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J. D. Marsack, J. D. Elswick; Use of a Scalable Template in the Correction of Keratoconus Higher-Order Aberration. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1574.
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© ARVO (1962-2015); The Authors (2016-present)
Anterior HOA through the 10th radial order were derived from 7mm topographic data collected on 52 keratoconic eyes. Right eye data was reflected to represent left eye data. Data were divided into groups based on the Zernike mode with the largest magnitude. In this sample, 29 eyes were grouped by negative vertical coma. From this group, 15 were further sub-grouped by low levels of horizontal coma. For this sub-group, 3rd - 10th order Zernike coefficients for each subject were normalized to the level of vertical coma and a scalable template was defined as the average coma-normalized coefficients across subjects. Correction of HOA was simulated by scaling the template by the level of coma present for a subject and mathematically combining it with the original aberration structure.
The sub-group comprised 29% of the original keratoconic sample. All 15 subjects experienced a reduction of HO RMS with an average reduction from 2.08±1.17µm to 0.94±0.59µm (paired t-test: p < 0.001). Maximum reduction and minimum reduction for any given individual were 77% and 21% respectively. The number of subjects experiencing a reduction of HO RMS of 0-19%, 20-39%, 40-59%, 60-79% and 80-100% with the custom template was 0, 3, 7, 5 and 0 respectively.
Reduction of higher order aberration is mathematically possible with a correction defined from a scalable template. The real-world applicability of this technique in a custom soft contact lens for a given individual will depend on obtaining a large dataset representative of keratoconus and definition of the number of sub-groups required to provide adequate correction on an individual basis. Clinical utility of the method will be diminished if a large number of sub-groups are identified. Lens movement and the subject’s perceived visual quality may also limit the real-world applicability of the technique.
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