Patti S. Fuhr

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.

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 ...

The effects of peripheral flicker on foveal spectral sensitivity

A flickering surround reduced sensitivity to large, briefly flashed monochromatic stimuli superimposed on a steady white background, compared to sensitivity measured when the surround was steady. The flickering surround had no effect on stimuli that were large and of long duration or small in size. Increasing the diameter of the background reduced the magnitude of the effect, but did not eliminate it.

Influence of reference frames on asymmetries in Troxler's effect.

In 1804, Troxler discovered that, when an observer fixates on a point in central vision and attends to a peripheral stationary stimulus, the peripheral stimulus eventually fades from awareness. This phenomenon is known as Troxlers effect and is allegedly influenced by spatial attention. Asymmetries in Troxlers effect along horizontal and vertical meridian were a recent discovery. However, viewer- and environment-centered reference frames were aligned in prior studies, making it impossible to assess whether asymmetries correspond to viewer-versus environment-centered coordinate systems. This study was undertaken to (a) replicate the asymmetries in the upright condition among 39 participants without health issues and (b) use the asymmetrics to test contrasting predictions made by viewer- and environment-centered coordinate systems when they are decoupled using an experimental head-tilt condition. The horizontal and vertical asymmetries were replicated and consistent with a viewer-centered rather than an environment-centered reference frame.

Use of Ready-made Spectacles to Meet Visual Needs in a Low-resource Adult Population

Purpose In affluent societies, distance and near vision problems are typically corrected with custom-made eyeglasses. Many persons in less affluent areas do not have the resources for such. The purpose of this study was to assess the use of less expensive ready-made (RM) bifocals and readers to correct distance and near refractive error and presbyopia in an outreach clinic in Nicaragua. Methods This is a retrospective review of records of all patients older than 34 years who presented for an eye examination in an outreach clinic in Granada, Nicaragua, in 2010. A visual satisfaction questionnaire had been administered to patients before they were examined and after RM plus sphere bifocals or plus sphere reading spectacles were dispensed. The main outcome measures included pre– and post–distance and near visual acuities, vision satisfaction and difficulty ratings, and perceived cost and willingness to pay for replacement rating. Results Ready-made plus sphere spectacles (bifocals or single-vision readers) were dispensed to 95.4% of those examined. The remaining 4.6% required custom prescriptions because of astigmatism, myopia, or anisometropia. The RM bifocals were very well accepted, with high visual satisfaction ratings with the bifocals improving from a presenting value of 11 to 89.4% at distance and from 6.6 to 89.4% at near. Percentage of patients achieving visual acuity of 20/40 or better improved from 60 to 84.5% at distance and from 44 to 97% at near. Percentage achieving functionally good near vision (20/40 or better) improved from 38 to 97% with RM readers. Patients reporting highest satisfaction with near vision improved from 6.3 to 86.6%. Patients indicated that, on average, they would be willing to pay US

Suppressive effects of peripheral flicker on foveal bichromatic mixture thresholds

18.39 to replace the bifocals and US

Visually impaired caregivers: perspectives from patient focus groups.

16.67 to replace the readers. Conclusions Ready-made bifocals and RM single-vision readers may be an acceptable and affordable alternative for many patients with hyperopia and/or presbyopia where access to custom-made eyeglasses is difficult.