PURPOSE: To determine if the resting position of the upper eyelid is affected by darkness. METHODS: Palpebral fissure images of normal subjects were acquired in photopic conditions and in total darkness. The subjects were divided in to three groups aged 2-11 months, 22-36 months and 19-61 years. The first palpebral fissure image was acquired in photopic conditions. The lights were then turned off and a second image of the same eye was obtained in total darkness. For both images the distance between the midpupil and upper eyelid margin was measured. RESULTS: Darkness increased this distance in all subjects. The increment in palpebral position was greater in children. CONCLUSION: Darkness provoked upper eyelid retraction in all subjects tested. This effect probably results from stimulation of the sympathetic tone to Müller's muscle.
Darkness; Eyelids; Age groups; Infant; Child, preschool
