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Biomedical subjects

I L Bailey

Publications and source records attributed to I L Bailey.

36 records · Page 2Linked to original sources
PubMed1989

Stand magnifiers: an evaluation of new optical aids from COIL.

This paper discusses stand magnifiers and the optical parameters that clinicians should know in order to understand the viewing requirements and the expected resolution for low vision patients. We report on measurements made of key optical parameters of a new series of stand magnifiers from Combined Optical Industries Limited (COIL) and comparison is made to the previous series of stand magnifiers from the same manufacturer. These results illustrate that manufacturers' specifications of optical parameters are generally inaccurate and misleading. We urge manufacturers to provide clinically relevant information about their optical products.

Equipment Design↗
PubMed1988

Task performance with base-in and base-out prism.

The effects of base-in (BI) and base-out (BO) prism upon performance of four occupational-like tasks were measured on a group of 10 subjects who had normal binocular vision. Performance on tasks which required depth perception was significantly poorer when subjects wore prism glasses with 8 and 12 delta BI and BO, whereas 4 delta BI and BO did not significantly affect performance. The performance decrements with prism (3.0 to 6.7%) were considerably less than those induced by denial of binocularity (20 to 30%) as measured in a previous study. Thus, vergence-inducing prism does impair task performance but not as much as does the denial of binocularity. The reading and counting tasks did not require critical depth judgement and were much less affected by the prism than the needle-threading and pointers-and-straws tasks.

Adult↗
PubMed1987

Optics of progressive addition lenses.

The optical characteristics of the major progressive addition lenses were measured using an automated lensometer with a specially designed lens holder to simulate eye rotation. Measurements were made every 3 degrees (about 1.5 mm) and graphs of isospherical equivalent lines and isocylinder lines were developed. Generally the near zone of these lenses is narrower and lower than in bifocal or trifocal lenses. Distinct differences exist between the various progressive lenses. The width of the near zone, rate of power progression, amount of unwanted cylinder (level with the distance center), and clarity of the distance zone are compared for the various lenses. The optical measurements demonstrate an apparent trade-off between the size of the cylinder-free area of the lens and the amount of the cylinder.

Humans↗
PubMed1987

Readability of computer display print enlarged for low vision.

A letter counting task was presented on a Macintosh computer screen using two different versions of 24 point Times Roman print. One version, called "grainy," had 12 matrix units per font height and the other, called "smooth," had 24. A mixed group of low vision subjects and a normally sighted group had speed and accuracy measured as they performed the test task from two different viewing distances. For both population groups, the remote test distances were arranged individually so that the letters subtended an angular size scarcely larger than threshold. The close distances were fairly representative of practical working distances. It was shown that, for both groups of subjects, smooth letters allowed faster performance for the closer working distances only. Smoothing the letters helped accuracy of performance at the far distances, and at the close distances, smoothing improved the accuracy for the low vision group but not for the normals. The implications are discussed.

Adult↗
PubMed1986

Binocular vs. monocular task performance.

Functional advantages of binocularity were investigated by having 13 subjects perform a group of occupational-type tasks under monocular and binocular conditions. Significant binocular advantages ranging from 29.5% (pointers in straws) to 3.7% (reading speed) were measured. Tasks with many disparity cues showed the greatest binocular advantage. This shows that patients with normal binocular vision use binocular cues, most likely stereopsis, to enhance performance. In a second experiment, three subjects with normal binocular vision underwent monocular occlusion for 5 days to investigate whether monocular skills improved to compensate for the loss of binocular vision. During that period binocular performance was consistently better than monocular performance, and both monocular and binocular performance improved, even though the subjects were only gaining monocular experience. Although the 5 day occlusion period does not simulate the long-term denial of normal binocularity that strabismics or monocular patients experience, it shows that binocular superiority remains after short-term loss of binocularity.

Functional Laterality↗
PubMed1985

Bioptic telescopes.

Explore the source record for details and available documents.

Automobile Driving↗
PubMed1984

Effect of luminance, contrast, and eccentricity on visual acuity in senile macular degeneration.

