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PubMed1982

The temporal properties of rod vision.

1. Profiles which represent rod thresholds for flickering fields seen against backgrounds of various intensity have shapes which depend on flicker frequency. Low frequency profiles rise smoothly as background intensity is increased. High frequency profiles are only affected by bright backgrounds, which cause them to rise steeply. Intermediate frequency profiles contain two distinct branches which resemble separate increment threshold functions. 2. The high intensity branches of two-branched threshold profiles cannot be attributed to cone intrusion. Instead, both branches of such profiles are mediated by visual mechanisms which have the spectral properties, the dark adaptation properties and the directional insensitivity of rod vision. Thus, the stimuli are detected by rods. 3. Plots of critical flicker frequency (c.f.f.) as a function of intensity contain two rising branches which are separated by a plateau (when modulation depth is large), or they form two enclosed lobes so that only intermediate frequencies, but neither high nor low ones, are seen (when modulation depth is small). C.f.f. is profoundly depressed by very bright light (above 100 scotopic trolands) which saturates rod vision. 4. In dim light rod modulation sensitivity functions resemble those of low-pass filters, but in bright light they resemble those of band-pass filters. 5. Several forms of rod mediated interference occur at moderate intensities, where rod vision's temporal properties ordinarily improve abruptly. With certain stimuli, rod signals conveying temporal information disrupt one another so completely that suprathreshold flicker cannot be seen within a ten-fold intensity range. 6. Many of these observations can be explained by the hypothesis that rod vision comprises two temporal channels which have different properties.

Flicker Fusion↗
PubMed1988

Parallel integration of vision modules.

Computer algorithms have been developed for several early vision processes, such as edge detection, stereopsis, motion, texture, and color, that give separate cues to the distance from the viewer of three-dimensional surfaces, their shape, and their material properties. Not surprisingly, biological vision systems still greatly outperform computer vision programs. One of the keys to the reliability, flexibility, and robustness of biological vision systems is their ability to integrate several visual cues. A computational technique for integrating different visual cues has now been developed and implemented with encouraging results on a parallel supercomputer.

Algorithms↗
PubMed2005

The development of the Indian vision function questionnaire: questionnaire content.

AIM: To elicit problem statements describing the consequences of vision impairment as a first step towards the development of a vision related quality of life instrument for use in India METHODS: 46 focus groups were conducted in three regions of India. Separate focus groups were held for men and women and according to disease categories: cataract (24), glaucoma (six), diabetic retinopathy or macular degeneration (10), and "mixed low vision" (six). Facilitators followed a topic guide and sessions were audio taped and transcribed. Problem statements were extracted and coded and summarised into major problem domain areas. RESULTS: Nearly 5000 problem statements, an average of 15 statements per participant, were consolidated into 18 broad domain areas. The most important problem areas accounting for over 50% of all statements were ambulation, household or occupational activities, vision symptoms, and people recognition. A further quarter of statements related to difficulties with eating and drinking, psychological concerns, self care, reading, and watching television. Problem statements were similar across the disease groups, although rankings varied. CONCLUSIONS: The functional and psychological impacts described by visually impaired participants in India are similar to those reported in other population settings although the context and impact of problems vary.

Activities of Daily Living↗
PubMed1999

Diabetic versus non-diabetic colour vision after cataract surgery.

AIMS: To examine whether the colour vision abnormalities found in phakic patients with diabetes mellitus is preserved after removal of the lens by cataract surgery. METHODS: 21 diabetic (16 IDDM and five NIDDM) and 19 non-diabetic patients of comparable age, postoperative visual acuity, and sex distribution, all aphakic or pseudophakic following cataract surgery, had their monocular colour vision examined using the Farnsworth-Munsell 100 hue test. The fundus status of the diabetic patients ranged from no retinopathy to photocoagulation treated proliferative diabetic retinopathy. Patients with macular oedema were specifically excluded from the study. RESULTS: The error scores of both the diabetic (mean 146 (SD 94)) and the non-diabetic patients (83 (79)) did not deviate significantly from the age related normal range. The error score in the diabetic group was significantly higher than in the non-diabetic group (p=0.02) but the amplitude of the difference was small in comparison with previous studies of phakic subjects. The error scores in the diabetic group were not correlated with the degree of retinopathy (p>0.2). CONCLUSION: After cataract surgery only a minor difference exists between the colour vision scores of diabetic and non-diabetic patients. This indicates that accelerated yellowing of the lens in diabetes is the predominant cause of the colour vision anomaly found in phakic diabetic patients.

