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Biomedical subjects

S J Dain

Publications and source records attributed to S J Dain.

30 records · Page 2Linked to original sources
PubMed1988

Pressure testing of ophthalmic safety lenses: the effects on different materials.

The procedure of applying pressure to a lens until fracture occurs and the use of the fracture pressure as a measure of lens strength has been proposed as a quantitative alternative to the drop ball test. The fracture pressure or pressure resistance of untempered, thermally tempered, and chemically tempered glass lenses and CR39 lenses were compared. The results for the glass lenses were consistent with workplace experience and previous studies using the drop ball test. The results for glass and CR39 lenses showed the reverse to what was expected. In order to investigate the basis of this difference, a second procedure was followed in which the annulus supporting the lens and the steel ball applying the pressure to the lens were systematically changed. Glass lenses showed a highly statistically significant change in fracture pressure with decreasing ball size and a small but statistically significant change with annulus size. CR39 lenses showed no statistically significant change in fracture pressure with changing ball size but a highly statistically significant increase in fracture pressure with increasing annulus size. The mechanism of fracture is known to differ in the glass and plastics materials and it is concluded that this method should not be used to compare the performance of different materials.

Accident Prevention↗
PubMed1987

Analysis of the Mark II edition of The City University Colour Vision Test.

The City University (TCU) test was administered to 50 dichromats and 56 anomalous trichromats. Certain poorly performing plates are identified from the accuracy of diagnosis compared with the Nagel anomaloscope and the number of dichromats passing the plates. Some plates are indicated as providing a more reliable diagnosis, particularly when used in combination. The performance of the plates is compared with their colorimetric properties. The desaturated plates, which were not part of the Mark I test, are shown not to provide the intended extent diagnosis.

Color Perception↗
PubMed1987

An averaging method for the interpretation of the Farnsworth-Munsell 100-Hue Test--I. Congenital colour vision defects.

A method is described for identifying polarity in Farnsworth-Munsell 100-Hue test data. The method is facilitated by the use of a micro-computer and involves the plotting of "averaged" scores for each cap of the test. Results are presented for 30 protanopes, 30 deuteranopes, 1 tritanope and 2 typical rod monochromats. Analysis of the results shows that the proposed technique is compatible with standard methods of interpreting 100-Hue plots and is suitable to use when error scores are high and when polarity is difficult to interpret.

Adolescent↗
PubMed1987

An averaging method for the interpretation of the Farnsworth-Munsell 100-Hue Test--II. Colour vision defects acquired in diabetic retinopathy.

The Farnsworth-Munsell 100-Hue test is frequently used to assess acquired colour vision defects. In diabetic retinopathy the acquired defect is a mild or severe type III (Tritan) defect which may be coupled with poor overall hue discrimination. In consequence, error scores are often high and the 100-Hue polar diagram is difficult to interpret. In this study the averaging method of analysis proposed by Dain and Birch is used to examine 120 100-Hue plots obtained by patients with proliferative diabetic retinopathy. These plots have either moderate (150-300) or high error scores (greater than 300). The method of analysis is found to be effective in determining whether a Tritan defect is present or not.

Adult↗
PubMed1987

F-M 100-Hue total error scores have discrete values.

A proof is presented which shows that the total error scores derived from the Farnsworth-Munsell 100-Hue test are an integer multiple of 4. The one proviso for this relates to the way in which the first and last caps in a box are handled.

Color Perception Tests↗
PubMed1986

Red-green mixture thresholds in congenital and acquired color defects.

A color television display was used to measure thresholds for mixtures of red and green on a white background; red and green components could be either incremental, decremental or zero. Ellipses are fitted to a plot of green contrast as a function of red contrast, and it is argued that the length of the ellipse is a measure of red-green color discrimination and the width of the ellipse is a measure of luminance discrimination. It is shown that the technique reliably distinguishes normals from congenital color defectives and also protan from deutan subjects. For some cases of acquired color defects (e.g. optic neuritis), there is a roughly equal loss of color and luminance discrimination whereas, in other cases (e.g., hereditary optic atrophies), the loss of color discrimination is much greater than the loss of luminance discrimination.

Adult↗
PubMed1986

Color preferences in films for fundus photography.

Photographs that provide a colorimetrically faithful image of the original object are known to be subjectively unacceptable. Color photographic films depict a distortion of the color of the original in order to produce a subjectively acceptable reproduction. The distorsions involved may not be appropriate for the reproduction of ocular fundus photographs. This paper assesses the performance of a variety of color slide films in producing photographs of the ocular fundus that are subjectively acceptable. Assessments were made of the photographs of the fundi of blond, dark Asian, and Indian patients. The result of the assessment is a recommendation that points toward the photographic film that will produce the subjectively most acceptable color reproduction.

Color↗
PubMed1986

Spectral transmittance of tinted hydrogel contact lenses.

The visible light and ultraviolet (UV) radiation transmission was measured for four different tints from two contact lens companies. It was found that luminous transmittance ranged from 60 to 82% and mean UV transmission from 15 to 74% for the lenses under investigation. Differences in luminous transmittance between the two lenses of each tint evaluated were generally within 1%, which was also the approximate accuracy of the technique.

Color↗
PubMed1985

Color mixture thresholds measured on a color television--a new method for analysis, classification and diagnosis of neuro-ophthalmic disease.

A color television display can be used to determine color and brightness discrimination thresholds using identical adaptation conditions and experimental technique. The color discrimination threshold is measured by using an equiluminous test spot--i.e. one which differs in color from the surrounding screen but has the same luminance. Because there is no brightness clue, the subject is forced to detect such a spot by using color discrimination. It is shown how color and brightness thresholds may be determined from threshold measurements of different color-mixtures even though it is not known beforehand which stimulus will be equiluminous for the subject. Results are shown for normal subjects, congenital color defectives and for two patients having optic nerve disease who show respectively non-selective and selective loss of color discrimination compared to brightness discrimination. Normal control data are presented, illustrating the effect of eccentricity, optical blur, viewing distance, pupil size and age. It is concluded that the technique is relatively insensitive to moderate variations in these factors and that it is more sensitive in detecting selective color loss than a spectral sensitivity technique which has been described previously.

Adult↗