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PM Akaishi, LC V Neves, C Polegato, AA V Cruz; The Effect of Darkness on the Upper Eyelid Position . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3029.
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Purpose: It is well established that darkness changes the balance between the sympathetic and parasympathetic tone on the ciliary body and iris muscles. The purpose of the presence work was to determine if the resting position of the upper eyelid is also affected by darkness Methods: Palpebral fissure images of 18 normal subjects (10 females and 8 males with ages ranging from 19 to 52 years) were acquired in photopic conditions and in total darkness. In order to obtain both images a CCD with infrared red sensibility connected to a Macintosh microcomputer was used. For all subjects, the initial procedure was to line up the camera with the eye under measure while the subject was fixating a target located at 1 meter of distance. Only the right eye was imaged. The first palpebral fissure image was acquired in photopic conditions. The lights were then turned off and a second image of the right eye was obtained in total darkness. To obtain this image an infrared source was employed to increase the image quality. The whole procedure lasted less than 1 minute. For both images the distance between the mid-pupil and upper eyelid margin (MPMD) was measured with the NIH image 1.62 software Results: Darkness increased the MPMD for all subjects. The increment in MPMD ranged from 0.2 to 2.6 mm with a mean of 1.23 mm. Conclusion: Darkness provoked upper eyelid retraction in all subjects tested. This effect probably results from stimulation of the sympathetic tone to the Müllers’s muscle.
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