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At least 523 records · Page 29Linked to original sources
PubMed1989

Psychophysics of reading. VI--The role of contrast in low vision.

The effect of contrast on reading performance was measured in 19 low-vision observers with a wide range of visual disorders and degrees of vision loss. The observers read text composed of 6 deg letters, ranging in contrast from 0.96 down to contrast threshold for reading. Reading performance was characterized by two parameters: peak reading rate is the reading rate at maximum contrast, and critical contrast is the contrast at which reading rate drops to half its maximum value. Peak reading rates were lower in observers with central field loss than in observers with intact central vision. In 16 of 19 cases, critical contrasts were higher for low-vision observers than for normal observers (averaging 3.9 times higher), indicating a decreased tolerance to contrast reduction. Values of critical contrast were closely linked to contrast sensitivity for letters (r = 0.87), but did not vary systematically with type of vision loss. Five observers read white-on-black text faster than black-on-white at both high and low contrasts. Four of the five had cloudy ocular media. We attribute this contrast polarity effect to abnormal light scatter in eyes with cloudy media. We examined the hypothesis that our low-vision observers' deviation from normal performance could be characterized (1) by a contrast scaling factor representing an attenuation of effective contrast and (2) that this scale factor could be identified with reduced contrast sensitivity. Such a description provided a good account for subjects with cloudy ocular media, where contrast attenuation results from intraocular light scatter. It provided a first order, but incomplete account for subjects with field loss where contrast attenuation is related to contrast sensitivity losses due to neural factors.

Adult↗
PubMed2005

Visual outcome and risk factors for light perception and no light perception vision after vitrectomy for diabetic retinopathy.

PURPOSE: To assess the visual outcome following vitrectomy for diabetic retinopathy compared with previous studies; to evaluate risk factors for light perception (LP) and no light perception (NLP) vision after diabetic vitrectomy. DESIGN: Retrospective medical record review. METHODS: The charts of 100 consecutive patients who underwent vitrectomy for proliferative diabetic retinopathy between November 1, 1997, and November 30, 1998, were reviewed. Surgical technique included standard pars plana vitrectomy with combination of delamination and segmentation of gliotic tractional membranes using bimanual techniques. All patients had post-operative follow-up of at least 12 months. Several factors were analyzed for their effect on poor visual outcome (LP and NLP) using Fisher's exact test. RESULTS: Post-vitrectomy, 73% of diabetic patients had stable or improved vision; 16% had worsened but functional vision, defined as worse but still >or= 20/400; 4% had worsened but ambulatory vision, defined as worse but still count fingers (CF) or hand motion (HM); and 7% had poor visual outcome, LP or NLP. Resultant visual acuity was >or=20/40 in 38% of patients, 20/50 to 20/100 in 34%, 20/120 to CF in 18%, HM in 3%, LP in 4%, and NLP in 3%. Risk factors for eyes with LP and NLP vision included pre-operative iris neovascularization (INV), P = .05, post-operative INV, P = .02, post-operative macular ischemia, P = .0001, and post-operative vitreous hemorrhage (VH), P = .02. CONCLUSIONS: Pre-operative and post-operative INV, post-operative macular ischemia, and post-operative VH appear to be risk factors for LP and NLP vision following diabetic vitrectomy, whereas overall improvements in surgical technique and visual outcome continue to be reported.

Adult↗
PubMed2006

Longitudinal cohort study of patients with birdshot chorioretinopathy II: color vision at baseline.

