L. Jiménez del Barco

Effect on laser-ablation algorithms of reflection losses and nonnormal incidence on the anterior cornea

In this paper, we provide an analytic expression for an adjustment factor in ablation algorithms for photorefractive laser surgery which take into account reflection losses and the nonnormal incidence on the cornea. We evaluate the influence of this factor on certain ocular parameters, calculating alterations in the radius of anterior cornea and corneal asphericity when we use the algorithm given by Munnerlyn’s paraxial formula. Our data indicate that this adjustment factor should be considered in the ablation algorithms that are currently being proposed in customized corneal ablation and that need great accuracy for the correction of eye aberrations.

Temporal aspects of color discrimination

Experimental results obtained for different observers and stimuli are analyzed to study the influence of the exposure time of the test on the differential thresholds of color. Exposure times from 0.2 to 9 sec are studied. A minimum for the differential thresholds of luminance and chromaticity and for the global differential threshold is found around 1 sec.

Binocular summation of chromatic changes as measured by visual reaction time

We determined visual reaction times to monocular and binocular changes in the luminance of isochromatic stimuli and to monocular and binocular changes in the color of isoluminant stimuli. Two isoluminant color changes were tested: chromatic variations along the red—green axis of Boynton’s (1986) two-stage color vision model and chromatic variations along the yellow—blue axis of the same model. The results indicate a greater degree of binocular summation for luminance change than for color change. This result was largely independent of the motor component of reaction time.

Optimum corneal asphericity of myopic eyes for refractive surgery

Abstract In this work, an improvement to the Munnerlyn formula used in refractive surgery is proposed by selecting the final corneal asphericity. A theoretical optical analysis has been performed by adopting the RMS (root mean square) spot size as a merit function. Two different sets of myopes having refractive errors ranging up to —7D have been tested. The results show that a corneal asphericity of around Q=—0.61, with the radius provided by the emmetropization formula based on thin lens theory, may improve image quality after surgery. This value could be used in practical surgery because it is easy to implement in the ablation algorithm and it requires no additional data from other clinical surgery instrumentation.

Some classical color differences calculated with new formulas

An evaluation of chromatic and color-threshold differences was carried out by using the CMC(l:c) and the BFD(l:c) color-difference formulas [ J. Soc. Dyers Colour.100, 128 ( 1984); J. Soc. Dyers Colour.103, 86 ( 1987)] from experimental threshold results obtained with visual colorimeters [ J. Opt. Soc. Am.32, 247 ( 1942); J. Opt. Soc. Am.39, 808 ( 1949); J. Opt. Soc. Am.47, 137 ( 1957); J. Opt. Soc. Am.61, 1135 ( 1971)]. The good results previously reported on the use of these two new formulas with surface colors are also found for the chromatic differences calculated, especially with the BFD(1:1) formula. In the case of color differences BFD(0.6:1) improves the results achieved with BFD(1:1) and gives results similar to those of CMC(1:1). The claim of CMC(l:c) and BFD(l:c) as sometimes superior alternatives to the currently recommended CIE formulas CIELUV and CIELAB can be supported by the present results.

Optimization of color reproduction on CRT‐color monitors

In the present experimental study, we quantify the influence of the brightness and contrast levels of a CRT- color monitor in the color reproduction of 60 Munsell chips distributed throughout the chromatic diagram. The images were captured by two CCD cameras, and the color differ- ences were evaluated after reproducing the chips on a color monitor (the experiment was performed with 3 different monitors) for 9 combinations of brightness-contrast levels. We evaluated the color differences with 3 different formu- las: CIELAB, CIELUV, and CIE94. The results indicate that the optimal settings of a monitor, to minimize the color differences, is a medium or minimum brightness level in combination with a maximum contrast level. This combina- tion ensures a more faithful color reproduction with respect to the original image.© 1999 John Wiley & Sons, Inc. Col Res Appl,

Influence of the Luminance and Opponent Chromatic Channels on Stereopsis with Randomdot Stereograms

The present work examines the relationship between random-dot stereograms (via the disparity range parameter) and color-vision mechanisms (via the luminance channel and red-green and tritan directions at isoluminance). The results clearly indicate that the variations in the stereograms along red-green confusion lines contribute to stereopsis. Stereoscopic perception depends on spatial information for stereograms generated with variations along tritan confusion lines. For observers who perceive stereopsis via tritan directions, the results show a gradation in the disparity range, with the disparity range for stereograms generated by luminance variations being greater than for stereograms generated in red-green directions; the latter range is, in turn, greater than for stereograms generated along tritan directions.

Retinal image quality in myopic subjects after refractive surgery

Abstract In the present work, we offer a theoretical analysis of retinal image quality for different groups of myopes (-2D, -4D, -8D, -12D) subjected to refractive surgery. For this, the polychromatic optical MTF (modulation transfer function) corresponding to the far point of a myopic eye was compared with the image for the infinity point after refractive surgery. The optical quality of the retinal image was studied, considering the defocusing corresponding to chromatic aberration and the spherical aberration. The results for retinal image quality show a general deterioration, which was accentuated with the degree of myopia. The results suggest that refractive surgery could be improved by modifying the asphericity of the anterior surface of the cornea, which, in addition to making the eye emetropic, would optimize the MTF of the subjects. We also present a theoretical analysis involving non-spherical surfaces before and after operation, testing the influence of corneal asphericity in this case, as well as the possible optimization of the polychromatic MTF.

Contribution to the experimental review of the colorimetric standard observer

The color-matching functions of six observers have been measured in the range of 400–700 nm in intervals of 10 nm using two modified Donaldson-type colorimeters at a luminance of 4.5 cd/m. A statistical study has been carried out to determine the interobserver variability (in our results), and the results of other authors using various representational color systems have been compared with ours. The most important findings are that, although a common mathematical mean cannot be found, the shape of the curves for the color-matching functions obtained in our laboratory for all the observers is very close to that of other authors, thereby implying that the overall color response of the human visual system is similar in all observers. In addition, the results show that, for the long wavelengths (around 600 nm), a great amount of desaturant primary (460 nm) is necessary, indicating possible rod intrusion under our experimental conditions.© 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 377–388, 1999

A comparative study of successive and simultaneous methods in colour discrimination

Simultaneous and successive methods of comparison of stimuli are studied by comparing experimental results of colour discrimination experiments. In this way, colour differential thresholds for two normal observers and four different stimuli were measured by the two methods. In most cases, the capacity to discriminate colour decreased when the successive method was used, although no differences were found in qualitative aspects of discrimination. These results differ somewhat from previous reports in this field, probably because of experimental differences in the method of obtaining the thresholds.