Ronald A. Schuchard

Eye and visual function in traumatic brain injury

Combat blast is an important cause of traumatic brain injury (TBI) in the Department of Veterans Affairs polytrauma population, whereas common causes of TBI in the civilian sector include motor vehicle accidents and falls. Known visual consequences of civilian TBI include compromised visual acuity, visual fields, and oculomotor function. The visual consequences of TBI related to blast remain largely unknown. Blast injury may include open globe (eye) injury, which is usually detected and managed early in the rehabilitation journey. The incidence, locations, and types of ocular damage in eyes without open globe injury after exposure to powerful blast have not been systematically studied. Initial reports and preliminary data suggest that binocular function, visual fields, and other aspects of visual function may be impaired after blast-related TBI, despite relatively normal visual acuity. Damage to the ocular tissues may occur from blunt trauma without rupture or penetration (closed globe injury). Possible areas for research are development of common taxonomy and assessment tools across services, surgical management, and outcomes for blast-related eye injury; the incidence, locations, and natural history of closed globe injury; binocular and visual function impairment; quality of life in affected service members; pharmacological and visual therapies; and practice patterns for screening, management, and rehabilitation.

Tracking retinal motion with a scanning laser ophthalmoscope

The vast majority of people with low vision retain some functional vision to perform everyday tasks. To study the effectiveness and efficiency of the visual tasks performed by people with low vision, knowing the movement patterns of their preferred retinal locus (PRL) used for fixation, saccade, and pursuit is critical. The scanning laser ophthalmoscope (SLO) has been used to acquire retinal images while a subject is performing a visual tracking exercise. SLO data has traditionally been analyzed with the use of manual techniques that are both time-consuming and prone to errors due to operator fatigue. To improve the speed and accuracy of the analysis of retinal motion from SLO image sequences, we developed an automated image processing technique and tested it using MATLAB(TM) (The MathWorks, Natick, MA) software. The new software technique was experimentally tested on both normal- and low-vision subjects and compared with the results obtained using manual techniques. The findings indicate that the new technique works very well for most subjects, fairing poorly only in subjects where the quality of the SLO images was substandard.

Age Effects on Visual-Perceptual Processing and Confrontation Naming*

ABSTRACT The impact of age-related changes in visual-perceptual processing on naming ability has not been reported. The present study investigated the effects of 6 levels of spatial frequency and 6 levels of contrast on accuracy and latency to name objects in 14 young and 13 older neurologically normal adults with intact lexical-semantic functioning. Spatial frequency and contrast manipulations were made independently. Consistent with the hypotheses, variations in these two visual parameters impact naming ability in young and older subjects differently. The results from the spatial frequency-manipulations revealed that, in general, young vs. older subjects are faster and more accurate to name. However, this age-related difference is dependent on the spatial frequency on the image; differences were only seen for images presented at low (e.g., 0.25–1 c/deg) or high (e.g., 8–16 c/deg) spatial frequencies. Contrary to predictions, the results from the contrast manipulations revealed that overall older vs. young adults are more accurate to name. Again, however, differences were only seen for images presented at the lower levels of contrast (i.e., 1.25%). Both age groups had shorter latencies on the second exposure of the contrast-manipulated images, but this possible advantage of exposure was not seen for spatial frequency. Category analyses conducted on the data from this study indicate that older vs. young adults exhibit a stronger nonliving-object advantage for naming spatial frequency-manipulated images. Moreover, the findings suggest that bottom-up visual-perceptual variables integrate with top-down category information in different ways. Potential implications on the aging and naming (and recognition) literature are discussed.

Models of reading performance in older adults with normal age-related vision

Reading rate with print size (reading performance) was studied in a group of 132 older readers with normal age-related vision using the Minnesota Low Vision Reading Acuity (MNREAD) test. Regression by a monotonic Weibull model had greater convergence success with lower residual error than either Logistic or Gompertz models. Reading performance by Weibull model regression was characterized by inflexion slope, critical print size, and maximum reading rate. Successive shortening of the data set length before regression by the monotonic Weibull model gave decreased fitting error. This finding suggests that some individual reading rates, rather than asymptoting at the largest print size, may give nonsigmoidal responses. Shortening the data set length decreases regression error but significantly changes regression parameter values. A nonmonotonic Weibull model that was sensitive to declining reading rate at large print size improved regression on 22% of our data. This result indicates that a subgroup of subjects had response falloff at large print size and reading performance characteristics that included incremental and decremental reading rate slopes at different print sizes, which were separated by a reading rate plateau.

Evaluating Barten Image Metric for Predicting Character Recognition in People with Low Vision

Electronic devices with small visual displays (SVDs) are often inaccessible to the millions of Americans with vision loss. The Barten square root integral (SQRI) is an image quality metric that has been shown to predict whether people with normal vision can see images on a cathode ray tube monitor. The present proof-of-concept study begins to explore whether the same metric could predict the ability of users with low vision to see images on SVDs. In a sample population of 33 adults with low vision, the Barten SQRI was the best predictor of the ability to recognize low-contrast single digits on a screen (r(2) = 0.80, p < 0.01), followed by the Pelli-Robson Contrast Sensitivity Chart (r(2) = 0.69, p < 0.01). Visual acuity was not significantly predictive of the ability to read low-contrast characters on a display. Further work will explore whether the Barten SQRI remains predictive of the ability of people with low vision to use actual devices that have SVDs.