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Biomedical subjects

O W Richards

Publications and source records attributed to O W Richards.

18 recordsLinked to original sources

Variation of the green-red ratio with refractive error.

The relationship of refractive error to green-red ratios among color normals was investigated by asking 27 subjects to match a standard yellow with a mixture of red and green primaries using a Nagel anomaloscope. Green-red ratios did not show any regular change with refractive error. Differences in refractive error, natural or induced, among color normal persons did not change the measurements of color vision with the Nagel anomaloscope.

Color Perception

Limited improvement of color deficient vision with colored filters.

For over a hundred years, colored filters have helped people with less than normal color vision, to discriminate colors. Filtered light does not restore missing or abnormal pigments within the defective eye. Contrast and discrimination provided by a suitable colored filter can help discrimination of a given set of colors, but may prevent seeing other sets of colors. The use and limitations of color filters are described as aids for color deficient vision.

Color Vision Defects

Cool white, Ultralume, and Vita-Lite fluorescent lamps for use in color vision testing.

Thirty-one normal and 20 color vision-deficient persons were tested with the Hardy-Rand-Rittler (HRR) Pseudoisochromatic Plates, Farnsworth's D-15 and 100-Hue tests, and the Davidson & Hemmendinger (D & H) Color Rule using Vita-Lite, Ultralume, and Cool White fluorescent lamps to determine their usefulness for color vision measurement. The persons with deficient color vision were classified with a Nagel anomaloscope. The Macbeth Easel lamp was the reference for determining relative lamp performance. No normal was misclassified with any of the lamps. Scores with the Vita-Lite lamp were qualitatively and quantitatively most similar to those with the Macbeth lamp. The Ultralume gave intermediate results, and the Cool White was the least satisfactory substitute. Norms for the metameric D & H Color Rule for each lamp were different, which prevented intercomparisons. Best separation of the scores of deficient from normal persons with the D & H Rule occurred with the Macbeth and Vita-Lite lamps. Better performance with the Vita-Lite and Ultralume lamps can be expected from protans with the HRR and 100-Hue Tests and poorer performances from deutans on the HRR tests than with the standard Macbeth Lamp. The Cool White lamp was judged an unsuitable substitute for color vision testing.

Adolescent

Night myopia at night automobile luminances: final report.

One-hundred seventy-five persons viewed test letters of 35 and 11% contrast at 0.1 and 0.01 fL chart luminance while lenses (+0.25 to -1.50 D in 0.25-D steps) were placed before their eyes (and glasses, if they wore them). With one or more of the minus lenses, only 9% of the subjects obtained improved acuity by one or more lines on the chart. The most common optimum lens power was -0.75 D.

Adult

Effects of luminance and contrast on visual acuity, ages 16 to 90 years.

Visual acuity of persons aged 16 to 90 years was measured with Snellen letters of varied contrast at 10, 1, 0.1, and 0.01 fl chart luminances. Percentage losses of seeing with age were computed. At 10 fl luminance, perception of high- and medium-contrast letters has changed little at age 40, but about twice as much light is needed to see low-contrast letters as at age 20. By age 70, no 2-min-subtense (20/40) letters were seen at 0.01 fl luminance. The need of older people for increased lighting during indoor tasks and night driving is discussed.

Adolescent

Instrument myopia--microscopy.

Looking through optical instruments stimulates the eye to accommodate more than would be necessary for naked eye viewing; this increased near power is called instrument myopia. The amount (up to -5 diopters) varies with the observer and the conditions of viewing. Using microscopes produces -1.5 to -2 diopters of instrument myopia. More instrument myopia is found with low-power magnification, inexperienced users, and when focusing form minus blur to sharp image. Physiologically, the instrument myopia appears to be associated with an accommodative equilibrium position and, psychologically, with a sensing of proximity.

Accommodation, Ocular