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PubMed2001

What causes specificity of practice in a manual aiming movement: vision dominance or transformation errors?

The withdrawal of vision of the arm during a manual aiming task has been found to result in a large increase in aiming error, regardless of the amount of practice in normal vision before its withdrawal. In the present study, the authors investigated whether the increase in error reflects the domination of visual afferent information over the movement representation developed during practice to the detriment of other sources of afferent information or whether it reflects only transformation errors of the location of the target from an allocentric to an egocentric frame of reference. Participants (N = 40) performed aiming movements with their dominant or nondominant arm in a full-vision or target- only condition. The results of the present experiment supported both of those hypotheses. The data indicated that practice does not eliminate the need for visual information for optimizing movement accuracy and that learning is specific to the source or sources of afferent information more likely to ensure optimal accuracy during practice. In addition, the results indicated that movement planning in an allocentric frame of reference might require simultaneous vision of the arm and the target. Finally, practice in a target-only condition, with knowledge of results, was found to improve recoding of the target in an egocentric frame of reference.

Adult↗
PubMed2006

Methods for measuring personal costs associated with vision impairment.

PURPOSE: To describe and evaluate the procedures used to collect personal costs associated with vision impairment using diaries. METHODS: Participants with impaired vision (VA < 6/12 or > or = 6/12 with restricted visual fields) were recruited. Twelve-monthly diaries, provided in large print and electronic format (with audio and Braille instruction manuals and personal assistance), were used to record vision-related expenditures grouped under four categories. Two questionnaires were used to collect additional information and to test the validity of the self-reported costs. RESULTS: Of 227 people who consented to participate, 66% (n = 150; 91 females; mean age = 64.8 years) completed > or = 3 monthly diaries. Of the 150 eligible participants, 68% completed the diaries over 12 months, indicating a relatively high completion rate. The median total cost was AUD 2,417 dollars per annum and median values for the four expenditure categories ranged between AUD 206 dollars and AUD 872 dollars per annum. The data were consistent across different months with no significant difference found between any monthly comparison (t-test; p > Bonferroni-adjusted value). Data at 1, 3, and 6 months, extrapolated to annual figures, showed no significant difference from annual total costs, indicating consistency in the data collection periods. A significant association was found between diary data and similar entries in the follow-up questionnaire, confirming the validity of the recorded expenditures (Spearman; p < 0.01). Participants commented that the diary method was useful to obtain personal costs. CONCLUSION: A high response rate was achieved by using diaries and additional assistance methods. The diary provided an accurate and reliable strategy to determine the major personal costs associated with vision impairment.

Aged↗
PubMed2003

Computer-enhanced stereoscopic vision in a head-mounted operating binocular.

Based on the Varioscope, a commercially available head-mounted operating binocular, we have developed the Varioscope AR, a see through head-mounted display (HMD) for augmented reality visualization that seamlessly fits into the infrastructure of a surgical navigation system. We have assessed the extent to which stereoscopic visualization improves target localization in computer-aided surgery in a phantom study. In order to quantify the depth perception of a user aiming at a given target, we have designed a phantom simulating typical clinical situations in skull base surgery. Sixteen steel spheres were fixed at the base of a bony skull, and several typical craniotomies were applied. After having taken CT scans, the skull was filled with opaque jelly in order to simulate brain tissue. The positions of the spheres were registered using VISIT, a system for computer-aided surgical navigation. Then attempts were made to locate the steel spheres with a bayonet probe through the craniotomies using VISIT and the Varioscope AR as a stereoscopic display device. Localization of targets 4 mm in diameter using stereoscopic vision and additional visual cues indicating target proximity had a success rate (defined as a first-trial hit rate) of 87.5%. Using monoscopic vision and target proximity indication, the success rate was found to be 66.6%. Omission of visual hints on reaching a target yielded a success rate of 79.2% in the stereo case and 56.25% with monoscopic vision. Time requirements for localizing all 16 targets ranged from 7.5 min (stereo, with proximity cues) to 10 min (mono, without proximity cues). Navigation error is primarily governed by the accuracy of registration in the navigation system, whereas the HMD does not appear to influence localization significantly. We conclude that stereo vision is a valuable tool in augmented reality guided interventions.

