The Dry Eye Zone

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Abstract: Impact of tear break up on vision

Measurement of the time course of optical quality and visual deterioration during tear break-up.
Invest Ophthalmol Vis Sci. 2010 Jun;51(6):3318-26. Epub 2010 Jan 27.
Liu H, Thibos L, Begley CG, Bradley A.
School of Optometry, Indiana University, Bloomington, Indiana 47405, USA. hailiu@indiana.edu

Abstract
PURPOSE: To compare changes in optical quality and visual performance that accompany tear break-up (TBU) during blink suppression.

METHODS: A three-channel optical system was developed that simultaneously measured refractive aberrations (Shack-Hartmann aberrometer), 20/40 letter contrast sensitivity (CS), and TBU (retroillumination, RI). Ten wearers of silicone hydrogel contact lenses were asked to keep one eye open for approximately 18 seconds, while CS, wavefront aberrations, and RI images were collected. The wavefront was reconstructed by zonal methods, and image quality was quantified with a series of metrics including RMS fit error. Novel metrics for quantifying TBU over the contact lens surface were developed by quantifying the contrast of the RI image and by using Fourier descriptors of the first Purkinje (PJ) image shape.

RESULTS: There was a full range of TBU over the lens surface, with four subjects showing TBU across the corneal center and one subject with TBU in the inferior peripheral pupil. Among the four subjects with central corneal TBU, RMS fit error, RI contrast, and PJ Fourier descriptors showed high correlation with CS (r(2) range, 0.9187-0.9414, 0.6261-0.975, and 0.4917-0.8986, respectively). Some of the general optical-quality metrics such as blur strength, neural sharpness, and area of modulation transfer function (MTF) also showed that change correlated with CS loss.

CONCLUSIONS: Optical metrics of tear quality and retinal image quality are associated with the decline in vision that occurs with TBU. The evidence supports the hypothesis that blurry vision symptoms reported by contact lens wearers are caused by poor quality of the retinal image due to TBU.
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