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At least 1,171 records · Page 65Linked to original sources
PubMed1966

The effect of orientation on the visual resolution of gratings.

1. Visual resolving power is known to be poorer for objects oriented obliquely as compared with horizontal and vertical orientations. Experiments were designed to evaluate the optical and neurophysiological factors involved.2. Gratings with a sinusoidal light distribution were generated on the face of an oscilloscope. Spatial frequency and contrast could be varied while keeping the mean luminance of the grating constant.3. Using a homatropinized eye with an artificial pupil and carefully corrected refraction, high resolution in the vertical and horizontal meridians as compared with the oblique meridians was found for gratings ranging in spatial frequency from 1 to 35 c/deg.4. It is concluded from the similar behaviour of low and high frequency gratings that neither focus errors nor optical aniseikonia can account for these findings.5. Additional proof that optical factors cannot significantly account for these preferred directions of resolution was obtained by forming interference fringes directly on the retina using a neon-helium laser as a coherent light source.6. Similar orientational changes in resolution were found by by-passing the dioptrics with interference fringes. It is concluded that the effect is due to some orientational inequality in the visual nervous system.

Accommodation, Ocular↗
PubMedDate not supplied

Calculation of ocular single-pass modulation transfer function and retinal image simulation from measurements of the polarized double-pass ocular point spread function.

The single-pass modulation transfer function (MTF(sgl)) is an important numerical parameter that can help elucidate the performance and some processes of the human visual system. In previous studies, the MTF(sgl) was calculated from double-pass point spread function (PSF) measurements. These measurements include a depolarized reflection component from the retina that introduces a measurement artifact, and they require long acquisition times to allow averaging to reduce speckle. To solve these problems, we developed a new ocular PSF analysis system (PSFAS) that uses polarization optics to eliminate the depolarized retinal reflection component, and a rotating prism to increase measurement speed. Validation experiments on one patient showed that the MTF(sgl) measured by PSFAS agrees closely with the MTF calculated from contrast sensitivity measurements. A simulated retinal image was calculated by convolution of Landolt rings with the calculated single-pass PSF provided by the PSFAS. The contrast characteristic then was calculated from the simulated retinal images. These results indicate that the MTF(sgl) obtained using the PSFAS may be a reliable measure of visual performance of the optics of the eye, including the optical effects of the retina. The simulated retinal images and contrast characteristics are useful for evaluating visual performance.

Adult↗
PubMed2005

Developmental outcome of the use of etamsylate for prevention of periventricular haemorrhage in a randomised controlled trial.

OBJECTIVE: To compare neurodevelopmental outcome of survivors of the multicentre trial of etamsylate (the iRNN for ethamsylate) for prevention of periventricular haemorrhage in very low birthweight infants. DESIGN: Double blind, single observer, prospective follow up of placebo controlled study. SETTING: Six neonatal intensive care units in the United Kingdom. Neurodevelopmental outcome was assessed in health premises or children's homes. SUBJECTS: 268 of 276 survivors of the original study were seen between 3.5 and 4.2 years of age. All were inborn and weighed 1500 g or less at birth. INTERVENTION: Etamsylate 12.5 mg/kg or placebo six hourly from within one hour of delivery for four days. MAIN OUTCOME MEASURES: McCarthy scales of children's abilities, standardised neurological examination, full physical examination, functional assessment, seven letter Stycar vision test, and audiometry. RESULTS: There was no difference between the groups in neuromotor outcome (cerebral palsy) or in the general cognitive index (GCI) of the McCarthy scales (mean GCI was 93.3 for the etamsylate group (n = 133) and 89.7 for the placebo group (n = 131); p = 0.10). There were more children with GCI < 70 (9 v 19; p = 0.047) or </= 50 (3 v 11; p = 0.03) in the placebo group. Fewer children in the etamsylate group had squints (17 v 30; p = 0.042) or required surgery for patent ductus arteriosus (1 v 8; p = 0.036). CONCLUSIONS: Etamsylate was not associated with a reduction in cerebral palsy. Severe cognitive impairment was reduced, but more children died and the improvement may be because fewer survived with low GCI.

Cerebral Hemorrhage↗
PubMed1996

Retinal toxicity in long term hydroxychloroquine treatment.

