[Quantitative assessment of quality of vision]

Abstract

The importance of quality of vision (QOV) along with quality of life (QOL) in medicine has been recently widely recognized. We have conducted studies to quantitatively analyze factors related to QOV. Irregular astigmatism can be a significant obstacle for achieving satisfactory QOV. Videokeratography data were broken down using Fourier harmonic series analysis into spherical power, regular astigmatism (second harmonic component, n = 2), asymmetry (n = 1), and higher order irregularity (n > or = 3). The irregular astigmatism component calculated by the Fourier analysis significantly correlated with best spectacle-corrected visual acuity. Software was developed to display color-coded maps for the four Fourier indices. The normal range was defined for each Fourier index, and eyes with pathologic and postsurgical conditions were evaluated using the normal range. Progression of keratoconus over time was quantitatively described by Fourier analysis of the videokeratography data. Using the Fourier method, changes in corneal topography following suture removal after penetrating keratoplasty were evaluated. Fourier analysis of videokeratography data significantly facilitated determination of refraction and measurement of best spectacle-corrected visual acuity in eyes with corneal irregular astigmatism such as post-penetrating keratoplasty eyes. Higher-order wavefront aberrations of the cornea were calculated by expanding videokeratography elevation data into Zernike polynomials, and coma and spherical aberrations were computed. For ocular aberrations, the data obtained with the Hartmann-Shack sensor were decomposed into Zernike polynomials. Coma aberrations of the cornea significantly correlated with age, while corneal spherical aberrations showed no age-related changes. The time-course of changes in corneal higher-order aberrations was reported for photorefractive keratectomy and laser in situ keratomileusis (LASIK). For ocular aberrations, the degree of tilting of the suture-fixed intraocular lens significantly correlated with the amount of coma aberration of the eye. In normal eyes, the ocular coma increased with age mainly because of the increase in the corneal coma, and the ocular spherical aberration increased with age because of the increase in spherical aberration in the internal optics including the crystalline lens. The conventional LASIK significantly increased ocular higher-order aberrations, which compromised postoperative contrast sensitivity and low contrast visual acuity. Both corneal and ocular wavefront aberrations were analyzed in cataract, pseudophakic and aphakic eyes, and the equilibrium of spherical aberrations between the cornea and the eye in those conditions was investigated. In pseudophakic eyes, coma aberrations of the cornea, along with the corneal multifocality, significantly contributed to apparent accommodation. Computer simulation indicated that a focus shift of 0.5 diopters deteriorated the retinal image significantly more in eyes without higher-order aberrations than in eyes having a moderate amount of coma aberrations. Clinical results of aspherical intraocular lens were reported for wavefront analysis and contrast sensitivity measurements, and retinal images were analyzed by simulation. For the assessment of vision-related QOL, National Eye Institute Visual Functioning Questionnaire 25 (NEI-VFQ 25) was translated into Japanese. After the validation study, the influence of cataract surgery on QOL was investigated. The QOL score was severely impaired in patients with bilateral cataract, which was significantly and dramatically improved by surgery. Forward scattering, backward scattering, and wavefront aberration induced by the crystalline lens were quantified, and the impact of these factors on visual function was analyzed according to the type of cataract. The degree of QOL improvement by surgery was assessed in relation to the type of cataract and intensity of scattering and aberration. By comprehensively analyzing these factors, quantitative parameters could be developed in the near future to describe progression of cataract and determine the indication for cataract surgery.