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At least 1,369 records · Page 76Linked to original sources
PubMed1973

Relationships between luminance and visual acuity in the rhesus monkey.

1. The ability of rhesus monkeys to detect the gap in Landolt ring test-objects that were presented against background luminances between 5 x 10(-5) cd/m(2) and 5 x 10(3) cd/m(2) was compared with similar human data.2. At high luminance-levels the acuity of human observers is slightly better than that of rhesus, but rhesus have better acuity at scotopic luminance-levels. Both species have distinct photopic and scotopic acuity functions that cross at 6 x 10(-3) cd/m(2).3. The threshold for light detection is estimated to be the same for both species when specified in quanta incident on the retina.4. It is concluded that the receptor and neural mechanisms that mediate visual-acuity function similarly in rhesus and man, and that the differences in acuity that were measured in the two species may be attributed to optical rather than to physiological factors.

Animals↗
PubMed1999

A logistics evaluation of visual acuity as applied to the Bailey-Lovie chart.

AIMS: To discover whether as a result of the increasing use of the Bailey-Lovie chart some classes of patients may not be affected by the crowding of the smaller test characters, whose spacing is proportional to their size; and to determine acuities with a logistic function so that all of a patient's responses may be utilized. METHODS: 112 patients were tested both with the original chart and one in which the horizontal distance is kept constant, i.e., the letters are arranged in vertical columns. All of a patient's responses were recorded so that the constants of the logistic function might be determined. RESULTS: No difference was found for very high and very low acuity scores, but, for intermediate ones, the vertical columns yielded acuity ratings increased by some 13%. CONCLUSION: The use of the logistics function was successful in that the correlation between stimulus and response was between 0.9 and 1 for some 80% of those examined. A constant horizontal spacing may be of advantage to some patients with a conventionally measured visual acuity of approximately 0.9.

Adolescent↗
PubMed1997

[Dim the light! Glare problems in a world with ever increasing demands on visual acuity].

Ocular tissue transparency is dependent on the regular lattice configuration of lens and corneal fibres of uniform diameter. Ageing is associated with degeneration of both lens and cornea, which lose some of their structural order and eventually their transparency, though this process is not uniform. The structural changes are local and result in ocular media opacities. When the opacities increase in number and extension, they begin to affect visual acuity. As the loss of acuity becomes clinically significant, we speak of clinically relevant cataract. Retinal exposure to light diffused by intraocular light scattering induces optical glare, one of two forms of glare. The other form is transient glare--i.e., glare due to adaptation problems in an environment with rapidly changing ambient luminance. Contemporary society is characterised by increasing emphasis on visual information in such forms as texts, icons, signs and symbols. The computer revolution has been accompanied by further stress on the importance of the detection and interpretation of written instructions.

Adaptation, Ocular↗
PubMed2005

Retinal stretching limits peripheral visual acuity in myopia.

Axial elongation of the myopic eye has the potential to stretch the retina, thereby reducing the sampling density of retinal neurons. Resolution acuity in the peripheral field of normal eyes is known to be sampling-limited, which suggests that retinal stretching in the myopic eye should have a direct effect on resolution acuity everywhere in the visual field except perhaps the fovea, which is usually optically limited. We tested this prediction that neural sampling density is reduced in myopic eyes by measuring resolution acuity for sinusoidal gratings in the fovea plus five peripheral locations in 60 myopic subjects exhibiting a wide range of refractive errors. Control experiments using a detection paradigm to provoke spatial aliasing verified that peripheral resolution was sampling limited. Retinal spatial frequencies of the grating stimulus were computed assuming Knapps' Law of visual optics, which ensures that retinal image size (in mm) is independent of refractive error when axial myopia is corrected by a spectacle lens located in the anterior focal plane of the eye. Results obtained at every retinal locus showed that resolution acuity declined linearly with magnitude of refractive error. Regression of the population data indicated that approximately 15 D of refractive error doubles the spacing between retinal neurons, thereby halving peripheral resolution acuity relative to the emmetropic eye. Several subjects also demonstrated sampling-limited performance in the fovea, which indicated that optical filtering by the eye's optical system failed to protect the fovea from aliasing artifacts of neural undersampling in these eyes. We conclude that stretching of the retina is a primary cause of reduced spatial resolution of the peripheral field, and occasionally of the fovea, in myopic eyes. Stretching appears to be locally uniform over the central +/-15 degrees of visual field but is globally non-uniform since the foveal region appears to stretch more than the globe itself.

