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Biomedical subjects

D B Elliott

Publications and source records attributed to D B Elliott.

17 recordsLinked to original sources
PubMed1992

Simulating age-related optical changes in the human eye.

The decline in visual function observed in older adults has been attributed to a deterioration in optical quality, decreased neural function, or a combination of both of these factors. One way of separating their contribution is to design a simulation of the optics of the elderly eye and examine its effect on the visual performance of younger observers. The age-related reduction in pupil size was simulated by the administration of an ophthalmic miotic drug, whilst a neutral density filter was included to account for the increased absorption of the ocular media. An optical cell containing a critical concentration of 500 nm diameter polystyrene microspheres in suspension was used to simulate light scatter. The spatiotemporal contrast sensitivity of an older group of observers was then compared with that of a younger group with and without the optical simulation. The contrast sensitivity of the younger group was consistently better than that of the older, and the presence of the optical simulation produced no significant effect on performance. This suggests that, under normal viewing conditions, it is primarily neural factors which underlie the deterioration in visual quality experienced by older observers.

Adult↗
PubMed1992

How useful are contrast sensitivity charts in optometric practice? Case reports.

There are now a number of commercially available contrast sensitivity (CS) charts for clinical use. Although a great deal has been written about CS, there is little information regarding its usefulness in optometric practice. In this study 3 commercially available charts (the Vistech system, Pelli-Robson, and Cambridge charts) were used by 6 optometrists in clinical practice over a 14-month period. This report includes a review of the research literature on clinical CS testing, and contains case records from the in-practice study which indicate situations in which the measurement of CS proved useful.

Adult↗
PubMed1992

Clinical contrast sensitivity chart evaluation.

Three different types of contrast sensitivity chart were used on normal patients by six optometrists in clinical practice. The charts were the Vistech, the Pelli-Robson and the Cambridge low-contrast gratings test. We examine the data in terms of the differences between optometrists and the variation of contrast sensitivity with the age of the patient. There was a highly significant difference between the scores from different optometrists for all three charts. We attribute this to variability in measurement technique. There was also a highly significant effect of age for all three charts, with older observers tending to exhibit lower contrast sensitivity. On the Vistech chart, this sensitivity deficit was most pronounced at higher spatial frequencies. The level of redundant information in the tests is discussed.

Adolescent↗
PubMed1992

Variations in hyperacuity performance with age.

The term hyperacuity has been applied to a group of stimuli which produce spatial thresholds smaller than those expected given the relatively large receptor spacing and the retinal image quality of the human eye. It is not yet firmly established whether hyperacuity performance declines with increasing age in the same way as most other measures of visual ability. This is perhaps due to the use of varying task configurations and criterion-dependent psychophysical techniques. The present study examines age-related performance in three different hyperacuity tasks using a criterion independent forced-choice method. Both displacement and bisection thresholds were found to increase with age, but there was no significant change in vernier acuity. This indicates that age has a differential effect on thresholds for various hyperacuities depending upon the task requirements. No significant age-related trend was observed in hyperacuity bias, which represents the difference between subjective and true physical alignment.

Adolescent↗
PubMed1991

Factors affecting light scatter in contact lens wearers.

We measured forward light scatter at 3.5, 10, and 28 degrees using a portable stray light meter. Subjects included 66 normal subjects (age range 19 to 79 years), 17 established hydrophilic contact lens wearers, and 15 rigid gas permeable (RGP) contact lens wearers. Contact lens deposits were measured using a modified Rudko procedure and a Leitz/Wild Makroscope M240. Corneal health was assessed using slitlamp biomicroscopy. Results showed a significant increase in light scatter with age, particularly after the age of 40 years. Stray light scores were significantly lower in pigmented non-Caucasian subjects, particularly at larger angles. The stray light scores were significantly greater in contact lens wearers than in age-matched normals, but were not found to correlate with the amount of lens deposits. Scores from hydrophilic lens wearers after removal of their lenses were significantly higher than results from RGP wearers after removal of their lenses and from age-matched normals. This suggests the presence of subclinical corneal edema in some of these subjects.

Adult↗
PubMed1991

Spatial summation determines the contrast response of displacement threshold hyperacuity.

The effect of line length on displacement threshold hyperacuity at various levels of contrast was investigated. At high contrasts there was no significant effect of line length, but as contrast was reduced thresholds for shorter line lengths increased rapidly. Thresholds at longer line lengths demonstrated a form of contrast saturation which differed from vernier acuity whose thresholds increased consistently with a reduction in contrast. As line length in the displacement threshold task was reduced, the amount of contrast saturation became less and displacement thresholds therefore resembled the contrast response of vernier acuity. Results are explained in terms of spatial summation along the length of the lines, the effects of which depend upon the spatial configuration of the hyperacuity stimulus under consideration.

