Biomedical subjects
Publications and source records attributed to G A Fry.
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.
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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.
The new role is brought about by new laboratory practices in the use of stock semifinished and uncut lenses in filling orders and in the changes in standards for design requirements. A partial solution to this problem is proposed.
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.
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.
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.
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.
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.
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.
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.
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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.
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.