Effect of breathing 100 per cent oxygen upon visual field and visual acuity.
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Humans↗
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Results for “Visual Acuity”
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Operant measurement of subjective visual acuity in non-verbal children.
The present experiment sought to develop a reliable procedure for measuring visual acuity in non-verbal retarded children. Five non-verbal retarded children and two literate adults were examined. The two adults were included in the experiment so that verbal communication with them could validate certain assumptions regarding the experimental procedures. By utilizing a lever press as the criterion response signifying a visual discrimination and employing the Snellen "E" discriminanda, a reliable subjective measure was obtained, not unlike those measures taken from verbal adults. Contrary to several antecedent procedures, a relatively precise measurement of subjective acuity was shown to be obtainable from non-verbal retarded children. Additionally, the procedure was successful in evaluating the effectiveness of prosthetic lenses previously prescribed for two of the children.
Journal Article↗
Dynamic visual acuity during transient and sinusoidal yaw rotation in normal and unilaterally vestibulopathic humans.
The vestibulo-ocular reflex (VOR) stabilizes gaze to permit clear vision during head movements. It has been supposed that VOR function might be inferred from dynamic visual acuity (DVA), the acuity during imposed head motion. We sought to determine effectiveness of DVA for detection and lateralization of unilateral vestibulopathy, using rigorous psychophysical methods. Seventeen normal and 11 unilaterally vestibulopathic subjects underwent measurement of optically best corrected DVA during head motion. A variable size letter "E" 6 m distant was displayed in oblique random orientations to determine binocular DVA by a computer controlled, forced choice method. Three types of whole-body yaw rotation were delivered by a servo-controlled chair synchronized with optotype presentation. Two types of motion were predictable: (1) steady-state 2.0-Hz rotation at 10-130 degrees/s peak velocity with repetitive optotype presentation only during head velocity exceeding 80% of peak; and (2) directionally predictable transients at peak accelerations of 1000, 1600 and 2800 degrees/s2 with optotype presentation for 300 ms. For neither of these predictable motions did DVA in vestibulopathic subjects significantly differ from normal, with suggestions from search coil recordings that this was due to predictive slow and saccadic eye movements. Unilaterally vestibulopathic subjects experienced a significant decrease in DVA from the static condition during ipsilesional rotation for all three peak head accelerations. Only during directionally unpredictable transients with 75 ms or 300 ms optotype presentation was the sensitivity of DVA in unilaterally vestibulopathic subjects significantly abnormal during ipsilesional rotation. The ipsilesional decrease in DVA with head motion was greater for 75 ms than 300 ms optotype presentation. Search coil recordings confirmed hypometric compensatory eye movements during DVA testing with unpredictable, ipsilesional rotation. Receiver-operator characteristic analysis indicated ideal detection and lateralization of unilateral vestibulopathy by DVA tested with a 75-ms optotype exposure for unpredictable transient rotations to a peak acceleration of 2800 degrees/s. DVA can reliably detect unilateral deafferentation only if precautions are taken to prevent compensation by predictive slow eye movements and saccades.
Adaptation, Physiological↗
Visual acuity, spectacle blur and slit-lamp biomicroscopy on asymptomatic contact-lens-wearing recruits.
Refraction data of 644 Dutch Army and Air Force recruits wearing contact lenses or spectacles were statistically compiled and correlated with the type of lenses worn. Visual acuity with contact lenses was far from optimal because the power of the lenses was incorrect or the optical quality poor. This applied particularly to soft contact lenses. On the other hand, spectacle blur was rare with soft lenses and less evident with gas-permeable hard lenses compared with conventional hard lenses. Less corneal staining occurred with gas-permeable hard lenses compared with conventional hard lenses (P=0.02). Corneal neovascularization, conjunctival hyperaemia, papillary changes in the tarsal conjunctiva, corneal opacifications and ghost vessels were seen more often in wearers of soft rather than hard lenses. In this study, in which we examined objective parameters of contact lens efficiency, the gas-permeable hard lenses appeared most favourable.
