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At least 1,045 records · Page 58Linked to original sources
PubMed1998

Repeatability of refraction and corrected visual acuity in keratoconus. The CLEK Study Group. Collaborative Longitudinal Evaluation of Keratoconus.

PURPOSE: The purpose of the test-retest phase of the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study was to determine the repeatability of the various parts of the CLEK Study protocol. This paper presents the test-retest parameters of the refraction protocol. METHODS: We examined 138 CLEK Study-eligible patients on two occasions (median, 90 days; range, 22 to 268 days). All patients underwent subjective refraction on two occasions, and contact lens over-refractions were performed either over the patient's habitual rigid contact lenses or over a trial rigid contact lens equal in base curve to the steep keratometric reading in nonrigid contact lens wearers. RESULTS: Mean interoccasion differences +/- SD were -0.32 +/- 2.91 D and -0.17 +/- 1.39 D for subjective refraction sphere and cylinder power, respectively, and the mean absolute difference for subjective refraction cylinder axis was 18.1 +/- 20.2 degrees. The mean interoccasion difference +/- SD for high-contrast visual acuity with subjective refraction was 0.38 +/- 10.9 letters correct. Mean interoccasion differences +/- SD were -0.11 +/- 0.81 D and 0.02 +/- 0.67 D for contact lens over-refraction sphere and cylinder power, respectively, and the mean absolute difference for contact lens over-refraction cylinder axis was 11.6 +/- 9.9 degrees. The mean interoccasion difference +/- SD for visual acuity with contact lens over-refraction was 0.50 +/- 5.2 letters correct and 0.71 +/- 6.9 letters correct for high- and low-contrast visual acuity, respectively. CONCLUSIONS: The repeatability of subjective refraction in keratoconus patients is good but somewhat lower than that found in nondiseased eyes. Only 36% of our repeat measures of sphere power from subjective refraction fell within 0.50 D of each other, compared with more than 90% in studies of normal eyes.

Adult↗
PubMed2002

Visual acuity thresholds of juvenile loggerhead sea turtles (Caretta caretta): an electrophysiological approach.

Visual evoked potentials measure dynamic properties of the visual system by recording transient electric responses of neural tissue identified to correspond to a specific visual stimulus, such as light or a striped grid. In this study, visual evoked potentials were used to test the visual acuity of juvenile loggerhead sea turtles (Caretta caretta) in water. Subject animals were fitted with a Plexiglas goggle filled with filtered seawater. Stimuli of black and white striped gratings were presented to the turtles using a slide projector directing an image onto a screen via a rotatable mirror that shifted the striped pattern laterally one-half cycle. Bioelectric activity was collected using a digital averaging computer and subdermal platinum electrodes, implanted under the head scutes directly above the optic nerve and the contralateral optic tectum. To isolate the response signal from the noise, signal averaging techniques were used when collecting visual evoked potentials. The resulting response waveforms included a robust positive-negative compound that was used to track the turtle's response to visual stimulation. Acuity thresholds for these sea turtles, which were derived from linear regressions analysis of the positive-negative compound amplitudes versus stripe size, ranged from 0.130 to 0.215. This acuity level is comparable to other inshore, shallow water marine species.

Age Factors↗
PubMed2000

"With the rule" astigmatism is not the rule in the elderly. Reykjavik Eye Study: a population based study of refraction and visual acuity in citizens of Reykjavik 50 years and older. Iceland-Japan Co-Working Study Groups.

PURPOSE: To study refractive state and visual acuity in citizens of Reykjavik 50 years and older. METHODS: 1700 persons were randomly selected from the national population census. 1379 could be located and qualified whereof 1045 participated. Evaluation of refraction was performed using Nidek ARK 900 autorefracto-keratometer. Visual acuity was tested on a Snellen chart. RESULTS: The prevalence of hypermetropia increases with age by 0.3 D in five years. The prevalence of "against the rule" astigmatism increased on average 5.3% and oblique 3.9% in five years. Analysis of corneal astigmatism measured by keratometer shows an "against the rule" change with age. CONCLUSIONS: Hypermetropia increases by age. The prevalence of astigmatism increases and the axis turns to "against the rule". The changes in total astigmatism and corneal astigmatism is almost parallel which might indicate that the "against the rule" change is related to changes in the cornea.

Aged↗
PubMed1989

[Effect of visual acuity and changes in refraction following retinal surgery on binocular function].

In a retrospective study, 18 patients aged between 17 and 65 were examined between 12 and 23 months after successful surgery for retinal detachment with detached macular region. Visual acuity, refraction, steropsis, fusion and aniseikonia were determined. Visual acuity in the eyes operated on was between 0.1 and 1.0, refractive changes ranged from 0 to 4 D. No disturbances of binocular function resulting from acquired aniseikonia were found. Postoperatively acquired strabismus was diagnosed in three patients. Good to very good steropsis (30-240") was found with the TNO test, while fusion was reduced in some cases; even suppression was found, for small objects (1 degrees). The results are discussed in the light of the pathophysiological changes following retinal detachment including detachment of the macular area.

