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H. Liu, L. Thibos, A. Bradley, C. Begley, K. Haggerty, K. Moody; Real Time Analysis of Optical Quality and Visual Performance During Tear Breakup. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2024.
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The purpose of this study was to identify optical and novel metrics that best describe the impact of in vivo contact lens wetting on visual performance.
A Shack-Hartman wavefront sensor was customized to allow simultaneous aberrometry and contrast sensitivity (CS) measurements while viewing tear break-up (TBU) within the pupil by retroillumination (RI) via an infrared light source. Ten hydrogel contact lens wearers were asked to keep one eye open for approximately 18 sec, while CS, wavefront aberrations and RI were collected. The wavefront was reconstructed by zonal methods, and image quality was quantified using a series of optical quality metrics. Novel metrics for quantifying changes due to tear break-up over the contact lens surface were developed from the changing contrast of the RI image and by using Fourier analysis of the irregularity of the first Purkinje shape.
There was a full range of in vivo lens wetting as measured by TBU over the lens surface (extensive to none), with 5 subjects showing significant TBU. Changes in 31 optical quality metrics showed variable correlations with CS loss, with the blur strength, neural sharpness and area under the MTF showing the highest correlations (R2 =0.77, 0.83, 0.83) among the 5 subjects with TBU. Two novel metrics were developed from the RI image (RI image contrast and a Fourier descriptor of the first Purkinje image shape) which showed high correlations (R2 =0.978, 0.85) with CS in subjects with TBU. Two subjects with TBU experienced a monotonic decline in their MTF at 12c/d which mirrored the change in CS of 20/40 letters.
Two novel metrics of tear quality, one employing light refracted by the tear film (RI contrast) and one light reflected from the tear film (regularity of the 1st Purkinje image shape), and several optical quality metrics, correlate well with the decline in vision that occurs with TBU over the lens surface. Thus, real time in vivo lens wetting can be monitored using objective optical quality metrics based on RI and catoptric imaging.This project was supported by a grant from Faculty Research Support Program (FRSP) of Indiana Univeristy
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