Adult↗
PubMed1986

Contrast sensitivity versus visual acuity in retinal disease.

A large group of individuals with retinal disease were tested prospectively for contrast sensitivity by means of Arden gratings. A subgroup of 19 were also tested with the Nicolet automated television system. Individuals with macular or peripheral dystrophy showed a general reduction in contrast sensitivity as visual acuity decreased. The loss of contrast sensitivity was more prominent for high spatial frequencies (6.4 cycles per degree) than for low ones (0.2 cycles per degree). Similar results were obtained for patients with achromatopsia and congenital stationary night blindness. Patients with functional complaints, but no organic basis for decreased acuity, showed greater scatter in their test scores. The Nicolet results showed somewhat smoother curves, but were no more specific in separating normality from abnormality. Contrast sensitivity testing was not specific for the retinal disease entities considered, but may be useful in recording a degree of retinal damage and a degree of functional visual disability. Contrast sensitivity appeared to be reduced whenever acuity was reduced, so that a distinction could be made between patients having a loss of contrast beyond the expectations for their level of acuity and those in whom a loss of contrast simply corroborates the reduction of acuity.

Adolescent↗
PubMed1991

Effect of donor cornea preservation in tissue culture and in McCarey-Kaufmann medium on corneal graft rejection and visual acuity.

In a retrospective study the rate of rejection and clouding of the donor cornea for other reasons was investigated in 230 penetrating keratoplasties performed between 1984-1986. Donor corneas were stored in McCarey-Kaufmann Medium (MK) at 4 degrees C or in a modified Minimal Essential Medium (MEM) at 31 degrees C. No statistical differences in rejection rate, cloudiness due to other causes or visual acuity was found between MEM- and MK-stored donor corneas.

Adult↗
PubMed2005

Improved visual acuity and macular thickness 1 week after intravitreal triamcinolone for diabetic macular oedema.

PURPOSE: To evaluate the clinical and volumetric improvement 1 week after an injection of intravitreal triamcinolone acetonide in eyes with diabetic macular oedema. METHODS: Seven phakic eyes of seven diabetic patients diagnosed with clinically significant macular oedema were treated with a single 4-mg intravitreal injection of triamcinolone acetonide (0.1 ml). LogMAR best corrected visual acuity (logMAR BCVA), best corrected reading ability (RA), and central macular thickness (CMT) with optical coherence tomography (OCT) were assessed prior and 1 week subsequent to treatment. RESULTS: Mean improvement in logMAR BCVA was 0.146 (P=0.03). Mean reduction in CMT was 150.9 mum (P=0.02, Wilcoxon signed-rank test). Mean improvement in RA was 3 lines. CONCLUSION: Reduction in macular oedema was demonstrated on OCT at 1 week, in most cases associated with improvement in central visual function, in particular, reading ability. Total resolution of diabetic macular oedema may occur at 1 week following intravitreal steroid injection.

Aged↗
PubMed2002

Visual acuity and retinal function in infant monkeys fed long-chain PUFA.