Conjunctival Diseases↗
Visual acuities in infants with congenital cataracts operated on prior to 6 months of age.
Seven infants with complete bilateral cataracts were operated on and fitted with extended-wear silicone contact lenses. The infants were matched to 16 normal control subjects. A modified preferential looking technique was used to assess visual acuity; the Bayley Scale of infant Development was administered to measure psychological development. Of the seven infants with cataracts, those operated on prior to 8 weeks of age seemed to have normally developing vision. All others showed a substantial visual lag when compared with the control group. Bayley scores for infants operated on early (before 8 weeks) fell within the range of normal variability. The infants operated on later demonstrated a statistically significant lag in development. Also, a pendular nystagmus was noted in those infants with cataracts who were operated on later.
Age Factors↗
Combined gaze-angle and vergence variation in infantile nystagmus: two therapies that improve the high-visual-acuity field and methods to measure it.
PURPOSE: To investigate the convergence-induced waveform and high-acuity-field improvements resulting from different therapies in two subjects with infantile nystagmus (IN) that was damped by convergence and to report a new finding in one of the subjects. METHODS: Infrared reflection was used to measure eye movements during fixation of targets at different gaze and convergence angles and the expanded nystagmus acuity function (NAFX) to evaluate the IN waveform's foveation quality at all fixation points. RESULTS: Recordings demonstrated that, at far, both subjects exhibited classic nulls (high NAFX values) with NAFX reduction at gaze angles lateral to the null. S1 was treated with prisms and S2 with surgery. When converged at near or at far with base-out prisms (S1) or after bimedial recession and bilateral tenotomy surgery (S2), NAFX was higher at both the null and lateral gaze angles; the null region was broadened. The longest foveation domain (gaze angles where the NAFX is within 10% of its peak) at near was three times wider than at far for S1 and two times wider after than before surgery for S2. The therapeutic improvement domain (gaze angles where the posttherapy NAFX is higher than pretherapy) was even broader. At fixed gaze angles in the central 20 degrees of gaze, S1's NAFX variation with vergence exhibited hysteresis, higher during divergence than convergence; S2 exhibited no hysteresis after surgery. CONCLUSIONS: Damping IN by means of convergence, induced either surgically or with prisms, broadened the range of gaze angles with higher foveation quality, mimicking the null-broadening effects of tenotomy. The discovery of vergence hysteresis may reflect pulley movement and might allow higher acuity, if a near point is transiently fixated just before a far target. The acuity domains provide new and more comprehensive evaluations of both pre- and posttherapy visual function than do primary-position acuity measurements, suggesting that high-visual-acuity fields should be included in clinical measures of visual function in nystagmus.
Adolescent↗
Gaze-dependent and time-restricted visual acuity measures in patients with Infantile Nystagmus Syndrome (INS).
PURPOSE: We report a new method of measuring visual function in patients with INS by demonstrating the effects of eccentric gaze and forced time restriction on optotype recognition. DESIGN: Cross-sectional, comparative case-series. METHODS: No-time-restricted acuity (NTRA) and time-restricted acuity (TRA) for 19 patients and 18 controls were measured at multiple horizontal gaze angles. RESULTS: INS patients showed a significant lower visual acuity than controls (P < 0.0001). The TRA were significantly decreased in most gaze positions relative to NTRA in INS patients (P = 0.03) while there were no difference among controls. About half of the INS patients showed that their best visual acuity was gaze dependent, matching the preferred head posture in both NRTA and TRA paradigms. CONCLUSIONS: Gaze-dependent visual acuity tested with and without time restriction may be a useful measure of visual function in INS patients and could be used in interventional clinical trials.
Adult↗
Visual acuity and contrast sensitivity in patients with neovascular age-related macular degeneration. Results from the Radiation Therapy for Age-Related Macular Degeneration (RAD-) Study.