We examined the effect of luminance on low contrast visual acuity in six patients with mild reductions in vision due to senile macular degeneration (SMD) and in six normals of approximately the same age. At the highest luminance tested the SMD patients showed a reduction in acuity compared to the controls, with eccentricity and contrast effects clearly shown. The SMD patients had difficulty performing the acuity task at the lower luminances (0.26 and 0.75 cd/m2); they showed little or no increase in visual acuity with increasing contrast levels at the lower luminances. Acuity was slightly influenced by target eccentricity at these luminances. These data suggest that the adaptation mechanisms allowing the normal visual system to operate efficiently over a wide range of luminances are affected in SMD, even when clinically measured acuity is only moderately depressed.

Aged↗
PubMed1984

Visual acuity and chart luminance.

It is desirable to standardize the conditions under which visual acuity is measured because of its importance in determining whether subjects meet occupational vision standards and as an indicator of the extent or stability of pathological conditions. The chart luminance is one parameter which needs to be standardized, and the effect of the luminance level upon acuity measurement is a critical factor in this determination. These data are measured for a subject population using Landolt rings and British letters. Over a "normal" photopic range of 40 to 600 cd/m2 the relation between the logarithm of the minimum angle of resolution (log MAR)) and log L (luminance) can be approximated by a straight line. A doubling of the luminance level within this range improves the acuity measurement by approximately one letter on a five-letter row. Landolt ring acuities are less affected by luminance than letter acuities. The application of these results to establishing a standardized luminance level and tolerance range is discussed.

Adult↗
PubMed1983

Recent advances in clinical low-vision care.

In the past decade there has been a growth in the awareness of the impact that low vision has on the individual and on society in general. The clinical eye-care professions have become more conscious of their responsibility to assist partially sighted patients and low-vision care is becoming a specialty area within optometry and ophthalmology. This paper reviews recent advances in the optical devices and prescribing procedures that have contributed to improving the care that is available to assist low-vision patients with distance-vision tasks, near-vision tasks and visual-field problems.

Distance Perception↗
PubMed1982

Visual factors and orientation-mobility performance.

The ability of the person with low vision to achieve successful orientation and mobility depends on residual vision, age of onset of visual impairment, posture and balance, intelligence, body image, auditory-tactile abilities, and personality. This study assesses the role of the residual vision and looks in particular at visual fields, spatial contrast sensitivity, and visual acuity. Correlation coefficients indicate that, for low vision patients, spatial contrast sensitivity and visual fields each have more influence on orientation-mobility than does visual acuity.

Age Factors↗
PubMed1980

The design and use of a new near-vision chart.

This paper describes the design of a new near-vision chart that uses unrelated words arranged in a logarithmic progression of size and that has standardized the test task by controlling typeface, spacings, and number of words per row, and making each group of words of approximately equal difficulty. These charts offer special advantages for systematic assessment of reading acuity and visual efficiency for reading. The logarithmic progression of print size on these charts can be used to facilitate prediction of the magnitude of changes in visual performance resulting from changes in optical parameters, and the magnitude of changes in optical parameters required to achieve desired levels of visual performance. Simple methods for converting from point size scaling to M units or Snellen equivalents are also described.

Humans↗
PubMed1978

New method for determining the magnifying power of telescopes.

A new method of measuring the power of optical telescopes is described. This method makes use of the vergence amplification that occurs when the light incident on the objective lens at a telescope is divergent or convergent. The relation between the vergence incident on the objective and vergence emergent from the eyepiece depends on the magnifying power and the length of the telescope. The method is most simple to apply to short-length, low-powered Galilean tesescopes, such as those used as low vision aids, in sports glasses, and in telescopic loupes. With such telescopes, holding a lens of known power against the objective and measuring the back vertex power of the lens-telescope combination using the lensometer and then measuring the telescope length allows the determination of the magnifying power of the telescope. The method can be adapted to determine the magnification rating of near-vision telescopic loupes.

Eyeglasses↗
PubMed1976

New design principles for visual acuity letter charts.

This paper intoduces new principles for the design and use of letter charts for the measurement of visual acuity. It is advocated that the test task should be essentially the same at each size level on the chart. Such standardization of the test task requires the use of letters of equal legibility, the same number of letters on each row, and uniform between-letter and between-row spacing. It is also advocated that, combined with the test task standardization, there should be a logarithmic progression of letter size. Charts incorporating these design features have been made. These charts facilitate the use of nonstandard testing distances which might be used when there is low visual acuity, when examination room layout prevents testing at the standard distance, or when it is necessary to validate visual acuity scores or detect malingering. Adjusting the visual acuity score according to the chosen testing distance is simplified by the use of logarithmic scaling.

Humans↗