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Regression of lid-induced corneal topography changes after reading
Michael J Collins1, Kristian Kloevekorn-Norgall, Tobias Buehren
1Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Victoria Park Road, Kelvin Grove 4059, Brisbane, Australia. m.collins@qut.edu.au
Purpose:
The purpose of this article is to investigate the magnitude of lid-induced corneal topography changes as a function of time spent reading and the subsequent time course of regression of these changes.
Methods:
Six young subjects, five myopes and one emmetrope with normal ocular health, participated in the study. Corneal topography of one eye was measured with videokeratoscopy before four reading sessions of 10, 30, 60, and 120 min duration performed on four separate mornings. Corneal topography was again measured at fixed intervals up to 180 min after each reading session. A control trial without reading was also performed on a separate morning.
Results:
All six subjects showed significant changes in corneal topography directly after each of the reading sessions. Longer reading periods caused larger corneal changes. Local instantaneous power changes reached up to 5.95 D (+/- 2.80 D), whereas refractive power changes in the superior cornea ranged up to 1.26 D (+/- 0.44) for the 120-min reading trial. The duration of regression of corneal changes showed slower recovery times after longer reading periods. The pattern of regression was similar for all reading times, showing a rapid recovery within the first 10 minutes followed by a slower regression period.
Conclusions:
The length of time spent reading has a cumulative effect on the period over which corneal topography remains altered as a result of lid forces.