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Perceived luminance through small aperture greater than expected

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LISBON, Portugal — The perceived brightness with a small aperture is 30% to 60% greater than should be theoretically expected, according to a poster study presented here.

One of the potential issues with small aperture inlays or IOLs is that they reduce retinal illuminance. However, there is a significant history of clinical data showing that patients report less significant reduction in perceived brightness than expected.

“Due to neuroadaptation, the eye with a small aperture is somehow tuning the response and adjusting the difference in brightness,” Pablo Artal, PhD, said during the discussion of his poster at the European Society of Cataract and Refractive Surgeons meeting.

The poster reported the first part of a long-term study to quantify the relative perceived brightness when looking through a small aperture. Using a laboratory prototype instrument based on adaptive optics, five normal subjects were asked to alternatively look with one eye at an object through a large 3-mm and a small 1.6-mm aperture.

“With equal transmittance in both apertures, a flickering is perceived due to the different retinal illuminance. Subjects were then asked to attenuate light transmittance through the large pupil until flickering was minimized. This transmittance value indicates the relative perceived brightness reduction,” Artal said.

The perceived luminance ranged between 38.5% and 46.9%, while the theoretical value based on mathematics should be 29%.

“Under real visual conditions, this effect could be even more significant since binocular effects and temporal adaptation may further increase the perceived brightness with the small aperture,” Artal said. – by Michela Cimberle

Reference:

Artal P, et al. Perceived brightness with small aperture. Presented at European Society of Cataract and Refractive Surgeons meeting; Oct. 7-11, 2017; Lisbon, Portugal.

 Disclosure: Artal reports he is a consultant for AcuFocus.