Accuracy and precision of objective refraction from wavefront aberrations

Abstract

We determined the accuracy and precision of 33 objective methods for predicting the results of conventional, sphero-cylindrical refraction from wavefront aberrations in a large population of 200 eyes. Accuracy for predicting defocus (as specified by the population mean error of prediction) varied from -0.50 D to +0.25 D across methods. Precision of these estimates (as specified by 95% limits of agreement) ranged from 0.5 to 1.0 D. All methods except one accurately predicted astigmatism to within +/-1/8D. Precision of astigmatism predictions was typically better than precision for predicting defocus and many methods were better than 0.5D. Paraxial curvature matching of the wavefront aberration map was the most accurate method for determining the spherical equivalent error whereas least-squares fitting of the wavefront was one of the least accurate methods. We argue that this result was obtained because curvature matching is a biased method that successfully predicts the biased endpoint stipulated by conventional refractions. Five methods emerged as reasonably accurate and among the most precise. Three of these were based on pupil plane metrics and two were based on image plane metrics. We argue that the accuracy of all methods might be improved by correcting for the systematic bias reported in this study. However, caution is advised because some tasks, including conventional refraction of defocus, require a biased metric whereas other tasks, such as refraction of astigmatism, are unbiased. We conclude that objective methods of refraction based on wavefront aberration maps can accurately predict the results of subjective refraction and may be more precise. If objective refractions are more precise than subjective refractions, then wavefront methods may become the new gold standard for specifying conventional and/or optimal corrections of refractive errors.

Objective Amplitude of Accommodation Computed from Optical Quality Metrics Applied to Wavefront Outcomes

“…These criteria were applied after the subject's medical history. Accommodation anomalies in young subjects were detected when the accommodative amplitude measured using negative lenses (see next subsection) was always smaller than the minimum one suggested by the Hofstetter formula 22 and the accommodative flexibility was smaller than 11 cycles per minute, under monocular conditions.…”

“…In this sense, we need to choose a metric that quantifies image quality and then we have to look for the target vergence that maximizes that metric. A variety of optical-quality metrics are available for this purpose, many of which were evaluated by Thibos et al 22 for predicting the refractive state of the relaxed eye. Some metrics quantify the quality of the eye's wavefront aberration function, whereas others quantify the quality of the point spread function or of the optical transfer function associated with the retinal image.…”

Medida da visão em candelas: description of a psychophysical technique to quantify luminous intensity

“…Todos os métodos de medida existentes, através de testes psicofísicos, desrespeitam o SI, apesar de aprimorados através de escala logarítmica (7) . A medida da visão em cd é uma possibilidade fomentar a discussão científica sobre os testes de medida da acuidade visual (AV), e as inúmeras conotações que vem sendo empregadas e publicadas por inúmeros autores (1,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) . Para uso da unidade cd sugerimos o emprego do submúltiplo picocandela (pcd); pois esse submúltiplo (x10 -12 ) é mais apropriado na avaliação de indivíduos normais.…”

Comparing the Optical Properties of Soft Contact Lenses On and Off the Eye

“…29 Paraxial sphere powers were obtained by first converting the Zernike coefficients into the power vector components J 0 , M, and J 45 . 30 We found the paraxial spherical equivalent, M, by Equation 5 31 , which effectively sums the r 2 components of both C 2 0 and C 4 0 . 30 (5) Astigmatism (first order) was included in the determination of the final clinical paraxial sphere power, using the methods of Thibos et al 30 Zernike spherical aberration was converted to the clinically relevant units of peak-to-valley longitudinal spherical aberration (LSA) at the pupil margin by Equation 6, (6) where LSA is the longitudinal spherical aberration in diopters, C 4 0 is the OSA normalized Zernike spherical aberration coefficient value in microns, and r 2 is the pupil radius in mm squared.…”