Previous randomized clinical trials suggest that supplementation of the human infant diet with up to 0.35% DHA may benefit visual development. The aim of the current study was to assess the impact of including arachidonic acid (AA) and a higher level of DHA in the postnatal monkey diet on visual development. Infant rhesus monkeys were fed either a control diet (2.0% alpha-linolenic acid as the sole n-3 FA) or a supplemented diet (1.0% DHA and 1.0% AA) from birth. Visual evoked potential acuity was measured at 3 mon of age. Rod and cone function were assessed in terms of parameters describing phototransduction. Electroretinogram (ERG) amplitudes and implicit times were recorded over a wide intensity range (-2.2 to 4.0 log scot td-sec) and assessed in terms of intensity response functions. Plasma DHA and AA were significantly increased (P < 0.001) in the diet-supplemented monkeys compared with the control monkeys. There was an approximately equal effect of diet for the rod phototransduction parameters, sensitivity, and capacitance but in the opposite directions. Diet-supplemented monkeys had significantly shorter b-wave implicit times at low retinal illuminances (<-0.6 log scot td-sec). There were no significant effects of diet for visual acuity or the other 23 ERG parameters measured. The results suggest that supplementation of the infant monkey diet with 1.0% DHA and 1.0% AA neither harms nor provides substantial benefit to the development of visual acuity or retinal function in the first four postnatal months.

Animals↗
PubMed1984

Evaluation of visual acuity during laser photoradiation therapy of cancer.

Visual function for ten patients undergoing HPD-PRT was tested using 1) the Graham Field Eye Chart for distance vision, 2) pseudo-isochromatic plates for color vision, and 3) Amsler grid for changes in macular function. Whereas some increases and decreases in ocular function were observed, no clear patterns or changes of significance were observed.

Adult↗
PubMed2006

[Visual acuity and work and leisure abilities].

The visual medical ability is necessary for a large number of jobs, sports and for vehicles driving. A high heterogeneousity exists in the required standards, the measurement techniques and the people who realize these visual abilities. This heterogeneousity is too rarely correlated to an accidentology which is increased by a lack of scientific study. A review non exhaustive of jobs and occupations is here presented.

Activities of Daily Living↗
PubMed1978

A behavioral method for efficient screening of visual acuity in young infants. II. Clinical application.

Visual performance in 130 infants was assessed in a clinical setting with the forced-choice preferential looking (FPL) method described by Dobson et al.5 Over 90% of infants completed testing. Testing usually required less than 10 min. One group of infants tested also underwent complete ophthalmic examination. The second, larger group was screened with handlight examinations and FPL testing; any abnormalities detected were evaluated by full ophthalmic examination. Results so far indicate that the FPL test accurately identifies babies with binocular visual problems and that, when coupled with a handlight examination, it provides efficient screening for ocular problems in infants 0 through 16 weeks of age (postterm).

Age Factors↗
PubMed1985

Long-term visual acuity results after penetrating and perforating ocular injuries.

Of 33 consecutive patients (30 males and three females, ranging in age from 5 to 48 years) with penetrating ocular injuries, 13 had retained metallic intraocular foreign bodies. The remaining 20 had no retained foreign bodies and their injuries were generally more severe lacerating or double perforating injuries. Magnet extraction was used for foreign body extraction when possible, and pars plana posterior vitrectomy was used only for late complications. The long-term visual acuity results indicated that wound repair, conventional magnet extraction, and removal of traumatic cataract and anterior vitreous blood through a limbal incision is still a viable treatment for many such injuries.

Adolescent↗
PubMed2007

Public health impact of neovascular age-related macular degeneration treatments extrapolated from visual acuity.

PURPOSE: To estimate the potential public health impact of treatment with new medications intended to preserve vision in patients with neovascular age-related macular degeneration (AMD). METHODS: A Markov model was used to simulate the natural history of AMD over the lifetime of patients with diagnosed neovascular AMD from clinical trials and epidemiologic surveys. It applied to a cohort of patients aged 75 years, with newly diagnosed neovascular AMD in one eye, whose visual acuity was 0.7 logMAR. Probabilities were calculated for the risk of AMD in the remaining eye and for premature mortality. Results of the model were expressed as the duration of low vision (worse eye VA>1.0 and better eye VA>0.7 logMAR) and blindness (bilateral VA >1.0 logMAR). Health consequences of blindness and low vision were estimated for depression, hip fractures, institutionalization, and life expectancy. RESULTS: For AMD patients with a 50% probability of VA >1.0 logMAR at 1 year, in one eye, the probability of lifetime bilateral blindness was >47%. The patients would live approximately 7 years with monocular vision >1.0 logMAR and an additional 4 years with bilateral blindness and a >15% probability of depression due to AMD. Life expectancy was decreased by approximately 2 years, >90/1000 patients would sustain a new hip fracture, and 1.5% of the patients would require institutional care for visual impairment due to AMD. To achieve a defined public health outcome (visual impairment and consequent comorbidity), it was necessary for the VA effectiveness of new treatments to increase in parallel with disease severity. CONCLUSIONS: Comorbidity related to visual impairment contributes significantly to the public health impact of AMD. Aggressive lesions need highly effective treatments. Models may be used to compare the public health impact of placebo-controlled clinical trial results.