PURPOSE: To describe color vision at the baseline examination of 80 participants in a longitudinal cohort study of birdshot chorioretinopathy and to identify relationships between color vision and visual acuity, symptoms, and ophthalmic signs. DESIGN: Single center cross-sectional study. METHODS: Color vision was evaluated with the desaturated Lanthony 15-Hue test. Relationships were sought between the square root of the color confusion scores (CCS) and the following factors: best-corrected visual acuity (BCVA), symptoms, cataract, vitreous inflammatory reactions, retinal vasculitis, cystoid macular edema (CME), and birdshot lesion characteristics. RESULTS: When compared with published, age-matched normal control subjects, 49 patients (61.3%; 76 eyes [47.5%]) had abnormal CCS values. Abnormal CCS values were found in nine of 51 phakic eyes (18%) with normal BCVA (>or=1.0) and without cataract. Although most eyes did not have classifiable defects, 30 eyes (18.8%) had tritan (blue-yellow) defects (88% of eyes with classifiable defects). With the use of multivariate analyses, there were significant associations between increased CCS values and the symptoms of altered color vision (P = .005) and altered contrast sensitivity (P = .015). There was a significant, but weak, relationship between CCS values and birdshot lesion morphologic condition (P = .049), but no relationships were found with other lesion characteristics or with vitreous inflammatory reactions, retinal vasculitis, or CME. CONCLUSION: The Lanthony 15-Hue test provides an objective technique to assess complaints of altered color vision in people with birdshot chorioretinopathy. Color vision can be abnormal in eyes with normal visual acuity; therefore, this parameter may be useful as an additional measure for monitoring the disease.

Adult↗
PubMed2026

Noncombustible Nicotine or Tobacco Product Use After Smoking Cessation and Major Vision-Impairing Diseases: A Nationwide Cohort Study.

OBJECTIVE: We assessed the risk of major vision-impairing eye diseases among smokers who quit combustible cigarettes (CC) and switch to noncombustible nicotine or tobacco products (NNTPs) compared with those who completely quit using tobacco. DESIGN: Retrospective cohort study. PARTICIPANTS: About 179 273 adults from the Korean National Health Insurance Service who smoked CC in 2011 to 2012 and reported cessation in 2018 to 2019, classified into complete quitters and NNTP switchers. METHODS: This nationwide longitudinal cohort study followed participants for up to 6 years and identified incident major vision-impairing eye diseases (cataract, glaucoma, age-related macular degeneration, diabetic retinopathy, and refractive and accommodation disorders) using standardized diagnostic codes. Propensity score matching was applied to emulate a pseudo-randomized comparison, balanced on key demographic, clinical, comorbidity, and lifestyle characteristics. Subdistribution hazard ratios (SHRs) were evaluated using the Fine-Gray subdistribution hazards model accounting for all-cause mortality as a competing risk. MAIN OUTCOME MEASURES: Adjusted SHRs for incident major vision-impairing eye diseases. RESULTS: Among 32 316 matched participants followed for a mean of 4.6 years, 6328 incident major vision-impairing eye disease events occurred. The incidence was 41.1 and 44.0 per 1000 person-years for complete quitters and NNTP switchers, respectively. Switching to NNTPs was associated with an increased risk of major vision-impairing eye disease (SHR, 1.07; 95% CI, 1.02-1.13). The risk elevation was most pronounced for diabetic retinopathy (SHR, 1.24; 95% CI, 1.00-1.53) and refractive and accommodation disorders (SHR, 1.07; 95% CI, 1.01-1.12). These findings were robust across inverse probability-weighted and Cox proportional hazards models. The association remained consistent in sensitivity analyses and across clinical subgroups. CONCLUSIONS: Transitioning from CC to NNTPs is associated with a modest but consistent increase in the risk of major vision-impairing eye diseases compared with complete nicotine abstinence. These findings challenge the assumption that substituting NNTPs for CCs is visually harmless and indicate that, from an ophthalmic perspective, complete cessation of all nicotine products should remain the preferred cessation goal.

Humans↗
PubMed2004

Surveillance of the eye and vision in a clinical trial of MART1-transformed dendritic cells for metastatic melanoma.