Adolescent↗
PubMed2004

A simple model to predict the sensitivity to change of visual acuity measurements.

BACKGROUND: Estimates of test-retest variability (TRV) in the form of a 95% range have been suggested as providing a cutoff value (or "change-criterion") against which measured acuity changes can be judged to decide whether they are indicative of a clinically important change. This approach is based on ensuring that the specificity of the procedure is 95% in individuals with no real change. In an earlier article we investigated empirically the ability of the procedure to detect varying degrees of change (its sensitivity). In this article, we develop a simple statistical model to examine further the sensitivity of the approach. METHODS: A statistical model was developed, and predictions from the model were compared with empirical visual acuity data. RESULTS: The model predicts that for changes equal in size to the magnitude of the change-criterion, sensitivity will be 50%. For changes 1.65 times the change-criterion, sensitivity is 90% and increasing to 95% for changes 1.84 times the size of the change-criterion. Predicted sensitivities agreed well with those measured empirically. CONCLUSIONS: The 95% range for TRV is often used to decide whether measured changes are indicative of clinically important changes. Evaluating the performance of visual acuity charts using a method analogous to that of estimating the sensitivity and specificity of a screening test highlights some limitations of this method. Use of the 95% range as a change-criterion ensures a high specificity, but a simple statistical model indicates that changes must approach twice the size of the change-criterion before they will be detected with sensitivity in excess of 95%. This has implications for the clinician attempting to assess the reliability of visual acuity charts, and in other similar tests, to detect change.

Humans↗
PubMed1984

Developmental physiological optics and visual acuity: a brief review.

The development of optical and neural factors affecting visual acuity is reviewed with the aim of determining the age at which the relationship between optical and neural factors become mature. Delayed development of extrastriate cortical and indirect visual pathways may account for differences in acuity assessed by preferential looking and pattern reversal VEPs.

Adult↗
PubMed1994

Effect of fixation disparity on distance binocular visual acuity.

Subjects with appreciable values (2 delta and greater) of associated 'phoria, as measured by a Mallett unit, had their distance monocular and binocular visual acuities measured. In the latter case measurements were taken both with the associated 'phoria corrected by prisms and without such a correction. The improvement in binocular acuity compared to monocular acuity was less than would occur in normal subjects with minimal associated 'phorias although the improvement differed accordingly as to whether the readings were eso- or exo-in mature. When the associated 'phorias were corrected with prisms the improvement in binocular over monocular visual acuity was similar to that found in normal subjects.

Adult↗
PubMed1984

Visual acuity in optic atrophy: a quantitative clinicopathological analysis.

Analysis of clinicopathological data from 14 eyes with optic atrophy from various causes revealed a simple relationship between visual acuity and the number of surviving axons in the temporal quadrant of the optic nerve head. This provides support for the theory that the minimum angle of resolution (inverse of visual acuity) is directly proportional to the spatial separation of transmitting foveal cones. The theory allows estimation of the functional fraction of foveocortical neural channels from clinical acuity measurements.

Adult↗
PubMed1988

Topographic analysis and visual acuity after radial keratotomy.

Using a computerized corneal topographic mapping system that allows detailed examination of the corneal curvature in the vicinity of the visual axis, we identified separate regions of differing corneal curvature in three of 11 eyes after radial keratotomy. In these eyes, the excellent uncorrected visual acuity appeared to be inconsistent with the postoperative spherical equivalent as determined by refraction and corneal curvature by standard keratometer measurements. The distinct regions of corneal curvature appeared to serve as alternative effective optical zones, thus allowing the patients to have excellent visual acuity. In essence, the cornea became a multifocal lens. Although degradation in the contrast of the image as well as monocular diplopia are possible, our patients had no significant complaints.

Cornea↗
PubMed2003

New visual acuity chart: modification for clinical practice and research.

The authors created numeric optotypes by steps following the standard Sloan letters and developed a visual acuity test chart using Logarithm of the Minimal Angle of Resolution (Log MAR) such as the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. Legibility of new numeric optotypes was presented in per cent of correct response at threshold. Only seven numbers (0, 2, 3, 5, 6, 8, 9) were used as optotypes and the average of per cent of correct response at threshold equal to 80.7 which was slightly less than standard Sloan letters (82%). The comparison between results of visual acuity level from the new chart and ETDRS showed that the ETDRS chart was slightly more legible than the new chart. It can be used universally especially with Thai people for clinical practice and research.

Adult↗
PubMed1992

Trends in cataract surgery in Milan (Italy) from 1956 to 1987. Relationship to age and visual acuity.

In order to test whether the mean age at cataract surgery has changed over the course of the last 30 years, a hospital series of 5443 patients undergoing cataract extraction between 1956 and 1987 is reviewed. All cases attended the same University Eye Clinic of Milan and most were resident in the same geographical area. Cases with macular or optic nerve diseases were excluded. Results show that mean age at cataract surgery progressively increased from 67.5 to 71.5 years (slope = +0.096 years of age per year, p = 0.0001) as did visual acuity at surgery (patients with visual acuity levels greater than or equal to 1/10 at time of cataract surgery rose from 3.2% to 47.9%). These results can be interpreted in terms of a change in age composition of the Italian population, improved access to health services for the elderly, and an improvement in surgical and rehabilitation techniques.

