Influence of power and the time of application of fogging lenses on accommodation.

Fogging is a non-invasive technique based on the use of positive spherical power lenses to relax accommodation during refraction that is commonly used as an alternative to cycloplegic drugs. Although the mechanism of the fogging technique has been described, some aspects of its methodology remain unclear. The main purpose of this work was to determine which lens power and time of application are more suitable for achieving a successful relaxation of accommodation by analyzing the changes in accommodation when fogging lenses of different powers were placed in front of the participants' eye for a certain timespan. The results of this analysis showed, in general, that low-power lenses and timespans of less than half a minute provided the highest relaxation of accommodation. However, high inter-subject variability was found in the two variables (power and time).

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.

Speckle reduction in double-pass retinal images.

The double pass (DP) technique quantifies the optical quality of the eye by measuring its point spread function. The low reflectivity of the retina requires the use of a high-brightness, point-like illumination source, and thus, DP systems use laser diodes (LDs). However, LDs light produces speckle, and a low-cost solution to reduce speckle is to include a vibrating mirror in the beam path. With the goal of finding an all-optical solution, here we perform a comparative study of the amount of speckle produced by three semiconductor light sources: an LD, a light emitting diode (LED), and a superluminescent diode (SLED). We also compare the results with the speckle reduction that is obtained with a vibrating mirror. We find that the SLED is a good alternative to LD illumination, as the amount of speckle in the image is almost as low as that obtained with an LD and a vibrating mirror in the beam path.

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.

Binocular open-view system to perform estimations of aberrations and scattering in the human eye.

We present a system that integrates a double-pass (DP) instrument and a Hartmann-Shack (HS) wavefront sensor to provide information not only on aberrations, but also on the scattering that occurs in the human eye. A binocular open-view design permits evaluations to be made under normal viewing conditions. Furthermore, the system is able to compensate for both the spherical and astigmatic refractive errors that occur during measurements by using devices with configurable optical power. The DP and HS techniques provide comparable data after estimating wavefront slopes with respect to the intersections of an ideal grid and compensating for residual errors caused by the optical defects of the measuring system. Once comparable data is obtained, it is possible to use this combined manner of assessment to provide information on scattering. Measurements in an artificial eye suggest that the characteristics of the ocular fundus may induce deviations of DP with respect to the HS data. These differences were quantified in terms of the modulation transfer function in young, healthy eyes measured in infrared light to demonstrate the potential use of the system in visual optics studies.