PURPOSE: To report the protocol for surveillance of the eye and vision in a clinical trial of MART1-transduced dendritic cells for metastatic melanoma. METHODS: In a phase I/II clinical trial of dendritic cell-based genetic immunotherapy for metastatic cutaneous melanoma, ophthalmic evaluation is performed prior to immunization (Baseline Evaluation), 56+/-7 days after first vaccination (mid-study evaluation), when dendritic cell injections are complete 112+/-7 days after first vaccination (end-study evaluation) and 168+/-7 days after first vaccination (post-study evaluation). RESULTS: The protocol for baseline, mid-study and end-study evaluations of the eye and vision includes ophthalmic history, comprehensive ophthalmic examination, psychophysical and electrophysiological visual function assessment, fundus photography and fluorescein angiography. Post-study evaluation consists of the 25-item visual functioning questionnaire augmented to elicit autoimmune manifestation with complete ophthalmic evaluation if vision-related symptoms or abnormalities are noted during or after the vaccination. CONCLUSION: Limited adverse effects on the eye and vision have been reported in melanoma immunotherapy trials, although this novel mode of therapy has the potential to induce melanoma paraneoplastic syndromes known to severely impair vision. Therefore, surveillance of the eye and vision should be considered in melanoma immunotherapy trials.

Antigens, Neoplasm↗
PubMed2005

Color vision and contrast sensitivity in epilepsy patients treated with initial tiagabine monotherapy.

The purpose of the study was to determine whether the use of a GABAergic antiepileptic drug (AED), tiagabine, affects color vision and contrast sensitivity. Twenty newly diagnosed patients with partial epilepsy (aged 19-72 years), receiving tiagabine as their initial monotherapy for 5-41 months were examined. Color vision was examined with the Standard Pseudoisochromatic Plates 2 (SPP2), with the Farnsworth-Munsell 100 Hue Test (FM100) and with the Color Vision Meter 712 (CVM) anomaloscope. Contrast sensitivity was measured with the Pelli-Robson letter chart. Three patients excluded from the color vision evaluation for congenital red-green color vision defects. Seven out of 17 patients (41%) had acquired color vision deficit examined with the FM100. The CVM anomaloscope revealed minor defects in two patients. Contrast sensitivity function was within normal ranges. The present study suggests that AED therapy with tiagabine, like with other established and newer AEDs may interfere with color perception.

Adult↗
PubMed2004

Causes of blindness, low vision, and questionnaire-assessed poor visual function in Singaporean Chinese adults: The Tanjong Pagar Survey.

OBJECTIVE: To determine the prevalence rates and causes of low vision, blindness, and patient-assessed deficient visual function among Singaporean Chinese adults. DESIGN: Population-based cross-sectional survey. PARTICIPANTS: Singaporean Chinese adults 40 to 79 years old (n = 1152). METHODS: From an initial sampling frame of 40- to 79-year-old Chinese in the Tanjong Pagar district in Singapore, 2000 subjects were selected using a disproportionate, stratified, clustered, random-sampling method. Of 1717 eligible subjects, 1232 were examined (participation rate = 71.8%), and 80 adults who did not have visual acuity (VA) data were excluded from the analysis. MAIN OUTCOME MEASURES: Bilateral low vision was defined as best-corrected VA (BCVA) worse than 6/18 and 3/60 or better, and bilateral blindness as BCVA worse than 3/60 in the better eye or constriction of the visual field to within 10 degrees of fixation, in accordance with the World Health Organization criteria. Patient-assessed visual function was measured using a modified VF-14 questionnaire. RESULTS: The age- and gender-adjusted prevalence rates were 1.1% (95% confidence interval [CI], 0.6-1.8) for bilateral low vision and 0.5% (95% CI, 0.2-1.1) for bilateral blindness, and the mean visual function score was 98.6. The rates of bilateral low vision and blindness increased with age, whereas visual function scores decreased with age, even after adjusting for gender and education. Cataract accounted for 58.8% of bilateral low vision, 20.0% of bilateral blindness, and 52.0% of poor visual function (score<90). Glaucoma contributed to 60.0% of bilateral blindness. CONCLUSION: The age- and gender-adjusted rates of low vision and blindness were 1.1% and 0.5%, respectively. Glaucoma is a leading cause of blindness in Singaporean Chinese adults, in addition to well-recognized causes in the rest of Asia such as cataract.

