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TF Buehren, MJ Collins, LG Carney; Corneal Topography Following Reading . Invest. Ophthalmol. Vis. Sci. 2002;43(13):151.
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Purpose: To investigate the effects of eyelid pressure on corneal topography after reading. Method: Twenty young subjects (mean age 27 years) were recruited for the study. The subjects were selected so as to have normal ocular health, corneal topography within normal limits and to have a range of refractive errors. The experiment was conducted early in the morning, with subjects instructed not to perform any significant reading prior to the experiment. Corneal topography of one eye was measured 6 times using a videokeratoscope prior to reading and then again after a 60 minute reading task. To investigate the potential association between lid position during reading and changes in topography, the natural position of the eyelids and pupil was photographed in primary gaze and during the reading task. Results: Twelve of the twenty corneas showed significant changes in topography immediately following reading, seven of which occurred within the central 4 mm of the cornea. The location of the changes corresponded closely to the angle and position of the subject's eyelids during reading. The topographical change was best described as a wave-like distortion which significantly altered some corneal wavefront Zernike coefficients. For a 4 mm pupil size the terms that changed significantly (t-tests) were primary astigmatism (p < 0.05), primary vertical coma (p < 0.001), trefoil (along 30°) (p < 0.05), and secondary astigmatism (p < 0.05). There was a significant correlation between the changes in primary vertical coma and trefoil (along 30°). Corneal root-mean-square error (RMSE) was significantly increased for individual photopic pupil sizes (p = 0.013) as well as for fixed pupils of 5 mm (p = 0.036) and 6 mm (p = 0.022) respectively. Within the central 4 mm of the cornea there were significant changes in overall refractive power, astigmatism and the RMSE for some individuals. Conclusion: The changes we observed in corneal shape seem to be directly related to the force exerted by the eyelids during reading. Since the cornea is the major light-refracting surface of the eye, eyelid forces can significantly change the optical characteristics of some eyes during reading. These findings may have important implications for the definition of refractive status and may also aid in the understanding of the relationship between reading and refractive error development.
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