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John R Hetling, Shresta Patangay, Jason C Park, J Jason McAnany; Evaluation of a Contact Lens Electrode Incorporating a Light Diffusing Element. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5023.
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© ARVO (1962-2015); The Authors (2016-present)
One potential source of variability in full-field flash ERG responses is inconsistency of alignment between the stimulus source and the eye, from improper positioning of the source by the tester, or improper direction of gaze by the subject (poor cooperation or involuntary eye movement). Inconsistent alignment results in inconsistent magnitude and/or spatial distribution of illuminance at the retina. Here we explore the utility of a contact lens electrode that incorporates a light-diffusing element, as a potential means of reducing variability in retinal illuminance and, therefore, ERG responses.
A silicone electrode substrate was designed to conform to the anterior surface of the eye and position a ring-shaped electrode outside the margin of the dilated pupil. The substrate extends beneath the eyelids for stability, and is shaped to prevent blinking. The distal surface of the substrate is planar, and in one version includes a layer of high-index glass microspheres, creating an effective light-diffusing element. The two electrode styles (clear and diffusing) were compared using full-field flash stimuli in dark-adapted healthy subjects, during proper eye/stimulus alignment, and poor eye/stimulus alignment. Light scattering was quantified by directing a collimated laser beam through the center of the lens substrate, and evaluating the full width at half maximum (FWHM) of the illuminance profile one cm from the lens.
With proper eye/stimulus alignment, a-wave amplitudes recorded with clear and diffusing electrodes were not significantly different. With poor eye/stimulus alignment (head turned 30 degrees in nasal direction), a-wave amplitudes were reduced by approximately 25% (compared to proper alignment) for the clear electrode, and were unaffected for the diffusing electrode. For a 5 mm collimated beam passing through the diffusing electrode, the FWHM was 41 mm at a distance of 1 cm.
The reduced transmission due to backscatter in diffusing electrodes is likely compensated for by directing more light to the peripheral retina, producing equal amplitude responses. The very low sensitivity to eye/stimulus misalignment suggests that diffusing electrodes should produce more consistent ERG response amplitudes where alignment cannot be precisely controlled.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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