Thomas Kuyk

Visual correlates of mobility in real world settings in older adults with low vision

Purpose. To determine the effects of reducing light level from photopic to mesopic on performance of real world mobility tasks and how performance of these tasks relates to measures of visual sensory and perceptual function. Methods. The visual functions, acuity, peak letter contrast sensitivity, visual field extent, glare disability, color confusion, motion sensitivity, spatio-temporal contrast sensitivity, scanning ability, and figure-ground discrimination were measured to determine their ability to predict mobility performance of visually impaired adults on indoor hallway and outdoor residential travel routes under photopic and mesopic lighting conditions. Results. Time to complete routes and number of mobility incidents were significantly increased under mesopic conditions. Depending on the task, lighting conditions, and performance measure, predictive models consisting of 4 vision variables were able to account for 30 to 42% of the variance in overall performance. The two most important variables in these models were visual field extent and scanning ability, followed by color confusion, grating contrast sensitivity, or spatial resolution. Conclusions. Reducing illumination levels from photopic to mesopic has an adverse effect upon mobility in older visually impaired adults. The aspects of vision which best predict performance include measures of sensory and perceptual visual function. The results compare well with those obtained under controlled laboratory conditions.

Mobility function in older veterans improves after blind rehabilitation.

This study was conducted to investigate the effects of blind rehabilitation training on self-reported mobility function in visually impaired adults. Mobility function was assessed with a questionnaire administered before and 2 months after subjects completed a comprehensive blind rehabilitation program that included orientation and mobility training. Subjects rated the level of difficulty performing in 26 of 34 mobility situations as significantly lower after rehabilitation. Subjects also rated their confidence as higher after rehabilitation. Substantial improvement occurred in the self-reported mobility function of visually impaired adults after blind rehabilitation and mobility training.

Visual search training in subjects with severe to profound low vision

Effects of practicing on feature search tasks (a 2 degrees square target amid 1 degrees square distracters) for 5 days were compared between 45 visually impaired (VI) subjects with severe to profound low vision and 23 age-matched normal controls (NV). Search accuracy and speed improved in both groups. VI subjects had larger training gains than NV subjects, but their proportional gains were similar to that of NV subjects. There were no significant differences in training effect at different set sizes in both groups. Search performance on a 40 degrees field improved more than that on a 10 degrees or 20 degrees field in VI subjects, but not in NV subjects. No significant change was found between day 5 and 1-month follow-up. The fact that feature search training is equally efficient in VI and NV subjects encourages development of general purpose perceptual training protocols for low vision rehabilitation.

Feature search in persons with severe visual impairment

Feature search performance was measured in visually impaired (VI) and age-matched controls with normal vision (NV). All VI subjects were legally blind. The task was to search for a 2 degrees x 2 degrees square target among smaller 1 degrees x1 degrees distracters. Targets and distracters were white and presented on a dark background that subtended 69 degrees by 58 degrees . Three field-sizes (10 degrees , 20 degrees , and 40 degrees ) and three set sizes (8-, 16-, and 32-items) were tested. The VI subjects searched more slowly than the NV subjects, but the reaction time of both groups of subjects did not rise with increasing number of items. The latter is consistent with a parallel search. Both groups searched more slowly when field-size increased, but the VI group was affected more by the increase than the NV group.

Relationships between feature search and mobility performance in persons with severe visual impairment.

Purpose. Because visual search requires both the ability to discriminate visual features and the ability to process information in a large field of view, the association between feature search and mobility of visually impaired (VI) subjects was studied. Methods. Forty-four subjects with severe visual impairment participated in the study. Feature search performance (2 × 2 deg square target amid 1 × 1 deg square distracters) was measured for 8- to 16- and 32-item set-sizes on 10 × 10, 20 × 20, and 40 × 40 deg fields. Mobility was evaluated on indoor high-density obstacle courses under photopic and mesopic illumination. Results. In feature search, VI subjects were slower and made more errors than normal subjects, but they searched in a parallel fashion. On the mobility task, VI subjects walked slower and made more obstacle contacts than age-matched normal controls. In VI subjects, performances on feature search and mobility tasks were significantly associated, with 37.5% to 66.9 of variations in the mobility measurements being accounted for by visual search speed. Conclusions. Feature search reaction time can be a good predictor of VI patients’ mobility.

