MA). Each subject had pERG testing at 7 different spatial frequencies (0.125, 0.25, 0.5, 0.75, 1, 2, and 5 cycles-per-degree (CPD)). At each CPD, subjects were tested across 7 black-and-white contrast intensities including 100%, 95%, 90%, 85%, 80%, 75% and 70% contrast. Each individual subjects’ data was then averaged to produce a single N95 amplitude value for each combination of contrast intensity and CPD. The contrast intensity at which the N95 amplitude of the response was half that at 100% contrast was determined for each data series.

Results : There was a linear decrease in the N95 amplitude as contrast intensity decreased, across all CPD/spatial frequency trials for all subjects. The half maximal N95 amplitude occurred at increasing contrast intensities between 0.125 and 0.25 CPD and subsequently decreased until 5 CPD for all subjects.

Conclusions : For healthy eyes, the half maximal N95 response produces an inverted “U”-shaped curve of increasing, followed by decreasing contrast sensitivity function at increasing spatial frequencies. This curve is similar to the inverted "U"-shaped curve of contrast sensitivity function produced using subjective methods of contrast detection. This can be a useful tool for objectively measuring contrast sensitivity function.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.