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Paul Ludington, Kristen Hovinga, Mohinder Merchea; Predicted logMAR Image Resolution During Dehydration for Silicone Hydrogel Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4636.
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© ARVO (1962-2015); The Authors (2016-present)
To analyze the image stability and predicted logMAR retinal image resolution of one investigational (samfilcon A) and three commercially available contact lenses as the lenses dehydrate with time.
Thirty -3.00D lenses of each lens type (samfilcon A, senofilcon A, lotrafilcon B, and comfilcon A) were analyzed on an optical imaging bench. The bench uses a diamond-turned model cornea that mimics the optics and physical dimensions of an average human eye, and relays the retinal plane image of a target (US Air Force) to a CCD camera. Multiple images were captured through each lens over time with a target at optical infinity. Each lens was blotted to remove excess packaging solution and conformed to a 7.8mm radius PMMA model cornea with +0.18 microns of spherical aberration over a 6mm aperture. One or two drops of rewetting solution were used to simulate the tear film. Images were acquired every 10s, as the lens was dehydrating, up to 30s following application of the drops. A pattern-matching and contrast algorithm was used to estimate the logMAR score for each image.
A Repeated Measures ANOVA was conducted on the individual predicted logMAR scores for the four different lens types alongside a Tukey post-hoc analysis. The test lens (samfilcon A) had better predicted logMAR scores at time-zero and at each additional time (10s, 20s, and 30s) compared to the three commercial lens products (p < 0.01 in all cases). At time-zero, the test lens had at least a one-line improvement in predicted logMAR acuity compared to the three commercial lenses. After 30s, the test lens had a 1.3 line mean improvement over the senofilcon A lens, a 3.2 line mean improvement over the lotrafilcon B lens, and a 3.5 line mean improvement over the comfilcon A lens.
This novel in-vitro method quantitates the predicted logMAR score based on optical image quality as the lens dehydrate with time. The test lenses exhibited better optical image quality than the three commercially available lenses at all times during the test. The samfilcon A test lens start out producing a clearer image and remained clearer during the entire 30s test. Further research is needed to understand the clinical impact to visual stability.
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