Adult↗
PubMed2006

Three presentations of monocular vision loss.

BACKGROUND: Carotid artery disease is estimated to affect 30% of persons older than 50. Risk factors include hypertension, cigarette smoking, hyperlipidemia and diabetes mellitus. Symptoms ascribed to carotid artery lesions with stenosis of the artery or plaque formation include monocular vision loss and transient ischemic attacks. Patients can present with transient monocular vision loss as their initial symptom. CASE REPORTS: Three patients from a geriatric clinic in Wilmington, Delaware presented with different complaints of vision loss with similar overall outcomes. Patient A was an 87-year-old woman who presented with dimming of vision on extreme left head turn. Dilated fundus examination found a retinal arterial emboli in the left eye (O.S.). Carotid duplex examination found 50% to 79% left internal carotid stenosis with no hemodynamic stenosis of the right internal carotid. Patient B was a 78-year-old woman who presented with a right superior altitudinal defect and transient vision loss in the right eye. Dilated fundus examination found retinal arterial emboli in the right eye (O.D.). Carotid duplex examination found 50% to 79% carotid stenosis in both the left and right internal carotids. Patient C was an 84-year-old man who complained of a superior altitudinal visual field defect O.D. Dilated fundus examination found a retinal arterial emboli O.D. Carotid duplex results showed calcified atherosclerotic plaques present at the level of the common carotid artery bifurcations bilaterally, with 50% to 70% narrowing of the right internal carotid artery with no significant narrowing of the left internal carotid artery. CONCLUSIONS: These 3 presentations show that in patients older than 50 who present with chief complaints of monocular vision loss, a differential diagnosis of carotid artery disease must be considered. Patients who exhibit retinal arterial emboli are at increased risk for stroke and vascular death. Appropriate measures for confirming a diagnosis include duplex ultrasound imaging, magnetic resonance angiography (MRA), and carotid angiography. Surgical techniques such as carotid angioplasty and carotid endarterectomy may be recommended.

Aged↗
PubMedDate not supplied

Computer vision syndrome: a review.

As computers become part of our everyday life, more and more people are experiencing a variety of ocular symptoms related to computer use. These include eyestrain, tired eyes, irritation, redness, blurred vision, and double vision, collectively referred to as computer vision syndrome. This article describes both the characteristics and treatment modalities that are available at this time. Computer vision syndrome symptoms may be the cause of ocular (ocular-surface abnormalities or accommodative spasms) and/or extraocular (ergonomic) etiologies. However, the major contributor to computer vision syndrome symptoms by far appears to be dry eye. The visual effects of various display characteristics such as lighting, glare, display quality, refresh rates, and radiation are also discussed. Treatment requires a multidirectional approach combining ocular therapy with adjustment of the workstation. Proper lighting, anti-glare filters, ergonomic positioning of computer monitor and regular work breaks may help improve visual comfort. Lubricating eye drops and special computer glasses help relieve ocular surface-related symptoms. More work needs to be done to specifically define the processes that cause computer vision syndrome and to develop and improve effective treatments that successfully address these causes.

Asthenopia↗
PubMed2006

Vision-limiting complications in open-globe injuries.

BACKGROUND: To correlate vision-limiting complications of open-globe trauma with anatomical zone and mechanism of injury. METHODS: Retrospective review of 235 patients with open-globe injuries at the Massachusetts Eye and Ear Infirmary. Vision-limiting complications were assessed at 2 to 3 months after the injury. RESULTS: Traumatic cataracts and corneal scarring were the most prevalent vision-limiting complications in patients with zone I (cornea-only) lacerations. The most common vision-limiting factors in eyes with zones II and III lacerations (involving sclera) were cataracts and retinal detachments. In patients with penetrating injuries, predominant vision-limiting findings were traumatic cataracts and corneal scarring. In patients with blunt-force ruptures, leading causes were traumatic cataracts and retinal detachments. There were increased rates of phthisis and enucleation surgery in patients with ruptures and zones II and III injuries. In cases of penetrating and zone I injuries, significantly more patients achieved visual acuities better than 20/50 when compared with eyes that had ruptures or zones II and III injuries. INTERPRETATION: Traumatic cataracts were the most common vision-limiting factor in all subcategories of open-globe injuries. Injuries in zones II and III and blunt-force ruptures were associated with increased rates of retinal detachments, phthisis, and enucleation, contributing to the poorer visual prognosis in these patients.