Adult↗
PubMed2003

Detecting chloroquine retinopathy: electro-oculogram versus colour vision.

AIM: To investigate the relative sensitivity and specificity of two tests of retinal function (the electro-oculogram (EOG) and a computerised colour vision test) in screening for ocular toxicity caused by chloroquine and hydroxychloroquine. METHODS: 93 patients with rheumatic diseases receiving long term chloroquine and hydroxychloroquine therapy were followed for an average of 2.6 years. Clinical examination, an EOG, and a quantitative test of colour vision were carried out every 6 months. RESULTS: Mild fundus changes were observed in 38 patients. Four patients developed typical bull's eye maculopathy, three of whom had received 250, 365, and 550 g total dose of chloroquine, and one 1500 g of hydroxychloroquine. Statistical analysis of all patients showed that for those with no fundus changes or stippled pigmentation a number showed elevation of tritan threshold, so that if macular stippling is a sign of mild retinopathy the test on tritan changes has a 64% sensitivity and 63% specificity for an upper threshold value of 7%. All four patients with bull's eye lesions showed a marked disturbance of tritan colour vision, with a threshold of 14.8%, a sensitivity of 75%, and a specificity of 94%. For protan colour vision a threshold of 10% gives 75% sensitivity and 91% specificity. By contrast, neither an absolute nor a relative EOG reduction was a valid criterion for early or late chloroquine retinopathy. In advanced retinopathy an Arden coefficient (AQ) <180% yields 50% sensitivity and 54% specificity. When AQ <160% is the threshold, sensitivity does not increase but specificity rises to 82%. Occurrence of marked corneal deposits on clinical examination yields 50% sensitivity and 90% specificity in this situation. CONCLUSION: Screening for chloroquine retinopathy can be improved by using a sensitive colour test. Disturbance of the tritan axis appears to occur first. A normal test result on computerised colour testing virtually excludes any retinopathy by antimalarials. The EOG is of little diagnostic value.

Aging↗
PubMed1980

Relevance of colour vision and diabetic retinopathy to self-monitoring of blood glucose.

A study was performed to determine the effect of colour vision defects and diabetic retinopathy on diabetic patients' ability to use a visual method of measuring their own blood glucose concentrations. Forty-eight diabetics whose colour vision and retinal status was assessed by an ophthalmologist carried out 311 blood glucose estimations using oxidase-peroxidase test strips which were then compared with laboratory values. There was a trend towards poor performance with advancing age but neither colour vision nor diabetic retinopathy had a significant effect on patients' ability to use this visual method of estimating blood glucose concentrations. The vast majority of diabetics who will benefit from being able to monitor their own blood glucose control should have no difficulty in using a visual method of testing, even if they do have defects of colour vision.

Adolescent↗
PubMed2006

Low vision rehabilitation services in Michigan viewed against the national backdrop.

The diagnosis and treatment (including low vision rehabilitation) of permanent vision impairment due to ocular disease and trauma are gaining increased emphasis around the world. In the United States, this emphasis is due to both changing demographics and emerging policies issued by the US Centers for Medicare and Medicaid Services (CMS). In this de facto report, we trace the evolution of low vision rehabilitation service in Michigan, highlighting the role of public appropriations initiated in the mid 1960s and continuing today. An array of state, private, nonprofit, and clinical services for vision rehabilitation in Michigan are described in the context of the historical roots, current roles, and future trends related to emerging policies and systems of care.

Delivery of Health Care↗
PubMed2006

Low vision service models in Alberta: innovation, collaboration, and future opportunities.

As Alberta's population ages over the next 20 years, the number of older adults experiencing age-related blindness or vision loss is likely to at least double. To prevent a crisis in low vision service provision, we need to build upon, and extend, existing partnerships between the CNIB and ophthalmologists, optometrists, government policy makers, and other service providers. Future service models for low vision rehabilitation should also emphasize interventions such as counselling and peer support that enhance quality of life. With thoughtful planning, adequate funding, and involvement of all stakeholders, Alberta has the potential to become a world leader in the field of low vision treatment and rehabilitation.

Alberta↗
PubMed1975

Progressive changes in kitten striate cortex during monocular vision.

