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Bhavatharini Ramakrishnan, Scott B Stevenson; Effect of Alternating and In phase flicker occlusion on vergence eye movements. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2825.
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Rapid alternate occlusion of the eyes has been shown to improve stereoacuity and visual acuity in some amblyopic subjects1. Previously we looked at the effect of alternate occlusion on vergence eye movements in subjects with normal ocular health. In this current study, we want to compare the effect of alternate vs. in phase occlusion of different frequency on vergence eye movements and to see if it is the presence of flicker per se or alternate occlusion of the eyes that has an effect on vergence.Reference:1 A flicker therapy for the treatment of Amblyopia, Fuensanta. A. Vera-Diaz, Bruce Moore, Eric Hussey, Gayathri Srinivasan, Catherine Johnson, Vision development and Rehabilitation, Volume 2 Issue 2, June 2016.
Vergence eye movements were measured using a dual Purkinje image eye tracker. The stimulus used for the testing was a filtered noise pattern of spatial frequency 0.25 or 2 c/deg with a bandwidth of 1 octave and variable contrast. Trials were 2 seconds long, with a near or far 1 deg disparity step at either 250 or 350 msec into the trial. Both alternating and in-phase flickers of different frequencies (2, 4, 8, 16, 32 Hz) were used. Data were collected in blocks of 240 trials (6 contrast x 5 flickers x 2 directions x 2 onset times x 2 phases) in shuffled order. Data were collected in 2 subjects and for two spatial frequencies (2 and 0.25 cycles per degree) in separate sessions. Three variables were analyzed and compared between the two phases of flickers: Latency to reach half the amplitude, Peak velocity, and the final amplitude.
At higher flicker rates of 16 and 32 Hz, Vergence responses were robust, with peak velocities of 4 to 6 degrees per second and reaching the 1-degree demand within one second. At lower flicker rates, 2 and 4 Hz, and to a lesser extent at 8Hz, alternating flicker reduced vergence amplitude and increased latency dramatically while in phase flicker had only a small effect.
The results of this study show that vergence responses are disrupted by alternate flicker more than in phase flicker, particularly at lower frequencies. With alternate occlusion at 8 Hz, which has been used in Amblyopia treatment, vergence is intact but somewhat impaired. Results of this study will be helpful in refining Flicker glasses as a therapy for Amblyopia.
This is a 2021 ARVO Annual Meeting abstract.
Peak velocity scatter plot for both subjects(first 2 rows= subject 1 and last two rows= subject 2)
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