The AMA Guides functional vision score is a better predictor of vision-targeted quality of life than traditional measures of visual acuity or visual field extent

OBJECTIVE: The purpose of this study was to determine if combining visual acuity (VA) and visual field (VF) measures in the manner proposed in the 1999 Guide for the Evaluation of Visual Impairment1and incorporated into the 5thEdition of AMA Guides for the Evaluation of Permanent Impairment2(Guide) would be more predictive of self-reported vision-targeted quality of life than standard vision measures of VA or VF alone. DESIGN: Visual function and quality of life (QOL) were assessed in 200 visually impaired individuals. Tests included visual acuities, visual fields, and vision specific QOL using the National Eye Institute Visual Function Questionnaire (NEI VFQ). Visual acuities and visual fields were scored in the usual manner and then rescored using methodology proposed in the Guide to derive measures of functional vision. Relationships among the visual function, functional vision and QOL outcomes variables were determined using correlation and stepwise regression analyses RESULTS: High correlations were ...

Macular Pigment and Visual Performance in Low-Light Conditions.

PURPOSE By reducing rod intrusion and improving efficiency of neural signaling throughout the visual system, macular pigment (MP) could improve many aspects of visual performance in low-light level conditions. Our study examined this possibility for a variety of visual performance parameters, including spatial resolution, dark adaptation kinetics, and color detection. METHODS Twenty-seven subjects participated in the study. Spatial profiles of MP optical density (MPOD) were determined by using heterochromatic flicker photometry. Mesopic- and scotopic-adaptation level experiments were conducted in Maxwellian view. RESULTS Subjects with higher MPOD required significantly lower contrast to detect the mesopic-level resolution targets; this effect became stronger with increasing spatial frequency. Dark adaptation recovery times were significantly faster as a function of MPOD (by nearly 2 minutes for the lowest mesopic-level task [high versus low MPOD]; P < 0.001). Absolute scotopic thresholds were also significantly associated with MPOD (P < 0.001). Macular pigment optical density was inversely associated with detection of yellow (P < 0.001), and, paradoxically, approached a significant positive correlation with the detection of blue (P = 0.06). CONCLUSIONS Macular pigment appears to enhance visual function in low-light conditions. Based on the results of this study, it can be said that MP extends the range of foveal vision into lower light. Additionally, MP appears to enhance dark adaptation kinetics, which suggests that increased MPOD leads to more efficient photopigment regeneration. The findings of the color detection portion of the study are suggestive of an active compensatory mechanism that offsets absorption by MP in order to maintain normal color perception.

Suppressive effects of peripheral flicker on foveal bichromatic mixture thresholds

Increment thresholds were determined for bichromatic mixtures of 660 and 520 nm (red + green), and 440 or 460 and 570 nm (blue + yellow). These measurements were made against a 1000-td white background that was surrounded by a larger, luminance matched annulus that appeared steady or flickered at 10 Hz. Targets were circular spots that subtended 60 and 15 min arc and had durations of 10 and 200 msec. All mixture thresholds with the steady surround were non-additive. The flickered surround gave rise to a periphery effect (PE), in the form of elevated mixture thresholds compared to those using the steady surround, for both red + green and blue + yellow mixtures when the 60 min arc, 10 msec spot was used. A PE was not consistently observed for the other three stimulus conditions. We propose the non-additive results indicate parvocellular (P-) pathway involvement in detection, which occurred under all stimulus conditions tested. Furthermore, that the PE were found when mixture stimuli were large, and brief indicates magnocellular (M-) pathway involvement in detection.

