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D. R. Neal, F. Chinisci; Influence of Wavefront Aberration on Visual Performance After Orthokeratology: A Case Study. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1573.
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Orthokeratology has become a relatively common procedure in optometry practice, with many companies offering products and services. However, there are a percentage of patients that are unable to wear the lenses due to degraded visual performance. While Ortho-K can be used to reshape the cornea to change the net refraction, it may also induce aberrations that result in undesirable visual effects.
An Ortho-K subject was followed as a case study throughout the fitting process with wavefront measurement and analysis. Key aberrations were observed (namely spherical aberration) and correlated to reduction in visual acuity daily during the initial Ortho-k lens fitting. The effect of aberrations on the pupil dependent refraction was calculated from the wavefront measurements.
Figure1 shows the comparison of uncorrected to 10-day refractions for 3- and 5-mm pupil. The higher order aberrations and spherical aberration more than doubled for each eye after 10 days as shown in Fig. 1. After one week the subject complained of variable vision during different parts of the day (particularly at night). The presence of these HOA introduced a substantial pupil-dependent refraction change (OD/OS:1.15/0.88 D in sphere).
The large variation in refraction at different pupil sizes is due to the increased spherical aberration. While several different Ortho-k lens designs were attempted, for this subject they were ineffective at reducing the aberration. Ortho-K was not ultimately successful for this subject, but this is not indicative for a large population. Pupil size and aberration effects should be considered in the design and fitting process.
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