Peripheral vision in children

A comparison of peripheral vision in adults and children showed that children had reduced sensitivity in a standard visual field examination. The constriction of the visual field amounted to 0.4 log units at 30 degrees excentricity in a static perimetric test. This loss was maintained in a spatial forced choice experiment without foreknowledge of target location. However, in a temporal forced choice experiment with foreknowledge of target position the difference between children and adults was reduced to 0.1 log units. It is thought, therefore, that the former visual loss in children is due to the nature of the task rather than to deficiencies in the visual mechanisms.     

A multidiscipline approach in low vision rehabilitation

The first low vision clinic was instituted at the Industrial Home for the Blind in 1953 in response to a growing demand that more effective use be made of the residual vision in blind persons. The technology was there. Eye practitioners certainly knew enough about vision problems to offer many of these people an opportunity to enter a new life. The problem was: how to put that knowledge to work through a sound service delivery system. By its twentieth anniversary in 1973 the clinic had seen almost 5,000 patients for low vision evaluation and had built a service which consistently provided substantial and useful improvement in vision through the use of optical aids to a majority of its patients. The low vision optometric staff works as an integral part of a rehabilitation team. That team consists of a number of professionals, including ophthalmologists, social workers, teachers, and a variety of rehabilitation instructors. All members work simultaneously to create a total program of rehabilitation for thepartially sighted. We feel this teamwork approach is of basic importance to effective rehabilitation.     

Overview of technology for low vision

This article provides an overview of technology resources and services to assist persons with low vision in maintaining independent function in the home, community, and educational and vocational settings. Case studies are provided to demonstrate the integration of technology into the lives of persons with low vision.     

Clinical low vision resource usage prediction

In an era of increased demands and constrained budgets, it is necessary to make the best use of all available resources. This is difficult when specialized vision care, such as low vision clinical assessment, is involved because of the heterogeneity of the patient populations seen by such clinics. PURPOSE. This research attempts to discover if these diverse patient populations can be identified and clustered into groups based upon similarity of clinical resources use. Specifically, the inquiry examines the potential for a low vision patient resource utilization classification scheme at the Low Vision Clinic (LVC) in the Centre for Sight Enhancement (CSE), University of Waterloo. METHODS. From a sample of 99 patients consulting the LVC in a 3-month period, retrospective data collection involved abstracting and coding medical records containing information detailing each patient's demographic, diagnostic, therapeutic, and resource utilization characteristics. Cluster analysis using Hartigan's block clustering algorithm was then applied to the data. A replication study was completed using a sample of 99 patients visiting the LVC 1 year later. RESULTS. Patients can be classified into five iso-resource groups, hereby termed low vision patient resource groups (LVPRGs). The clusters represent a resource consistent and clinically coherent scheme for classifying low vision patients based upon resource requirements. As a measure of repeatability, the groups reemerged in the replication study. CONCLUSIONS. If the groupings demonstrate robustness in a field test, clustering algorithms in general, and LVPRGs in specific, may offer useful tools to enhance resource utilization in the LVC setting.     

National survey of blindness and low vision in Lebanon

Here we report a case that presented with sudden onset of neurological symptoms and was treated with ganciclovir. Polymerase chain reaction analysis for human herpes virus-6 (HHV-6) from his cerebrospinal fluid was later found to be positive. He subsequently recovered with minimal residual neurological symptoms. Encephalitis secondary to this virus may be more common than previously thought in patients undergoing bone marrow transplantation. This condition should be considered in the differential diagnosis of sudden onset neurological symptoms after bone marrow transplantation.     

Color improves object recognition in normal and low vision.

