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Biomedical subjects

G A Fry

Publications and source records attributed to G A Fry.

At least 19 recordsLinked to original sources
PubMed1992

Foveal photopigments.

The relative rates of absorption of quanta per unit of energy for the various wavelengths can be assessed for the human red, green, and blue photoreceptors by assuming that the responses generated by a photoreceptor are proportional to the rate of absorption of quanta. We start by selecting three points on the color mixture diagram to represent the fundamental colors. The mixture diagram is then transformed to a constant luminance diagram in which the fundamental colors serve as primaries. The V(lambda) values are then multiplied by the chromaticity coordinates (r, g, and b) to determine the response curves of red, green, and blue cones. The values of V(lambda)r, V(lambda)g, and V(lambda)b are divided by the transmittance of the ocular media and the wavelength to give the relative absorptions. No allowance has been made for self-screening or population densities. I have used the Judd (V(lambda) curve and the Wright-Guild mixture data. I have found three fundamental colors which yield predictions for the absorption curves of the photopigments of the foveal cones which conform well to the absorbance curves measured directly.

Color Perception↗
PubMed1992

Spectral response curves of congenital dichromats.

In a previous paper I have derived spectral response curves for the foveal cones of the CIE normal observer. These are based on the 1931 mixture data, the Judd 1951 V (lambda) curve, and the absorbance data of the pigments in the human cones. In the present paper I have found that the spectral response curves of congenital dichromats may be assumed to be similar to those of the CIE normal observer.

Color Vision Defects↗
PubMed1988

A model for the visual perception of direction.

An attempt is made to explain how the eyes can be moved with respect to the head and the observer can still assess the direction of an object in space fixed with respect to the head. My explanation is based on the assumption that the subject is made aware of the direction in which the eyes are pointing by the output from the brain center controlling the direction of fixation. He associates this signal with an awareness of "looking in a certain direction." The image falling on a certain point of the retina (usually near the center of the fovea), which I call the anchor point, is perceived as lying in the direction in which he "perceives himself to be looking." The directions of other objects are judged relative to the object that forms its image on the anchor point.

Humans↗
PubMed1988

Stiles-Burch two-degree color mixture data.

The 2 degree color mixture data of Stiles and Burch have been analyzed to study the differences between individual subjects and the lack of precision at the blue end of the spectrum. The luminous efficiency data have been compared to those of Judd's 1951 observer and the 1931 standard observer. The mixture data have been compared to those of Wright and Guild and have been related to mixture data of dichromats. One of the ten observers was found to have a luminous efficiency curve similar to that of a protanope and was excluded from the average data.

Color↗
PubMed1987

Color mixture data for normals and tritanopes.

In the author's theory of color vision the blue and the green fundamental fall on a tritanopic confusion line. This provides the basis for comparing the mixture data of a tritanope with those of a normal. At the red end of the spectrum the data conform very well to what is predicted by theory. At the blue end the data point to the possibility that the pigment responsible for the red response may differ from the pigment involved at the red end of the spectrum.

Color Perception↗
PubMed1986

Dichromatic confusion lines and color vision models.

An attempt has been made to explain how dichromatic confusion lines can be used in building a model for color vision. In the König color vision model the fundamental colors are located on the mixture diagram at the copunctal points for protanopes, deuteranopes, and tritanopes. In Fry's model the copunctal points fall on the alychne and cannot represent the fundamental colors. On a constant luminance diagram the confusion lines for the different dichromats are sets of parallel lines. This arrangement of the confusion lines can be explained in terms of a zone theory of color vision.

Color Perception↗
PubMed1979

Luminous efficiency in the red-green region of the spectrum.

Monochromatic-test stimuli were produced with a double monochromator with a neutral wedge linked to the mechanism for changing wavelength. Only minor adjustments of the width of the entrance slit were required to produce monochromatic stimuli of equal luminance. For any given wavelength, the radiance of the stimulus was proportional to the width of the entrance slit. These test stimuli were adjusted to equal luminance, using various criteria: (1) flicker, (2) direct comparison, (3) distimulus matching, and (4) step-by-step. For two out of three subjects, measurements made by the distimulus method agree with flicker measurements when the primaries are adjusted to be equal by flicker photometry. They provide a test for additivity. Red and green, which are equal in luminance to yellow by flicker photometry, are brighter than yellow by direct comparison and also by the step-by-step method of assessment. The step-by-step data prove that the discrepancy between flicker and direct comparison involves more than confusion between saturation and brightness and is consistent with the notion of summation of responses in the chromatic and achromatic channels, as proposed by Ives and others.

