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David Rio, Jos J Rozema, Gareth D Hastings, Jason D Marsack; The impact of misalignment on the optical and visual image quality of template-based corrections in keratoconus. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5804.
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© ARVO (1962-2015); The Authors (2016-present)
This experiment builds on techniques established in the literature by assessing the impact of decentration and rotation of higher-order aberration (HOA) compensating templates combined with static, optimized lower-order corrections (LOC) on the resulting optical and visual image quality for a simulated population of wavefronts (WF) with keratoconus (KC).
Five previously defined HOA correcting templates (approximating a contact lens correction) were applied to the optical aberration structure of 100 simulated WF with KC with no misalignment of the template and underlying WF. For each WF, the template resulting in the lowest higher-order RMS (HORMS) was identified. The LOC (approximating a spectacle lens correction) optimizing the visual Strehl ratio (VSX) was also identified through a brute force method. The best template combined with the best LOC defined the best possible correction of this WF. The impact of movement of the template behind the LOC was assessed by moving the template through a set of rotations (from -10 to +10° in 1° steps) or decentrations (all combinations from -0.3 to +0.3mm in vertical and horizontal directions in 0.05mm steps) with respect to the simulated WF. The resulting HORMS and logVSX were calculated over a 4-mm pupil for each condition to assess optical and visual quality. A threshold of -1.87logVSX (1SD below the average VSX of KC eyes wearing scleral lenses) was considered acceptable.
The average HORMS for all conditions was 0.51±0.05µm (first quartile (1Q): 0.37µm, median (M): 0.49µm, third quartile (3Q): 0.61µm). Average RMS of rigid lenses (RGP) wearers with KC is 0.59µm in the literature. The poorest HORMS was 1.28µm. When considering the influence of both lower and HOA, the mean maximum difference between best and worst logVSX for all WF was 3.8. LogVSX 1Q was -2.34, M was -1.92 and 3Q was -1.57. More than half of the WF were predicted to have an acceptable predicted visual image quality according to the abovementioned threshold.
The average level of HORMS in the presence of misalignment is comparable to levels reported for RGP wearers with KC. Investigation is currently focused on improving resulting VSX through optimization of the association of LOC and higher-order template. Prototyping of such optical designs is a future direction.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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