Following initial rearing in either total darkness or normal illumination, kittens at different ages were subjected to right-eye closure and various periods of vision through the left eye. After the period of monocular vision, single units in striate cortex were tested for visual responsiveness through each eye. A severe reduction in the proportion of units responsive to the deprived eye occurred over the first few days of monocular vision. Functional abnormalities were variably present after 1 day, marked after 2.5 and 3.5 days, and complete after 10 days. Monocular vision produced very much the same effect on ocular dominance of striate units, provided age and duration of suture were identical, regardless of whether kittens had received prior dark- or light-rearing.

Animals↗
PubMedDate not supplied

Behavioral, morphological and physiological correlates of diurnal and nocturnal vision in selected wading bird species.

We examined in selected wading bird species if diurnal or nocturnal foraging and the use of visual or tactile feeding strategies could be correlated with retinal structure and function. The selected species were the Yellow-crowned Night Heron (Nycticorax violaceus), a crepuscular and nocturnal forager, the Great Blue Heron (Ardea herodias), a mainly crepuscular, but also diurnal and nocturnal feeder, the Roseate Spoonbill (Ajaia ajaja), a mainly crepuscular feeder which forages more at night than during the day, the Cattle (Bubulcus ibis) and Tricolored (Egretta tricolor) egrets and the American White Ibis (Eudocimus ruber) which forage only during daytime. Herons and egrets are visual foragers; ibises and spoonbills are tactile feeders. Electroretinograms were obtained from anesthetized birds in photopic and scotopic conditions to a wide range of light intensities, following which the retinae were processed for histological analysis. Based on rod densities and rods:cones ratios, nocturnal vision capability is greater in the Yellow-crowned Night Heron, followed by the Great Blue Heron and the spoonbill, then by the egrets and the ibis. Visual feeders that forage near dawn or dusk or at night have a higher rods:cones ratio, and consequently a greater night vision capability, than visual feeding species which forage only during daytime. Visual nocturnal feeders have a night vision capability greater than tactile diurnal as well as tactile nocturnal feeders. However, based on maximum scotopic b-wave amplitudes, all species studied have roughly comparable night vision capability. The factor that best discriminates between wading bird species appears to be the daytime visual capabilities. Indeed, the diurnal ibis and egrets have similar cone densities, cones:rods ratios, and photopic a-wave amplitudes, values which are greater than those measured in the two nocturnally active heron species.

Animals↗
PubMed2006

A re-evaluation of the role of vision in the activity and communication of nocturnal primates.

This paper examines the importance of vision in the lives of nocturnal primates in comparison to diurnal and cathemeral species. Vision is the major sense in all primates and there is evidence that the eyesight of nocturnal species is more acute and variable than has previously been recognized. Case studies of the behaviour of a galago and a loris in open woodland habitats in relation to ambient light show that Galago moholi males are more likely to travel between clumps of vegetation along the ground when the moon is up, and during periods of twilight, whereas they retreat to more continuous vegetation and travel less when the moon sets. This is interpreted as a strategy for avoiding predators that hunt on the ground when it is dark. The travel distances of Loris lydekkerianus are not affected by moonlight but this species reduces its choice of food items from more mobile prey to mainly ants when the moon sets, indicating the importance of light when searching for high-energy supplements to its staple diet. Evidence is presented for the first time to indicate key aspects of nocturnal vision that would benefit from further research. It is suggested that the light and dark facial markings of many species convey information about species and individual identity when animals approach each other at night. Differences in the colour of the reflective eye-shine, and behavioural responses displayed when exposed to white torchlight, point to different kinds of nocturnal vision that are suited to each niche, including the possibility of some degree of colour discrimination. The ability of even specialist nocturnal species to see well in broad daylight demonstrates an inherent flexibility that would enable movement into diurnal niches. The major differences in the sensitivity and perceptual anatomy of diurnal lemurs compared to diurnal anthropoids, and the emergence of cathemerality in lemurs, is interpreted as a reflection of evolution from different ancestral stocks in very different ecosystems, and not a recent shift towards diurnality due to human disturbance.

Animals↗
PubMed1994

Surgical approach to children with craniopharyngiomas and severely impaired vision: special considerations.