Contrast Sensitivity↗
PubMed1990

Comparing clinical tests of visual function in cataract with the patient's perceived visual disability.

Conventional techniques for assessing the visual function of cataract patients include visual acuity (VA), contrast sensitivity (CS) and glare disability (GD). The extent to which these measurements provide accurate information about a patient's perceived visual disability is not known. In this study, binocular and monocular VA and CS and monocular GD measurements were made using commercially available techniques on 33 cataract patients. VA was measured using a Ferris-Bailey LogMAR chart and CS by the Pelli-Robson letter CS chart. Glare disability was measured using the Mentor Brightness Acuity Tester in conjunction with both the LogMAR and Pelli Robson charts. Each patient's perceived visual disability was quantified using a 20-point questionnaire about the effect of vision on everyday activities. There was little correlation between subjective visual disability and monocular or binocular VA measurements. Measurements of binocular CS, however, were highly correlated with the patient's perceived visual disability, particularly their subjective assessment of the effect of vision on their mobility-orientation. We suggest that binocular CS measurements using the Pelli-Robson chart provide useful additional information regarding the need for surgery in cataract patients.

Activities of Daily Living↗
PubMed1990

Simple clinical techniques to evaluate visual function in patients with early cataract.

Among the 80 subjects who were recruited with normal retinal and neural function, 54 had cataract and a visual acuity (VA) better than 6/24. The 26 age-matched subjects had clear media. Contrast sensitivity (CS) at low and intermediate spatial frequencies was measured using the Pelli-Robson letter chart. Two measures of glare disability (GD) were obtained using the Mentor Brightness Acuity Tester (BAT) in conjunction with a logMAR VA chart and the Pelli-Robson chart. Although CS is predominantly affected at high spatial frequencies in early cataract, we found that some subjects had reduced scores on the Pelli-Robson chart. This CS loss could not be predicted from VA measurements and was particularly found in subjects with posterior subcapsular cataract. High GD scores were found in a number of subjects with relatively good VA and could not be predicted from results of VA or CS. We suggest that CS and GD measurements using the Pelli-Robson chart and the BAT provide valuable information regarding the management of patients with early cataract.

Aged↗
PubMed1990

Differences in the legibility of letters at contrast threshold using the Pelli-Robson chart.

One disadvantage of using high-contrast letters as test objects when measuring visual acuity is the fact that they are not of equal legibility. A number of charts are now commercially available that assess contrast sensitivity using letter targets. This study attempted to assess the legibility of letters at contrast threshold on the Pelli-Robson letter contrast sensitivity chart by determining the percentage of correct responses for each of the ten Sloan letters at contrast threshold. Results of 493 contrast sensitivity measurements taken in optometric practice indicated that there is a definite difference in legibility between letters at contrast threshold as for letters at acuity threshold. The data suggest that the probability of correctly identifying two out of a group of three letters at threshold on the Pelli-Robson chart varies between 67% and 97% due to letter type alone. Because of the very regular and pronounced miscalling of the letter C as an O, we suggest that this should be accepted as a correct call during threshold measurements on the Pelli-Robson chart. This helps to balance the legibility of different groups of letters.

Contrast Sensitivity↗
PubMed1990

The reliability of the Pelli-Robson contrast sensitivity chart.

Normative contrast sensitivity (CS) data were obtained using the commercially available Pelli-Robson chart from the dominant eye of 30 young (mean (+/- SD) age 22.5 +/- 4.3 years) and 42 older (mean (+/- SD) age 70.2+/- 6.7 years) subjects with normal healthy eyes. The majority of young subjects were found to have a CS of 1.80 log units or above. The majority of the older subjects were found to have a CS of 1.65 log units or above. CS results were obtained using both sides (A and B) of the Pelli-Robson chart from 30 (15 young and 15 older) of these subjects. These measurements were repeated under identical conditions, 2 weeks later. There was no significant difference between the results from sides A and B of the chart. The CS scores were shown to be repeatable to within +/- 0.15 log units or +/- 1 step. Therefore a significant change in CS score is +/- 2 steps or 0.30 log units. Slight improvements in reliability could be obtained by more careful permutation of letters on each step and a smaller step size. The restriction against these changes is the ensuing increased chart size.

Adult↗
PubMed1989

Assessing the effect of cataract: a clinical evaluation of the Opacity Lensmeter 701.

The efficacy of a new clinical instrument which measures light backscatter from the crystalline lens--the Opacity Lensmeter 701--was assessed. Repeated measurements were made on 83 normal subjects in the age range 15 to 82 years, and on 38 eyes of subjects with cataract but normal retinal and neural function. The cataract scores were compared against results of Logmar visual acuity (VA) and glare disability measurements from the same subjects. The Lensmeter was found to be simple to use and gave quick, repeatable, objective measurements of light backscatter. Scores correlated well with normal age changes in noncataractous lenses and in cataracts of pure nuclear morphology, but not in cortical or posterior subcapsular cataracts.