OBJECTIVE: To report clinical experience from patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) who were receiving recommended doses of hydroxychloroquine for more than six years, and were monitored for evidence of hydroxychloroquine related retinopathy every six months. METHODS: A prospective (and continuing) evaluation was made of the potential retinal toxicity of hydroxychloroquine in a cohort of 360 Greek patients followed for RA and SLE, 58 of whom have received long term treatment ( > six years). Fundoscopy, colour vision tests, dark adaptation tests, visual field testing, automated perimetry, and electroretinogram were performed every six months. RESULTS: Among 58 patients receiving hydroxychloroquine for more than six years, two relatively young women (3.5%), one treated for RA and the other treated for SLE, developed characteristic hydroxychloroquine related toxic retinal lesions after cumulative doses of 700 g (6.5 years) and 730 g (8 years) of hydroxychloroquine, respectively. Bilateral visual acuity was 6/6 and 6/7.5, respectively; both patients had normal colour perception. Despite an early diagnosis and cessation of treatment, permanent visual field paracentral scotomata in both patients, and persisting lesions in fluorescein angiography in the patient with SLE, were observed at 4.5 and 3 years of follow up, respectively. No other specific cases of hydroxychloroquine related retinopathy have to date been identified in the remaining 302 patients. CONCLUSION: Cases of irreversible, hydroxychloroquine related retinopathy in patients who did not receive overdoses have not been reported previously. The present observations in two relatively young patients should raise our concern regarding the long term usage of an increasingly popular medication in rheumatology practice.

Adult↗
PubMed2006

In the absence of strabismus what constitutes a visual deficit in children?

AIM: To examine the range of monocular crowded logMAR acuity and cycloplegic refraction of children aged 3 years and 4 years without strabismus. METHODS: Data were collected prospectively. All children had full orthoptic and ophthalmic examination. Inclusion principally required the absence of strabismus, symptoms, and ocular pathology. Criteria were used to categorise the refraction findings as normal, borderline, or abnormal. RESULTS: 118 children aged 3 years (mean 3 years 6 months (SD 2 months) and 67 children aged 4 years (mean 4 years 4 months (SD 3 months) fulfilled the inclusion criteria. For the children with normal refraction, the mean monocular logMAR acuity was 0.200 (SD 0.09) for 3 year olds (n = 84) and 0.140 (SD 0.08) for 4 year olds (n = 45); the mean interocular acuity difference (IAD) was 0.03 (SD 0.06) for 3 year olds and 0.03 (SD 0.04) for 4 year olds. The 95% confidence limits were calculated for monocular acuity and IAD and compared to the acuity scores of the children with borderline (n = 17) and abnormal refractive error (n = 38). 15 borderline and 16 abnormal cases had a visual acuity within these limits. CONCLUSION: A wide range of refraction may be associated with a good level of visual acuity in children aged 3 years and 4 years.

Child, Preschool↗
PubMed2006

Contrast sensitivity and visual hallucinations in patients referred to a low vision rehabilitation clinic.

AIM: To examine the association of reported visual hallucinations and measured visual parameters in adult patients referred for low vision rehabilitation. METHODS: All patients (N = 225) referred to a low vision rehabilitation clinic for a calendar year were asked a standardised question about symptoms of formed visual hallucinations. Best corrected visual acuity and contrast sensitivity using the Pelli-Robson chart were measured. We conducted multiple logistic regression analysis of the association between visual hallucinations and visual parameters. RESULTS: Of the total cohort, 78 (35%) reported visual hallucinations. Visual acuity and contrast sensitivity were considered in four quartiles. In multiple logistic regression controlling for contrast sensitivity, age, gender, report of depression and independence, measured acuity in each of the poorer three categories (compared to the best) was not associated with reported hallucinations. Contrast sensitivity in the three poorer quartiles (compared to the best) was strongly associated with the report of hallucinations (OR 4.1, CI 1.1, 15.9; OR 10.5, CI 2.6, 42.1; OR 28.1, CI 5.6, 140.9) after controlling for acuity, age, sex, depression and independence. CONCLUSIONS: Lowest contrast sensitivity was the strongest predictor of reported hallucinations after adjusting for visual acuity.

Aged↗
PubMed1977

A note on stray light in the Tübingen perimeter.

Measurements were made of the relative intensity of light scattered in the neighbourhood of the large and small targets on the Tübingen perimeter. Two target intensities were studied. The scattered light fraction ranged from 0-1 to 25% and its effect was detected more readily by young than by older observers.

Adult↗
PubMed1984

Acquired colour defects under restricted viewing time: a new diagnostic technique?

