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As people age they are more susceptible to various problems in the visual system. The optometrist is in the position to take care of many of the functional losses that result from age-related problems and diseases. With increased awareness of basic low vision and rehabilitation services, the practitioner can continue to care for the visual needs of the older patient.
We used the Teller Acuity Cards (TAC) to test 7 groups of 20 healthy infants and children ranging in age from 1 week to 36 months. We also tested 27 of these children at least twice within their first year. We had two primary goals: (1) to provide normative data on the development of visual acuity as assessed with the new version of the TAC (Vistech, Inc.) and (2) to investigate the predictive value of the TAC. The results from the cross-sectional samples show that our estimates of visual acuity are consistent with those reported by other researchers who used earlier versions of the TAC. The longitudinal data indicate that, on the average, an early estimate of visual acuity was not predictive of a later estimate, at least within the first year. The results are discussed in terms of the usefulness of the TAC for testing normal and clinical populations.
Contrast sensitivity (CS) was measured in children ages 3 to 7 years using the Vistech Contrast Sensitivity distance chart (VCTS 6500). The purpose of the study was to determine how effectively the technique could be used with young children and to establish normative data for this age group. Of 286 children participating in a vision screening, the contrast sensitivity function (CSF) was measurable on 241 (84%) under binocular conditions and 229 (80%) under both binocular and monocular conditions. The 219 binocular CSF's and 208 monocular CSF's obtained from visually normal children were used to establish normative data and then compared to similar data from 50 visually normal young adults. The results indicated that there is an effect of age between 3 and 7 years, children are significantly less sensitive than adults, and adult-like levels of CS are not yet reached at 7 years of age. In addition, although the children's mean contrast thresholds fell within the norms provided with the VCTS 6500, the variability in the children's CSF's precludes using the Vistech data for diagnostic purposes in the young. The normative data are presented to assist the clinician in evaluating CS in young children when using the VCTS 6500.
This study is a sequel to a previous publication that introduced the multimeridional apparent frontoparallel plane (MAFPP) as a method of measuring aniseikonia. As the term implies, apparent frontoparallel plane (AFPP) responses are obtained not only in the horizontal meridian, but also in oblique meridians. Since the introductory publication, the method has been applied extensively for measuring aniseikonia and has been found to be reliable, accurate, and easily adapted to clinical purposes. This study presents a more detailed and comprehensive account of the underlying theory than did the introductory report. It clarifies some problems inherent in the method originally presented and describes a simplified and improved procedure for measuring aniseikonia. It describes the application of the theory to a number of specific clinical situations. Finally, it is suggested that the method has a much broader application than the clinical measurement of aniseikonia.
Previous experiments that have compared monocular vernier acuity in amblyopic, monocularly blind, and normal binocular subjects have been confined to the center of the retina. Based on brain changes that accompany the early disruption of form vision in one eye, monocularly blind subjects (that is, those who have completely lost the ability to process form vision in one eye) and amblyopic subjects are expected to have better vernier acuity in their normally functioning eye than subjects with normal binocular vision. Results from such studies have been ambiguous. This experiment was set up to study monocular vernier acuity in the central and peripheral retina of the three groups of subjects mentioned above. The results show that, at the center, monocularly blind subjects have the best vernier acuity followed by the amblyopic subjects and, finally, the normal binocular subjects have the worst acuity. In the peripheral retina, no significant differences were found between the three groups. A possible explanation has been provided for this finding.
We compared the fixation disparity measurements obtained with the Disparometer to those of the Wesson Card. Previous studies suggest that the measurements obtained by these two instruments gave different results. The results of previous studies were based on the analysis of pooled data, which may have led to spurious results. Analysis of our data done in this manner (pooled data) revealed the same findings. However, after analysis of the data based on the separation of subjects according to phoria (exophoria/esophoria), no statistically significant difference was found between the measurements obtained with the Wesson Card and those with the Disparometer.
The clinician involved in cataract assessment is often faced with a deterioration in visual performance which may or may not be totally attributable to the cataract. Neural changes may occur concurrently and contribute toward the reduced performance. This paper reviews the methods which attempt to discriminate between changes due to cataract development and changes produced by neural degeneration. New techniques have been developed with more emphasis on quantitative rather than qualitative assessment. These techniques are discussed critically with particular reference to their ability to distinguish between the contributions of optical and neural change. This has particular application in predicting the visual outcome after cataract surgery.