Depth Perception↗
PubMed2001

Zinc supplementation might potentiate the effect of vitamin A in restoring night vision in pregnant Nepalese women.

BACKGROUND: Zinc deficiency may result in abnormal dark adaptation or night blindness, a symptom primarily of vitamin A deficiency. During a placebo-controlled trial in Nepal, weekly vitamin A supplementation of women reduced but failed to eliminate the incidence of night blindness during pregnancy, suggesting a role for zinc. OBJECTIVE: The study examined the efficacy of daily zinc supplementation in restoring night vision of pregnant women who developed night blindness while routinely receiving either vitamin A, beta-carotene, or placebo in a field trial. DESIGN: Women (n = 202) who reported to be night blind during pregnancy were randomly assigned in a double-blind manner, stratified on vitamin A, beta-carotene, or placebo receipt, to receive 25 mg Zn or placebo daily for 3 wk. Thus, the 6 groups studied were as follows: beta-carotene + zinc, beta-carotene alone, vitamin A + zinc, vitamin A alone (vitamin A + placebo), zinc alone (zinc + placebo), and placebo (2 placebos: one for the vitamin A or beta-carotene study and one for the zinc study). Women underwent a clinic-based assessment that included pupillary threshold testing and phlebotomy before and after supplementation. Supplement use and daily history of night blindness were obtained at home twice every week. RESULTS: Zinc treatment increased serum zinc concentrations, but alone (zinc alone group), failed to restore night vision or to improve dark adaptation. However, women in the vitamin A + zinc group who had baseline serum zinc concentrations <9.9 micromol/L were 4 times more likely to have their night vision restored (95% CI: 1.1, 17.3) than were women in the placebo group and tended to have a small improvement in pupillary threshold scores (by 0.21 log candela/m2; P = 0.09). CONCLUSION: These data suggest that zinc potentiated the effect of vitamin A in restoring night vision among night-blind pregnant women with low initial serum zinc concentrations.

Adult↗
PubMed2006

The impact of assistive device use on disability and depression among older adults with age-related vision impairments.

OBJECTIVE: One can conceptualize adaptive technology as a resource used by disabled older adults in order to maintain competence in everyday life. This study examined the independent relationships between optical and adaptive device utilization and change in functional disability and depression among older adults with age-related vision impairments. METHODS: We interviewed older adults (n = 438) with a recent vision impairment applying for vision rehabilitation services both pre-service and at the 6-month follow-up. We conducted hierarchical regression analyses with functional disability and depressive symptoms as criteria. In order to identify their independent direct effects, we entered optical and adaptive device use into the final step, preceded by Time 1 criterion scores, demographics, baseline disability or depression (depending on criterion), and total rehabilitation service hours. RESULT: Optical, but not adaptive, device use was significantly associated with declines in functional disability and depressive symptoms over time. DISCUSSION: We propose that these differential effects result from the fact that optical devices optimize residual vision and thus allow for greater continuity in the way tasks are accomplished (i.e., reading still performed visually), whereas use of adaptive aids (e.g., talking books) involves learning new methods in order to compensate for lost functions and thus is not as desirable either functionally or psychologically.

Activities of Daily Living↗
PubMed1996

An orientation to vision loss program: meeting the needs of newly visually impaired older adults.

An Orientation to Vision Loss program was developed to meet the needs of individuals, and their families, new to the difficult experience of vision loss. Program components address: education regarding services and resources, issues around the emotional response to vision loss and adjustment, tips and ideas for daily functioning, and enhancing families' awareness of how the vision loss "looks." Peer counselors co-facilitate the experience. Evaluations have been overwhelmingly positive, with participants expressing satisfaction and recognizing value in their participation.