Does color improve object recognition? If so, is the improvement greater for images with low spatial resolution in which there is less shape information? Do people with low visual acuity benefit more from color? Three experiments measured reaction time (RT) and accuracy for naming food objects displayed in 4 types of images: gray scale or color, and high or low spatial resolution (produced by blur). Normally sighted Ss had faster RTs with color, but the improvement was not significantly greater for images with low spatial resolution. Low vision Ss were also faster with color, but the difference did not depend significantly on acuity. In 2 additional experiments, it was found that the faster RTs for color stimuli were related to objects' prototypicality but not to their color diagnosticity. It was concluded that color does improve object recognition, and the mechanism is probably sensory rather than cognitive in origin. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A systems model for low vision rehabilitation. II. Measurement of vision disabilities

BACKGROUND: This study presents and tests a method of measuring vision disabilities. Based on the model presented in the first paper of this series, cognitive and motor activities ("tasks") are organized in a hierarchy that identifies the tasks' behavioral goals (purposes) and the social objectives the goals serve. Two latent variables important to the definition of vision disability are identified: "value of living independently" and "visual ability for independent living." The basic principles of the Rasch measurement model are reviewed, and Rasch models are used to measure the two variables that define vision disability. The need for rehabilitation to meet each goal is represented by "rehabilitative demand," a mathematical function of the measurements made of the value and difficulty of achieving each goal independently. METHODS: Over 400 patients with low vision rated both the importance and difficulty of independently achieving each of 24 goals. Rasch analysis was used to derive interval measures of the social value of each goal, the value that individual patients placed on each goal relative to the derived social definition of independence, the visual ability required to achieve each goal without help, and the visual ability of individual patients to live independently. A rehabilitative demand function was ascertained from the judgments of 17 AAO Diplomates in Low Vision through triadic comparisons and multidimensional scaling. RESULTS: Self-care had the greatest "social value" for independence; performing music had the least. Recreational reading required the greatest "visual ability" to accomplish independently; self-care required the least. Rehabilitative demand was linear with value and nonmonotonic with difficulty. CONCLUSIONS: Rehabilitative demand, an algorithm for defining vision disability, incorporates interval measures of visual ability and the value of independent living estimated from patient-based assessments, a social scale of the value of activities relative to independent living, and a consensus opinion of low vision experts on the prioritization of the need for rehabilitation.     

Specific retinal breaks in aphakic retinal separation

The frequency and location of specific retinal breaks in a consecutive series of 169 phakic and 121 aphakic primary nontraumatic rhegmatogenous retinal separations categorized into lattice and nonlattice groups was determined. Small horseshoe tears in the oral region of the retina at the posterior vitreous base were responsible for 44.1% of aphakic nonlattice detechments. Aphakic detachments associated with lattice degeneration had a greater relative frequency of associated nonlattice tractional breaks in addition to lattice breaks.     

Psychophysics of reading--XVI. The visual span in normal and low vision

The visual span in reading is the number of characters that can be recognized at a glance. The shrinking visual span hypothesis attributes reading deficits in low vision, and slow reading in normal vision at low contrast, to a reduction in the visual span. This hypothesis predicts that reading time (msec/word) becomes increasingly dependent on word length as text contrast decreases. We tested and confirmed this prediction using the rapid serial visual presentation (RSVP) method. Estimates of the visual span ranged from about 10 characters for high-contrast text to less than two characters for low-contrast text. Eye-movement recordings showed that longer reading times at low contrast are partitioned about equally between prolonged fixation times and an increased number of saccades (presumably related to a reduced visual span). RSVP measurements for six out of seven low-vision subjects revealed a strong dependence of reading time on word length, as expected from reduced visual spans.     

A simplified screening test for identifying people with low vision in developing countries

Simple but effective tests have been produced for screening subjects with low vision in developing countries. These tests of distance and near vision, based on the E test, were evaluated and validated in trials with people aged 4-90 years, and have been field tested in the health, education and rehabilitation services in 32 developing countries. Their sensitivity and specificity as screening tools for low vision have been calculated; sensitivity of 85% and specificity of 96% for the distance vision test, and sensitivity of 100% and specificity of 84% for the near vision test. The content and format of the tests have been demonstrated to be appropriate for developing countries, and their effectiveness for screening for low vision has been confirmed.     

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.     

Neuro-psychological development of vision in children older than 6 years of age

In snails maintained at 20 degrees C rediae of Fasciola hepatica merge from sporocysts from 11 days after infection onwards. The number of mother rediae rises steadily thereafter until at least 40 days after infection. Daughter rediae are seldom observed in mother rediae dissected from snails maintained at 20 degrees C. Their production can, however, be stimulated by subjecting the snail host to starvation, to low, and to high temperature shocks. The parasite is susceptible to stress from immediately after infection for about 16 days, when maintained at 20 degrees C. In general, the more extreme the shock, the greater is daughter redial production. Increasing the length of the period of stress from 12 h up to 9 days does not increase the production of daughter rediae, nor does repeated on/off cold shocks or continuous maintenance at 10 degrees C. Daughter rediae develop more rapidly than cercariae and leave the mother rediae several days earlier. There is no evidence that presence of daughter rediae coincides with the suppression of cercarial production. The findings are discussed with reference to possible mechanisms by which parasite development might be controlled.     

