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Biomedical subjects

J E Sheedy

Publications and source records attributed to J E Sheedy.

At least 37 records · Page 2Linked to original sources
PubMed1986

Effect of a central fusion stimulus on fixation disparity.

Fixation disparity (FD) measurements were made with a 1.5 degree diameter fusional stimulus both with and without a central fusion stimulus. Measurements were made at 40 cm with no prism, 5 delta base-in (BI) and base-out (BO), and 10 delta BI and BO, on a group of asymptomatic subjects. The central fusion stimulus results in less variable measurements and a flatter slope of the fixation disparity curve (FDC). Implications of the use of the central stimulus for clinical measurements are discussed.

Accommodation, Ocular↗
PubMed1986

Should a central fusion stimulus be used on the disparometer?

Clinical measurements of fixation disparity made with the disparometer have used a 1.5 degree diameter peripheral fusion stimulus. The addition of a central fusion stimulus decreases the variability of test measurements and more closely simulates everyday visual tasks. However, this also changes the fixation disparity measurement, associated phoria, slope of the curve, and possibly the curve type. Normative data and correlation data to other clinical tests are not available for the central fusional measurements as they are for the peripheral fusional measurements. More importantly, the peripheral fusional measurements have been shown to correlate with patient symptoms, whereas such studies have yet to be performed with the central stimulus. Until normative and discriminative information data are available for the central fusional stimulus, the peripheral stimulus is more useful clinically.

Fixation, Ocular↗
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↗
PubMed1986

Contact lenses for police officers.

Most municipalities require that police officer applicants have a minimum level of uncorrected visual acuity. The primary basis for the uncorrected acuity standards is that an officer can have spectacles forcibly removed and would need a minimum level of vision to continue performing his/her duties. This article discusses the pros and cons of allowing contact lens wearers to bypass the uncorrected visual acuity standard. Although there are several factors that can make the contact lens wearer a less desirable recruit, a good contact lens wearer who doesn't meet the uncorrected standard could safely and efficiently perform the duties of a police officer. It is recommended that a municipality may consider waiving the uncorrected visual acuity standard for a good contact lens wearing candidate. Suggested guidelines for implementing this policy are discussed.

Contact Lenses↗
PubMed1984

Surrogate color vision by luster discrimination.

A selective filter, such as the X-chrom lens, which is placed before one eye, serves to create a luminance difference between the two eyes. The amount of the luminance difference is dependent upon the wavelength distribution of the stimulus and could therefore serve as a clue to assist color discrimination. The ability to detect and discriminate levels of luster is investigated. One of three subjects shows a crude ability to discriminate levels of luster. The performance level is such that a filter may aid dichromacy but not anomalous trichromacy.

Color↗
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↗
PubMed1984

Fire fighter vision standards.

Fire fighting is a physically and visually demanding occupation. Because of the severe visual demands and the high costs of nonperformance it is necessary to establish minimum vision levels that become requirements for new fire fighters. These vision standards must be based as nearly as possible upon the specific visual needs of the occupational tasks. This paper examines the visual tasks of fire fighters and recommends visual standards.

Fires↗
PubMed1983

Pseudoisochromatic plate design--Macbeth or tungsten illumination?

Three sets of pseudoisochromatic plates were evaluated by photometry and colorimetry. The luminance contrast between the figure and background was measured and compared with a contrast detection threshold. The chromaticity coordinates of the figure and background were evaluated on the basis of how closely they approached a dichromatic line of confusion. The separation of the coordinates of the figure and background are a measure of the severity of the defect for which the plate tests. The plates were evaluated under both Macbeth (C) and tungsten (A) illuminants; two sets of plates were found to be better designed for tungsten illumination.

Color Perception Tests↗
PubMed1983

Recommended vision standards for police officers.

A recommended vision standard for police officers is presented. The visual capabilities needed to perform various police duties are described. A specific vision standard, along with criteria for screening referral or screening failure are given for each category of visual skills required for police work.