Aged↗
PubMedDate not supplied

A neural mechanism improving visual acuity by contrast enhancement, a study of foveal vision.

Analysis of synaptic connections between neurons in the retina (Sjöstrand, 1958, 1974, 1989, 1990, 1998a,b,d) has revealed a pattern of connections between rods, cones and bipolar cells that shapes neural interaction to generate spatial brightness contrast enhancement, explaining the Mach band phenomenon (Mach, 1865). Using the Mach band effect at boundaries between fields of different brightness it was revealed that the phenomenon applies to foveal vision. The contrast enhancing distortion of brightness was confined to zones, the width of which approached visual resolution. The distortion also applied to boundaries between fields of different colors when differing in brightness. The distortion involved an achromatic component. The quality of vision deteriorated with decreasing illumination at the same rate enhancement of contrast faded. Spatial brightness contrast enhancement is therefore a major factor contributing to visual acuity and fading of enhancement explains the deterioration of the perceived image at low illumination.

Contrast Sensitivity↗
PubMed1996

Interrelations of age, visual acuity, and cognitive functioning.

It has recently been suggested that a large proportion of the age-related influences on many measures of cognitive functioning is mediated through a single common factor. This hypothesis has been supported by the discovery that much of the age-related variance in different cognitive measures is shared, and is not distinct or independent. These earlier results were replicated in this project, and it was also discovered that measures of corrected visual acuity and processing speed share a very large proportion of the age-related variance in measures of working memory, associative learning, and concept identification. The apparent implication is that the common factor that appears to contribute to age-related differences in many cognitive measures is quite broad and may reflect a relatively general reduction in central nervous system functioning.

Adult↗
PubMed1999

[Twilight visual acuity after correction of myopia with LASIK].

BACKGROUND: Data on mesopic vision after LASIK are not available to date. We therefore evaluated mesopic vision in myopic eyes before and after LASIK. PATIENTS AND METHODS: Sixty-seven eyes (34 patients) treated using the Automatic Corneal Shaper and the Keracor 117CT spot-scanning excimer laser were included. All eyes had best-corrected vision of 20/25 or better preoperatively. We measured spectacle refraction, visual acuity, and mesopic vision without and with glare (Nyktometer, Rodenstock) both preoperatively and 1 year after LASIK. Results were evaluated in three groups with reference to baseline refraction, and numbers of patients who saw a contrast of 1:5 or less were compared. RESULTS: Myopia -1 to -5 D (group 1; n = 26): Preoperatively (postoperatively), 89% (96%) (P = 0.03) of eyes identified a contrast of 1:5 or less without glare, while 65% (73%) achieved that level with glare. Myopia -5.1 to -10 D (group 2; n = 24): Preoperatively (postoperatively), 83% (75%) of eyes identified a contrast of 1:5 or less without glare, while 50% (21%) achieved that level with glare. Myopia -10.1 to -15 D (group 3; n = 11): Preoperatively (postoperatively), 73% (55%) of eyes identified a contrast of 1:5 or less without glare, while 46% (27%) achieved that level with glare. CONCLUSIONS: LASIK seems to cause a reduction of mesopic vision under glare conditions in corrections of more than -5 D. In corrections of more than -10 D, mesopic vision without glare is reduced, too. However, differences were not statistically significant when comparing vision at contrasts of 1:5 and lower. In addition, mesopic is considerably reduced in high myopes even preoperatively.

Adult↗