• Luigina Sorbara, Desmond Fonn, Trefford Simpson, Fenghe Lu, and Richard Kort.
• Centre for Contact Lens Research, School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. gsorbara@uwaterloo.ca
• Optom Vis Sci. 2005 Jun 1; 82 (6): 512-8.

Purpose: The purpose of the study was to monitor the efficacy of corneal refractive therapy (CRT) lenses to reduce myopia over a 4-week period. Refractive error, keratometry, high and low contrast acuity, and subjective vision after 28 days of using CRT contact lenses were measured.Methods: Twenty-three myopes wore CRT HDS lenses, Dk = 100. The Nikon autokefractor/keratometer was used to measure the refractive error and keratometric changes. Visual acuity was measured using computerized high and low contrast charts and the subjects completed visual analog scales characterizing their vision on a daily basis. Measurements were performed at baseline (before lens insertion before sleep), immediately after lens removal the next morning and at 1, 3, 7, and 14 hours after eye opening. Measurements were made on the days following 1, 4, 10, and 28 nights of lens wear. After 72 hours of no lens wear, these parameters were again measured to assess corneal recovery.Results: The pretreatment manifest refraction (mean of OD and OS +/- standard deviation [SD]) was -2.72 DS +/- 1.06 and -0.55 DC +/- 0.40. Myopic spherical equivalent refractive error (+/- SD) decreased by 1.30 DS +/- 0.53 (range 0-3 D) immediately after lens removal on day 1 and by 2.59 DS +/- 0.77 by day 28 (range 1.25-3.88 D). The cylinder remained unchanged. Uncorrected visual acuity improved by 5 lines after one night and reached 0.00 LogMAR (6/6) by day 4. Visual acuity was maintained throughout the day by day 10. The day and time effect of the spherical equivalent change and the central corneal radius of curvature were statistically significant (p < 0.01) up to day 10 and remained the same until day 28. Central (autokeratometer) Ks flattened by 1.28 D +/- 1.35 after one night and 2.33 D +/- 1.30 by day 28. The subjective vision improved significantly from day 1 to day 28 (p < 0.01) and was maintained throughout the day from day 4 to day 28 (p < 0.01). All measures did not recover completely to baseline after 72 hours of no lens wear.Conclusions: CRT lenses significantly reduced myopia, improved visual acuity and subjective vision, and flattened central corneal curvature. Maximal effect was achieved after 10 days and was maintained for the rest of the study period.

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