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N.J. Keir, T. Simpson, L. Jones, D. Fonn; Factor Analysis of Postoperative Outcome Variables for a CustomCornea® LASIK Clinical Trial . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4352.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate whether a large set of variables (40) collected for a group of myopic patients with and without astigmatism following CustomCornea® LASIK can be explained largely or entirely in terms of a smaller number of factors. Methods: LASIK was performed on 163 myopic eyes with or without astigmatism (82 patients) using the LADARVision® laser coupled with the LADARWave® Measurement Device. Mean preoperative sphere was –2.70±1.34D (range –0.25 to –6.50D) with mean cylinder –0.88±0.74D (range 0 to –3.25D). High contrast (HC) and low contrast (LC) uncorrected and best–corrected visual acuity (UCVA and BCVA, respectively) were measured using ETDRS charts and contrast sensitivity using the VectorVisionTM CSV1000 at 4 spatial frequencies (3, 6, 12 and 18 cycles/degree). Subjective responses were collected using a descriptive rating questionnaire. Data for this analysis was from the 3 month postoperative visit and only the right eyes were included (n=82). Exploratory factor analysis was completed using Statistica 7 for 40 variables. A Scree test and a varimax rotation were used to determine and interpret the factors. Results: 62% of the variability of the data could be explained using 5 factors. Factors 1, 2, 3, 4, and 5 could each explain 25%, 17%, 9%, 6% and 4% of the variability of the data, respectively. Based on weighting scores, the primary factor was high luminance vision (HC and LC UCVA and BCVA). The second factor was sensory ratings (light sensitivity, glare and haloes). Other separate factors consisted primarily of spherical ametropia (sphere and spherical equivalent), contrast sensitivity (high and moderate luminance and different spatial frequencies) and finally ocular discomfort (burning, tearing and dryness). Conclusions: It can be concluded that there are a variety of factors that contribute to the outcome variables for this data set and multiple variables for each factor are clinically important. The key factors (in rank order) are high luminance vision, sensory ratings, ametropia, contrast sensitivity and ocular discomfort.
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