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Deepa Dhungel, Scott Stevenson; Measurement of Contrast Sensitivity using Vertical Vergence Eye Movements. Invest. Ophthalmol. Vis. Sci. 2020;61(7):5087.
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© ARVO (1962-2015); The Authors (2016-present)
The current psychophysical methods for measuring the spatial contrast sensitivity function (CSF) require subject compliance, attention and active participation of the subject in the task. This poses a challenge for subjects with compromised communication or comprehension ability. Measuring vertical vergence, a reflex eye movement can be used as an alternative method for determining contrast sensitivity in such cases. The purpose of the study was to measure contrast sensitivity using vertical vergence eye movements and compare with the results from a psychophysical method.
Subjects were 3 adults with normal vision. A Dual Purkinje image eye tracker was used for eye tracking. Vertical vergence was measured in response to full screen vertical disparity modulation of horizontal sine wave gratings modulated sinusoidally at a frequency of 0.25 Hz with amplitude of 0.5 degrees. Each trial was 16 seconds long. A block of trials comprised combinations of 8 contrasts [0%, 1%, 2%,4%,8%,16%,32%,64%] and 8 spatial frequencies [0.125, 0.25, 0.50, 1, 2, 4, 8 and 16cycle per degree] presented in shuffled order. Oculometric contrast thresholds were determined by interpolating the contrast values at which the mean response curves cross a criterion line. The criterion was defined as the upper 95% CI above the mean for responses to 0% contrast. The psychophysical CSF was obtained with a 2AFC staircase method for the same spatial frequencies.
Vertical vergence responses were robust for middle spatial frequencies (0.5 to 4 cpd) with contrast thresholds close to or better than 1% in all three subjects (sensitivities at or above 100). The responses for lower and higher spatial frequencies were less reliable showing lower contrast sensitivities. The shape of the oculometric CSF was similar to that of psychometric CSF. The thresholds obtained from the two methods for middle ranged spatial frequencies were also comparable.
The results of this study suggests that vertical vergence can be used as a reliable method for measuring contrast sensitivity. Refining the number of trials will possibly make it feasible to use it as an efficient way of measuring CSF.
This is a 2020 ARVO Annual Meeting abstract.
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