Adult↗
PubMed1976

Visual acuity and retinal changes in South Australian Aborigines.

Eye examinations were carried out a four Aboriginal reserves. Of 361 Aboriginal adults tested, 64 had a visual defect (visual acuity of 6/9 or worse) in each eye, a prevalence of 18%, with an additional 79 (22%) with a similar loss of acuity in one eye only; these were more frequently seen at the urbanized reserve of Koonibba. Only one full blood Aboriginal child within the less urbanized communities had a reduced visual acuity, whereas seven (10%) part blood children at a more urbanized reserve had reduced vision in both eyes, with a further nine (13%) in one eye only, not unlike figures quoted for South Australian school children. Vascular changes in the fundus oculi were observed and occurred more often when hypertension and/or hyperglycaemia were present. They consisted of arteriovenous crossing changes (26%), swelling of the retinal veins (3%) and altered light reflex (41%) and were not infrequently seen in the younger adult (20% of adults under 30 years had AV crossing changes and 46% had widened light streak). Analysis suggests that, although hypertension and hyperglycaemia are related to retinal vascular changes, other factors, as yet unidentified, are present in the Aboriginal population under consideration.

Adult↗
PubMed1983

The maturation of visual acuity in neurologically normal and abnormal newborn infants.

The maturation of visual acuity was studied in 162 neurologically normal and 96 neurologically abnormal newborn infants. Ninety-five percent of the neurologically normal infants developed an acuity of 80 min arc by 35 weeks postmenstrual age (PMA) but only 50% developed an acuity of 40 min arc by 40 weeks PMA. Neurologically abnormal infants, and in particular those with periventricular haemorrhage (PVH), had a delay in the development of acuity. There was a close correlation between the development of 80 min arc acuity and the appearance of the first positivity of the flash visually evoked potential (VEP).

Cerebral Hemorrhage↗
PubMed2004

Duration of long-chain polyunsaturated fatty acids availability in the diet and visual acuity.

BACKGROUND: Little is known about the critical period during which the dietary supply of long-chain polyunsaturated fatty acids (LCPUFAs) may influence the maturation of visual cortical function in term infants. AIM: To define the relationship between duration of dietary LCPUFA supply and visual acuity at 52 weeks of age. STUDY DESIGN: Data from 243 infants who participated in four randomized clinical trials of LCPUFA supplementation of infant formula at a single research center were combined. The primary outcome was visual acuity at 52 weeks of age as measured by swept visual evoked potentials (sweep VEP). RESULTS: Longer duration of LCPUFA supply was associated with better mean acuity at 52 weeks of age (r=-0.878; p<0.001). The relationship between duration of dietary LCPUFA supply and sweep VEP acuity at 52 weeks was similar whether the LCPUFAs were provided via formula containing 0.36% DHA and 0.72% ARA or human milk. Duration of breast-feeding was associated with individual infants' sweep VEP acuity outcomes at 52 weeks (r=-0.286; p<0.005). The duration of LCPUFA supply during infancy has a similar relationship to sweep VEP acuity at 52 weeks in breastfed infants regardless of birth order. CONCLUSION: A continued benefit from a supply of LCPUFAs is apparent in infants through 52 weeks of age, suggesting that the brain may not have sufficient stores of LCPUFAs from an early postnatal supply to support the optimal maturation of the visual cortex.

Evoked Potentials, Visual↗
PubMed1987

Visual acuity of human infants at scotopic, mesopic and photopic luminances.

Visual acuity of 2-month-old infants and adults was measured between -2.6 and +2.7 log10 cd/m2 using standard psychophysical techniques. The acuity-vs-luminance curve was similar for infants and adults: acuity improved with increasing luminance until 0.0 log cd/m2, and was constant above that luminance. However, the infant curve was slightly shallower than the adult curve, and infant acuity was over 3.5 octaves poorer than adult acuity at all luminances. The infant acuity-vs-luminance curve was compared with adult curves measured 21 degrees and 51 degrees from fixation, and at 21 degrees with +8, +/- 3.25 and 0.0 D of experimental refractive error. The results indicated that infants' poor acuity cannot be fully explained by: refractive error, foveal immaturity, scotopic detection of stimuli, functional similarity between infant vision and adult vision in the periphery, or by an overall reduction in visual sensitivity.

Adult↗
PubMed1995

A pupillometric correlate of scotopic visual acuity.

While not easily fit into the classic descriptions of the pupillary light reflex, previous studies reported that changes in the spatial composition of the retinal image can evoke a pupillary response. The present study extends this observation by showing that the pupil constricts in response to scotopic as well as photopic spatial patterns. Moreover, the amplitude of the scotopic response decreases with increasing spatial frequencies suggesting a pupillary spatial acuity of about 3 c/deg. The scotopic pupil acuity is similar to the scotopic perceptual visual acuity measured in the same observers.

Adult↗