The purpose of this study is to investigate the usefulness of a random dot stereogram for the detection of refractive blur by determining the relative sensitivity of random dot stereoacuity (RDS) and Snellen visual acuity to the effects of optically induced blur. Measurements of Snellen and stereoacuity were compLeted on four young adult subjects under cycloplegia and through artificial pupils. Optical blur was varied binocularly and monocularly in 0.50 D steps up to +/- 6.00 D while the subjects viewed targets composed of stimuli arranged in 0.1 log unit size increments. The results show the relation between RDS and Snellen acuity to be SA = 1.341 (VA) + 0.281 for equal amounts of binocularly induced optical blur. Moreover, the RDS appeared more highly sensitive when the blur in the 2 eyes was unequal [SA = 3.774 (VA) - 1.180], a condition approximating refractive anisometropic amblyopia. These results provide a rationale for the use of random element stereograms for the detection of refractive amblyopia and ametropia in the vision screening of children.
The three-dimensional optometer (TDO III) was used to measure accommodative responses when gazing at a spotlight that changed its diameter in an otherwise completely dark room. Three emmetropic females served as subjects and the stimuli were presented at 33 cm (-3 D) from the subjects. The subjects felt that the spotlight approached them when its diameter increased. However, the magnitude of accommodation when viewing the smaller diameter spotlight was greater than that for the larger diameter spotlight. This means that the eye accommodated less, although the spotlight was felt to be nearer, and contradicts the common belief based on the subjectively measured data reported earlier. By conducting several supplemental experiments, we infer that this phenomenon comes from the effort in reducing accommodation lag dynamically in order to see the smaller target more clearly.
People with central field defects resulting from age-related macular degeneration (ARMD) read very slowly. In this study, oral reading rates were determined for unrelated sequences of words in samples of normal young and old subjects with simulated central scotomata of 2 degrees, 4 degrees, and 8 degrees. Scotomata were stabilized at the fovea of the right eye by electronic feedback of eye position, monitored using a SRI dual-Purkinje Eyetracker. Reading rates were determined by jumping print after each stationary presentation through an increasing number of character spaces on different trials. This procedure mimicked the sequence of retinal images produced during the saccades and fixations of normal reading, but without requiring subjects to make accurate eye movements. In Experiment 1, the letter size that yielded the optimal reading rate was found to increase systematically with scotoma size. However, the optimal reading rate decreased more or less linearly as the scotoma size increased. Experiment 2 showed that the optimal reading rate was obtained for essentially the same duration of text presentation, regardless of scotoma size. Experiment 3 investigated the effect of spatial remapping, in which print obscured by the scotoma was stretched electronically to reappear at the scotoma margin. Compared to a nonremapped control condition, spatial remapping produced small but significant increases in reading rate for both 4 degrees and 8 degrees scotomata. Across experiments, average reading rates were faster for the young than the old subjects. Overall, the results define how reading rate is expected to decrease for central scotomata of different sizes and suggest that spatial remapping of print may improve reading rates in patients with ARMD.
OBJECTIVE: To compare the comprehensive care plan assessment (Minimum Data Set, MDS) of vision with the clinically evaluated visual status of nursing home residents to determine the accuracy of the vision care plan. DESIGN: Descriptive study. SETTING: One publicly funded and four privately owned long-term care nursing facilities. PARTICIPANTS: 151 nursing home residents undergoing vision examination at the nursing home request. Mean age of 81, range 34 to 97 years. MAIN OUTCOME MEASURE: The charted MDS assessment for vision patterns was compared with the MDS plan which would have been formulated based on direct clinical vision examination. Determinations were made based on the three areas required by MDS: visual acuity (VA), peripheral vision, and presence of prosthetic visual devices. CONCLUSIONS: The MDS care plan for vision and actual visual status agreed in only 34% (52/151) of persons. The Vision (VA) subsection overestimated VA in 41% and underestimated VA in 11%. Concordance for VA was extremely poor (kappa 0.176). In no participants did the MDS indicate a visual field defect, whereas 16.5% (25/151) did show visual field restriction on examination. Care plan assessments also failed to note the use of visual prosthetic devices in 17% (26/151). These results indicate that MDS care plan assessment for vision is often inaccurate and may result in the lack of appropriate vision care being triggered through resident assessment protocols (RAP).
We examined the binocular vision of 14 patients with esotropia under a dynamic background. The objective and subjective angles of the patients were measured using a phase difference haploscope under three conditions: no background (A), a static background produced by an image slide (B), and a dynamic background produced by 8-mm movies (C). The objective angle remained the same under different backgrounds. On the other hand, the subjective angle tended to become 0 degree under condition C; that is, more harmonious abnormal retinal correspondence (HARC) was obtained under C. Therefore, it was concluded that HARC was more easily detected under the dynamic background than under the static or no background conditions.
