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Pauline Kang, Merrilyn Lee, Lynn Lee, Helen A Swarbrick; Characterizing corneal changes induced by orthokeratology using high resolution OCT: 1998 revisited. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6090.
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© ARVO (1962-2015); The Authors (2016-present)
To confirm early research that used superseded technologies, we re-investigated changes in epithelial and stromal corneal thickness along the horizontal and vertical corneal meridians after overnight OK lens wear using a high resolution Tomey CASIA optical coherence tomographer (OCT).
28 subjects (22.3 ± 1.9 years) were fitted with Paragon CRT lenses (Paragon Vision Sciences Inc, USA) in both eyes and wore lenses overnight only for 28 days. Visual acuity, objective refraction (Shin-Nippon NVision-K 5001 autorefractor), corneal topography (Medmont E300) and OCT scans (Tomey CASIA OCT) were taken at baseline and after 28 days of OK. Repeated-measures ANOVA, Friedman test and linear mixed model analysis with post-hoc t-tests were used to analyse changes in visual acuity, refraction, and epithelial and stromal corneal thickness. Analysis was limited to right eye data.
Spherical equivalent refraction significantly reduced from -2.16 ± 1.06D to -0.27 ± 0.64D (p<0.001) after OK and there was no change in best corrected visual acuity (p=0.794) over the lens wear period. Corneal thickness reduced in the center and increased in the mid-peripheral cornea after 28 days of lens wear. Specifically, the epithelium significantly thinned at center (-19.1 ± 8.2μm) and thickened at 3mm nasal (+3.1 ± 6.1μm) and 3mm inferior (+3.1 ± 7.2μm)(all p<0.05). Stromal thickness increased at center (+11.6 ± 10.0μm) and 3mm superior (7.7 ± 6.2μm)(all p<0.05).
Utilizing a high resolution OCT, significant changes in central and mid-peripheral corneal thickness were measured along the horizontal and vertical meridians after 28 days of OK. The study confirmed earlier reports and demonstrated that central corneal thinning is primarily epithelial and the increase in mid-peripheral corneal thickness after OK is a combination of epithelial and stromal tissue changes. Application of Munnerlyn’s formula indicates that changes in corneal thickness account substantially for the central refraction change measured after OK.
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