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P.S. Kollbaum, A. Bradley; Optical Signature, Structural Mechanism, And Chronology Of Corneal Refractive Therapy (crt) . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1541.
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Purpose: The purpose of this experiment was to determine the optical signature and chronology of eyes wearing Paragon CRT contact lenses, and determine how these relate to the structural mechanism. Methods:Three myopic patients were fit with CRT lenses. Following the first night, 1 week, and 1 month of nightly lens wear, repeated whole eye aberrations (COAS) and corneal aberration measurements (ORBSCAN) were acquired hourly from the time of eye opening (8 am) until bedtime (9 pm). Measurements were also taken on one of these subjects when ceasing treatment, on the first through fourth day following discontinuing wear, and then again at 1, 2, 3, and 4 weeks. Wavefront variances were calculated and retinal images simulated for 3mm and 5mm pupil sizes. Results:As expected, after wearing the lenses myopia was decreased from – 3.49±0.80 D at baseline to – 0.52±0.24 at 1 month. However, with this decrease in myopia, spherical aberration increased from + 0.07±0.05 D at baseline to a maximum of +0.32D±0.05 D after 7 days, and then leveled off to + 0.19±0.07 at 1 month. Over this same initial 7 day period, a 1 D reduction in anterior corneal curvature resulted in a 1 D reduction in myopia. However, following this time a further reduction in myopia occurred, while anterior corneal curvature remained the same. Anterior and posterior corneal curvature changes occurred at roughly the same rate initially, and showed a similar regression throughout the day. However, following 3 weeks of lens wear, the posterior curvature remained roughly constant throughout the day, however the anterior curvature still regressed slightly. Correspondingly, aberrations were initially less stable throughout the day, showing an increase in myopic defocus of – 0.043D/hr. at day 1, but became more stable by 1 week (– 0.033D/hr.), and even more stable at 1 month (– 0.023D/hr.). Conclusions: In agreement with published reports of acuity data, if the lenses are worn nightly for two weeks, CRT can provide an effective method of myopia correction, which is quite optically stable throughout the day. However, an increase in spherical aberration can accompany the reduction in myopia, especially initially. The structural mechanism appears to be complex, involving an initial corneal stromal reshaping, compounded by further longerterm epithelial changes.
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