Adolescent↗
PubMed1989

The subjective assessment of cataract.

The medical treatment of cataract now appears to be a distinct possibility. A number of anti-cataract formulations are being clinically tested, and more clinical trials are being planned. To obtain a true assessment of a drug's efficacy, a battery of tests are needed which can accurately assess cataract progress. A clinical trial of the proposed anti-cataract drug Bendalina is being conducted. The six subjective methods used to assess cataract progression in the trial are presented. These are refractive error, LogMAR visual acuity, contrast sensitivity, glare sensitivity, retinal visual acuity and displacement threshold hyperacuity. The reasons for using each technique and their method of measurement is explained.

Aged↗
PubMed1989

Contrast sensitivity and glare sensitivity changes with three types of cataract morphology: are these techniques necessary in a clinical evaluation of cataract?

LogMAR visual acuity, contrast sensitivity and glare sensitivity measurements were made on 39 eyes of 18 cataractous subjects and compared against normative data. Only cataracts of one of the main three morphological cataract types were used--cortical, nuclear and posterior subcapsular. Results indicate that contrast sensitivity decline with cataract is an intermediate and high spatial frequency loss. For nuclear and cortical cataracts with a LogMAR visual acuity of less than 0.5 (Snellen equivalent better than 6/18), there was no loss of contrast sensitivity at the lowest spatial frequency (1 c/deg). For posterior subcapsular cataracts, low spatial frequency contrast sensitivity loss did occur but was unrelated to visual acuity. Glare sensitivity increased for all cataract types. This was related to visual acuity for both cortical and nuclear cataracts but was not for the posterior subcapsular type. It was concluded that contrast and glare sensitivity measurements are a useful part of the assessment of visual function in patients with posterior subcapsular cataract.

Aged↗
PubMed1988

The use of accurate visual acuity measurements in clinical anti-cataract formulation trials.

A standardized visual acuity technique is presented for use in anti-cataract drug trials. Ferris Logmar charts were used in repeatability studies of vision, visual acuity and pinhole visual acuity measurements for twenty normal subjects (mean (+/- SD) age 64 +/- 6.3 years). Visual acuity measurements were shown to be the most repeatable and thought to be the most suitable for monitoring cataract progression. Repeated visual acuity measurements were made on 29 cataractous eyes of 15 subjects (mean (+/- SD) age 67.8 +/- 7.2 years). A Logmar score change of 0.1 (one line) was shown to be a statistically significant change. This value can be used in statistical analyses of drug efficacy. The normal data gives a mean Logmar visual acuity of 1.15 (Snellen equivalent 6/5). This indicates the inadequacy of using 6/6 as a norm value for visual acuity, even for older patients. As the possibility of reversal of cataract theoretically exists in the early stages of cortical and capsular cataracts, patients with small amounts of these types of cataract are ideal patients for anti-cataract formulation trials. The normal visual acuity results indicate that the inclusion criteria for clinical trials can include patients with cataracts with visual acuity as good as 6/6.

Aged↗
PubMed1987

Contrast sensitivity decline with ageing: a neural or optical phenomenon?

Previous studies of contrast sensitivity changes with age have produced conflicting results. Most recent reports indicate that, with increasing age, contrast sensitivity at medium and high spatial frequencies decreases. Whether this is caused by reduced retinal illumination due to senile pupillary miosis and increased lens absorption, by the greater light scatter of the aged eye or by retinal and neural cell loss and degeneration is also in doubt. We measured the contrast sensitivity functions of 16 young (mean age 21.5 +/- 2.7 years) and 16 older (mean age 72 +/- 4.3 years) subjects with normal healthy eyes, using a modified Rodenstock retinometer and a monitor-based computer system. The former method bypasses the effects of the optical media to measure the contrast sensitivity function of the retinal and neural system alone, while the latter measures the contrast sensitivity function of the whole visual system, including media. The results show the older group to have significantly lower contrast sensitivity at medium (4 c deg-1, p less than 0.1) and high (10.6 c deg-1, p less than 0.001; 16.5 c deg-1, p less than 0.001) spatial frequencies. They also suggest that this is due primarily to retinal and neural changes with age, with optical factors having a slight effect at the highest spatial frequency only.

Adult↗
PubMedDate not supplied

Changes in macular function throughout adulthood.

Recent reports suggest that the neural system is the principal cause of loss of visual function with age and that senile lenticular and pupillary changes are of minor importance. In order to investigate this neural deterioration further we measured Logmar visual acuity and photostress recovery time (PSRT) in 61 subjects over an age range of 19 to 78 years. The magnitude of the PSRT reflects the efficiency with which the visual system recovers from exposure to a glare source and is principally dependent upon the integrity of the photoreceptors and the retinal pigment epithelium. The results indicate that macular function declines significantly throughout adulthood.

Adult↗