Activities of Daily Living↗
PubMed2003

Complex distribution of avian color vision systems revealed by sequencing the SWS1 opsin from total DNA.

To gain insights into the evolution and ecology of visually acute animals such as birds, biologists often need to understand how these animals perceive colors. This poses a problem, since the human eye is of a different design than that of most other animals. The standard solution is to examine the spectral sensitivity properties of animal retinas through microspectophotometry-a procedure that is rather complicated and therefore only has allowed examinations of a limited number of species to date. We have developed a faster and simpler molecular method, which can be used to estimate the color sensitivities of a bird by sequencing a part of the gene coding for the ultraviolet or violet absorbing opsin in the avian retina. With our method, there is no need to sacrifice the animal, and it thereby facilitates large screenings, including rare and endangered species beyond the reach of microspectrophotometry. Color vision in birds may be categorized into two classes: one with a short-wavelength sensitivity biased toward violet (VS) and the other biased toward ultraviolet (UVS). Using our method on 45 species from 35 families, we demonstrate that the distribution of avian color vision is more complex than has previously been shown. Our data support VS as the ancestral state in birds and show that UVS has evolved independently at least four times. We found species with the UVS type of color vision in the orders Psittaciformes and Passeriformes, in agreement with previous findings. However, species within the families Corvidae and Tyrannidae did not share this character with other passeriforms. We also found UVS type species within the Laridae and Struthionidae families. Raptors (Accipitridae and Falconidae) are of the violet type, giving them a vision system different from their passeriform prey. Intriguing effects on the evolution of color signals can be expected from interactions between predators and prey. Such interactions may explain the presence of UVS in Laridae and Passeriformes.

Amino Acid Sequence↗
PubMed1997

Color vision of ancestral organisms of higher primates.

The color vision of mammals is controlled by photosensitive proteins called opsins. Most mammals have dichromatic color vision, but hominoids and Old World (OW) monkeys enjoy trichromatic vision, having the blue-, green-, and red-sensitive opsin genes. Most New World (NW) monkeys are either dichromatic or trichromatic, depending on the sex and genotype. Trichromacy in higher primates is believed to have evolved to facilitate the detection of yellow and red fruits against dappled foliage, but the process of evolutionary change from dichromacy to trichromacy is not well understood. Using the parsimony and the newly developed Bayesian methods, we inferred the amino acid sequences of opsins of ancestral organisms of higher primates. The results suggest that the ancestors of OW and NW monkeys lacked the green gene and that the green gene later evolved from the red gene. The fact that the red/green opsin gene has survived the long nocturnal stage of mammalian evolution and that it is under strong purifying selection in organisms that live in dark environments suggests that this gene has another important function in addition to color vision, probably the control of circadian rhythms.

Amino Acid Sequence↗
PubMed1976

Effect of tinted contact lenses on color vision.

This study was designed to investigate the effects of various contact lens tints on color vision. Color vision performance of eight subjects was evaluated with the Farnsworth-Munsell 100 Hue Test while each subject wore each of 13 differently tinted contact lenses. No significant differences in color vision were found with the various lenses. However, performance on the test was affected by repetition. Regardless of the lens tints tested, color discrimination for the blue quadrant of the 100 Hue Test was the poorest. Further research is needed to determine the effect of tinted contact lenses on scotopic and mesopic vision.

Adult↗
PubMed1993

Vernier acuity through night vision goggles.

Night vision goggles (NVG's) are being used increasingly in military and civilian environments. Despite the use of these devices, relatively few tests exist to assess visual performance through NVG's. Hyperacuity tasks may provide a sensitive index of performance through night vision devices. In this study, grating vernier acuity was measured through NVG's. As reported previously, a power law relation was observed between vernier acuity and stimulus contrast. Comparison of vernier acuity with and without NVG's indicated that performance is limited by the contrast transfer of the device. Vernier acuity measurements can be used to assess the quality of vision and quantity of contrast transferred through night vision devices.