A series of 30 children with craniopharyngiomas is presented, analyzing visual sequelae following surgery. All were operated on with the goal of total removal. Surgical routes used were subfrontal prechiasmatic or translamina terminalis, pterional interopticocarotid, transcallosal, or a combination of these various avenues. The choice of the approach depended upon the type, pre- or retrochiasmatic, of the tumor expansions. Children with large cysts and preoperatively low vision, or vision at risk of rapid deterioration, were submitted to a protocol aiming to preoperatively decompress the visual pathway by repeated aspirations of the cyst with the hope this would improve vision before surgery and limit risks of postoperative visual deterioration. In these cases, the removal of the tumor was postponed until vision had reached a stable new level. The authors emphasize the interest of this procedure in reducing the rate of postoperative visual sequelae. However, they also point out that the interopticocarotid route carries a nonnegligible risk of postoperative visual worsening.

Adolescent↗
PubMed1994

[Low-Vision Training For Better Usage of Magnifying Visual Aids].

During 1990-1991 263 low-vision aids were prescribed to visually impaired elderly people. 22% of them did not use their magnifying systems. With the help of a low-vision trainer, who taught them how to use their magnifying system correctly, the failure rate could be remarkably reduced. In 1992, low-vision aids were prescribed to 121 of 158 patients; 110 of these patients had low-vision training. Only 3% of them failed to use the magnifying system.

Aged↗
PubMed2003

Dynamic interactions of eye and head movements when reading with single-vision and progressive lenses in a simulated computer-based environment.

PURPOSE: To assess dynamic interactions of eye and head movements during return-sweep saccades (RSS) when reading with single-vision (SVL) versus progressive-addition (PAL) lenses in a simulated computer-based business environment. METHODS: Horizontal eye and head movements were recorded objectively and simultaneously at a rate of 60 Hz during reading of single-page (SP; 14 degrees horizontal [H]) and double-page (DP; 37 degrees H) formats at 60 cm with binocular viewing. Subjects included 11 individuals with normal presbyopic vision aged 45 to 71 years selected by convenience sampling from a clinic population. Reading was performed with three types of spectacle lenses with a different clear near field of view (FOV): a SVL (60 degrees H clear FOV), a PAL-I with a relatively wide intermediate zone (7.85 mm; 18 degrees H clear FOV), and a PAL-II with a relatively narrow intermediate zone (5.60 mm; 13 degrees H clear FOV). RESULTS: Eye movements were initiated before head movements in the SP condition, and the reverse was found in the DP condition, with all three lens types. Duration of eye movements increased as the zone of clear vision decreased in the SP condition, and they were longer with the PALs than with the SVL in the DP condition. Gaze stabilization occurred later with the PALs than with the SVL in both the SP and DP conditions. The duration of head movements was longer with the PAL-II than with the SVL in both the SP and DP conditions. Eye movement peak velocity was greater with the SVL than the PALs in the DP condition. CONCLUSIONS: Eye movement and head movement strategies and timing were contingent on viewing conditions. The longer eye movement duration and gaze-stabilization times suggested that additional eye movements were needed to locate the clear-vision zone and commence reading after the RSS. Head movements with PALs for the SP condition were similarly optically induced. These eye movement and head movement results may contribute to the reduced reading rate and related symptoms reported by some PAL wearers. The dynamic interactions of eye movements and head movements during reading with the PALs appear to be a sensitive indicator of the effect of lens optical design parameters on overall reading performance, because the movements can discriminate between SVL and PAL designs and at times even between PALs.

Aged↗
PubMed2006

Perceived barriers to care and attitudes about vision and eye care: focus groups with older African Americans and eye care providers.

