System for Objective Assessment of the Accommodation Response During Subjective Refraction.

Purpose: To evaluate a system based on a Hartmann-Shack wavefront sensor attached to a phoropter that allows the user to obtain real-time information about the refractive state of the eye and the accommodation response (AR). Methods: The objective refractions (ME) and ARs of 73 subjects (50 women, 23 men; ages, 19-69 years) were assessed with the system developed while placing in the phoropter the subjective refraction (MS) plus a set of trial lenses with differences in spherical equivalent power (ΔM) between ±2 diopters (D). Results: The objective estimations (ME) showed a good correlation with the subjective values (MS) (r = 0.989; P < 0.001). The means of the ARs presented a region where the accommodation remained stable (ΔM from +2 D to about 0 D), followed by another in which the response increased progressively (ΔM from about 0 to -2 D) with the magnitude of the accommodation stimulus. The analysis of variance within subjects applied to ARs introducing age and MS as covariates showed an increasing effect size of age from medium to large between ΔM of -0.5 and -2 D. In contrast, MS had a medium effect size (between ΔM of +2 and 0 D). Conclusions: The implemented system permitted an objective estimation of the refraction of the eye and its AR. Because it is coupled to a phoropter, the system can be used to retrieve the AR during subjective refraction procedures. Translational Relevance: The developed system can be used as a supporting tool during subjective refraction to provide certainty about the true state of accommodation.

Implementation of the Frequency Scatter Index in Clinical Commercially Available Double-pass Systems.

A previous work has reported a methodology to quantify intraocular scattering using a high sensitivity double-pass instrument with a robust index, the frequency scatter index. The purpose of our study was to evaluate an adaptation of the frequency scatter index for use in clinical double-pass systems. A prospective observational study was carried out in a group of patients with nuclear cataracts (n = 52) and in a control group (n = 11) using conventional double-pass systems. The frequency scatter index and the objective scatter index were used to assess the scattering. The Spearman coefficient was calculated to assess the correlation between both indexes, obtained from the double-pass images. Simultaneous measurements were performed with a double-pass and with a Hartmann-Shack wavefront sensor in the control group. The root-mean-square wavefront error and the full width at half maximum of the double-pass image were used to quantify the residual aberrations introduced by the variations in pupil size and retinal eccentricity. Measurement in eyes with different grades of cataracts shows a strong correlation (ρ = 0.929, p < .0001) between the frequency scatter index and the objective scatter index. A certain degree of correlation was observed between the objective scatter index and the root-mean-square and between the objective scatter index and the full width at half maximum, both for measurements with a different pupillary diameter and with a different retinal eccentricity (p < .05). No relationship was observed between the frequency scatter index and the root-mean-square or between the frequency scatter index and the full width at half maximum (p > .05). We have introduced and evaluated an adaptation of a methodology proposed recently for the measurement of intraocular scattering using the double-pass technique with a robust index, which is less affected by ocular aberrations. The frequency scatter index can be applied to conventional double-pass instruments available in clinical environments.

Method to reduce undesired multiple fundus scattering effects in double-pass systems.

Double-pass systems rely on backscattering of light by the human ocular fundus to assess the optical quality of the eye. In this work, we present a method to reduce double-pass image degradation caused by undesired multiple scattering effects in the eye fundus. The reduction is based on combined data processing of simultaneous measurements using two different configurations: one symmetric with equal entrance and exit pupils and another asymmetric with unequal entrance and exit pupils. Under certain conditions, such scattering effects may be effectively suppressed. Measurements of human eyes show that, although multiple fundus scattering imposes a shift on the estimations, double-pass systems can be used to predict the optical quality of the eye within a population.

Quantification of forward scattering based on the analysis of double-pass images in the frequency domain.

PURPOSE: To assess forward intraocular scattering by means of a new parameter (Frequency Scatter Index, FSI3 ) based on the analysing double-pass retinal images in the frequency domain, which minimizes the impact of aberrations on the results. METHODS: A prospective observational study was carried out in the Department of Ophthalmology, Hospital Universitari Mútua de Terrassa (Spain) on a group of 19 patients diagnosed with nuclear cataracts of various LOCSIII grades and a control group (CG) with nine healthy eyes. We recorded double-pass retinal images with a custom set-up based on a high-sensitivity digital camera. The FSI3 was then computed using spatial frequencies below three cycles per degree. A preliminary validation of the FSI3 was performed on an artificial eye and two eyes of volunteers with and without commercial diffusers, and under defocus. RESULTS: The FSI3 was hardly affected by defocus values up to 2.50 D. The mean (and standard deviation) FSI3 values were as follows: for the CG, 1.19 (0.21); and for LOCSIII grades nuclear opacity 1, 2 and 3, 1.30 (0.12), 1.62 (0.21) and 1.85 (0.21), respectively. Eyes with cataracts showed FSI3 values significantly different than healthy eyes (p = 0.001). A good correlation (ρ = 0.861, p < 0.001) was found between the FSI3 and objective scatter index provided by a commercial instrument. CONCLUSION: Since aberrations have little impact on the FSI3 , the light scatter assessment becomes less dependent on the patient's refractive error compensation and the presence of higher-order aberrations. The FSI3 can further the clinical and scientific understanding of forward intraocular scattering.

Comparison of the Adaptive Optics Vision Analyzer and the KR-1 W for measuring ocular wave aberrations.

