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White light interferometry was performed on 21 eyes of 19 patients presenting for posterior capsulotomy following uncomplicated extracapsular cataract surgery. The white light interferometer was able to predict post-operative visual acuity to within one Snellen line in 56 per cent of eyes and to within two Snellen lines in 76 per cent of eyes.
Postsurgical or spontaneous iris cyst is a rare finding. Unfortunately, all treatments are complicated and the results may be disappointing. We report a case of postsurgical iris cyst treated by sector iridectomy with satisfactory recovery of visual acuity.
The visual resolution acuity of hooded rats was measured with an avoidance technique, using large, high contrast square-wave gratings of high mean luminance. Measurements were taken before and after ablation of either posterior cortex or the superior colliculus. The cortical lesions included both striate and temporal cortex, and caused retrograde degeneration throughout the dorsal lateral geniculate nucleus. Neither group showed signs of detecting even coarse square-wave gratings when first tested after operation. The animals with collicular lesions quickly relearnt, and their acuity was unaltered. After extensive training 3 out of 4 cortical animals relearnt to detect gratings, and their acuity was reduced to about one-third of its preoperative value. It seems likely that in rats the geniculocortical pathway carries sufficient information for the normal detection of high spatial frequencies. Whether a pathway from superior colliculus to neocortex via a thalamic relay also carries this information is uncertain.
OBJECTIVE: To determine the influence of frequency and direction of head movement and type of vision chart on the score of a clinical test of dynamic visual acuity (DVA). METHODS: The subjects were 31 healthy individuals (22 to 79 years old) and 10 patients (19 to 70 years old) with a unilateral vestibular deficit owing to surgical resection of an acoustic neuroma. They read a Snellen or an E-chart while their head was passively moved +/- 20 degrees back and forth in the horizontal or vertical direction at one of four frequencies (0.5, 1.0, 1.5, and 2.0 Hz). The DVA score was the difference in the number of lines on the vision chart that could be read with the head passively moved versus with the head immobile. RESULTS: Four healthy subjects had a low DVA score during horizontal head movements at the fastest frequency (2.0 Hz) with the Snellen chart. In patients, DVA scores significantly decreased as head movement frequency increased from 0.5 to 1.0 Hz and from 1.0 to 1.5 Hz, during horizontal and vertical movements, and with both vision charts (p < .001). The DVA scores of healthy subjects were more consistent across three trials with the E-chart than with the Snellen chart at 1.0 and 0.5 Hz (horizontal movements, p < .01) and at 1.5 and 1.0 Hz (vertical movements, p < .01). CONCLUSIONS: This study provides new indications on the optimal parameters for the clinical test of DVA. From the results, it is recommended that DVA be tested during horizontal and vertical head movements at a frequency of 1.5 Hz with the E-chart.
We treated a number of 141 patients suffering of herpetic keratitis--34 were treated with Acyclovir in the first 72 hours the symptoms started, 42 were treated with Acyclovir after this interval and 65 were treated with IDU. We compared visual acuity after six month and we proved that those that were treated with Acyclovir had the same or better visual performances in most cases. Recurrence rate was 0% in the first year and 2.94% in the second year for those witch were treated with Acyclovir in the first 72 hours symptoms started and 2.94% in the first year and 14.71% in the second year for those treated with Acyclovir after this interval. Patients treated with IDU had suffered 23.53% recurrences in the first year and 41.18% recurrences in the second year. Acyclovir treatment and its precociousness protect patients sight and reduce number of recurrences.
In a masked investigation, 34 preschool children (n = 34, 19 females and 15 males) between the ages of 3 and 5 years (mean age = 4.1 years) enrolled in Project Headstart had their monocular and binocular visual acuity measured using the Broken Wheel and Allen figure methods. The results showed that 1) a greater range in acuity values was found with the Allen figure than Broken Wheel test, despite the identical Snellen equivalent acuity levels and similar probability of guessing criteria used for both Broken Wheel and Allen figure acuity measurement e.g., no strong statistical correlation (rOD = +0.22, rOS = -0.11 and rOU = +0.04; rho OD = +0.22, rho OS = -0.11, rho OU = 0.00) for the two tests was found; and 2) the Broken Wheel test appeared to discriminate between 20/30 and 20/40 acuity performance more consistently than did Allen figure and in a way not attributable to chance (p less than or equal to 0.003). In a separate evaluation, the Broken Wheel test showed consistency in the acuity measured. Broken Wheel acuity measurement, even with an average variation of +/- 5.6 percent from the corresponding Snellen standard, appears to be a valuable clinical tool to measure acuity in young children.
