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PubMedDate not supplied

Prescribing near magnification for low vision patients.

Most patients with low vision request help with reading. Despite improvements in the assessment of visual functions, determining the appropriate magnification for reading still often involves a trial and error approach. Recent research has shown that with accurate and systematic assessments of vision, the required magnification can be predicted but this magnification needs to be much higher than has been previously recommended. This paper presents a systematic approach to enable practitioners to determine the power of a near addition or simple magnifier needed to assist patients with mild or moderate low vision who may present seeking help for reading. Guidelines for appropriate referral to low vision services are also provided.

Journal Article↗
PubMed2001

Reading performance in children with low vision.

PURPOSE: While educators and optometrists are concerned with reading efficiency in children with low vision, in most low vision assessments, children's reading performance is assessed only by a brief evaluation of reading fluency. We examined the relationships between clinical vision measures and reading performance in children with low vision. METHODS: Subjects were 71 students with low vision, aged seven to 18 years. The vision and reading performance measures were: high contrast distance visual acuity, contrast sensitivity using both the Pelli-Robson and LH symbol charts, near text visual acuity and reading rates on a range of print sizes. RESULTS: Most children achieved maximum reading rate at print sizes between 2.5 and seven times larger than threshold print size. Maximum reading rate increased significantly with age and near visual acuity. There was no significant relationship between reading rate and contrast sensitivity. CONCLUSIONS: The majority of children with low vision can achieve near normal reading rates with magnification. Age is the strongest predictor of reading rate in children with low vision. They need print sizes well above threshold to achieve maximum reading rate. Routine contrast sensitivity testing of visually impaired students is not indicated for reading assessment.

Journal Article↗
PubMedDate not supplied

Assisting low-vision patients in Japan.

1. Assisting low-vision patients in sitting down and in properly placing their heads for a slit-lamp examination is fundamental in low-vision patient care. 2. Ideally, chairs and other furniture in rooms used by low-vision should not be easily moved. Movable chairs are not stable, and thus could be dangerous, especially to people with low vision. Also, it is extremely important that objects are always placed at the same locations. 3. The staff should experience the difficulties encountered by low-vision patients by undergoing some of the same examinations that these patients undergo, and by walking while wearing some sort of vision reducer.

Humans↗
PubMed2002

A new method of biofeedback in the management of low vision.

Twenty-eight patients with low vision were enrolled into the study. A preliminary study was carried out on 18 eyes of 13 patients with low vision who underwent visual rehabilitation with a new instrument for biofeedback (BF) applied to vision; improved biofeedback integrated system (Ibis). Successively, eight patients (16 eyes) with bilateral low vision were subjected to biofeedback in one eye. The experimental and control eye were evaluated separately. Then a placebo training was developed on seven patients (12 eyes). Visual acuity, colour vision, automated perimetry, contrast sensitivity and flash VEP were evaluated. A brief review of the literature and the possible mechanisms behind the results are discussed.

Adult↗
PubMed2002

Planning low vision services in India : a population-based perspective.

OBJECTIVE: To assess the prevalence and causes of low vision in a population in southern India for planning low vision services. DESIGN: Population-based, cross-sectional study. PARTICIPANTS: A total of 10,293 persons of all ages from 94 clusters representative of the population of the Indian state of Andhra Pradesh. METHODS: The participants underwent a detailed eye examination, including measurement of visual acuity with logarithm of the minimum angle of resolution charts, refraction, slit-lamp biomicroscopy, applanation tonometry, gonioscopy, and stereoscopic dilated fundus evaluation. Automated threshold visual fields and slit-lamp and fundus photography were done when indicated using predefined criteria. MAIN OUTCOME MEASURES: Low vision was defined as permanent visual impairment that was not correctable with refractive error correction or surgical intervention. The participants with best-corrected distance visual acuity <6/18 to perception of light or central visual field <10 degrees because of an untreatable cause in both eyes were considered as having low vision. RESULTS: Low vision was present in 144 participants, an age, gender, and urban-rural distribution adjusted prevalence of 1.05% (95% confidence interval, 0.82%-1.28%). The most frequent causes of low vision included retinal diseases (35.2%), amblyopia (25.7%), optic atrophy (14.3%), glaucoma (11.4%), and corneal diseases (8.6%). Multivariate analysis showed that the prevalence of low vision was significantly higher with increasing age, and there was a trend for higher prevalence with decreasing socioeconomic status. Extrapolating these data to the estimated 1014 million population of India in the year 2000, 10.6 (95% confidence interval, 8.4-12.8) million people would have low vision. CONCLUSIONS: These data imply that there is a significant burden of low vision in this population, suggesting the need for low vision services.

