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The significance of changes in pupil size during straylight measurement and with varying environmental illuminance.

J Optom 2018, vol. 11, issue 3


In this work, we investigated the pupillary conditions during straylight measurement, and the potential effect this might have on the measured straylight.


Five young (26-29-years-old) and 15 older (50-68-years-old) individuals participated in this study. First, the pupil diameter of both eyes was measured at three room illuminances. Next, straylight was assessed at two room illuminances. Simultaneously, the change in pupil size of the fellow eye was registered by a camera.


Pupil size decreased with room illuminance and with age (both p


We conclude that the illuminance of the examination room during straylight assessment does not affect the outcome in normal eyes. In fact, under mesopic and scotopic conditions, the luminance of the test field is so much higher than that of the room so that it determines the pupil size. Regardless of the lighting level, straylight measured in a laboratory, is valid for photopic pupils at an adaptation level corresponding with about 400 lux room illuminance.

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