The hypothesis that reductions in Snellen acuities in patients with retinitis pigmentosa are due solely to losses of photoreceptors was tested by measuring the effects of random losses of sampling elements on letter identification. Sampling element losses were mimicked by setting the luminance of randomly selected pixels equal to the luminance of the surround. The amount of pixel blanking ranged from 0 to 90%. Letters varying in retinal subtense from 5 to 17 min arc were presented for 500 msec. Although letter identification accuracy decreased with increasing pixel blanking for all letter sizes, performance remained relatively high even when a majority of the pixels was blanked. The data suggest that unless the loss of cone photoreceptors in greater than 80%, loss of sampling elements alone can not account for letter acuities poorer than 20/40. In addition to loss of cone photoreceptors in patients with RP, there are histological reports of photoreceptor abnormalities and psychophysical studies of visual sensory deficits. It is conceivable that these alone, or in combination with losses of photoreceptors, could account for decreased visual acuity. In a series of experiments, stimulus parameters were manipulated in order to mimic the effects of some of these abnormalities and deficits and the effects on letter identification were examined. The results of these experiments demonstrated that sampling element loss interacts with sensory factors (e.g. luminance and contrast sensitivity) and perceptual factors (e.g. set size and letter orientation) to reduce letter identification accuracy. The implication of these results is that decreases in letter acuity observed in patients with retinitis pigmentosa cannot be attributed solely to a random loss of sampling elements in the underlying retina, but may be due to the combination of photoreceptor degeneration and other sensory and perceptual factors.
The author reports on improvement of visual acuity in cataract patients through placing a stenopacic opening before the eye. Recommendation is made as to the nature of such a visual aid.
This multicenter, parallel group study determined plasma phospholipid and red blood cell (RBC) phosphatidylcholine and phosphatidylethanolamine fatty acids, plasma cholesterol, apo A-1 and B, growth and visual acuity (using the acuity card procedure) in term infants fed from birth to 90 d of age with formula containing palm-olein, high oleic sunflower, coconut and soy oil (22.2% 16:0, 36.2% 18:1, 18% 18:2n-6, 1.9% 18:3n-3) (n = 59) or coconut and soy oil (10.3% 16:0 18:6% 18:1, 34.2% 18:2n-6, 4.7% 18:3n-3) (n = 57) or breast-fed (n = 56) with no formula supplementation. Different centers in North America were included to overcome potential bias due to differences in n-6 or n-3 fatty acids at birth or in breast-fed infants that might occur in a single-site study. Plasma and RBC phospholipid docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (AA, 20:4n-6), cholesterol and apo B were significantly lower in the formula- than breast-fed infants. There were no differences in looking acuity or growth among the breast-fed and formula-fed infants. No significant relations were found between DHA and looking acuity, or AA and growth within or among any of the infant groups. This study provides no evidence to suggest the formula provided inadequate n-6 or n-3 fatty acids for growth and looking acuity for the first 3 mon after birth.
BACKGROUND: A small, but statistically significant, improvement has previously been demonstrated when retesting visual acuity within 24 hours. Because letter chart testing procedures are familiar to most adult patients, this improvement may be due to memory of the chart letter subset, rather than increased familiarity with the test procedure. Chart letter subset memory does not appear to have previously been measured directly. METHODS: A letter recognition task was used to measure chart letter subset memory for groups of routine clinical patients. Comparisons were made between assessments after a single acuity measurement and assessments at increasing intervals after a routine examination involving several references to the same letter chart for both eyes. RESULTS: The recognition score for the 'one-minute-after a single acuity measurement group' was an average of 2.5 letters (range 0.7 to 4.7). Low levels of chart letter subset memory were found to persist for 10 days. CONCLUSION: The chart letter subset memory found is consistent with enhanced acuity scores that occur on retesting. Scores appear likely to have a greater chance of enhancement for a second eye measurement when it follows immediately after the first. Similarly, scores at the end of a full examination may be enhanced by memory that is accumulated during multiple measurements for both eyes using the same chart. Chart memory may be acquired when acuity is measured frequently in monitoring the progress of disease. Chart memory, or its loss over time, may contribute to measurement imprecision and associated expansion of the confidence limits for significant change in acuity.
Legibility of head-fixed displays in some motion environments is partially dependent upon visual suppression of the vestibuloocular reflex (VOR). This study investigates the effects of differing relationships between peripheral background movement and whole-body motion on the VOR and on visual performance. The purpose of the study is to explore factors in motion environments that influence performance limits and to develop procedures of potential usefulness in evaluating interacting visual and vestibular function. Visual performance and visual suppression of the VOR were markedly different, depending upon the relative direction of peripheral background movement. Visual suppression of the VOR, and visual performance, were disrupted far more when vestibular inputs and peripheral optokinetic inputs were discordant than when they were concordant. Results have potential implications for head-up displays and suggest a procedure for evaluating visual/vestibular function.
Night operations involve diverse mission areas and require an increased reliance on the use of night vision devices, such as night vision goggles (NVG's). Any reduction in goggle or visual performance which goes undetected can have a serious effect on flight safety and operational capability. Under controlled lighting conditions, a crewmember should be able to obtain the best possible goggle performance, and to determine if the goggle is functioning properly. These data represent a sample of 218 current USAF aircrew members representing all crew positions in both rotary and fixed-wing aircraft. Three measurements of goggle performance, expressed as NVG visual acuity, were obtained. The first measure, obtained after crewmembers adjusted the goggles with their usual adjustment methods, showed that they routinely obtain less than optimal acuity levels; i.e., averaging between 20/50 and 20/55. The second measure, taken when the NVG Resolution Chart was provided to augment their "usual" method of adjustment, showed improved performance; i.e., averaging 20/45. The third measure, taken following participation in an NVG Adjustment Procedures class, showed the greatest improvement, averaging between 20/35 and 20/40. In summary, it is reasonable to conclude that aircrew members who are able to obtain the best possible performance for their NVG's under controlled preflight conditions will obtain the best possible goggle performance under the widely varying flight conditions.
