Contrast Sensitivity Function and Ocular Higher-Order Aberrations following Overnight Orthokeratology
Takahiro Hiraoka,1 Chikako Okamoto,1 Yuko Ishii,1 Tetsuhiko Kakita,2 and Tetsuro Oshika1
PURPOSE. To evaluate relationships among contrast sensitivity function, ocular higher-order aberration, and myopic correction in eyes undergoing overnight orthokeratology for myopia. METHODS. A prospectivestudy was conducted in 46 eyes of 23 patients undergoing orthokeratology. Inclusion criteria were spherical equivalent refraction between –1.00 and – 4.00 diopters (D), refractive astigmatism up to 1.00 D, and best-corrected visual acuity of 20/20 or better. Ocular higher-order aberrations and contrast sensitivity function were determined before and 3 months after initiation of the procedure. Wemeasured three indices of contrast sensitivity function: contrast sensitivity, low-contrast visual acuity, and letter contrast sensitivity with the CSV-1000 charts (Vector Vision Co., Greenville, OH). Area under the log contrast sensitivity function (AULCSF) was calculated from the contrast sensitivity data. RESULTS. Orthokeratology signiﬁcantly improved logMAR uncorrected visual acuity (P 0.0001;paired t-test) but signiﬁcantly increased ocular higher-order aberrations (P 0.0001) and decreased contrast sensitivity function, including AULCSF (P 0.0001), low-contrast visual acuity (P 0.0025), and letter contrast sensitivity (P 0.0001; Wilcoxon signed-rank test). The induced changes in AULCSF, low-contrast visual acuity, and letter contrast sensitivity by orthokeratology showed signiﬁcantcorrelation with changes in third-order (Pearson r – 0.430, P 0.0026; r 0.423, P 0.0031; and Spearman rs – 0.351, P 0.0186, respectively), fourth-order (r – 0.418, P 0.0035; r 0.425, P 0.0029; and rs – 0.566, P 0.0001, respectively), and total higher-order (r – 0.460, P 0.0011; r 0.471, P 0.0008; and rs – 0.434, P 0.0036, respectively) aberrations. The induced changes in contrast sensitivity functionand higher-order aberrations signiﬁcantly correlated with the amount of myopic correction (P 0.01). CONCLUSIONS. Orthokeratology signiﬁcantly increases ocular higher-order aberrations and compromises contrast sensitivity function, depending on the amount of myopic correction. (Invest Ophthalmol Vis Sci. 2007;48:550 –556) DOI:10.1167/ iovs.06-0914 of specially designed rigid contact lenses. It wasintroduced in the early 1960s.1 The central cornea is ﬂattened and thinned, resulting in a reduction in myopia and an improvement in unaided vision.2–5 In the 1980s, application of the orthokeratology lens during sleep became possible with the development of higher gas-permeable lens materials. This wearing modality, called overnight orthokeratology, allowed satisfactory daytime vision withoutcontact lenses or eyeglasses. In addition, the advent of sophisticated lens designs (reverse geometry design) caused much faster, more accurate, and greater achievement of corneal and refractive changes.4,6 – 8 Overnight orthokeratology has come into greater use as a treatment modality to correct refractive errors, and its efﬁcacy has been conﬁrmed in terms of high-contrast visual acuity.4,7–9 Inrecent years, with the development of a wavefront sensing technique that can quantify optical aberration, increasing attention has been paid to changes in the optical quality of the eye after refractive procedures. Several studies have reported increases in ocular higher-order aberrations after photorefractive keratectomy (PRK)10,11 and laser in situ keratomileusis (LASIK).12–14 Increases inhigher-order aberrations are among the main causes of reduced visual performance after PRK and LASIK.10,11,15–18 These procedures are designed to correct defocus by surgical modiﬁcation of the corneal curvature and to produce a nonphysiological oblate cornea with a ﬂat central area and increasing power toward the periphery. Similarly, an oblate cornea is created by orthokeratology,7 and previous...
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