Neural bases of visual deficits during aging.

An optical coherence tomography device is disclosed for improved imaging. Reduced levels of speckle in the images generated by the device are obtained by forming a B-scan from a plurality of A-scans, wherein each resolution cell of the B-scan is generated through compounding of a subset of the A-scans and wherein at least some of the subset of A-scans are separated by at least half the diameter of a speckle cell both tangent to and orthogonal to the B-scan at that cell.

Spectral domain optical coherence tomography system

Publisher Summary This chapter provides a contemporary overview of one aspect of sensory aging, namely age-related changes in vision and low-level visual information processing. The ability to cope effectively with the environment begins with the capacity to process sensory input. Indeed, the senses have been carefully crafted by the forces of nature to effortlessly extract critical information from the world. Unfortunately, advancing adult aging brings with it systematic reductions in the efficiency of our sensory systems. This lost efficiency of low-level, automatic processing capacity often necessitates effortful, high-level compensatory processes that may tax already limited cognitive resources. Hence, sensory aging is of potentially great interest at all levels of psychological analysis. This focus on vision does not discount the critical role played by the other major sensory systems. Important domains of investigative inquiry are sampled with a focus on basic aspects of vision and aging that have received significant attention in the research literature during the past decade. Several excellent reviews of the sensory aging literature prior to the contemporary period are also presented in the chapter.

Vision and aging.

A method for obtaining a tomographic image of a fundus by optical coherence tomography includes the steps of setting a line, based on which the fundus tomographic image is to be obtained, on a first front image of the fundus, the first front image being a still image, establishing a positional correspondence between a second front image of the fundus and the first front image by matching the first and second front images, specifying a line on the second front image based on positional information on the line set on the first front image, and the established positional correspondence, and obtaining the fundus tomographic image that corresponds to the lines on the first and second front images by scanning measurement light with the use of an optical scanner provided to an interference optical system.

Ophthalmic photographing apparatus

Astigmatism and the development of myopia in children.

A line scan imager is used to determine the motion of a subject. Each line of image data from the line scan imager is compared with a reference image. The location of a matching line in the reference image reveals the displacement of the subject. The current subject displacement can be determined based on each line of image data. The resulting displacement information can be used to correctly place other optical beams on the subject. The method can be applied to tracking the human eye to facilitate measurement, imaging, or treatment with a beam of optical radiation.

Method and apparatus for measuring motion of a subject using a series of partial images from an imaging system

Traditional visual acuity is based on resolution of stimulus features, whereas hyperacuity (ie, vernier acuity) is based on relative localization of stimulus features. Since resolution acuity is influenced severely by optical degradation, it is often not a suitable measure of the status of the retinal/neural visual system in conditions of optical degradation. In the present study, the authors investigate the effect of optical degradation on various relative localization tasks. Thresholds for three types of hyperacuity stimuli (line vernier, two-dot vernier, and line tilt) were measured under various degrees of image degradation, produced by viewing the targets through ground glass. The results indicate that when a hyperacuity stimulus is optically degraded, relative localization threshold increases only slightly for certain separations of the comparison features. In comparison with resolution acuity, hyperacuity threshold at the optimum feature separation is quite resistant to image degradation. This finding demonstrates a potential for the clinical application of hyperacuity as a test of visual function in the presence of cataracts and other media opacities. Invest Ophthalmol Vis Sci 25:389-399, 1984 Hyperacuity is a term that describes a special class of visual responses including vernier acuity, detection of line tilt, stereoacuity, and other related tasks. 1 Common to these various responses is an extremely low performance threshold that is on the order of 3-5 sec of arc under optimal conditions, a value considerably below that of traditional visual acuity thresholds. In itself, the fact that a vernier acuity threshold of 3 sec of arc is nearly an order of magnitude smaller than the intercone spacing in the human fovea (25 to 30 sec of arc) implies that some additional information processing, beyond that available at the retinal level, is required for such fine relative localization of features in the visual field. 2 Other properties of the hyperacuity response, eg, the interocular transfer of the effects of interfering neighboring lines, 3 also suggest a central locus within the visual system for the neural processing subserving this visual ability. Our goal in the present study is to evaluate the influence of optical degradation of the retinal image on thresholds in selected hyperacuity tasks. In at least one respect, hyperacuity is not limited by the quality of

The resistance of selected hyperacuity configurations to retinal image degradation.

The resistance of certain types of hyperacuity tasks (eg, vernier acuity) to optical degradation of the retinal image has been demonstrated previously. This suggests that such a task might provide a means of filling the clinical need for a reliable test of retinal function in the presence of cataracts and other ocular opacities. In the present study, we measure several aspects of vernier acuity performance in cataract patients. These data provide an early basis for the development of a vernier acuity test to detect retinal/neural visual loss prior to cataract surgery. We report the results of measurements in 15 cataract patients using a two-dot vernier acuity task with variable separation between the two dots (gap). The data indicate that the shape and mean level of the vernier threshold-versus-gap function co-vary with the functional severity of the opacity as corroborated by Snellen acuity measures. Furthermore, the optical effects of the cataracts we studied are very similar to the effects of degrading the visual stimulus by interposing ground glass for a normal observer. We conclude that the shape of the vernier threshold-versus-gap function is a good indicator of the functional severity of the cataract in patients with otherwise normal vision.

The effects of image degradation by cataract on vernier acuity.

Side lobe artifacts on point spread functions can be traced back to (1) fringe visibility variation across the spectrum, (2) errors in sampling instances, and (3) window functions. We demonstrate signal processing methods for correcting for all three of these issues. These methods require a system calibration step. If the systems slowly age, the recalibration step could be performed in the field with a fixtured target.

Achieving the ideal point spread in swept source OCT

One embodiment of the present invention is a method for providing a deviation map of an eye that includes: (a) acquiring data comprising a corneal topographic map; (b) determining locations of abnormal curvature within the topographic map; (c) determining a modified topographic map by removing data associated with locations of abnormal curvature; (d) computing a reference map from the modified topographic map; (e) computing a deviation map by combining the topographic map and the reference map; and (f) displaying or storing the deviation map. An additional embodiment includes the processing of pachymetric data in a similar fashion.

Rick A. Williams

Papers

Method and apparatus for measuring motion of a subject using a series of partial images from an imaging system

The resistance of selected hyperacuity configurations to retinal image degradation.

The effects of image degradation by cataract on vernier acuity.

Achieving the ideal point spread in swept source OCT

Mean curvature based de-weighting for emphasis of corneal abnormalities