BACKGROUND: Patients with advanced age-related macular degeneration (AMD) suffer not only from impairment in central visual acuity (VA), but also from reduction in contrast sensitivity (CS). We examined VA and CS changes over time in patients with subfoveal choroidal neovascularizations (CNV) as well as the correlation between the two parameters. METHODS: VA was determined according to a standardized protocol with the Early Treatment Diabetic Retinopathy (ETDRS) chart. CS was measured with Pelli-Robson charts. The angiographic characteristics of CNV and the presence of CNV in the fellow eye as well as gender and age were evaluated as possible prognostic factors of VA and CS progression. Two hundred and five patients with neovascular AMD were recruited within the Radiation Therapy for Age-Related Macular Degeneration (RAD) Study and were reviewed over 2 years. The treatment and control groups showed no significant difference for VA or for CS ( P>0.05), and both groups were considered together. RESULTS: At baseline, mean VA was 55.6+/-14.5 SD letters (EDTRS chart), and mean CS was 22.8+/-6.9 letters (Pelli-Robson chart). Spearman Correlation Coefficient ( r(s)) between VA and CS was r(s)=0.60, P=0.0001. Over 2 years the mean VA loss was 23.6+/-21.4 letters and mean CS reduction was 9.0+/-9.7 letters. Agreement between change of VA and change of CS was moderate ( r(s)=0.65, P=0.0001; kappa coefficient (grouped into VA loss < or =15, >15, >30 letters; CS loss < or =6, >6, >15 letters) kappa=0.43, 95% CI [0.32;0.54]). Proportional hazard models did not show any apparent influence of type of CNV, or CNV in the fellow eye, on change in VA and CS. CONCLUSION: The results indicate that VA and CS do not always show the same progression in visual function loss although they show a moderate correlation in eyes with neovascular AMD. Both parameters provide important information about visual disability and should be evaluated as outcome in interventional studies.
Aged↗
Topography and raytracing analysis of patients with excellent visual acuity 3 months after excimer laser photorefractive keratectomy for myopia.
We performed topography and raytracing analysis 3 months after surgery on five consecutive eyes of five patients, which had excimer laser photorefractive keratectomy for myopia. Three of the five eyes had uncorrected postoperative visual acuity of 20/20 or better. Two eyes had an uncorrected vision of 20/40. In three of five eyes, the area of excimer ablation was centered within 1.0 mm of the optical axis. Three other eyes showed decentration that ranged from 1.1 to 1.5 mm. The range of surface power seen within 2 mm of the central keratoscope ring was as follows: patient CK = 37.50 to 39.50 diopters; patient CA = 40.50 D to 44.80 D; patient CW = 37.90 D to 42.20 D; patient AC = 35.50 D to 39.00 D; patient DT = 34.50 D to 41.40 D. Topography patterns differed from eye to eye. A raytracing program modeled refraction of 20/80 and 20/20 "E" of 100%, 50%, 25%, 12.5% and 6.25% contrast through all measured points on the central 10 keratoscope rings of the five postoperative corneas. The five computer-derived images were ranked subjectively according to the observed degree of image degradation by three observers. Two eyes showed discernible 20/20 E's even at the 12.5% contrast level. Little to no ghost image was seen. Two eyes showed degraded but discernible 20/20 letters at higher levels of contrast only. These eyes showed moderate ghost images that were most apparent in the high-contrast 20/80 letters. One eye showed poor resolution of the 100% contrast 20/20 letter and moderately severe ghost images.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
A behavioral method for efficient screening of visual acuity in young infants. I. Preliminary laboratory development.