Adult↗
PubMed1998

Vision therapy to reduce abnormal nearwork-induced transient myopia.

After brief periods of nearwork, some younger patients complain of transient distance blur that is correlated with a transient pseudomyopic shift in their distance refraction. This phenomenon has recently been documented objectively. However, there is lack of objective documentation demonstrating the effects of conventional optometric vision therapy in symptomatic individuals manifesting this "abnormal nearwork-induced transient myopia" (ANITM). Five symptomatic subjects received 7 to 10 weeks (5 to 6 sessions) of accommodative facility vision therapy (i.e., lens flippers and Hart chart). Objective recording of their ANITM and its decay were taken before and after the vision therapy, using a Canon R-1 autorefractor. A daily log was maintained, describing qualitatively their nearwork-related symptomatology. After therapy, there was marked reduction of symptoms and considerable improvement in clinical accommodative facility measures, as well as improvement in the objective findings. These results demonstrate multi-faceted positive effects of optometric accommodative vision therapy in this diagnostic group of symptomatic individuals.

Accommodation, Ocular↗
PubMed2000

A randomized trial of the effect of single-vision vs. bifocal lenses on myopia progression in children with esophoria.

BACKGROUND: Bifocals have long been thought to reduce progression of childhood myopia. However, this hypothesis has not been definitively evaluated. METHODS: We conducted a randomized clinical trial to test the hypothesis that bifocals slow myopia progression in children with near-point esophoria. Eighty-two myopic children were randomized to single-vision glasses (n = 40) or to bifocals with a +1.50 D add (n = 42) and were followed for 30 months. Refraction was measured by an automated refractor after cycloplegia. The primary outcome was myopia progression defined as the difference between the spherical equivalent at baseline and at the 30-month examination, averaged over both eyes. RESULTS: Follow-up was incomplete for six children in the bifocal group and one child in the single-vision group. Among the children completing the 30 months of follow up, myopia progression (mean spherical equivalent of the two eyes) averaged 0.99 D for bifocals and 1.24 D for single vision (unadjusted, p = 0.106; adjusted for age, p = 0.046). Treatment groups differed in their cumulative distributions (Kolmogorov-Smirnov procedure, p = 0.031). Evidence for a treatment effect on growth in vitreous chamber depth was similar (p = 0.046 by K.S.). CONCLUSION: Use of bifocals, instead of single-vision glasses, by children with near-point esophoria seemed to slow myopia progression to a slight degree.

Aging↗
PubMed2000

Environmental factors which may have led to the appearance of colour vision.

It is hypothesized that colour vision and opponent processing of colour signals in the visual system evolved as a means of overcoming the extremely unfavourable lighting conditions in the natural environment of early vertebrates. The significant flicker of illumination inherent in the shallow-water environment complicated the visual process in the achromatic case, in particular preventing early detection of enemies. The presence of two spectral classes of photoreceptors and opponent interaction of their signals at a subsequent retinal level allowed elimination of the flicker from the retinal image. This new visual function provided certain advantages concerning reaction times and favoured survival. This assumption explains why the building blocks for colour vision arose so early, i.e. just after the active predatory lifestyle was mastered. The principal functions of colour vision inherent in extant animals required a more complex neural machinery for colour processing and evolved later as the result of a change in visual function favouring colour vision.

Animals↗
PubMed2004

Pupil size and night vision disturbances after LASIK for myopia.