Adolescent↗
PubMedDate not supplied

Night vision disturbances after corneal refractive surgery.

A certain percentage of patients complain of "glare" at night after undergoing a refractive surgical procedure. When patients speak of glare they are, technically, describing a decrease in quality of vision secondary to glare disability, decreased contrast sensitivity, and image degradations, or more succinctly, "night vision disturbances." The definitions, differences, and methods of measurement of such vision disturbances after refractive surgery are described in our article. In most cases of corneal refractive surgery, there is a significant increase in vision disturbances immediately following the procedure. The majority of patients improve between 6 months to 1 year post-surgery. The relation between pupil size and the optical clear zone are most important in minimizing these disturbances in RK. In PRK and LASIK, pupil size and the ablation diameter size and location are the major factors involved. Treatment options for disabling glare are also discussed. With the exponential increase of patients having refractive surgery, the increase of patients complaining of scotopic or mesopic vision disturbances may become a major public health issue in the near future. Currently, however, there are no gold-standard clinical tests available to measure glare disability, contrast sensitivity, or image degradations. Standardization is essential for objective measurement and follow-up to further our understanding of the effects of these surgeries on the optical system and thus, hopefully, allow for modification of our techniques to decrease or eliminate post-refractive vision disturbances.

Contrast Sensitivity↗
PubMedDate not supplied

Vision impairment and driving.

Driving is the primary mode of travel in many countries. It facilitates the performance of routine daily activities and is thus integral with the concept of quality of life. Vision is inarguably a fundamental component of safe driving. Drivers with certain eye conditions reduce their driving exposure and restrict their driving to the safest times, yet there is preliminary evidence that some eye conditions increase the risk of crashes. Visual acuity is only weakly related to crash involvement, whereas peripheral vision appears to play a more critical role. Color vision deficiency by itself is not a threat to safe driving. Based on the current literature, it is unclear whether other types of visual sensory impairment have a significant impact on driving safety and performance. Tests of visual attention and processing speed show great promise as methods of identifying high-risk drivers. There is a serious need for well-designed studies in key practical areas, such as the safety of low-vision drivers who use bioptic telescopes, the impact of monocular vision impairment on safety, and the effectiveness of vision rescreening policies after initial licensure. For ophthalmologists to guide patients about driving fitness, valid and reliable assessment tools must be developed and made widely available.

Accidents, Traffic↗
PubMed2001

Patterns of adherence to diabetes vision care guidelines: baseline findings from the Diabetic Retinopathy Awareness Program.