A technique for rapid behavioral screening of grating acuity in infants 1 to 4 months of age is described. The approach, called forced-choice preferential looking (FPL), depends upon the fact that normal infants will stare fixedly at acuity gratings with stripe widths above a rather abrupt cutoff width. The present task is to find the minimum stripe width, termed the diagnostic stripe width, to which infants with normal visual acuity will readily respond. The expectation is that infants with below-normal acuity will not be able to respond to diagnostic stripes so defined. To assess the feasibility of such a test procedure and define preliminary diagnostic stripe widths for infants 4, 8, 12, and 16 weeks of age, 76 presumptively normal infants were tested in the laboratory with a 40-trial FPL procedure. Sixty-nine infants (91%) completed the test procedure. For each age group, a preliminary estimate of the diagnostic stripe width was found. The group performance was uniformly high for the stripe widths designated as diagnostic and fell off sharply for finer stripes, confirming the feasibility of the approach.
Age Factors↗
[Refractive surgery--possibilities to maximize postoperative visual acuity].
Laser refractive surgery has an ascendant evolution on the context of the progress in the medical field. The functional result can be negatively influenced by residual errors, irregular astigmatism or anisometropia, situations in which rigid gas permeable (RGP) contact lenses are a successful alternative in optimizing visual acuity. The paper presents the particularities and the protocol of RGP fitting, outlining the contribution of the corneal topography in the ocular pre and post-operative evaluation.
Anisometropia↗
Visual acuity in an Australian aboriginal population.
BACKGROUND: Australia is a developed country. However, Aboriginal Australians have rates of blindness comparable to Third World countries. There have been well-funded eye health programs for 15 years in Central Australia. This paper examines if there has been an improvement in visual disability of one traditional group of Aboriginal Australians. METHODS: Results from an eye health survey of the Anangu Pitjantjatjara of South Australia in 1990 are presented. These data are compared with results for 'blindness' and 'poor vision' from a national survey undertaken in 1976. The two surveys were comparable in design, both were cross-sectional population-based prevalence surveys. Prevalence rates were adjusted for the size of the source population. RESULTS: Young rural Aboriginal Australians have good visual acuity. Low vision and blindness (WHO definitions) occur in 19.6% and 10.4% of 60+ year olds, respectively. Women were more likely than men to be blind or have low vision (OR = 1.93; 1.06-3.58). There was a decline in 'poor vision' between surveys (OR = 2.86; 1.86-4.75) but not in 'blindness'. CONCLUSION: Although there has been a reduction in the prevalence of visual disability in rural Aboriginal Australians, improvements in the provision of eye care for the elderly need to occur.
Adolescent↗
Distance visual acuity with diffractive multifocal and monofocal intraocular lenses.
A series comprising 166 eyes implanted with monofocal intraocular lenses and 143 eyes with diffractive multifocal lenses was examined. The implantations were performed intermittently and consecutively during 18 months by one surgeon using the same technique. The mean postoperative visual acuity was 0.5 line higher in the monofocal than in the multifocal group, a significant difference (P < .01). The better performance of the monofocal lens was almost constant in all six age groups (range: < or = 65 years to > or = 86 years).
Aged↗
Short-term, low-contrast visual acuity reduction associated with in vivo contact lens drying.
Hydrogel contact lens surfaces partially desiccate during extended interblink intervals, producing a microscopically rough and irregular surface that scatters light. Such light scattering could reduce retinal image contrast, elevating thresholds for target perception. To test this idea, we measured low (7%)-contrast visual acuity of subjects who wore: (1) hydrogel contact lenses, (2) rigid gas permeable (RGP) lenses, and (3) no contact lenses when the subjects blinked normally and when they suppressed blinking. Acuity thresholds were determined using computer-generated acuity stimuli and a staircase psychophysical procedure. Cessation of blinking resulted in small reductions in low-contrast acuity for subjects wearing RGP lenses (mean loss: 0.1 line) or no lenses (mean loss: 0.3 lines). Subjects wearing hydrogel lenses, however, generally exhibited substantial reduction of acuity (mean loss: 4.1 lines) when blinking was suppressed.
