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H.A. Swarbrick, E. Lum; Lens Dk/t Influences the Clinical Response in Overnight Orthokeratology . Invest. Ophthalmol. Vis. Sci. 2006;47(13):110.
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To investigate the influence of lens Dk/t on the clinical response to overnight orthokeratology (OK) lens wear over a 2–week lens–wearing period.
Eleven subjects (age 20 to 39 years) were fitted with reverse–geometry lenses for OK (BE; Capricornia Contact Lenses, Brisbane, Australia) in both eyes. Lenses in matched designs and fittings but different materials (Boston EO; nominal Dk/t = 26, and Boston XO; nominal Dk/t = 46) were worn overnight only in the two eyes over a 2–week period. Changes in logMAR visual acuity (Test Chart 2000 Pro), subjective refraction, corneal apical radius and asphericity (Medmont E 300), and central stromal thickness (Holden–Payor optical pachometer) were measured. Repeated measures ANOVA and protected post hoc paired t–tests were employed to compare changes from baseline between the two lens materials, with a critical p–value of 0.05.
Throughout the study, there was a clinically and statistically significant difference in outcomes between the two lens materials (ANOVA, p<0.001). After two weeks of overnight OK lens wear, changes from baseline with the EO lenses were significantly less than with the XO lenses for logMAR visual acuity (–0.72 ± 0.37 vs. –0.83 ± 0.41; p<0.05), refraction (best vision sphere; +2.34 ± 0.61D vs. +2.78 ± 0.71D; p<0.05), corneal apical radius (0.36 ± 0.08mm vs. 0.48 ± 0.11mm; p<0.001) and asphericity Q (0.26 ± 0.08 vs. 0.37 ± 0.08; p<0.001). After the first overnight OK lens wear, central stromal edema was greater for EO lenses compared to XO lenses (27 ± 36 µm vs. 10 ± 31 µm; p=0.05), but overnight edema was reduced after two weeks for both lens materials (8 ± 25 µm vs. –1 ± 33 µm; p>0.05).
An increase in lens Dk/t appears to increase the clinical effects of overnight reverse–geometry lens wear over the medium term. This suggests that the stroma plays an important role in the corneal changes induced by overnight OK. It also adds further support to the recommendation that high Dk materials should be used for overnight OK, not only to provide physiological advantages, but also to optimize clinical outcomes.
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