Biomedical subjects

P A Sample

Publications and source records attributed to P A Sample.

49 records · Page 3Linked to original sources

PubMed1994

Age-related changes in the human lens: a comparison of Scheimpflug photography and lens density index.

Two quantitative techniques, Scheimpflug photography and the lens density index (LDI), were used to measure lens density in 52 patients. In the Scheimpflug technique, a digitized slitlamp camera provides peak and average nuclear density based on a densitometric analysis of the lens nucleus. The LDI is a psychophysical measurement of the difference between retinal scotopic thresholds for two wave-lengths of light. Both the Scheimpflug technique and LDI revealed an age-related increase in lens density. Peak and average nuclear density were highly correlated with the LDI.

Adult↗

PubMed1994

Interpretation of automated perimetry for glaucoma by neural network.

PURPOSE: Neural networks were trained to interpret the visual fields from an automated perimeter. The authors evaluated the reliability of the trained neural networks to discriminate between normal eyes and eyes with glaucoma. METHODS: Inclusion criteria for glaucomatous and normal eyes were the intraocular pressure and the appearance of the optic nerve; previous visual fields were not used. The authors compared the backpropagation learning method used by automated neural networks to those used by two specialists in glaucoma to classify the central 24 degrees automated perimetric visual fields from 60 normal and 60 glaucomatous eyes. RESULTS: The glaucoma experts and a trained two-layered network were each correct at approximately 67%. The average sensitivity of this test was 59% for the two glaucoma specialists and 65% for the two-layered network. The corresponding specificities were 74% and 71% for the specialists and the two-layered network, respectively. The experts and the network were in agreement about 74% of the time, which indicated no significant disagreement between the methods of testing. Feature analysis with a one-layered network determined the most important visual field positions. CONCLUSIONS: The authors conclude that a neural network can be taught to be as proficient as a trained reader in interpreting visual fields for glaucoma.

Adult↗

PubMed1993

Short-wavelength color visual fields in glaucoma suspects at risk.

Glaucoma suspect eyes were seen during a five-year study on color visual fields that used a 440-nm test on a bright-yellow background (96 normal eyes, 55 suspect eyes, and 110 eyes that developed glaucoma). The predictive ability of the test was assessed in 25 eyes followed up for more than one year, five of which developed glaucoma. These five eyes and those at high risk showed higher mean defect (P < .0001) and number of defective points (P < .0001) than the other suspect groups, which were not significantly different from normal eyes. The mean defects (+/- standard deviations) and average number of defective points were 1.4 +/- 2.3 dB with 8.9 points (low-risk eyes), 1.1 +/- 1.2 dB with 8.0 points (medium-risk eyes), 6.7 +/- 2.8 dB with 27.7 points (high-risk eyes), and 9.3 +/- 1.8 dB with 39.4 points (eyes that developed glaucoma). Normal eyes had an average of 3.4 defective points. These results were similar when all 55 suspect eyes were analyzed. Color visual fields identify early functional loss in eyes at greatest risk for primary open-angle glaucoma.

Color Perception↗

PubMed1992

High-pass resolution perimetry in eyes with ocular hypertension and primary open-angle glaucoma.

We analyzed the results of high-pass resolution perimetry on normal eyes, eyes with ocular hypertension, and eyes with primary open-angle glaucoma. The subjects were matched for age and lens density. We controlled for refraction, visual acuity, pupil size, miotic medications, and learning effects. Under these conditions the glaucomatous eyes showed a significant reduction in overall resolution threshold compared to both normal (P less than or equal to .01) and hypertensive eyes (P less than .01). The hypertensive eyes were not significantly different from normal. Standard increment threshold fields and high-pass resolution visual fields had an agreement of abnormality of 67%. Resolution perimetry showed a 92% agreement with standard perimetry in the location of the defect, when the defect was apparent on both tests. These results indicated that resolution perimetry may be useful for diagnosis and management of primary open-angle glaucoma.

Aged↗

PubMed1992

Progressive color visual field loss in glaucoma.

Twenty one eyes with primary open angle glaucoma were tested with standard (white stimulus-on-white background) and color (blue stimulus-on-yellow background) visual fields over a range of 6-26 mo. There was no significant increase in threshold between the initial and final standard fields overall or by quadrant (P less than 0.188, overall field). A significant increase in mean log thresholds for all areas of the color visual field (P less than 0.019, overall field) was found. Of the 21 patients, nine worsened by greater than 0.2 log units, two improved by greater than 0.2 log units, seven worsened by less than 0.2 log units, and three improved by less than 0.2 log units. When these same patients were matched to 21 normal eyes by age, lens density, and acuity they showed significantly reduced thresholds throughout their color visual fields (P less than 0.023). Whereas normal age-related increases in threshold for the short-wavelength system are only 0.10 log units per decade (n = 88), 10 glaucomatous eyes with increases of 0.14-0.75 log units were found within only 26 mo. The authors conclude that color visual fields may indicate significant change in visual function before it is apparent on standard visual fields.

Adult↗

PubMed1991

Isolating the effects of primary open-angle glaucoma on the contrast sensitivity function.