PURPOSE: To examine whether standardized, preoperative evaluation of pupil sizes can predict the risk of night vision visual disturbances after bilateral laser in situ keratomileusis (LASIK) for myopia. METHODS: A prospective study was carried out involving 46 patients who underwent bilateral LASIK for myopia. Pupil sizes were measured before surgery using an infrared pupillometer under standardized settings. Pre- and postoperative refraction and best spectacle-corrected visual acuity (BSCVA) were registered. At the 3-month follow-up visit, the patients completed a questionnaire regarding night vision pre- and postoperatively. RESULTS: The mean bilateral, spherical equivalent refraction (SE) was - 8.76 D (range 6.32 to - 12.0 D) preoperatively, and - 1.69 D (range 0 to - 4.38 D) postoperatively. The mean bilateral BSCVA was not changed by the operations. We found a significant correlation between large scotopic pupil sizes and the impression of worsened night vision (p < 0.01). A significant correlation between gender (males) and subjectively reduced night vision postoperatively was also found (p < 0.05). CONCLUSION: Large pupil size measured preoperatively is correlated with an increased frequency of subjectively experienced post-LASIK visual disturbances during scotopic conditions. We recommend preoperative evaluation of pupil size in all patients prior to LASIK surgery.

Adult↗
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

Multi-disciplinary low vision care.

Case reports for three patients with low vision due to different ocular diseases are presented. In each case, a different rehabilitation professional was the main provider of the low vision care needed to meet the patient's goals. However, in all cases the patients benefited from the services of a range of professionals, agencies or groups for visually impaired people. The importance of defining patients' specific goals, referral to multi-disciplinary low vision services and regular reviews of vision and visual tasks is highlighted.

Journal Article↗
PubMed2004

Ecology and evolution of primate colour vision.

More than one hundred years ago, Grant Allen suggested that colour vision in primates, birds and insects evolved as an adaptation for foraging on colourful advertisements of plants--fruits and flowers. Recent studies have shown that well developed colour vision appeared long before fruits and flowers evolved. Thus, colour vision is generally beneficial for many animals, not only for those eating colourful food. Primates are the only placental mammals that have trichromatic colour vision. This may indicate either that trichromacy is particularly useful for primates or that primates are unique among placental mammals in their ability to utilise the signals of three spectrally distinct types of cones or both. Because fruits are an important component of the primate diet, primate trichromacy could have evolved as a specific adaptation for foraging on fruits. Alternatively, primate trichromacy could have evolved as an adaptation for many visual tasks. Comparative studies of mammalian eyes indicate that primates are the only placental mammals that have in their retina a pre-existing neural machinery capable of utilising the signals of an additional spectral type of cone. Thus, the failure of non-primate placental mammals to evolve trichromacy can be explained by constraints imposed on the wiring of retinal neurones.

Adaptation, Physiological↗
PubMed2006

Colour vision and retinal nerve fibre layer photography in patients with an Acrysof Natural intraocular lens.

PURPOSE: To study colour vision and retinal nerve fibre layer (RNFL) photographs in patients with an Acrysof Natural intraocular lens (IOL). METHODS: We carried out a randomized double-blind study. An Acrysof Natural IOL (model SN60AT) was implanted in 25 eyes of 19 patients and an Acrysof IOL (model SA60AT) was implanted in 27 eyes of 18 control patients. The patients returned for colour vision tests and fundus photography 1-6 months after the surgery. RESULTS: Standard pseudoisochromatic plates, part 2, were correctly interpreted and the Farnsworth-Munsell 100-hue test (FM 100) total and individual box scores were normal in all IOL eyes. In the FM 100 hue test there were no significant differences in the results of the total error scores or the error scores of the individual boxes between the eyes with Acrysof Natural and those with Acrysof lenses. The yellow coloration of the Acrysof Natural IOL did not affect the visibility of the RNFL in photographs. CONCLUSIONS: The Acrysof Natural IOL did not affect colour vision in the tested patients, even in the blue region of the spectrum, and can be implanted in patients who need to have normal colour vision for the purposes of their occupation. The Acrysof Natural IOL does not interfere with RNFL photography and can also be used in patients with glaucoma.

Acrylic Resins↗