PURPOSE: We assessed the reliability and validity of a new computer-assisted crossed-cylinder aberroscope technique which measures the monochromatic optical aberrations of the human eye. METHODS: Intra-image variability, the variability occurring when the same image is repeatedly measured, and inter-image variability, the variability occurring when different images collected from the same eye are measured, were assessed using 10 repeated measures on each of 10 different subjects. We compared the measurements made using the computer-assisted technique with manual measurements made when a human operator performed all the aberroscope grid intersection location tasks. RESULTS: One-way repeated measures analyses of variance (ANOVA) on the inter-image and intra-image variability showed that the mean of the measurements made was statistically independent of the occasion on which a group of subjects was measured, and inter-image variability was larger than intra-image variability. A two-way repeated measures ANOVA comparing computer-assisted results with manual results showed that the means of the measurements made with the two methods are not statistically different from one another. The manual results showed greater variability than computer-assisted measurements. CONCLUSIONS: The technique is reliable and valid compared to earlier objective crossed-cylinder aberroscopic techniques.
PURPOSE: This study compares the development of acuity in the same infants during one testing session using Teller acuity cards (TAC) and sweep visual evoked potentials (sVEP). We asked whether different testing methods in two centers would produce different developmental time courses. METHODS: Forty-eight infants were tested in two centers. The standard procedure for TAC was used. For sVEP acuity, the amplitude response curve derived from time-locked cortical activity was used to extrapolate to zero response, giving an acuity estimate for each infant. RESULTS: sVEP acuity was generally higher than TAC acuity. The rate of development was steeper for TAC than sVEP acuity with TAC starting at a much lower level. The ratio of sVEP to TAC acuity decreased exponentially with age reaching an asymptote of about 1.44 at 6 months. CONCLUSIONS: Results were indistinguishable between centers suggesting that comparison of acuity measures obtained using variations of these methods across centers is possible.
We previously reported that low vision readers do not benefit from a rapid serial visual presentation (RSVP) display relative to a scroll display. Each reader in those studies was presented with only one letter size, and it was the same for both displays. In the current study, we systematically varied the size of the letters and compared reading rates from the 2 displays for letters that were 2, 4, 6, 8, and 10 times each reader's acuity threshold. Using this paradigm, we found that subjects with normal vision (n = 12) read faster with RSVP for all text sizes. Low vision subjects (N = 20) showed no benefit of RSVP until the text was at least 8x their acuity threshold. As in our prior studies, there was a great deal of variability within the low vision group, and for a small number of subjects (25%), reading was faster from the scroll than from the RSVP display.
PURPOSE: To determine the effects of reducing light level from photopic to mesopic on performance of real world mobility tasks and how performance of these tasks relates to measures of visual sensory and perceptual function. METHODS: The visual functions, acuity, peak letter contrast sensitivity, visual field extent, glare disability, color confusion, motion sensitivity, spatio-temporal contrast sensitivity, scanning ability, and figure-ground discrimination were measured to determine their ability to predict mobility performance of visually impaired adults on indoor hallway and outdoor residential travel routes under photopic and mesopic lighting conditions. RESULTS: Time to complete routes and number of mobility incidents were significantly increased under mesopic conditions. Depending on the task, lighting conditions, and performance measure, predictive models consisting of 4 vision variables were able to account for 30 to 42% of the variance in overall performance. The two most important variables in these models were visual field extent and scanning ability, followed by color confusion, grating contrast sensitivity, or spatial resolution. CONCLUSIONS: Reducing illumination levels from photopic to mesopic has an adverse effect upon mobility in older visually impaired adults. The aspects of vision which best predict performance include measures of sensory and perceptual visual function. The results compare well with those obtained under controlled laboratory conditions.
BACKGROUND: Functional limitation because of visual impairment is one of the most important measures of low vision rehabilitation outcome because it represents the true impact of visual impairment upon the daily lives of individuals. The Low Vision Functional Status Evaluation (LVFSE) was designed to evaluate functional limitation because of visual impairment using both observed and self-reported performance on daily activities. METHODS: Performance on 27 daily activities was evaluated for 155 visually impaired subjects. Subjects also provided ratings of task difficulty. RESULTS: Correlations between observed performance and visual acuity, contrast sensitivity, and visual field loss severity were moderate, r = -0.60 to r = 0.34. Correlations between self-reported task performance difficulty and measures of visual clinical state were weaker, r = -0.44 to r = 0.21. CONCLUSIONS: The LVFSE shows promise as a sensitive measure of low vision-related functional status but more work is needed to refine the measure.
PURPOSE: To measure the changes in astigmatism when bilateral emmetropes accommodate. METHODS: Bilateral emmetropes accommodative responses were measured with an improved photorefractometer PR-1100, which measured binocular refraction in all meridians simultaneously as a fixation target was shown in natural space. RESULTS: The accommodative responses in the vertical meridian are greater than those in the horizontal meridian. In the horizontal meridian, the accommodative responses are less than the accommodative stimulus. CONCLUSIONS: When accommodating the majority of bilateral emmetropes show with-the-rule astigmatism and lag of accommodation in the horizontal meridian.