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Neural Adaptation to Brightness Perception in Patients Implanted with a Small Aperture Inlay


Purpose : Small apertures are successfully used to extend depth of focus in presbyopic patients implemented either as corneal inlays or intraocular lenses. Although the use of small apertures reduces retinal illuminance, patients report a less significant reduction in the perceived brightness as could be expected, suggesting an adaptation process. The purpose of this study was to quantify the relative perceived brightness in the two eyes of patients implanted monocularly with a small aperture inlay.

Methods : We used a binocular adaptive optics vision simulator to determine the relative perceived brightness. This allows full control over both the size and transmittance of the entrance pupils on both eyes. Four patients implanted monocularly with the KAMRA corneal inlay (1.6 mm) participated in the study. The projected pupil on the eye implanted with the inlay alternated in diameter between 0 and 2.5 mm (effective 1.6 mm) whilst the corresponding fellow eye projected pupil alternated between 0 and 3 mm or 0 and 4 mm at a frequency of 1 Hz. Alternation on both eyes was synchronized so that only one eye at a time had a non-blocked pupil. At equal transmittance, a flickering was perceived. Patients’ task consisted of modifying the transmittance of the pupil corresponding to the fellow eye until the perceived flickering, due to the different perceived brightness, was minimized. This equalizing transmittance (ET) value indicates the relative perceived brightness. The experiment was performed under 2 luminance levels (232 and 23.2 cd/m2) in green (550 nm) light.

Results : The average value of ET across subjects was compared with the expected value based on simple geometrical considerations. The results for both luminance levels were similar. ET measured was a factor of 2.0x and 2.7x the expected value for the cases with the fellow eye with pupil sizes of 3.0 and 4.0 mm respectively. In all cases the differences were statistically significant (Student’s t-test; p<0.01).

Conclusions : Patients implanted with the small aperture corneal inlay exhibited an enhanced brightness perception with the eye implanted in comparison with their untreated fellow eye. The amount of this increase is much larger than what could be expected due the Stiles-Crawford effect and was probably due to a neural adaptation process. This phenomenon could explain a reported equalization of brightness between eyes in patients with unilateral inlays.

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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