The effect of reduced viewing time on classification of colour vision by means of the City University Colour Vision Test is investigated in sufferers from diabetes and optic neuritis. The results suggest that patients with these conditions give non-normal responses when viewing time is reduced to 3.75 m. It may be possible to use the response obtained to diagnose the presence of ocular disease.

Adult↗
PubMed1991

Quality of vision through diffractive bifocal intraocular lenses.

Two elderly women have each received a monofocal intraocular lens in one eye and a 3M diffractive bifocal intraocular lens in the other eye. Both eyes were shown to have equivalent retinal/neural function by measuring contrast sensitivity to laser interference fringes which bypassed refractive and other defects of the ocular media. The eyes with a bifocal intraocular lens displayed a much greater depth of focus, though at the expense of diminished contrast sensitivity compared with the normal values expected for that age. Simulation experiments suggested that the observed reduction in contrast sensitivity was not adequately explained by a simple reduction in retinal illumination of the in-focus image as might intuitively be expected from the bifocal separation of incident light to two simultaneous focal points. The simultaneous superimposition of the out-of-focus image on the in-focus image must also be considered, since this caused a significant reduction in contrast sensitivity when the retinal illumination was insufficiently above the photopic luminance threshold.

Aged↗
PubMed1997

Usher syndrome in the city of Birmingham--prevalence and clinical classification.

AIMS: To estimate the prevalence of Usher syndrome in the city of Birmingham, and to establish a database of patients who have been classified into different clinical subtypes essential for future gene mutation analysis. METHODS: Symptomatic cases of Usher syndrome (US) resident in the city of Birmingham in June 1994 were ascertained through multiple sources. Ophthalmic and audiological reassessment together with examination of medical records and patient questionnaires allowed classification of three subtypes, US 1, US 2, and US 3. In addition, family pedigrees were examined and blood was taken from index patients for DNA extraction. RESULTS: In the population aged over 15 years the prevalence was 6.2 per 100 000 population for all US subtypes. The prevalence for US 1 and US 2 was 5.3 per 100 000 population. This is greater than previously reported. In the age group 30-49 years the prevalence approached 1 in 10 000. Clinical classification found 33% US 1, 47% US 2, and 20% US 3. CONCLUSION: This higher prevalence rate and greater frequency of US 2 and US 3 may reflect a more complete ascertainment.

Adolescent↗
PubMed1992

X linked progressive cone dystrophy with specific attention to carrier detection.

We investigated 111 members of a five generation family with X linked cone dystrophy. The patients showed the characteristic picture of cone dystrophy. Routine ophthalmological examination of the carrier women showed no abnormalities. However, with detailed colour vision testing we were able to detect 87% of all obligate carriers.

Adolescent↗
PubMed1968

Visual acuity.

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Accommodation, Ocular↗
PubMed1969

Color vision.

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Animals↗
PubMed2004

Circadian modulation of temporal properties of the rod pathway in larval Xenopus.

Circadian clocks are integral components of visual systems. They help adjust an animal's vision to diurnal changes in ambient illumination. To understand how circadian clocks may adapt visual sensitivity, we investigated the spatial and temporal properties of optomotor responses of young Xenopus laevis tadpoles (Nieuwkoop and Faber, developmental stage 48) using a modified 2-alternative preferential-viewing method. We maintained animals in constant darkness and measured temporal sensitivity during their subjective day and night. We found that their behavioral responses can be explained in terms of 2 mechanisms with different temporal properties. The more sensitive mechanism operates at low temporal frequencies and intermediate wavelengths (lambdamax = 520 nm), properties consistent with rod signals. Threshold for this mechanism is approximately 0.04 photoisomerizations rod(-1) s(-1), consistent with single-photon detection. A less-sensitive mechanism responds to higher temporal frequencies (cutoff = 12 Hz) and has broad spectral sensitivity (370-720 nm), consistent with multiple classes of cone signals. This cone mechanism does not change, but the cutoff frequency of the more sensitive rod mechanism shifts from 0.35 Hz at night to 1.1 Hz during the subjective day, thereby enhancing the animal's sensitivity to dim rapidly changing stimuli. This day-night shift in rod temporal cutoff frequency cycles in complete darkness, characteristic of an endogenous circadian rhythm. The temporal properties of the behaviorally measured rod mechanism correspond closely with those of the electrophysiologically measured retinal response, indicating that the rod signals are modulated at the level of the outer retina.

Animals↗