Adult↗
Improvement of visual acuity and corneal physiology in keratoconus by fitting aspherical, high oxygen-permeable contact lenses.
Keratoconus is a condition in which the cornea assumes a complex irregular curvature caused by central corneal thinning. The abnormal topography of the cornea in combination with central corneal scarring results in an impaired visual acuity. Even in mild cases spectacles do not correct vision adequately. The use of hard contact lenses with a spherical geometry in the past has already given a marked therapeutic improvement. The use of these lenses however, is complicated by hypoxia and mechanical trauma of the cornea. These complications could theoretically be avoided by fitting elliptical lenses with a high oxygen transmission. To investigate this hypothesis we compared low oxygen-permeable spherical lenses with high oxygen-permeable elliptical contact lenses in a group of twenty patients with mild keratoconus. Our results showed both a marked subjective and objective visual improvement after fitting elliptical lenses with a low incidence of complications.
Adult↗
Lid surgery to reduce discomfort produces an unexpected improvement in visual acuity--a case presentation.
A significant cause of blindness in leprosy is corneal scarring secondary to corneal anaesthesia and lagophthalmos (Brand & ffytche 1985). Such patients may continue to experience considerable ocular discomfort, particularly when there is associated ectropion of the lower lid, with inflammation of the exposed tarsal conjunctiva (Courtright & Johnson 1991). Where visual outcome is no longer the primary consideration, one may hesitate to subject patients to surgery, particularly in relatively unsophisticated field conditions, attempting instead to relieve the patient's discomfort by conservative treatment such as frequent topical ocular lubricants, use of protective spectacles or eye shades etc. A case is presented here in which minor surgery aimed solely at relieving ocular discomfort resulted in an unexpected improvement in visual acuity. This suggests that there are instances where a more aggressive approach to treatment of even severely damaged eyes could prove more rewarding than anticipated.
Eyelid Diseases↗
Relationships between mortality, visual acuity and microfilarial load in the area of the Onchocerciasis Control Programme.
The relationships between onchocercal infection, visual acuity and mortality have been examined using epidemiological data gathered by the Onchocerciasis Control Programme from 66 villages in West Africa. All of these villages were surveyed at least twice. 18,778 persons were registered at the first surveys which were conducted around the time when control activities started. The second surveys were conducted two to five years later. 14,961 persons (79.7%) were alive and registered again, 786 (4.2%) had died, 2776 (14.8%) had moved and 255 (1.4%) could not be traced. The prevalence of blindness and of visual damage other than blindness both increased markedly with age, and the degree of visual damage was strongly associated with level of microfilarial infection. Among adults, the prevalence of blindness was higher for males than for females at all ages. The prevalence and intensity of microfilarial infection were also higher among males but this was not sufficient to explain their excess blindness. Logistic regression analysis showed that males were 1.5 times more likely to be blind than females of the same age and same level of microfilarial infection. The presence of visual damage at the first survey considerably increased the risk of mortality between the first and second surveys for both males and females. Mortality rates were three to four times higher among the blind and about 1.5 times higher among those with visual damage other than blindness compared with those with no visual damage. There was some evidence, for males but not for females, that mortality was also directly related to microfilarial load.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Visual acuity after iridectomy or aspiration for congenital cataract: Experimental and clinical studies.
Studies with a camera and a model eye showed that the image produced by peripheral light rays is inferior to the image produced by paraxial rays. In a retrospective clinical study, we determined the best corrected visual acuity in 33 patients (52 eyes) who had had iridectomy (group I) or aspiration (group II) or both for central cataracts. Vision was significantly better (p less than 0.01) in group II than in group I, and postoperative complications of aspiration were minimal. Some patients had unilateral amblyopia or pendular nystagmus. We conclude that if vision is to be improved with a single procedure, aspiration - not optical iridectomy - is indicated. We could not identify any factors in early infancy that would have predicted which patients with congenital central cataracts required early surgery.
Cataract↗