PURPOSE: To identify by using focus group methods the perceived barriers to eye care and attitudes about vision and eye care among older African Americans as well as among ophthalmologists and optometrists serving their communities. METHODS: Seventeen focus groups of older African Americans residing in the Birmingham or Montgomery, Alabama, areas were led by an experienced facilitator. Discussion was stimulated by a semistructured script focused on their perceived barriers to eye care and attitudes about vision and eye care. Six focus groups of ophthalmologists and optometrists who practiced in this geographic region addressed the same topics. Discussion was audiotaped and transcribed. Comments were coded using a multistep content analysis protocol. RESULTS: One hundred nineteen African Americans (age range, 59-97 years) and 35 eye care providers (51% ophthalmologists, 49% optometrists) participated. The barrier-to-care problem most frequently cited by both African Americans and eye care providers was transportation. The next most common problems mentioned by African Americans were trusting the doctor, communicating with the doctor, and the cost of eye care; and for eye care providers, the next most common problems were cost, trust, and insurance. With respect to older African Americans' comments on their attitudes about vision and eye care, these comments were predominantly positive (69%), highlighting the importance of eye care and behavior in their lives and attitudes that facilitated care. However, when eye care providers relayed their impressions of African Americans' attitudes about vision and eye care, their comments were largely negative (74%) centering on concerns and frustrations that older African Americans did not have attitudes or engage in behavior that facilitate eye care. CONCLUSIONS: These results provide some guidance for the design of interventions to increase the use of routine eye care in this population. At a societal level, there is a need for affordable and accessible transportation services for older African Americans seeking eye care. For ophthalmologists, optometrists, and their staffs, there is a need for continuing education that imparts culturally sensitive and age-appropriate communication and trust-building skills for interactions with this population. In addition to reinforcing the generally positive attitudes of older African Americans toward the importance of eye care, community-based educational programs should be focused on strategies for overcoming the common barriers to care.

Black or African American↗
PubMedDate not supplied

Improving health care experiences of persons who are blind or have low vision: suggestions from focus groups.

Persons who are blind or have low vision face special challenges in obtaining care that is safe, effective, timely, and patient centered. To explore perceptions of care and recommendations for improvements, we conducted 8 interviews with experts and 2 focus groups with 19 persons, all of whom are blind or have low vision. Interviewees perceived that they confront special barriers to care because of being blind or having low vision. Barriers fell into 4 broad categories: basic respect, including concerns about physicians thinking they cannot participate fully in their own care; communication barriers, including difficulties interacting with physicians and office staff; physical access barriers, including difficulties getting to and around physicians' offices; and information barriers, including receiving written materials in inaccessible formats (eg, not in Braille, large print, or audiotape). Using common courtesy and individualized communication techniques, physicians and office staff could improve health care experiences of blind and low-vision patients.

Blindness↗
PubMed1987

Need for near vision in daily work in different occupational groups.

To evaluate the need, characteristics and proportion of occupational accurate close work in different socio-economic groups we sent a questionnaire to all 26- and 46-year-old people in the Jyväskylä district. 1,503 (75%) of the 26-year-old subjects and 1,035 (78%) of the 46-year-old subjects returned the questionnaire. 71% of the 26-year-old subjects and 68% of the 46-year-old subjects reported that they need accurate near vision in their daily work. Accurate near vision was needed for reading and writing in 61% in the younger and 55% in the older age group, industrial quality control in 14% in the younger and in 26% in the older age group, Visual Display Unit work in 7% in both age groups, and other accurate close work in 19% in the younger and in 12% in the older age group. The results show that there is a need for accurate near vision in most occupations and indicate that the visual acuity and refraction of the employee requiring occupational accurate near vision should be examined when newly employed and when having problems with near work.

Adult↗
PubMed2004

Attentional cueing improves vision restoration therapy in patients with visual field defects.

BACKGROUND: In patients with postgenicular lesions of the visual system, areas of residual vision (ARVs) are the main predictor of recovery induced by vision restoration therapy (VRT). In these partially defective regions, the elevated perceptual thresholds can be acutely reduced by attentional cueing. OBJECTIVE: To examine whether directing attention to ARVs using a visuospatial cue also increases long-term neural plasticity and thus enhances permanent training outcome. METHODS: In a prospective, randomized clinical trial, treatment outcome was compared in patients with postgenicular visual system lesions who received either standard VRT (control group [CG]; n = 10) or VRT with attentional cueing (experimental group [EG]; n = 9). Visual field size was determined before and after a 6-month treatment period using Tubingen Automated Perimetry and computer-based high-resolution perimetry (HRP) and in regular intervals throughout this period by HRP and detection performance in VRT. RESULTS: In the area of the cue, restoration of vision was significantly greater than during VRT without cueing: cued patients showed a much more pronounced shift of the visual field border toward the blind area than that observed in the CG or in uncued regions of the EG. Focusing attention at ARVs during treatment changed topographic and temporal patterns of recovery as compared with uncued regions of the visual field. CONCLUSIONS: Use of a visuospatial cue to focus attention at areas of residual vision amplifies long-term neuronal plasticity. The authors propose that top-down signals preactivate partially damaged areas of V1, thus linking visual and attentional neuronal networks, with the effect of permanently increasing conscious visual perception.

Adult↗