Scaling laser disability glare functions with "K" factors to predict dazzle

With the increasing availability of higher power laser pointers, there is growing coneem about disability glare or dazzle from laser illumination and the safe operation of aireraft and vehicles. A study was condueted to determine the ability of observers to discriminate targets over three log units of laser irradiance (from 0.6 μW·cm−2 to 600 μW·cm−2) and at adaptation levels that simulated twilight (3 cd·m−2), low daytime (30 cd·m−2) and daytime (3,400 cd·m−2) conditions. Other factors that were varied included: target size (0.7°-12°), laser exposure angle (0°-55°), and the presence or absence of an aireraft windscreen. The dazzle effect increased with laser irradiance and decreased as target size increased. The dazzle effect was also greater with a windscreen than without a windscreen, and dazzle increased as ambient luminance decreased. The glare obscuration with eccentricity from the laser source was subsequently used to calibrate the Commission Internationale de l’Eclairage (CIE) disability glare function with appropriate “K” factors, thus allowing a more accurate predietion of dazzle effects across other irradiances and adaptation levels.With the increasing availability of higher power laser pointers, there is growing coneem about disability glare or dazzle from laser illumination and the safe operation of aireraft and vehicles. A study was condueted to determine the ability of observers to discriminate targets over three log units of laser irradiance (from 0.6 μW·cm−2 to 600 μW·cm−2) and at adaptation levels that simulated twilight (3 cd·m−2), low daytime (30 cd·m−2) and daytime (3,400 cd·m−2) conditions. Other factors that were varied included: target size (0.7°-12°), laser exposure angle (0°-55°), and the presence or absence of an aireraft windscreen. The dazzle effect increased with laser irradiance and decreased as target size increased. The dazzle effect was also greater with a windscreen than without a windscreen, and dazzle increased as ambient luminance decreased. The glare obscuration with eccentricity from the laser source was subsequently used to calibrate the Commission Internationale de l’Eclairage (CIE) disability glare fun...

Color name training: Identifying colors through laser eye protection

Laser eye protection (LEP) that protect against visible lasers often impose limitations on visual compatibility with in-cockpit and out-of-cockpit color stimuli. Aircrew generally do not have accurate first-hand information about what color changes to expect, especially at first time use. Instead, experience is gained while flying with LEP. It may be possible to train aircrew prior to flight on how to accurately associate true color names with hues that are altered by LEP.We performed a proof of concept evaluation reaching a conclusion that color name training with LEP can lead to significant improvements in performance on a color naming (CN) test. The CN test was based on the color symbology identification (CSI) test designed to simulate colors and symbology seen in the cockpit. A second study was conducted to replicate the results of the concept with a larger number of naive observers to determine if the training effect persisted for a longer period of time and to compare results with those from a control group that received repeated administration of the CN test but no color name training.We demonstrated that most Individuals can significantly improve their ability to identify colors altered by LEP when they are given training that pairs the true name of the color with the altered color. The study also demonstrated that the improved ability can be retained for up to 14 days after training, and that subjects can learn a second color set with a second LEP as readily as they learned a first set.Laser eye protection (LEP) that protect against visible lasers often impose limitations on visual compatibility with in-cockpit and out-of-cockpit color stimuli. Aircrew generally do not have accurate first-hand information about what color changes to expect, especially at first time use. Instead, experience is gained while flying with LEP. It may be possible to train aircrew prior to flight on how to accurately associate true color names with hues that are altered by LEP.We performed a proof of concept evaluation reaching a conclusion that color name training with LEP can lead to significant improvements in performance on a color naming (CN) test. The CN test was based on the color symbology identification (CSI) test designed to simulate colors and symbology seen in the cockpit. A second study was conducted to replicate the results of the concept with a larger number of naive observers to determine if the training effect persisted for a longer period of time and to compare results with those from a contr...