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Biomedical subjects

P L Pease

Publications and source records attributed to P L Pease.

16 recordsLinked to original sources
PubMed1999

Effect of yellow filters on pupil size.

The purpose of this study was to investigate the size of the pupil while viewing through yellow and neutral density (ND) filters. Previous studies have shown that the pupil of the human eye is relatively more sensitive to short wavelengths than indicated by the photopic luminosity curve. We first measured the consensual horizontal pupil diameter of 11 observers as a function of luminance (0.144 to 18,150 cd/m2) to establish the luminance-response function for each observer. We then measured the pupil diameter while the observer viewed through a Corning Photochromic Filter (CPF) 550 lens and two ND filters (ND 0.5 and 1.0). The pupil diameters obtained with each filter were compared to the diameters at an equivalent luminance based upon each observer's luminance-response function. Our results show that the pupil diameter is larger with the yellow lens than when viewing a broad spectrum white field at an equivalent luminance. We speculate that our results may explain some, but not all, of the well-known subjective brightness enhancement that occurs when viewing through yellow filters.

Color↗
PubMed1991

Variables affecting the spectral transmittance of light through porcelain veneer samples.

The spectral transmittance of porcelain laminate veneers was measured at three different thicknesses (0.50, 0.75, and 1 mm) and three different opacities (25%, 75%, and 100%). The results indicated that the thickness of the porcelain veneer was the primary factor affecting light transmission and not the opacity. The measured values of transmittance were then used to estimate the setting time for light-cured luting agents of a porcelain veneer.

Analysis of Variance↗
PubMed1989

Axial chromatic aberration of the human eye: frequency or wavelength?

The axial chromatic aberration of the human eye is nearly perfectly described by a linear function when expressed in terms of frequency rather than wavelength. Since linear functions are simple to work with and more readily understood, there are advantages for the expression of these data in terms of frequency.

Analysis of Variance↗
PubMed1988

Longitudinal chromatic aberration of the human eye and wavelength in focus.

The wavelength in focus on the retina was determined for 14 observers from measurements of the longitudinal chromatic aberration of the eye. Measurements were made at two viewing distances: 3 m and 40 cm. The results show a large amount of individual variability for the wavelength in focus at each distance. The range of values at 3 m was 457 to 593 nm with a mean of 518 nm, and 375 to 548 nm with a mean of 468 nm at 40 cm. The chromatic aberration measured at 3 m is the same as previously reported data by other investigators for distant viewing. The average results of this study indicate very little difference for the chromatic aberration measured at near compared to distant viewing but, again, considerable individual variability exists.

Accommodation, Ocular↗
PubMed1988

A new test for screening color vision: concurrent validity and utility.

Recognizing the need for an effective test for screening color vision in young children, we have developed a new pseudoisochromatic (PIC) plate test which is useful for a wide variety of observers at different ages. The test consists of four plates and responses can be used to categorize color vision as normal or as either red-green or blue-yellow defective. Results of this validation study with adults, both color normal and red-green defective, show a high degree of correlation between the new test and the Nagel anomaloscope: there were no false positives and only a few false negatives, which occurred with mild deuteranomalous observers. The validity of the test compares favorably to the Ishihara, F-2, and the AO-HRR screening plates. Results with toddlers (3 to 6 years) indicate that the task demands of the test are well suited for testing young children. The percentage of color defectives identified in the toddler sample using the new test is closer to the adult prevalence than results obtained with the F-2 and AO-HRR screening plates, which gave dramatically higher failure rates. The new test is culture-free and can be administered rapidly to both verbal and nonverbal observers using pointing or preferential looking.

Adult↗
PubMed1987

Optical density of human macular pigment.

Foveal and parafoveal spectral sensitivities of the G cone mechanism were used to derive the difference spectrum for the macular pigment for 12 observers. Measurements of the peak density of the macular pigment were obtained with a shortened version of the same procedure for an additional 15 observers. The mean density for all 27 observers at 460 nm was 0.77 +/- 0.06 with a range of 0.21-1.22. The mean density is higher than that previously reported and, compared to the standard absorbance curve (Wyszecki and Stiles, 1967), the results indicate higher density values for wavelengths on the long wavelength side of the absorption maximum.

Adult↗
PubMed1983

Macular pigment difference spectrum from sensitivity measures of a single cone mechanism.

We have obtained the difference spectrum for the macular pigment by comparing the spectral sensitivity of the "green-sensitive" or G cone mechanism in the foveal and parafoveal region. The method overcomes objections to previous attempts to obtain a difference spectrum from the spectral sensitivities by isolating a single receptor mechanism; it also provides a relatively easy approach for obtaining a reliable measure of the optical density of the macular pigment for individual subjects. Our results using this method suggest a higher optical density for the macular pigment than that obtained from data where more than one cone type influenced the difference spectrum.

Color↗
PubMed1983

Discrepant results obtained with two versions of the Farnsworth Panel D-15 test in patients with acquired blue-yellow defects.

Two commercially available Panel D-15 tests were administered to two patients with acquired blue-yellow defects. The results obtained with each test were different and apparently influenced by the cap construction which is the only difference between the two tests. In one test the surface of the cap is concave and polished while in the other test the cap surface is flat and has a matte or dull finish. The mechanism accounting for the different results is not obvious.

Adult↗
PubMed1979

Clinical implications of color vision research.

The attributes of color and the mechanisms underlying normal and defective color vision are reviewed. The clinical implications of some research efforts bearing on congenital and acquired color defects, peripheral color vision, and the influence of photostable pigments on color vision and color vision tests is presented. This presentation is intended to illustrate how selected avenues of research have contributed to our understanding of color vision and to demonstrate the clinical utility of that research.

Color Perception↗
PubMed1971

Contours and contrast: responses of monkey lateral geniculate nucleus cells to luminance and color figures.

The responses of single units in the monkey lateral geniculate nucleus to different portions of figures which differed from their backgrounds in color and brightness were examined. Border enhancement was found in the response to luminance figures but not in the response to color figures. In addition, cells showed border enhancement only in the case of a figure which produced an increment (as opposed to a decrement) in their firing rates. In situations in which very striking brightness contrast is seen perceptually, the cells do not show the corresponding changes in firing rate across the whole pattern. The lateral inhibitory mechanisms found in the retina and geniculate can thus account for luminance border enhancement, but not entirely for simultaneous brightness or color contrast, for which other cortical processes of some sort must be responsible.

Animals↗