We evaluated spatial contrast sensitivity functions in age-matched and lens density-matched healthy eyes, eyes with primary open-angle glaucoma, and eyes with ocular hypertension. We also controlled for refraction, visual acuity, pupil size, and previous ocular history. We found an overall reduction in contrast sensitivity for the glaucomatous eyes with a significant difference at 12 cycles per degree (P less than .012). Eyes with ocular hypertension were not significantly different from normal eyes. Significant differences were noted at several spatial frequencies with less careful controls for age and lens effects. We concluded that spatial contrast sensitivity may be a useful adjunctive diagnostic test for glaucoma, but interpreting the results without other clinical data may lead to errors in diagnosis.

Aged↗

PubMed1991

Age-related changes in the human lens. Clinical assessment of age-related changes in the human lens.

We compared two methods for assessing changes in the human lens associated with age. The first is a subjective method for quantifying light absorption by the lens. It is useful for determining the functional effect of age-related increases in lens density, especially for short-wavelength light. The second method objectively and rapidly measures the increase in scattered light with increasing lens density. These two methods accurately measured age-related changes and were highly correlated with each other (r = 0.72, P less than 0.001). Both methods were evaluated in a population of normal eyes, eyes with ocular hypertension, and eyes with primary open angle glaucoma. We found ni significant differences among these groups with either method.

Adult↗

PubMed1990

Color perimetry for assessment of primary open-angle glaucoma.

The authors report the development of a color perimetry procedure which compares sensitivity of the short-wavelength color-vision mechanism in the peripheral visual field for normal eyes, eyes with ocular hypertension, and eyes with primary open-angle glaucoma. To isolate the short-wavelength cone mechanism, they modified an automatic projection perimeter to blue-on-yellow color perimetry and used a monochromatic 440-nm stimulus and a broad-band bright yellow background. The three groups of subjects were matched for age and lens density. Refraction, pupil size, acuity, and medication were controlled. Under these conditions, most glaucomatous eyes showed reduced sensitivities more than two standard deviations below normal. Normal control eyes were significantly different from eyes with ocular hypertension only in the superior nasal field (P less than 0.05), but normal eyes differed from eyes with primary open-angle glaucoma in all areas of the field (P less than 0.01).

Aged↗

PubMed1989

A practical method for obtaining an index of lens density with an automated perimeter.

Uncontrolled variables often limit meaningful assessment of visual sensitivity. Previously, we developed a procedure and apparatus for in vivo assessment of light absorption by the human lens. In the current study, we modified a widely used automated perimeter to include our procedure for obtaining an index of lens density. Nineteen individuals were tested on both the original apparatus and the modified perimeter. Results were comparable with a correlation of r = 0.92 (P less than 0.01). We conclude that employing the procedure on an automated perimeter is a practical method for obtaining an accurate lens density index.

Densitometry↗

PubMed1988

Isolating the color vision loss in primary open-angle glaucoma.

We evaluated the results of Farnsworth-Munsell 100-Hue tests in age- and lens density-matched eyes of normal subjects, glaucoma suspects, and patients with primary open-angle glaucoma. With these controls in place, no significant correlation between the test results and age or between the test results and lens density was found. However, a significant difference in the total error scores on the 100-Hue test remained. This difference could not be explained by pupil size or medications taken. We concluded that color vision loss in glaucoma is in part attributable to the disease process and cannot be explained solely on the basis of changes in age and lens density.

Aged↗

PubMed1988

The aging lens: in vivo assessment of light absorption in 84 human eyes.

We have developed an apparatus and psychophysical paradigm for the reliable and practical measurement of light absorption by the human crystalline lens. Using this procedure we can partition a loss of sensitivity with aging into that attributable to changes in the lens and that due to other factors. The procedure eliminates effects of inaccurate refractive correction and misalignment, and reduces the effects of pupil size. Results on 84 eyes showed a gradual decrease in sensitivity with age, especially for short wavelengths. We noted considerable individual variability, which points up the value of using a procedure that assesses sensitivity loss due to lens absorption for each tested individual.

Absorption↗

PubMed1980

Audiometric and tympanometric monitoring of a disease affecting nerve-muscle transmission.

Audiometric and tympanometric tests were used to identify patients with myasthenia gravis, a disease characterized by skeletal muscle weakness. Middle ear muscle reflexes in untreated myasthenics were found to be typically depressed or absent. Hearing was abnormally sensitive for some frequencies and middle ear pressures were often negative. Following drug administration, patients who were responding well to medication had more sensitive reflex thresholds, less sensitive hearing, and were able to equalize middle ear pressures. Tympanometric measurements have proved to be of value in the diagnosis of myasthenia and in monitoring the effects of therapy.

Acoustic Impedance Tests↗

PubMedDate not supplied

Acquired dyschromatopsia in glaucoma.

Recent studies have suggested that the recognition of blue-yellow color vision deficits may have some predictive value in determining which ocular hypertensives are at risk of developing glaucoma and in monitoring the progress of the disease in glaucoma patients. This article reviews current theories of normal color vision and the differences that may occur in glaucoma, outlining methods of color vision testing and interpretation, and summarizing the results of recent studies.

Adaptation, Physiological↗