Comparison of contrast sensitivity in photopic and mesopic conditions

Abstract

Purpose : Measurement of contrast sensitivity function (CSF) can reveal subtle defects of vision that are often missed by standardized testing using charts with 100% contrast optotypes. Clinically, CSF measures are performed with a bright background nearing photopic light levels. Given that CSF may aid in identifying night vision difficulty, we sought to compare the CSF functions in photopic and mesopic light levels.

Methods : Twenty-five individuals (26.7 mean age 4.6 SD) underwent ophthalmic evaluation including refraction and slitlamp examination. All individuals had a visual acuity of 20/20 or better on an ETDRS 100% contrast chart. Subjects underwent CSF measurement using CSV-1000E under binocular viewing conditions at a distance of 8 feet in both photopic and mesopic light levels in a randomized fashion. The light levels of CSV-1000E chart were 85 cd/m². The mesopic condition was simulated using 1.5 neutral density filter. The CSF was measured at spatial frequency of 3, 6, 12 and 18 CPD. A paired samples t-test was performed to evaluate the difference in mean CSF at various spatial frequencies. A regression analysis was performed between the photopic and the mesopic CSF.

Results : The table 1 provides the mean and standard deviation of CSF measured under photopic and mesopic condition at 3, 6, 12 and 18 CPD. The mean CSF, as expected, was significantly lower at mesopic levels when compared to photopic conditions. The regression analysis indicated that the correlation coefficient between the photopic and mesopic CSF levels at various CPD was weak, with R-square values ranging from 3-27%.

Conclusions : As expected, the CSF in mesopic condition is lower than as measured in photopic condition. It is interesting to note that photopic CSF is weakly correlated with mesopic CSF and cannot be used to predict the outcome of mesopic CSF.

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