Alexander Dubinin

Human eye anisoplanatism: eye as a lamellar structure

In this paper we consider anisoplanatism effect as a fundamental limitation on the size of high resolution area (isoplanatic patch) of retinal images obtained using fundus cameras equipped with adaptive optics. Isoplanatic patch size was estimated using experimental results for on-axis and off-axis eye aberrations measured by Shack-Hartmann technique. Isoplanatic patch size varied among examined subjects in the range from 1.5o to 2.5o which is in good agreement with results obtained using ray-tracing technique1. We estimated isoplanatic patch size for Gullstrand eye model and found it to be close to the values obtained from experimental results for subjects with good vision. We also discuss the possibilities of Gullstrand eye model modifications for modeling anisoplanatism effect for each particular subject. We also estimated the efficiency of multibeacon correction method and found out that this method allows us to almost twice increase the area with high resolution.

Human retina imaging: widening of high resolution area

In this paper we consider different methods of widening high resolution retinal image area. The first method is based on compensation of an average phase of two beacons formed on human retina within the isoplanatic patch. The second one is based on compensation of external corneal surface refraction with the help of immersion liquid. In both methods we use a single wavefront corrector conjugated to the pupil plane. The immersion method was found to be the most appropriate as it allows one to increase the area of high resolution almost twice without loss of image quality.

Anisoplanatism in human retina imaging

All extended optical systems with aberrations suffer from anisoplanatism effect. In this presentation we investigate anisoplanatism in human eye. For that purpose we use a reference source (beacon) obtained by focusing of a dim laser beam on the retina and consider increasing the retina resolution within anisoplanatic angle by means of ideal wavefront corrector and a real bimorph flexible one. The numerical simulations of isoplanatic patch size of human retina were made for different beacon positions and based on the aberrations measured by means of custom wavefront-guided aberrometer. We found out that in particular human eye the existence of optimal correction directions is possible. As the behavior of Zernike coefficients varies from subject to subject the existence of optimal correction angle is a feature of a particular eye. We also estimated the contribution of low-order and high-order aberrations in anisoplanatism effect for the subjects we measured. We found out that aberrations with strongly variable amplitude across the visual field have effect on the isoplanatic patch size most. In this paper we illustrated the isoplanatic patch enlargement with variation of beacon position by presenting two-dimensional retina and test object images. Also anisoplanatism in two-layer human eye model has been discussed. As the main part of the eyes aberrations is induced by the surfaces of the cornea and the crystal lens, our model consists of two thin phase screens that correspond to the cornea and the lens. Then we used such two-layer model to minimize residual mean-square error of correction by means of just one applied corrector.

Isoplanatism of the optical system of the human eye

The size of the isoplanatism zone is determined on the basis of experimental measurements of aberrations of the eye for various positions of the test point on the retina of the eye. For the patients examined here, the angular size of the zone varied from 1.5° to 2.5°.

Methods of isoplanatic patch widening in human eye retina imaging

We discuss possible ways to enlarge the size of high-resolution area (isoplanatic patch) in fundus imagers equipped with adaptive optics. We first developed customized human eye models of several subjects. Then we considered immersion and multiconjugate methods of isoplanatic patch widening. Using immersion method we obtained about twotimes enlargement of isoplanatic patch size for the developed eye models. For optimal configuration of a multiconjugate system with two correctors and five reference sources isoplanatic patch area increased two times if compared with the case of conventional correction. We consider immersion method to be more preferable due to its relative simplicity and low-cost.

Adaptive optics in ophthalmology: current techniques and new methods of increasing field-of-view of fundus cameras

In this paper we investigate anisoplanatism effect in human eye. We measured off-axis aberrations of eyes of several subjects and also performed measurements of corneal and internal optics aberrations. Using the results of the experiments we estimated anisoplanatism effect in human eye and developed human eye models reproducing on-axis and off-axis eye aberrations and their distribution between optical elements of the eye.

Widening of High Resolution Area of Fundus Imager

In this paper we estimate the size of isoplanatic angle of real human eye and consider methods for increasing it. For that purpose we apply the formalism of anisoplanatism developed for atmosphere turbulence to a human eye.

The influence of human eye aberrations on the resolution and field of view of fundus-cameras

In this paper we estimate isoplanatic patch size of human eye using experimental results of human eye aberrations measurements. For examined subjects it was found to be in the range 1.1° to 2.5°. The size of isoplanatic patch for Gulistrand-Navarro model was calculated, it was found to be close to values obtained experimentally. We also measured contribution of corneal surface and internal optics into total aberrations of the eye. We modified Gullstrand-Navarro eye model to reproduce on-axis and off-axis performance of the eyes of each measured subject. The distribution of aberrations between optical elements of the eye was taken into account when modeling. We also investigated isoplanatic patch size widening methods such as average phase correction using 2 beacons and immersion method based on compensation of external corneal surface refraction with immersion liquid. Immersion method was found to be the most appropriate for isoplanatic patch widening as it allows us to increase isoplanatic patch size almost twice without loss of image quality at the center of the image.

Human retina imaging: anisoplanatism considerations

In this presentation we report our results of investigation of anisoplanatism effect in human eye. We measured aberrations of human eye depending on the location of beacon source on the retina and determined the value of the isoplanatic patch. We show that the size of isoplanatic patch depends on the direction of compensation and determine an optimal direction for every patient. To enhance quality of retina image correction we introduce lamellar eye model where aberrations of human eye are considered to be induced in two thin phase screens corresponding to cornea and crystal lens locations. For that model we found the optimal corrector location which differs from the one for the one-layer eye model.