Adolescent↗
PubMed1992

The contrast sensitivity function in low vision.

The contrast sensitivity of 51 low vision patients (95 eyes) showed a substantial decrease in all spatial frequencies. The peak contrast sensitivity was shifted to 1 C/D from the normal 3-4 C/D. The high-frequency cut off is correlated to the visual acuity positively. Of the 33 patients, the preferred eye was the eye with better peak sensitivity in 28 patients (84%), while the preferred eye was the eye with better visual acuity in 22 patients (66%). It seems that the peak sensitivity is more important than visual acuity in determining eye preference. It provides a useful information for the clinician to determine which eye to train with low vision aids. Forty patients among 46 patients (87%) with RFN (Recognized Frequency Number) > or = 3 are able to read No.5 reading card, while 5 patients among 5 patients with RFN < 3 are not able to read No.5 reading card. The contributions of CSF to the low vision are evaluated.

Adolescent↗
PubMed1996

Psychophysics of reading. XV: Font effects in normal and low vision.

PURPOSE: Little is known about the effect of font on low-vision reading. In this study, the authors measured the influence of font in reading with normal and low vision. METHODS: Reading acuity, maximum reading speed, and critical print size (the smallest print that can be read with maximum speed) were measured in 50 normal subjects and 42 subjects with low vision. Data were collected using versions of the MNREAD Acuity Chart printed with the Times (proportionally spaced) and Courier (fixed-width) fonts. RESULTS: Reading acuity scores obtained with Courier were better than those obtained with Times for both normal (mean difference, 0.05 logMAR, P < 0.001) and subjects with low vision (0.09 logMAR, P < 0.001). Similarly, critical print sizes measured with Courier were smaller than those measured with Times (mean difference, 0.06 logMAR for normal subjects and subjects with low vision, P < 0.002). Maximum reading speeds for normal subjects were 5% faster with Times than with Courier (P < 0.001), but for subjects with low vision, maximum reading speeds were 10% slower with Times than with Courier (P < 0.05). For print smaller than the critical print size, the reading speeds of normal subjects and subjects with low vision were substantially slower (by as much as 50%) for Times than for Courier. CONCLUSIONS: There are small, but significant, advantages of Courier over Times in reading acuity, critical print size, and reading speed for subjects with low vision. For normal subjects, the differences are slighter, with an advantage in reading speed for Times. However, for print sizes close to the acuity limit, choice of font could make a significant difference in both normal and low-vision reading performance.

Adult↗
PubMed2002

A model of the prevalence and incidence of low vision and blindness among adults in the U.S.

Population-based vision screening studies of the prevalence rate of low vision and blindness in the U.S. are reviewed to evaluate the sources of disagreement among studies. The major reasons that studies disagree on prevalence rate estimates are differences in best-corrected visual acuity criteria for low vision and differences in the age range of the oldest age category. When corrections are made for these differences, the results of all prevalence rate studies, except the Mud Creek Valley Study, fit the same prevalence rate vs. age function. The greater prevalence rate of low vision and blindness for each age category that was observed in the Mud Creek Valley Study can be attributed to the higher prevalence rate of cataract associated with a paucity of health care services in the Mud Creek Valley population. The time-derivative of the prevalence rate vs. age function fit to the data provided an estimate of the annual incidence rate of low vision and blindness vs. age. The estimated annual incidence agreed with estimates from unpublished 8-year incidence data of the Baltimore Eye Survey. The incidence rate of low vision and blindness for Americans aged 40 to 60 years is higher among blacks than among whites. For Americans greater than age 60 years, the incidence rate for whites exceeds that for blacks. This observation probably reflects the different natural histories of glaucoma, a leading cause of low vision and blindness among black Americans, and age-related macular degeneration, a leading cause of low vision and blindness among white Americans. Using the age-dependent models of prevalence rate of low vision and blindness for white and black populations, an estimated 1.5 million Americans over age 45 years have a best-corrected visual acuity in the better eye that is < or = 20/70. Based on the incidence rate estimates, approximately 240,000 new cases of low vision and blindness occur each year. With the aging of the U.S. population, that number is expected to double over the next 25 years.

