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L. Ng, E. Myung, A.L. Nguyen; Effectiveness of Various Methodologies in Assessing Refractive Stability in De–Adapting Contact Lens Photorefractive Surgical Candidates . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3607.
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In current clinical practice photorefractive surgery candidates are asked to discontinue contact lens (CL) wear for an antecdotal period of time so their true refractive state can be measured and treated. Manifest refraction and keratometry may be the only tools used to confirm refractive stability. The purpose of this study was to compare these traditional methodologies vs newer technologies (corneal topography, optical pachymetry, Hartmann–Shack aberrometry) to assess corneal recovery from chronic CL induced changes. This study investigated the timeline differences between these technologies in determining refractive stability in corneal refractive surgery patients.
This was a masked clinical prospective cohort study of 15 full time soft contact lens (SCL) subjects and 5 non–CL controls; all eligible for refractive surgery. Each subject discontinued any CL wear within 2 hours prior to their initial study visit and were asked to remain out of their CL for the remainder of the study. At each scheduled visit, manifest refraction, keratometry, corneal topography, optical pachymetry, and Hartmann–Shack aberrometer were performed. Refractive stability was reached when at least 4 of 5 methods had consistent findings between two consecutive visits.
The mean number of days until refractive stability of the 15 test subjects (5 controls) was 11.4 (8.8) days with manifest refraction, 16.5(12.2) days with keratometry, 27.2 (10.5) days with topography and 34.8 (22.7) days with pachymetry. Regression analysis found a statistically significant difference in the number of days until stability as determined by the various methods, and further suggested that depending which single method was used, the timeline until stablity changed by a factor of 7.89 OD and 6.27OS. Contrast Analysis also showed an overwhelming difference between the traditional vs newer methods for determining time to stability (p<0.0001). Surprisingly the type of SCL worn (daily wear, extended wear, silicon hydrogel, frequent replacement, toric/sphere) was an insignificant factor in determining stability timing.
The newer technologies were significantly more sensitive at determining corneal instabilities than the traditional methods. In light of this the current protocol (refraction and keratometry) for determining the surgical readiness of our corneal refractive patients after discontinuing their CL may be inadequate.
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