OBJECTIVES: (1) To describe baseline patterns of adherence to American Diabetes Association and American Academy of Ophthalmology vision care guidelines for diabetes in the Diabetic Retinopathy Awareness Program, and (2) to evaluate factors associated with nonadherence. This paper describes the baseline characteristics of a population enrolled in a prospective, randomized clinical trial. DESIGN: Cross-sectional study. PARTICIPANTS: Between October 1993 and May 1994, the study identified 2308 persons with diabetes, 18 years of age or older, who were residents of Suffolk County, New York, via a multimedia community-wide recruitment campaign. INTERVENTION AND METHODS: Eligibility for the trial was determined during a 20-minute phone interview, which included questions about vision care practices; diabetes management; and knowledge, attitudes, and beliefs about diabetes, vision, and diabetic retinopathy. This paper describes these patient characteristics at baseline. Eligible patients would be randomized subsequently to a 2-year diabetes educational intervention arm, which included mailed packets and newsletters focused on vision care, or to a control nonintervention arm. MAIN OUTCOME MEASURE: Nonadherence to guidelines at baseline was defined as the absence of a dilated eye examination during the year before recruitment into the study. RESULTS: Of the 2308 persons interviewed, 813 (35%) did not follow the vision care guidelines; two thirds of this group reported no eye examination in the year before the interview, and one third had an undilated examination. Ophthalmologists performed 49% of the examinations in the nonadherent group, versus 86% in the adherent group. In logistic regression analyses, factors related to nonadherence were: younger age (odds ratio [OR] = 0.97), type 2 diabetes with or without insulin use (OR = 1.62 and 1.99, respectively), shorter diabetes duration (OR = 0.97), last eye examination performed by an optometrist (OR = 5.32) or other nonophthalmologist (OR = 4.29), less practical knowledge about diabetes (OR = 1.57), and no prior formal diabetes education (OR = 1.30). CONCLUSIONS: Within this population, more than one third of participants had not been following vision care guidelines. Nonadherence was linked to several potentially modifiable factors; changes in these factors could enhance the early detection of diabetic retinopathy.

Adolescent↗
PubMed2003

Incidence of blindness and low vision in a sample population: the Priverno Eye Study, Italy.

PURPOSE: To study the incidence of blindness and low vision over a 7-year period. DESIGN: Population-based cohort study. PARTICIPANTS: The survivors of the original cohort of 860 persons from Priverno, Italy, aged 45 to 69 years, were reexamined. Of the 760 eligible survivors, 619 (81.4%) had a 7-year follow-up visit. METHODS: Baseline and follow-up examinations included the collection of anamnestic and ophthalmologic data by the same observers using the same methods and classification criteria to minimize sources of variability. MAIN OUTCOME MEASURES: Best-corrected visual acuity (VA) measured at 4 m by standardized logarithmic chart was expressed as the logarithm of the minimum angle of resolution (logMAR). World Health Organization definitions of blindness and low vision were adopted (respectively, VA > 1.3 logMar and VA > 0.6 to 1.3 logMar in the better eye or in either eye). Participants at risk for visual impairment were those without blindness or low vision in one or both eyes at baseline; participants at risk for one-eye visual impairment were those without blindness or low vision in both eyes at baseline. RESULTS: A total of 33 participants were defined as incident cases of visual impairment. The overall incidence figures for blindness, low vision, one-eye blindness, and one-eye low vision were respectively 0.2% (95% confidence interval [CI], 0.0-0.9), 1.3% (95% CI, 0.7-2.6), 1.2% (95% CI, 0.6-2.4), and 2.9% (95% CI, 1.8-4.6). CONCLUSIONS: This study provides population-based estimates of the incidence of visual impairment in an adult, free-living European population. With respect to the younger participants, older subjects at baseline were at higher risk for incident visual impairment, the main causes of which were cataract, myopia, and diabetic retinopathy. The incidence of visual impairment in the subgroup aged 55 to 64 years at baseline was significantly higher than that found in Beaver Dam 5-year study and similar to that found in Beaver Dam 10-year Study, when the same definitions were adopted. This difference may be partially explained by social and cultural habits of the female samples, but many other factors may play a role.

Aged↗
PubMed1997

The impact of blurred vision on functioning and well-being.

OBJECTIVE: To determine the impact of blurred vision on functional status and well-being, the authors used a cross-sectional analysis of Medical Outcomes Study (MOS) 2-year follow-up data. METHODS: One thousand six hundred forty-two respondents were asked to report how often they experienced blurred vision not correctable by glasses or contact lenses, as well as other various symptoms, at the 2-year follow-up. Participants completed the SF-36, a general functioning and well-being instrument. Demographic, medical, and other data also were collected. The association of these symptoms, including blurred vision, and tracer medical conditions with SF-36 scores were evaluated. RESULTS: The unique impact of blurred vision on role limitations due to physical health problems was significantly greater than the impact of hypertension, history of myocardial infarction, type II diabetes mellitus, indigestion, trouble urinating, and headache. Blurred vision also had a significantly greater negative impact on energy than Type I diabetes mellitus, on social function than indigestion, and on physical functioning than trouble urinating. CONCLUSIONS: Having blurred vision more than once or twice a month has a detectable and significant impact on functional status and well-being, especially in role limitations due to physical health problems. This demonstrates the impact of a common visual symptom on health status and well-being, as measured by the SF-36. In addition, comparison of the impact of various symptoms and conditions provides important and potentially clinically relevant information.