Color Perception↗
PubMed1979

Standards and technology.

Improvements in standards and technology go hand in hand. A careful study of standards as related to the state of the art always brings to light the need for improving technology. The study involved in revising the 1972 ANSI Z80.1 Standard for Ophthalmic Lenses has focused attention on several new and upcoming developments. These relate (1) to the predetermination of the edger setting, and the use of the perimeter of a lens, (2) the accurate control of centers, (3) the measurement of power and axis, and unwanted power in the periphery, (4) the use of computers in generating the shape of a lens and the location of the MRP, and (5) the standardization of shapes.

Computers↗
PubMed1978

Choosing the base curve for an ophthalmic lens.

Although optometrists can be expected to be responsible for the base curve, which determines the form of the lens they prescribe, they seldom specify the base curve to the optical laboratory. They may ask for a corrected-curve lens without specifying the kind of corrected-curve lens. If optometrists were to specify what they want in terms of a convex spherical base curve and allow the laboratory a leeway of p1.00 D, the laboratory could probably fill the order with an uncut lens from stock. With a series of semifinished lenses with convex spherical base curves spaced 2.00 D apart, the laboratory can supply a finished lens that will meet almost any need. For glasses to be used for distant objects, first consideration is usually given to minimizing the unwanted sphere and cylinder in the periphery of the lenses. For those who want to aim at this objective, I have worked out a series of convex spherical base curves that can be used for various combinations of spheres and cylinders.

Eyeglasses↗
PubMed1978

Relative tensions in the extraocular muscles.

Two methods have been devised to assess the relative tensions required to point the eye in a given direction. One method uses an ophthalmotrope, which will assess the tensions and the lengths of the muscles. The second uses a computer program. In each method the direction of the eye is analyzed into components of elevation, azimuth, and cyclorotation. Such a combination of devices is needed in finding the patterns of innervation involved in Listing's law, cyclorotation associated with convergence, and also cocontraction associated with convergence.

Computers↗
PubMed1978

Pathology of Bolivian Hemorrhagic fever in the African green monkey.

Gross and microscopic pathological findings are presented for an African green monkey model of fatal Bolivian hemorrhagic fever. Six animals were inoculated with 1,000 plaque-forming units of Machupo virus, the etiological agent of Bolivian hemorrhagic fever. Five of the monkeys died within 13 days with signs of fever, anorexia, shock, and hemorrhage. The sixth monkey survived until the 24th day and died with signs of central nervous system disease. Gross lesions in the five monkeys that die in the acute stage included hepatic necrosis, necrotic enteritis, bronchopneumonia, and hemorrhages in the subcutis, lungs, intestine, liver, and lymph nodes. Microscopically, necrosis was consistently seen in liver, intestine, skin, oral cavity, and adrenal cortex. Acute thrombosis was observed in four monkeys, in blood vessels of the intestine, lung and choroid of the brain. Gram-negative bacteria were seen in many tissues, suggesting terminal bacteremia. The sixth monkey was emaciated and had bronchopneumonia, but did not have the necrotic hepatic and enteric lesions observed in the other five monkeys. The significant microscopic lesions in this monkey included encephalomyelitis, ganglionitis, and bronchopneumonia.

Animals↗
PubMed1978

Face-form frames.

Face-form frames may be appropriate for sunglasses but present many problems if used for prescription lenses especially when the power is strong. Angling the lenses affects the power and location of the cylinder axis and makes it difficult to attain the right P.D. The problems of mounting the lenses in the frame are magnified. Angling also generates unwanted sphere and cylinder in the periphery as well as distortion. These effects can be measured and even calculated ahead of time and cannot be dismissed lightly. The increased field of view is not needed.

Automobile Driving↗
PubMed1977

Displaying distortion in ophthalmic lenses.

A procedure is outlined for generating and displaying information about distortion in an ophthalmic lens. It involves a direct comparison of an object and its image as viewed at the entrance pupil of the eye. The same procedure may also be used to assess chromatic dispersion produced by the chromatic differences in magnification.

Eyeglasses↗
PubMed1977

Computation of unwanted sphere and cylinder in the periphery of a spectacle lens.

The author discusses practical issues relating to optometrists ordering and laboratories supplying ophthalmic lenses that meet the ANSI Z80. 1 Standard (1972) for minimizing unwanted spherical and cylindrical power in the periphery of lenses. He spells out the optical principles and formulas needed to develop a computer program that can be used by optometrists and opticians for designing lenses that meet the Z80. 1 Standard.

Eyeglasses↗