Adult↗
PubMed2005

Emergence of a rehabilitation medicine model for low vision service delivery, policy, and funding.

BACKGROUND: A rehabilitation medicine model for low vision rehabilitation is emerging. There have been many challenges to reaching consensus on the roles of each discipline (optometry, ophthalmology, occupational therapy, and vision rehabilitation professionals) in the service delivery model and finding a place in the reimbursement system for all the providers. METHODS: The history of low vision, legislation associated with Centers for Medicare and Medicaid Services coverage for vision rehabilitation, and research on the effectiveness of low vision service delivery are reviewed. RESULTS: Vision rehabilitation is now covered by Medicare under Physical Medicine and Rehabilitation codes by some Medicare carriers, yet reimbursement is not available for low vision devices or refraction. Also, the role of vision rehabilitation professionals (rehabilitation teachers, orientation and mobility specialists, and low vision therapists) in the model needs to be determined. In a recent systematic review of the scientific literature on the effectiveness of low vision services contracted by the Agency for Health Care Quality Research, no clinical trials were found. The literature consists primarily of longitudinal case studies, which provide weak support for third-party funding for vision rehabilitative services. CONCLUSIONS: Providers need to reach consensus on medical necessity, treatment plans, and protocols. Research on low vision outcomes is needed to develop an evidence base to guide clinical practice, policy, and funding decisions.

Delivery of Health Care↗
PubMed1997

Motion parallax: effects of blur, contrast, and field size in normal and low vision.

Can people with different forms of low vision use motion parallax to improve depth judgments? We used a staircase method to compare depth thresholds using motion parallax and static viewing. We tested eighteen normal-vision subjects with a range of simulated deficits in acuity, contrast sensitivity, and simulated peripheral-field loss, and ten low-vision subjects with a wide range of acuity, contrast sensitivity, and field loss. Subjects viewed three vertical cylinders monocularly and indicated which one was at a different depth from the other two. For motion-parallax trials, observers moved their heads (in a viewing assembly on rollers) from side to side over a range of 6-12 cm. For static trials, the viewing assembly was fixed in place. Normal-vision subjects' depth thresholds with motion parallax were significantly smaller than those with static viewing by an average factor of 1.95 (p < 0.05) across all levels of acuity and contrast. For low-vision observers, the depth thresholds exhibited large individual differences; however, the motion-parallax thresholds were smaller than the static thresholds by an average factor of 2.05 (p < 0.01). These findings indicate that motion parallax can provide useful depth information for people with low vision.

Adolescent↗
PubMed2005

Perceived barriers to the provision of low vision services among ophthalmologists in India.

PURPOSE: To identify and report the perceived barriers to the provision of low vision services among ophthalmologists in India. METHODS: Seventy nine ophthalmologists responded to a structured self-administered questionnaire. Information was collected to understand the level of awareness and barriers/constraints to provision of low vision services. Significant factors associated with each barrier/constraint and perceptions on providing low vision care were investigated. RESULTS: Lack of training/knowledge [65 (82.3%)], lack of awareness [59 (74.7%)] and non-availability of low vision devices [57 (72.2%)] were perceived as the major constraints / barriers to providing low vision care. At least one significant factor was found for each of the above constraints/barriers in providing low vision care. The perception of lack of awareness as being one of the constraints/barriers was significantly higher [OR 3.97 (95% CI, 1.02 - 7.8)] among ophthalmologists from organisations providing low vision services. The perception of lack of motivation as constraint/barrier was significantly higher [OR 3.62 (95% CI, 1.3 - 10.3)] among ophthalmologists from organisations providing low vision services and/or those involved in VISION 2020: The Right to Sight programmes [OR 3.83 (95% CI, 1.4 - 10.4)]. The likelihood of responding that low vision care is time consuming was greater for those belonging to a teaching institute [OR 7.19 (95% CI, 2.0 - 26.1)], those involved in low vision services [OR 5.45 (95% CI, 1.8 - 16.5)] and those who knew that low vision is a priority in VISION 2020 [OR 15.1, 95% CI, 1.5 -155.4]. CONCLUSION: Ophthalmologists need more education about the benefits of low vision care in order to increase their level of awareness and knowledge.