Adult↗
PubMed2006

Misperception, illusion and epistemological optimism: vision studies in early nineteenth-century Britain and Germany.

This article compares investigations of the process of vision that were made in early nineteenth-century Britain and the German lands. It is argued that vision studies differed significantly east and west of the North Sea. Most of the German investigators had a medical background and many of them had a firm grasp of contemporary philosophy. In contrast, the British studies on vision emerged from the context of optics. This difference manifested itself in the conceptual tools for the analysis of vision, deception and illusion and shaped the experiments on visual phenomena that were carried out. Nevertheless, both in Britain and in the German lands vision studies were driven by the same impetus, by epistemological concerns with the nature and reliability of knowledge acquisition in experience. The general epistemological conclusions drawn from researches on vision and deception were optimistic. Precisely because mechanisms of deception and illusion could be uncovered, the possibility of acquiring empirical knowledge could be secured.

Germany↗
PubMed2002

Prevalence and selected characteristics of childhood vision impairment.

The objective of this study was to examine the descriptive epidemiology of vision impairment among 6- to 10-year-old children in metropolitan Atlanta, Georgia, USA. Children with vision impairment (n=310; 42% black, 56% white; 57% male, 43% female), defined as a best corrected visual acuity in the better eye of 20/70 or worse, were identified through the Metropolitan Atlanta Developmental Disabilities Surveillance Program. The overall prevalence was 10.7 per 10,000 children. Fifty-nine percent had low vision; nearly two-thirds had coexisting disabilities. Educational program varied by vision impairment severity and presence of coexisting disabilities. The common presence of coexisting disabilities emphasizes the importance of multidisciplinary services. The inclusion of case ascertainment sources other than vision impairment classes is critical to ensure an accurate prevalence rate and unbiased description of children with vision impairment.

Child↗
PubMedDate not supplied

Molecular genetics of color-vision deficiencies.

The normal X-chromosome-linked color-vision gene array is composed of a single long-wave-sensitive (L-) pigment gene followed by one or more middle-wave-sensitive (M-) pigment genes. The expression of these genes to form L- or M-cones is controlled by the proximal promoter and by the locus control region. The high degree of homology between the L- and M-pigment genes predisposed them to unequal recombination, leading to gene deletion or the formation of L/M hybrid genes that explain the majority of the common red-green color-vision deficiencies. Hybrid genes encode a variety of L-like or M-like pigments. Analysis of the gene order in arrays of normal and deutan subjects indicates that only the two most proximal genes of the array contribute to the color-vision phenotype. This is supported by the observation that only the first two genes of the array are expressed in the human retina. The severity of the color-vision defect is roughly related to the difference in absorption maxima (lambda(max)) between the photopigments encoded by the first two genes of the array. A single amino acid polymorphism (Ser180Ala) in the L pigment accounts for the subtle difference in normal color vision and influences the severity of red-green color-vision deficiency. Blue-cone monochromacy is a rare disorder that involves absence of L- and M-cone function. It is caused either by deletion of a critical region that regulates expression of the L/M gene array, or by mutations that inactivate the L- and M-pigment genes. Total color blindness is another rare disease that involves complete absence of all cone function. A number of mutants in the genes encoding the cone-specific alpha- and beta-subunits of the cGMP-gated cation channel as well as in the alpha-subunit of transducin have been implicated in this disorder.

Animals↗