Objective Assessment of the Contrast Sensitivity Function using the nGoggle

Abstract

Purpose : Contrast sensitivity is one of the most important visual function measures, being strongly related to the ability to perform many daily tasks. Assessment of the contrast sensitivity function, however, is generally a subjective and cumbersome task. The nGoggle (nGoggle, Inc., San Diego-CA) is a portable brain-computer interface for objective assessment of visual function loss, which is able to successfully detect visual field loss in glaucoma. In the present study, we implemented modifications in the nGoggle visual function testing protocol and investigated its ability to objectively quantify the contrast sensitivity function.

Methods : This study included 16 eyes of 8 patients. Patients were tested with contrast sensitivity assessments using the nGoggle and the Pelli-Robson chart (Precision Vision, La Salle, IL). The nGoggle integrates wearable, wireless, dry electroencephalogram systems and a head-mounted display (HMD), allowing detection of steady-state visual evoked potentials (SSVEP) corresponding to pattern reversal visual stimuli. The visual stimulus presented on the nGoggle’s display consisted of Gabor patches flickering at 10 Hz with sweeping contrasts from low to high (0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0, and 96%) and five spatial frequencies (0.5, 1.0, 2.0, 4.0, and 8.0 cycles/degree). SSVEPs amplitudes were computed by discrete Fourier transform under all conditions. The relationship between the amplitude of SSVEPs and the results of Pelli-Robson chart for each eye was investigated using a linear regression model.

Results : Mean age of patients was 59.9 ± 20.5 years. Pelli-Robson chart mean contrast sensitivity was 1.49 ± 0.18 log units. The nGoggle mean SSVEP amplitude was 0.38 ± 0.11µV. The amplitude of SSVEPs at a contrast level of 16.0% and spatial frequency of 2.0 cycles/degree was strongly associated with contrast sensitivity measured by the Pelli-Robson chart (R²=65.6%; P<0.001).

Conclusions : The nGoggle was able to objectively assess contrast sensitivity and its measurements were strongly associated with conventional metrics. The portability and objectivity of the nGoggle may facilitate measurement of the contrast sensitivity function in practice.

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

 

A subject with the nGoggle.

 

Relationship between steady-state visual evoked potential (SSVEP) amplitude at contrast level of 16.0% and spatial frequency of 2.0 cycle/degree, and contrast sensitivity measured by Pelli-Robson chart for each eye.