Health Knowledge, Attitudes, Practice↗
PubMed1995

Low vision aids training in the home.

BACKGROUND: In a continuing effort to better serve the low vision community, The Center for the Partially Sighted has developed an in-home low vision aids training (LVAT) program. Of interest to anyone working in the field of low vision is a description of our training materials and methodology, and a discussion of the efficacy of this program. METHODS: The previous literature on low vision was evaluated and organized into an orderly program geared toward the visual rehabilitation of low vision patients. RESULTS: Implementation of LVAT in the home began as a pilot project directed toward patients with macular degeneration who have begun reading as a primary goal of rehabilitation. CONCLUSIONS: Successful vision rehabilitation with low vision devices can be accomplished with proper training. Typically the exam does not allow ample opportunity to ensure that a patient is proficient in the use of a device. Follow-up training in the home environment may provide the necessary intervention to maximize patients' comfort and efficiency with low vision devices and their ability to accomplish near point tasks.

Home Care Services↗
PubMed2001

[An epidemiological survey of blindness and low vision in Meixian County].

OBJECTIVE: To study the status of blindness and low vision in Meixian County. METHODS: The stratified random sampling rule and the standard grading system of blindness set by WHO were adopted in the study, and 11 327 subjects were enrolled (a sampling fraction of 2.01%) in the whole county. RESULTS: The prevalence of bilateral blindness and low vision was found to be 0.47% and 0.89%; that of monocular blindness and low vision was 0.72% and 0.59%, respectively. Subjects over 50 years old had a significantly higher prevalence of blindness and low vision. The causes leading to blindness and low vision were, in falling order, cataract, glaucoma, ametropia/amblyopia and pterygium. CONCLUSION: The treatment of cataract is the main measure to decrease the prevalence of blindness and low vision.

Adolescent↗
PubMed2005

Visual difficulties reported by low-vision and nonimpaired older adult drivers.

Nonimpaired and low-vision older adults responded to a questionnaire regarding the types of visual difficulties experienced while performing daily tasks and while driving. Using the factors produced from a factor analysis as predictors, a discriminant analysis was performed to determine whether significant differences in visual problems existed between the groups. The majority of participants reported that they currently required more time than in the past to perform tasks that depended on their vision, regardless of their visual status. All participants reported experiencing significant difficulties with static and dynamic acuity, peripheral vision, illumination problems, and contrast sensitivity. Both nonimpaired and low-vision older adult drivers reported experiencing difficulty with glare, peripheral vision, and night driving. Low-vision drivers reported experiencing unique difficulties with near acuity, distant acuity, and physical obstructions. Potential applications of this research include suggestions for redesigning automobiles and highway signs for safer use and viewing.

Aged↗
PubMed1999

Relative locations of macular scotomas near the PRL: effect on low vision reading.

Patients referred for low vision rehabilitation had Minnesota Reading Acuity (MNRead), visual acuity (VA), and scanning laser ophthalmoscope (SLO) macular function testing performed in their initial evaluation to determine whether dense macular scotomas near the preferred retinal locus (PRL) have a significant effect on the characteristics of reading based on rate. The 99 subjects had macular scotoma characteristics relative to the fovea/PRL of: 22% only to the right; 15% only to the left; 26% both the right and left; 19% above or below; 17% had no dense scotomas. Reading performance (maximum reading speed, critical print size, and reading acuity) was significantly different between the non-scotoma group and all of the scotoma groups. There was no statistically significant difference in the characteristics of reading based on rate between the four scotoma groups: within each there was a wide variation in the characteristics of reading based on rate not fully explained by either VA or scotoma location. The position of the scotoma relative to the PRL was not a statistically significant factor in determining reading rate as found in studies on normally sighted people with artificial scotomas. Other factors (e.g., maybe PRL ability in fixation and saccadic eye movements and/or cognitive ability) are significantly involved in determining reading rate characteristics in people with macular scotomas.

Humans↗
PubMed1989

Clinical study of low vision. Part I: Refraction and the aided distance vision.

Eighty three cases of low vision patients (144 eyes) were examined with distant visual aids. The average visual acuity of the 144 eyes before refraction was approximately 0.07, while the counterpart afterwards was about 0.1 (p less than 0.01). With the 4x monocular focusable aid, acuity improved in 142 eyes out of the 144 eyes. The combined use of clip-on distance aid and the spectacle reading aid was observed to be especially suitable for partially sighted students. The mean MEF of 142 eyes was 0.9435 +/- 0.2068. The paired T-test between the difference of actual magnification and theoretical magnification was not significant at the 5% level. The factors contributing to the variance of MEF were discussed.

