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E. Lum, J. Kim, L. Lin, S. Lee, L. Nguyen, H. A. Swarbrick; Corneal Topographic Correlates of Refractive Error Change in Orthokeratology. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5390.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate differences in corneal topographic variables for two different targeted refractive error corrections in overnight orthokeratology (OK) lens wear, over an 8-day lens-wearing period.
Thirteen subjects (age 21 to 27 years) were fitted with reverse-geometry lenses for OK (MeniconZ CRT; Paragon Vision Sciences, Arizona, USA) in both eyes. Lenses in matched designs and fittings but different targeted refractive error corrections (-1.00DS and -4.00DS) were worn overnight only in the two eyes over an 8-day period. Changes in subjective refraction, corneal apical radius and asphericity (Medmont E-300) were measured. The diameter of the treatment zone was measured from the topography plots using standard techniques. Paired Student t-tests were employed to compare changes from baseline between the two targeted corrections, with a critical p-value of 0.05.
After eight days of overnight OK lens wear, there were statistically and clinically significant differences between the two eyes (-1.00DS versus -4.00DS target refractive correction) for changes in refraction (best vision sphere; -1.32 ± 0.49D vs. -2.54 ± 0.97D; p<0.01), corneal apical radius (0.20 ± 0.04mm vs. 0.42 ± 0.13mm; p<0.001) and asphericity Q (0.17 ± 0.13 vs. 0.28 ± 0.14; p<0.01). There was no significant difference between the two eyes in the treatment zone diameter along the horizontal (4.95 ± 0.65mm vs. 5.09 ± 0.55mm; p>0.05) or vertical (5.13 ± 0.54mm vs. 5.43 ± 0.76mm; p>0.05) meridians.
Differences in targeted refractive error correction in overnight OK do not appear to influence the size of the treatment zone in the short term, over the range of myopic corrections studied. This challenges traditional thinking which assumes that treatment zone diameter decreases as the refractive error correction increases. Analysis of more complex aspects of corneal shape and power changes across the treatment zone appears to hold the key to explaining differences in refractive outcomes in overnight OK.
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