Two pigeons were trained to discriminate a grating stimulus from a blank stimulus of equivalent luminance in a three-key chamber. The stimuli and blanks were presented behind a transparent center key. The procedure was a conditional discrimination in which pecks on the left key were reinforced if the blank had been present behind the center key and pecks on the right key were reinforced if the grating had been present behind the center key. The spatial frequency of the stimuli was varied in each session from four to 29.5 lines per millimeter in accordance with a variation of the method of constant stimuli. The number of lines per millimeter that the subjects could discriminate at threshold was determined from psychometric functions. Data were collected at five values of stimulus luminance ranging from--0.07 to 3.29 log cd/m2. The distance from the stimulus to the anterior nodal point of the eye, which was determined from measurements taken from high-speed motion-picture photographs of three additional pigeons and published intraocular measurements, was 62.0 mm. This distance and the grating detection thresholds were used to calculate the visual acuity of the birds at each level of luminance. Acuity improved with increasing luminance to a peak value of 0.52, which corresponds to a visual angle of 1.92 min, at a luminance of 2.33 log cd/m2. Further increase in luminance produced a small decline in acuity.
Sixty-two patients, 48 with a diagnosis of persistent hyperplastic primary vitreous (PHPV) and 14 with monocular congenital cataract (MCC) are reported. Nineteen patients with a diagnosis of PHPV and all patients with MCC received surgery with attempted visual rehabilitation. Early age of surgery, prompt optical correction with contact lens and aggressive patching therapy are required for successful visual rehabilitation. Glaucoma, retinal or optic nerve pathology, surgery later than three months of age or combinations of these factors were associated with poor prognosis. Isolated microphthalmos was not correlated with poor prognosis. Binocular fixation pattern was used to monitor patching therapy. Optokinetic nystagmus, visual evoked potentials or forced preferential looking were not employed. Of the 33 patients who underwent surgery, 10 (30%) achieved good (greater than or equal to 20/50) visual acuity, 8 (24%) achieved fair (20/60 to 20/100) and 15 (46%) achieved poor vision. In selected patients with the diagnosis of PHPV or MCC, visual rehabilitation can be achieved.
Evaluation of multifocal IOLs suggests the possibility of two retinal images, one for near and one for distant vision. But the optic principles of multifocal IOLs created overlying images and incident light division. We performed this study to evaluate visual acuity and contrast sensitivity for two types of bifocal IOLs (3M bifocal and IOLAB bifocal IOL) and for a control group of monofocal IOL testing in different levels of luminance simulating the normal environmental conditions of the patient's experience. The results showed a visual functional loss especially at the low luminance level for the 3M bifocal group and at bright luminance for the IOLAB bifocal group, which was previously unknown with and consequences for the indications and exclusions of this kind of IOL.
In identical experimental situations we tested 22 adults with our proposed Landolt C wall-chart and the so-called TNO Landolt-C chart. Contrary to theoretical expectations, it appeared that there was only a slight difference in the measured visual acuities. Further study will show whether this is an incidental or a structural occurrence.
Discoloration of hydrogel contact lenses is frequently encountered in clinical practice and often precipitates lens replacement. This investigation sought to determine if lens discoloration was associated with a compromise in low or high contrast, high illumination visual acuity. This association would lead to a more scientific rationale for lens replacement. Amber lens discoloration was achieved using human-worn 55% water hydrophilic contact lenses (Methafilcon-A) heated in a 1% potassium sorbate, low pH saline solution. A spectrum of 6 discolored lenses was obtained with a peak absorbance at 320 nm. Fifteen subjects, between the ages of 22 and 38 years, were tested wearing each of the discolored lenses. None of the differences in high or low contrast acuity between our discolored and nondiscolored lenses were found to be statistically significant using a paired t-test at the 99% significance level.
Although 90% of children with trisomy 18 (Edwards syndrome) die in the first year of life, a small proportion survive into the second and third decade. Many do not have associated ocular abnormalities that might affect vision. Measurable visual acuity has not been reported in these profoundly developmentally delayed individuals. Five children with trisomy 18, aged six months to eight years, underwent complete eye examination including assessment of binocular grating acuity with Teller acuity cards and assessment of binocular vernier acuity with vernier cards. All children were nonverbal with profound developmental delay. Binocular grating acuity ranged from 0.9 cycles per degree (cpd) to 2.2 cpd. This represents a reduction of 1.9 to 5.1 octaves (mean 3.5 octaves, SD 1.3 octaves) compared to age matched norms. None of the children responded to any of the vernier offsets, including the largest of 64 minutes of arc. All children with trisomy 18 demonstrated a measurable grating acuity that was well below normal for age, consistent with profound developmental delay.