Causes of low vision and blindness in south western Saudi Arabia. A hospital-based study

The authors studied 1,681 consecutive patients who attended their ophthalmic outpatient clinics over a period of 12 months to determine the patients' visual acuity status and the causes of any visual loss. Using the World Health Organization criteria for definition of visual acuity status, 1004 (59.7%) patients had normal vision. Four hundred and thirty-one (25.6%) patients had low vision or visual impairment and 246 (14.6%) patients were blind. Twenty-eight (1.9%) patients had no light perception in both eyes. Cataract, both in isolation and co-existing with other ocular pathology, was the major cause of both low vision and blindness (58.5% and 81.7%, respectively). A concerted attack on cataract alone will markedly reduce blindness and low vision in this region.     

Behavioural adjustment in school of very low birthweight children

The school-based behavioural adjustment at 7-8 years of a cohort of 243 prematurely born, very low birthweight (< 1501 g) children and their normal birthweight controls is reported. The findings indicate that the children born preterm (both male and female) were rated by their teachers as expressing more behaviour problems than their controls, and were less well adjusted to the school environment. The deficits noted in the preterms applied across the social classes, with no amelioration noted in preterms of higher social class. It is speculated that the problem behaviours reflect a failure in self-regulatory functions.     

Changes in the visual system in low birth weight children

PURPOSE: Evaluation of the visual system, especially refraction, in children with low birth weight under observation between 1990-1992. MATERIAL AND METHODS: 248 children with birth weight 600-2500 g and gestational age 26-37 weeks underwent ophthalmological examination including USG, ERG and VER. The children were first examined between 3-4 weeks of life, then at 8 and 12 weeks and 6, 12, 18 and 24 months. RESULTS: Refractive errors were found in 216 of patients, in 85.2% hypermetropia. ROP occurred in 7 children with birth weight below 1500 g and gestational age 27-32 weeks. Other ocular changes were observed in 19 (7.6%) of the examined children.     

Cystoid macular edema associated with latanoprost in aphakic and pseudophakic eyes

PURPOSE: To describe four patients who developed cystoid macular edema shortly after onset of treatment with latanoprost. METHOD: Retrospective review of medical records of patients with open-angle glaucoma who developed cystoid macular edema shortly after starting latanoprost. RESULTS: The use of topical latanoprost was temporally related to the development of cystoid macular edema in four patients (six eyes; two aphakic eyes and four pseudophakic eyes). Cystoid macular edema resolved in all patients after latanoprost was discontinued. CONCLUSIONS: Cystoid macular edema is a potential complication of latanoprost therapy. Further observations are needed to determine if the risk of cystoid macular edema is limited to or greatest in patients who are pseudophakic or aphakic.     

The impact of cataract surgery on low vision patients. A population based study

PURPOSE: To assess the impact of cataract surgery on low vision patients. METHODS: Self-estimated ability to perform visually demanding tasks before and after cataract surgery and expectations and satisfaction with the surgery were analysed in all low-vision patients (n = 52), who during a one-year period underwent surgery at Norrlands University Hospital in Ume?, Sweden. Self-administered questionnaires were used and the records of the patients were studied. RESULTS: The majority (81%) of the low vision patients reported an improved ability to perform visually demanding tasks after surgery. The number of patients who were unable to read newspaper-size print decreased significantly, from 44% to 21% after surgery. The subjectively improved visual ability as well as the augmentation of VA of the operated eye were both significantly related to satisfaction with the outcome of surgery. CONCLUSION: Most low-vision patients with significant cataract benefit from surgery, both subjectively by increased ability to perform visually demanding tasks as well as by an improved visual acuity. Particularly patients with loss of peripheral visual fields subjectively gain in orientation ability. It is important to reduce unreasonable expectations about the outcome of the surgery.