Abstract
Purpose: :
The Collaborative Longitudinal Evaluation of Keratoconus reported that 2% of their sample of keratoconus (KC) subjects wore soft contact lenses (SCL) bilaterally. This low percentage is due, in large part, to the fact that SCLs cannot adequately correct higher order aberration (HOA). It is known that KC patients exhibit similarities in corneal asymmetry, suggesting a set of common HOA structures and the design of scalable (depending on disease severity) corrections, as in sphero-cylindrical corrections. If common scalable corrections for HOA exist for KC and are implementable in SCL form, the percentage of KC subjects benefitting from the increased comfort and wear time of SCLs will increase. The purpose of this investigation is to assign a sample of KC eyes to sub-groups and simulate the optical performance of a common scalable correction for each sub-group.
Methods: :
HOA was recorded over a 5mm pupil on 111 KC eyes and divided into 5 sub-groups. One additional sub-group was composed of eyes not fitting any of the 5 WFE patterns. From each sub-group, three eyes were randomly removed for later evaluation. For each sub-group, principal components analysis was performed. The first principal component was negated and scaled in magnitude to form a set of corrections. Simulated correction of the 15 test eyes was performed by identifying the magnitude that provided the lowest level of residual higher order RMS wavefront error (HORMS). Residual uncorrected HORMS was calculated for the 15 eyes and compared to RGP-corrected levels of HORMS reported by Kosaki et al.
Results: :
Ninety of the 111 eyes (81%) were included as members of 1 of the 5 sub-groups. Twenty one eyes (19%) did not fit into a WFE pattern and were excluded from analysis. All 15 test eyes experienced a reduction in HORMS. Median HORMS reduced from uncorrected levels of 1.889µm to 0.830µm. On average, the 15 subjects experienced a 46% ± 20% reduction in HORMS (p < 0.01). The reduction ranged from 16% to 78% (residuals ranging from 0.39µm to 2.51µm). When compared to the data reported by Kosaki, 9 of the 15 eyes experienced residual uncorrected HORMS at levels within limits associated with RGP wear.
Conclusions: :
This study simulates the application of common corrections to KC eyes. All eyes experienced a reduction in HORMS. In 9 of the 15, levels are consistent with residual HORMS experienced with RGP correction. Importantly, each correction is common to more than one subject.
Keywords: keratoconus • aberrations • contact lens