Background/aims: Anecdotal evidence indicates that corneal reshaping contact lenses may slow myopia progression in children. The purpose of this investigation is to determine whether corneal reshaping contact lenses slow eye growth. Methods: Forty subjects were fitted with corneal reshaping contact lenses. All subjects were 8 to 11 years and had between −0.75 D and −4.00 D myopia with less than 1.00 D astigmatism. Subjects were age-matched to a soft contact lens wearer from another myopia control study. A-scan ultrasound was performed at baseline and annually for 2 years. Results: Twenty-eight of 40 (70%) subjects wore corneal reshaping contact lenses for 2 years. The refractive error and axial length were similar between the two groups at baseline. The corneal reshaping group had an annual rate of change in axial lengths that was significantly less than the soft contact lens wearers (mean difference in annual change = 0.16 mm, p = 0.0004). Vitreous chamber depth experienced similar changes (mean difference in annual change = 0.10 mm, p = 0.006). Conclusion: Results confirm previous reports of slowed eye growth following corneal reshaping contact lens wear.

https://bjo.bmj.com/content/bjophthalmol/early/2009/05/04/bjo.2008.151365.full.pdf

Corneal reshaping and myopia progression

Night Vision Disturbances After Corneal Refractive Surgery

Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia

BACKGROUND: Photorefractive keratectomy causes marked alteration to anterior corneal topography, and is likely to induce major changes to the optical aberrations of the eye. METHODS: Six diopters (D) of myopia correction was attempted on one eye of 50 patients, randomly allocated to one of three different treatments: 5-mm or 6-mm single ablation zone, or a double ablation (multizone; -5.00 D correction over 4.6 mm and -1.00 D over 6 mm). Topographic data was used to estimate corneal aberration coefficients. These were compared for effect of ablation zone, before and 1 year after photorefractive keratectomy. The coefficients were used to derive modulation transfer functions for the anterior corneal surface. RESULTS: Corneal spherical aberrations and coma-like aberrations both increased significantly following photorefractive keratectomy (p < 0.001). The mean spherical aberration coefficient increased from 0.36 +/- 0.11 before, to 0.91 +/- 0.37 after treatment, while the mean coma-like aberration coefficient changed from 0.28 +/- 0.16 before, to 0.60 +/- 0.31 after treatment. Ablation zone form had a significant effect on spherical aberration (p = 0.030), but not for coma (p = 0.96). The spherical aberration coefficient increased least for the 6-mm ablation (by 0.38 +/- 0.17), compared with the 5-mm ablation (0.69 +/- 0.45) and the multizone (0.62 +/- 0.38). Corneal modulation transfer functions were reduced significantly following the photorefractive procedure. The effect was greatest for large pupil diameters and for spatial frequencies between 2 and 15 cycles per degree. CONCLUSIONS: Corneal modulation transfer function calculations suggest that a significant loss of visual performance should be anticipated following photorefractive keratectomy, the effect being greatest for large pupil diameters. Results for three ablation zones show that induced aberrations are least for the largest (6 mm) ablation zone.

Corneal optical aberrations induced by photorefractive keratectomy.

Objective: To prospectively examine the effect of excimer laser photorefractive keratectomy (PRK) on best-corrected visual performance using psychophysical tests that were likely to be more sensitive to image degradation than high-contrast Snellen visual acuity. Design: Prospective cases series. Patients: A cohort of 18 subjects with an average of -5.08 diopters (D) of myopia (SD=±1.63 D) was tested before PRK and at 3, 6, and 12 months after PRK. Intervention: Photorefractive keratectomy was performed using a laser (Excimed UV200, Summit Technology, Waltham, Mass) and a polymethylmethacrylate mask; a 5-mm ablation zone was used. Main Outcome Measures: Best-corrected highcontrast visual acuity, best-corrected low-contrast visual acuity (18% Weber contrast), and best-corrected letter-contrast sensitivity. Measurements were repeated with dilated pupils and in the presence of a glare source. Results: One year after PRK, the mean best-corrected high-contrast visual acuity was reduced by half a line (P=.01), and the mean best-corrected low-contrast visual acuity was reduced by 11/2 lines (P=.002). The losses were somewhat greater when the subject's pupils were dilated and a glare source was used. The reduction in dilated low-contrast visual acuity was positively correlated with the decentration of the ablation zone (r=0.47), providing evidence of an association between corneal topography and the functional outcome of PRK. Conclusion: Low-contrast visual acuity losses after PRK are notably greater than high-contrast visual acuity losses for best-corrected vision. Low-contrast visual acuity is a sensitive measure for gauging the outcome success and safety of refractive surgery.

https://jamanetwork.com/HttpHandlers/ArticlePdfHandler.ashx?journal=OPHTH&articleId=641919&pdfFileName=archopht_114_12_003.pdf

Visual performance after photorefractive keratectomy. A prospective study.

Objective: To determine the effects of the ablation diameter on the outcome of excimer laser photorefractive keratectomy. Design: Eighty patients were randomized to either a 5.00-mm or a 6.00-mm treatment group and within these groups underwent either a −3.00-diopter (D) ora −6.00-D correction based on their preoperative refraction. A Summit Omnimed excimer laser was used throughout the study. Results: In eyes treated with a 6.00-mm-diameter ablation, the initial hyperopic shift was reduced, with significant differences at 1 week with −3.00-D corrections and at 1 and 4 weeks with −6.00-D corrections (P Conclusions: Treatment with 6.00-mm ablation diameters precipitated less initial overcorrection, greatly improved the predictability of photorefractive keratectomy, and was associated with a reduction in complications impairing postoperative visual performance.

https://jamanetwork.com/HttpHandlers/ArticlePdfHandler.ashx?journal=OPHTH&articleId=641095&pdfFileName=archopht_113_4_026.pdf

Christopher P. Lohmann

Papers

The Effects of Ablation Diameter on the Outcome of Excimer Laser Photorefractive Keratectomy: A Prospective, Randomized, Double-Blind Study