David S. Loshin

Reading rates with artificial central scotomata with and without spatial remapping of print

People with central field defects resulting from age-related macular degeneration (ARMD) read very slowly. In this study, oral reading rates were determined for unrelated sequences of words in samples of normal young and old subjects with simulated central scotomata of 2 degrees, 4 degrees, and 8 degrees. Scotomata were stabilized at the fovea of the right eye by electronic feedback of eye position, monitored using a SRI dual-Purkinje Eyetracker. Reading rates were determined by jumping print after each stationary presentation through an increasing number of character spaces on different trials. This procedure mimicked the sequence of retinal images produced during the saccades and fixations of normal reading, but without requiring subjects to make accurate eye movements. In Experiment 1, the letter size that yielded the optimal reading rate was found to increase systematically with scotoma size. However, the optimal reading rate decreased more or less linearly as the scotoma size increased. Experiment 2 showed that the optimal reading rate was obtained for essentially the same duration of text presentation, regardless of scotoma size. Experiment 3 investigated the effect of spatial remapping, in which print obscured by the scotoma was stretched electronically to reappear at the scotoma margin. Compared to a nonremapped control condition, spatial remapping produced small but significant increases in reading rate for both 4 degrees and 8 degrees scotomata. Across experiments, average reading rates were faster for the young than the old subjects. Overall, the results define how reading rate is expected to decrease for central scotomata of different sizes and suggest that spatial remapping of print may improve reading rates in patients with ARMD.

Stereo-deficients and stereoblinds cannot make utrocular discriminations

In two separate experiments, we show that stereo-deficient observers are no better than stereonormals at discriminating the eye-of-origin of a monocular stimulation. Stereo-deficient observers are considered to have a preponderance of monocular neurons throughout their visual system, including the visual cortex. The results indicate that, in spite of their clear anatomical and physiological structure, such monocular neurons do not convey eye-of-origin information to consciousness.

Testing of remapping for reading enhancement for patients with central visual field losses

Retinal pathology often results in visual field loss. Age related macular degeneration (ARMD) and Stargardts disease (a congenital disease) typically affects the central macular region of the retina, resulting in visual field loss to the region of the retina with the highest resolution. Due to the central visual field losses, patients with ARMD and Stargardts disease often experience difficulty in visual tasks, such as reading and facial recognition. NASA Johnson Space Center has developed an electronic remapper that can warp an image from one coordinate system to another on a television screen. The remapper can be used with patients with central visual field loss to redistribute information projecting off of the macular lesion (corresponding to the central scotoma) and onto the still functioning peripheral retina. The purpose of this research project was to investigate whether remapping of text around the central scotoma improved reading performance (increased reading rate) for patients with ARMD or Stargardts disease. The subjects moved the text on the stage and read aloud random words of equal difficulty viewed on a closed circuit television screen. Reading speeds for normal and remapped text were obtained. Reading rates were determined for both free viewing and with stabilization of the position of the screen relative to the eye rotations. Results of these experiments are discussed.

Quasi-conformal remapping for compensation of human visual field defects - Advances in image remapping for human field defects

We are investigating image coordinate transformations possibly to be used in a low vision aid for human patients. These patients typically have field defects with localized retinal dysfunction predominately central (age related maculopathy) or peripheral (retinitis pigmentosa). Previously we have shown simple eccentricity-only remappings which do not maintain conformality. In this report we present our initial attempts on developing images which hold quasi-conformality after remapping. Although the quasi-conformal images may have less local distortion, there are discontinuities in the image which may counterindicate this type of transformation for the low vision application.

Some Examples Of Image Warping For Low Vision Prosthesis

NASA and Texas Instruments have developed an image processor, the Programmable Remapper 1, for certain functions in machine vision. The Remapper performs a highly arbitrary geometric warping of an image at video rate. It might ultimately be shrunk to a size and cost that could allow its use in a low-vision prosthesis. We have developed coordinate warpings for retinitis pigmentosa (tunnel vision) and for maculapathy (loss of central field) that are intended to make best use of the patients remaining viable retina. The rationales and mathematics are presented for some warpings that we will try in clinical studies using the Remappers prototype. (Recorded video imagery was shown at the conference for the maculapathy remapping.

Conformal and other image warpings for reading with field defect

Certain visual functions, such as reading, are dependent on the high resolution capability of the central visual field. When that area becomes dysfunctional the tasks become difficult or impossible. We have proposed an image warping prosthesis, in which the structure of the image that would otherwise be unseen owing to the scotoma is moved outward and onto portions of the retina that still function. Previously we used normally sighted volunteers with fixated foveation, synthetic scotomas, a limited form of image warping, and externally controlled reading saccades. Their reading rate showed improvement in a significant number of instances. In the next stage, we are prepared to use volunteers with actual, not synthesized, scotomas. The results will be used to design realistic prostheses. Different warpings may better help other visual tasks such as facial recognition. Some of the image warpings designed for reading are shown here and our rationale for considering them are given.

Design of a reading test for low vision image warping

NASA and the University of Houston College of Optometry are examining the efficacy of image warping as a possible prosthesis for at least two forms of low vision -- maculopathy and retinitis pigmentosa. Before incurring the expense of reducing the concept to practice, one would wish to have confidence that a worthwhile improvement in visual function would result. NASAs Programmable Remapper (PR) can warp an input image onto arbitrary geometric coordinate systems at full video rate, and it has recently been upgraded to accept computer- generated video text. We have integrated the Remapper with an SRI eye tracker to simulate visual malfunction in normal observers. A reading performance test has been developed to determine if the proposed warpings yield an increase in visual function; i.e., reading speed. We describe the preliminary experimental results of this reading test with a simulated central field defect with and without remapped images.

Reading rates of patients with central scotomas with electronic remappings

Central visual defect results in loss of vision in the region of retina with the highest resolution. Due to central visual field loss, these patients experience difficulty in visual tasks such as reading and recognizing faces. Age related macular degeneration (ARMD) and juvenile macular degeneration (JMD), destroy the function of the central retina. NASA Johnson Space Center has developed an electronic remapper that can warp from one coordinate system to another on a television screen. The remapper was used in this study to redistribute visual images projecting on the macular lesion to the still functioning peripheral retina. The purpose of this study was to investigate whether remapping of reading material around the central scotomas of patients with ARMD and JMD improved reading rates. Reading rates of nonremapped words and remapped words were compared under three viewing conditions: (1) Reading without stabilization under free viewing condition, (2) Reading with image stabilization through the eye tracker, (3) Reading without image stabilization through the eye tracker.

Image evaluation of ophthalmic devices

Methods used in the ophthalmic industry to evaluate the optical image quality of correcting lenses have remained the same over many years. This is especially true for single-vision ophthalmic lenses. With the development of new optical designs and materials for correcting refractive errors and presbyopia, new procedures for evaluating lens performance are being explored. One such method is the measurement of the modulation transfer function. Over the last 2 years, we have been measuring modulation transfer functions on a variety of single-vision and bifocal contact lenses, progressive addition spectacle lenses, holographic-diffractive lenses, and intraocular lenses. In this article, the modulation transfer function procedure and its application and results from one study on safety goggles will be presented and discussed.