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Biomedical subjects

G A Fry

Publications and source records attributed to G A Fry.

At least 37 records · Page 2Linked to original sources
PubMed1980

The Bezold-Brücke phenomenon for purple colors.

A bipartite stimulus 2 degrees in diameter was used to study the Bezold-Brücke phenomenon for purple colors. A mixture of 460 nm and 667 nm in one half at a given luminance was matched with a mixture of the same two wavelengths at a luminance level 10 times higher. The hue of the 667-nm stimulus was not affected by the change in luminance. There is one mixture of red and blue which remains unchanged in hue as the luminance increases. Reddish purples shift toward red and bluish purples toward blue. These findings are consistent with a zone theory of color vision such as proposed by Adams.

Color Perception↗
PubMed1980

The absence of the Ives effect in a deuteranope.

Ives found that when monochromatic stimuli are matched to white by flicker photometry, they are not equal in brightness to the white by direct comparison, and the discrepancy is minimal for yellow but is increased for longer and shorter wavelengths. On the two sides of yellow, the colors are more saturated, and Ives postulated that brightness involves the sum of a chromatic component and an achromatic component and that the chromatic component varies with the saturation. In the case of a deuteranope, one would expect a vigorous chromatic response for yellow and blue stimuli but a poor response for the neutral part of the spectrum. The Ives effect is virtually nonexistent for subject SR, who is a deuteranope. In terms of the zone theory of color vision, this would mean that the blue-yellow chromatic channel contributes little or nothing to brightness. In a normal observer, the blue-yellow mechanism can be isolated by using blues and yellows depurified with white, but in this case the Ives effect is found to exist.

Adult↗
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↗
PubMed1975

Ray tracing through a toric refracting surface.

A procedure has been developed for tracing a ray through a toric refracting surface. The surface is defined in terms of a rectangular coordinate system. The ray is specified by the rectangular coordinates of a point through which it passes and its direction-cosines.

Lenses↗
PubMed1975

Analysis of photometric data.

This paper describes how information about the configuration of the cornea can be derived from the raw data obtained with telecentric photokeratometers, and how such data can be expressed and used. It also deals with the interrelations of the different ways of expressing the data.

Cornea↗