Adolescent↗
PubMed2004

Enhanced low vision rehabilitation for people with age related macular degeneration: a randomised controlled trial.

AIM: To compare the effectiveness of three models of low vision rehabilitation for people with age related macular degeneration (AMD) referred for low vision rehabilitation (LVR): (a) an enhanced low vision rehabilitation model (ELVR) including supplementary home based low vision rehabilitation; (b) conventional low vision rehabilitation (CLVR) based in a hospital clinic; (c) CLVR with home visits that did not include rehabilitation (CELVR), intended to act as a control for the additional contact time with ELVR. METHOD: A single centre parallel group randomised controlled trial in participants' homes and the low vision clinic, Manchester Royal Eye Hospital. People referred for LVR with a primary diagnosis of AMD and visual acuity worse than 6/18 in both eyes and equal to or better than 1/60 in the better eye. The main outcome measures were vision specific quality of life (QoL) (primary outcome, VCM1) and generic health related QoL (SF-36); psychological adjustment to vision loss; measured task performance; restriction in everyday activities; use of low vision aids (LVAs). RESULTS: 226 participants were recruited (median age 82 years); 194 completed the trial (86%). Except for SF-36 physical and mental component summary scores, arms did not differ significantly for any of the outcomes. Differences for the VCM1 were ELVR v CLVR, 0.06 (95% CI to 0.17 to 0.30, p = 0.60); ELVR v CELVR, 0.12 (95% CI to 0.11 to 0.34, p = 0.31); CELVR v CLVR, -0.05 (95% CI -0.29 to 0.18, p = 0.64). Differences for the SF-36 favoured CLVR compared to ELVR (ELVR v CLVR: physical = -6.05, 95% CI -10.2 to -1.91, p = 0.004; mental = -4.04, 95% CI -7.44 to -0.65, p = 0.02). At 12 months, 94% of participants reported using at least one LVA. CONCLUSION: ELVR was no more effective than CLVR. Researchers should be wary of proposing new LVR interventions without preliminary evidence of effectiveness, given the manifest lack of effectiveness of the model of enhanced LVR evaluated in the trial.

Activities of Daily Living↗
PubMed2001

The development of the Melbourne low-vision ADL index: a measure of vision disability.

PURPOSE: To develop a new test of activities of daily living (ADLs) appropriate for the low-vision population: the Melbourne Low-Vision ADL Index (MLVAI). METHODS: The MLVAI was designed as a desk-based clinical assessment, comprising 18 observed items on complex ADLs in part (a) and 9 questions on broad self-care ADLs in part (b). Each item was rated on a five-level descriptive scale from 0 to 4, based on independence, speed, and accuracy of performance. It was designed to be administered under standardized conditions with regard to the instructions, illumination, and working distances. The validity and reliability of the new MLVAI was determined for 122 subjects who were representative of the general low-vision population, in a cross-sectional study. RESULTS: Two items were found to be redundant and were eliminated from the test. Thus, the final test comprised 25 items, with 100 being the highest possible score. Cronbach's alpha indicated an internal reliability of 0.96, and an intraclass correlation coefficient indicated an overall reliability of 0.95. The SE of measurement was 4.5. According to Spearman's correlation coefficient, the test-retest reliability was 0.94 (P < 0.001), and the interpractitioner reliability for five different pairs of practitioners was 0.90 or higher (P < 0.001). With regard to validity, there was a moderately high correlation with vision impairment (r = -0.68, P < 0.001). Using Rasch analysis, content validity was also demonstrated by good separation indexes (4.70 and 9.88) and high reliability scores (0.96 and 0.99) for the person and items parameters, respectively. Separate calculation of indexes and reliability scores for parts (a) and (b) indicated high content validity and reliability of each part. However, the separation indexes and reliability scores were higher for part (a) than for part (b). The correlation coefficient for part (a) and part (b) was 0.68. CONCLUSIONS: The MLVAI is a highly valid and reliable standardized test of ADL performance for the general low-vision population. It may be used to assess patients with low vision and has the potential to be used as a measure of low-vision rehabilitation outcomes.

Activities of Daily Living↗