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Shrikant R Bharadwaj, Vinay Kumar Nilagiri, Sangeetha Metlapally, Clifton Schor; Image Quality Analysis of Keratoconic Eyes Corrected with Spectacles and RGP Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2498.
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© ARVO (1962-2015); The Authors (2016-present)
It is a common clinical observation in eyes with keratoconus that 1) high-contrast visual acuity is better with RGP contact lenses (CL’s) than with spectacles and 2) visual acuity tends to remain similar for a range of sphero-cylindrical refractions, more so with spectacles than with CL’s. This study determined the optical basis for these clinical observations through a computational image quality (IQ) analysis in cases with bilateral keratoconus when corrected with spectacles and RGP CL’s, vis-à-vis, age-matched controls.
Best-corrected normalized peak IQ (no units), dioptric location of peak IQ (i.e. best focus in diopters) and depth of focus (DOF; dioptric range where IQ is better than 70% of peak IQ) of the right eye of 12 cases (21.1±4.9yrs) and 20 controls (20.5±1.0yrs) were derived from a through-focus analysis of logNS IQ metric from -4D to +4D defocus in 0.01D steps, induced over the subjects own higher-order aberrations (HOA’s). Lower-order aberrations were set to 0μ in all analyses. HOA’s were measured using the IRX3 Imagine Eyes® wavefront aberrometer for 5mm pupil diameter following cycloplegia.
Median (25th to 75th IQR) logMAR acuity of cases was significantly better with RGP CL’s [0.04 (-0.02 to 0.12)] than with spectacles [0.29 (0.10 to 0.52)] (p<0.001). Median RMS deviation of HOA’s (HORMS), peak IQ, best focus and DOF were 1.9µ (1.5 to 2.4µ), -1.5 (-1.7 to -1.3), 0.5D (-0.6 to 1.4D) and 1.1D (0.6 to 2.6D), respectively, with spectacles, and 0.6µ (0.5 to 0.8µ), -1.1 (-1.2 to -1.0), -0.7D (-1.2 to -0.2D) and 0.4D (0.3 to 0.8D), respectively, with RGP CL’s (p≤0.02 for all). All outcome measures of cases were significantly different from controls [logMAR acuity: -0.1 (-0.2 to -0.1); HORMS: 0.3µ (0.2 to 0.4µ); peak IQ: -0.7 (-0.8 to -0.6); best focus: -0.2D (-0.5D to -0.02D); DOF: 0.2D (0.2D to 0.3D)] (p≤0.008 for all).
Results of this computational analysis provide optical correlates of the aforementioned clinical observations, and reflect an improvement in the eye’s optical quality with RGP CL’s, vis-à-vis, spectacles. The difference in best focus with RGP CL’s and spectacles indicates that the clinical subjective endpoint of refraction of these eyes may shift significantly with the modality of optical correction. Even while RGP CL’s improve optical quality of keratoconic eyes over spectacles, it still remains inferior to that of age-matched controls.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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