BACKGROUND: The aim was to assess the agreement in the measurement of ocular aberrations between a new Adaptive Optics Vision Analyzer (AOVA, Voptica, Murcia, Spain) and a commercial aberrometer (KR-1 W, Topcon, Tokyo, Japan), both based on the Hartmann-Shack technique. METHODS: One experienced examiner measured 29 healthy right eyes nine consecutive times with the two instruments. The individual Zernike coefficients and the root mean square (RMS) of each order from the second to the fifth order, the higher-order RMS (RMSHOA ), the total RMS (RMSTOT ) and the values of the spherical equivalent (M) and Jackson cross-cylinder (J0 and J45 ) were compared. All aberrations were computed for a 4.0 mm pupil diameter. RESULTS: Bland and Altman analysis showed good agreement between instruments and most of the parameters showed no statistically significant differences. Although the largest mean differences were obtained for the defocus coefficient C(2,0) and the spherical equivalent (M) with a mean difference (and standard deviation) of 0.190 ± 0.099 µm and -0.150 ± 0.188 D, respectively, they were clinically acceptable and significant correlations were found between the AOVA and KR-1 W for the major refractive components such as spherical equivalent (r = 0.995, p < 0.001), J0 (r = 0.964, p < 0.001), J45 (r = 0.901, p < 0.001) and C(4,0) (r = 0.575, p = 0.001). CONCLUSION: The results suggest good agreement between instruments. Accommodation and misalignment of the measurements may play a role in some of the statistically significant differences that were obtained, specifically for defocus C(2,0), vertical coma C(3,-1) and spherical aberration C(4,0) coefficients; however, these differences were clinically irrelevant.

Response for light scattered in the ocular fundus from double-pass and Hartmann-Shack estimations.

Double-pass (DP) and Hartmann-Shack (HS) are complementary techniques based on reflections of light in the ocular fundus that may be used to estimate the optical properties of the human eye. Under conventional data processing, both of these assessment modes provide information on aberrations. In addition, DP data contain the effects of scattering. In the ocular fundus, this phenomenon may arise from the interaction of light with not only the retina, but also deeper layers up to which certain wavelengths may penetrate. In this work, we estimate the response of the ocular fundus to incident light by fitting the deviations between DP and HS estimations using an exponential model. In measurements with negligible intraocular scattering, such differences may be related to the lateral spreading of light that occurs in the ocular fundus due to the diffusive properties of the media at the working wavelength. The proposed model was applied in young healthy eyes to evaluate the performance of scattering in such a population. Besides giving a parameter with information on the ocular fundus, the model contributes to the understanding of the differences between DP and HS estimations.

Effects of aging on optical quality and visual function.

BACKGROUND: We assessed the effects of aging on visual function and optical quality in a healthy adult population and provide reference values for different age ranges. METHODS: We conducted a prospective study with 198 healthy volunteers from 31 to 70 years of age. The visual acuity (VA) and contrast sensitivity (CS) at 3, 6, 12 and 18 cycles per degree (cpd) frequencies were assessed, together with values of optical quality and intraocular scattering obtained with a double-pass system (Optical Quality Analysis System - OQAS), specifically the modulation transfer function cutoff frequency (MTFcutoff ), the Strehl ratio, the OQAS values (OV) at contrasts of 100, 20 and nine per cent and the objective scatter index (OSI). We studied the change of these variables with age and obtained standard values for optical quality and intraocular scattering parameters for four age groups: 31 to 40, 41 to 50, 51 to 60 and 61 to 70 years. RESULTS: We found significant correlations between age and all variables analysed and significant differences among the age groups considered except for CS (3 cpd) (p = 0.067). Ageing particularly affected low-contrast parameters, such as the OV nine per cent and the OSI, which decreased to 37 and 50 per cent of their original values, respectively. The OSI was found to provide high sensitivity and specificity values, when healthy and caratactous eyes were considered. The results suggest that optical deficits are compensated until 50 years of age with sensory and perceptual factors, as smaller changes were found for visual function than for objective measurements of optical quality and intraocular scattering. CONCLUSIONS: Measures of optical quality assessed by subjective psychophysical and objective techniques varied differently with age. Values obtained for each age group can be used to determine normal limits of optical quality and intraocular scattering for diagnosis of ocular conditions.

Optical quality and intraocular scattering in a healthy young population.

BACKGROUND: We objectively assessed the optical quality and intraocular scattering by means of parameters provided by a clinical double-pass system in healthy young subjects and thereby we obtained new reference data for clinical diagnosis. We calculated normal values of neural contrast sensitivity function (nCSF) from the measured modulation transfer function (MTF) and the contrast sensitivity function (CSF). METHODS: Eligible subjects were healthy adults aged from 18 to 30 years with a logMAR visual acuity (VA) of 0.0 or better and normal values of CSF. Optical quality measurements for a 4.0 mm pupil were performed using the Optical Quality Analysis System (OQAS) based on the double-pass technique. The following parameters were analysed: the modulation transfer function cutoff frequency (MTF(cutoff)), the Strehl(2D) ratio, the OQAS values (OV) at 100, 20 and nine per cent contrasts and the objective scatter index (OSI). RESULTS: A total of 178 volunteers responded to the call, of whom 181 eyes were finally part of the study taking into account the criteria for inclusion. The values for the optical quality parameters were: 44.54 ± 7.14 cpd (MTF(cutoff)), 0.27 ± 0.06 (Strehl(2D) ratio), 1.48 ± 0.24 (OV(100%)), 1.58 ± 0.32 (OV(20%)), 1.64 ± 0.39 (OV(9%)), and 0.38 ± 0.19 (OSI). The nCSF calculated was 1.76 ± 0.21 (3 cpd), 2.13 ± 0.23 (6 cpd), 2.01 ± 0.28 (12 cpd) and 1.86 ± 0.33 (18 cpd). CONCLUSION: The normal values provided can be a useful tool for discriminating healthy eyes from early abnormal ones in which the optical quality or sensory function is impaired.