Color Vision Defects↗
PubMed1981

The perceived stability of fixation.

Despite the small eye movements, we perceive a stable visual world and a relatively fixed fixation within that stable world. This study demonstrates a method by which we can be made aware of instability of the direction of fixation and it is also shown that we do not have a fixation "point," but rather a fixation "area." Analysis of the results shows why we are normally unaware of the magnitude of our small eye movements.

Eye Movements↗
PubMed1980

Fixation disparity analysis of oculomotor imbalance.

A device and method for measuring forced vergence fixation disparity curves in clinical situations are described. Phoria, vergence, and fixation disparity are measures of different functions of the oculomotor system. In decreasing order of diagnostic effectiveness, four features of the fixation disparity curve are curve type, slope, Y-intercept, and X-intercept. Patients with exophoria and non-Type I curves are likely to have ocular discomfort. The steeper the curve, the more likely the patient is to have symptoms. However, Type IV curves are usually flat, and many of these patients do have symptoms. Patients with Type I curves respond well to visual training, but those with Type II curves generally need lenses or prisms to obtain relief. The Y-intercept gives information that is particularly useful in exophoric patients. A complete analysis of the oculomotor system requires measurement of both phoria/vergence and fixation disparity.

Eyeglasses↗
PubMed1980

Actual measurement of fixation disparity and its use in diagnosis and treatment.

An instrument and technique are described which, for the first time, enable the eye care practitioner to measure the angle of fixation disparity. A forced vergence fixation disparity curve can be quickly measured in the office. Research findings and patient examples are used to show how a fixation disparity curve is analyzed to diagnose and prescribe for an oculomotor imbalance.

Eyeglasses↗
PubMed1979

Reflectance of visual acuity screens.

The luminance of the background and of the target (visual acuity letter) was measured for five commonly used visual acuity screen materials. Most materials were found to be highly nonlambertian. A greater than threefold difference in reflectance normal to the surface was found for the respective screens tested. The percent polarization maintained by each screen material, using American Optical Vectograph systems, was measured. The relative illuminations generated by eight projector systems were compared. A discussion of the factors and recommendations for improvements related to projected chart visibility are made.

Field Dependence-Independence↗
PubMed1978

Association of symptoms with measures of oculomotor deficiencies.

Phoria, vergence, and fixation-disparity were measured at near working distances for a nonclinical sample of 3rd-yr optometry students. A questionnaire divided the sample into 33 symptomatic and 44 asymptomatic subjects. Discriminant analysis was used to determine which clinical measures best predicted the group to which each subject belonged. Sheard's criterion was a good discriminator for exo deviations, and a variant of Percival's criterion was good for eso deviations. Fixation-disparity variables proved to be valuable diagnostically. The best fixation-disparity measures were the curve slope, curve type, and amount of fixation disparity.

Asthenopia↗
PubMed1978

Population study of fixation disparity, heterophoria, and vergence.

Data on phorias, vergences, and fixation disparities were gathered for distant and near viewing conditions from a nonclinical, young adult population. Normative values were computed from the data for analysis and comparison. Our study revealed slightly less exophoria at far and near than Morgan's study, together with large base-out vergence readings. We found proportionately more esophores with exo fixation disparity who require base-in prism to neutralize the fixation disparity than Ogle's studies found.

Adult↗
PubMed1977

Phoria, vergence, and fixation disparity in oculomotor problems.

Measures of horizontal phoria, vergence, and fixation disparity were obtained for 2 samples: 28 optometry students without symptoms and 32 orthoptic patients with symptoms associated with binocular oculomotor difficulties. Discriminant analysis was used to determine which tests or group of tests best discriminated between the 2 samples. Analysis was done for both samples and for exophoric and esophoric subsamples. Sheard's criterion was the best discriminator for the exophoric group, and amount of heterophoria was the best discriminator for the esophoric group. Fixation disparity was the next best discriminator for both groups.

Accommodation, Ocular↗