The effect of gender and iris color on the dark-adapted pupil diameter.

PURPOSE: The aims of this study were to assess the utility of digital color sensing to quantify iris color using digital photographs and to determine whether gender or iris color affects the dark-adapted pupil diameter (DAPD). METHODS: Subjects aged 18-80 years (N = 263) with no eye disease had their right DAPD measured after 2 min of dark adaptation at 1 lux using the NeurOptics pupillometer. A high-resolution digital slit lamp photograph of the iris was taken, and iris color was subjectively classified as blue, blue-green, green-brown, light brown, or dark brown. The digital photographs were objectively measured on-screen with the Minolta TV Color Analyzer II using the Commission Internationale de l'Eclairage system of color description. Regression analyses were performed to identify correlations between subjective iris color, Commission Internationale de l'Eclairage measurements, and DAPD. RESULTS: Gender and iris color had no effect on the DAPD. The Minolta TV Color Analyzer could discriminate all blue eyes (blue and blue-green) from all brown eyes (light and dark) but could not distinguish between shades of blue or shades of brown. Green-brown irises had no unique chromatic properties and could not be distinguished from other colors using our technique of digital color analysis. The Minolta device was simple and efficient to use. CONCLUSIONS: Contrary to long-held beliefs, female patients and blue-eyed patients do not have larger DAPD. Digital color sensing is a useful technique for objectively describing iris color.

Sustained pupillary constrictions mediated by an L- and M-cone opponent process.

We show that irradiance-coding alone cannot explain the sustained pupillary constrictions evoked by chromatic and luminance variations in a stimulus. For example, stimulus modulations that decremented the contrasts in L- and M-cones as well as rods and melanopsin photoreceptors produced sustained constrictions rather than the predicted dilations. Although the sustained responses are unidirectional, we confirm that they are at least partially mediated by an L- and M-cone opponent interaction. We discuss the implications of sustained unidirectional chromatic responses in view of the function of the pupil to improve the clarity of vision.

Statistical test of VEP waveform equality.

The aim of the study was to describe a theory and method for inferring the statistical significance of a visually evoked cortical potential (VEP) recording. The statistical evaluation is predicated on the pre-stimulus VEP as estimates of the cortical potentials expected when the stimulus does not produce an effect, a mathematical transform to convert the voltages into standard deviations from zero, and a time-series approach for estimating the variability of between-session VEPs under the null hypothesis. Empirical and Monte Carlo analyses address issues concerned with testability, statistical validity, clinical feasibility, as well as limitations of the proposed method. We conclude that visual electrophysiological recordings can be evaluated as a statistical study of n = 1 subject using time-series analysis when confounding effects are adequately controlled. The statistical test can be performed on either a single VEP or the difference between pairs of VEPs.

Pupillary correlates of light-evoked melanopsin activity in humans.

We investigated whether cones are the only photosensitive process mediating the photopic pupillary light reflex. New analyses were performed on previously published recordings, focusing on those evoked by the onset of photopically equated short- and long-wavelength stimuli. Comparisons between responses revealed contraction differences that slowly grew to a peak and gradually declined. The late contraction was associated with short wavelengths and appeared mostly at the higher stimulus intensities. We conclude that cones are not the only photoreception process mediating the photopic ON-reflex and infer that melanopsin is another. Melanopsin contributes to the steady-state pupil size in daylight illumination.

Pupil size and the ablation zone in laser refractive surgery: considerations based on geometric optics.

PURPOSE: To determine whether the currently accepted method of selecting a minimum ablation zone size for refractive surgery based on dark-adapted pupil diameter is substantiated by geometric optical analysis. SETTING: Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA. METHODS: An optical model of the anterior segment was developed to calculate the effective corneal refractive diameter (ECRD), which is the diameter of the area of cornea that refracts all incident light rays arising from objects along the line of sight though the physical pupil (PP). The concept of the entrance pupil (EP) was reexamined and developed, and the ECRD was calculated over a range of corneal curvatures (K), anterior chamber depths (ACDs), and EP sizes. The model was generalized to include oblique light rays. Calculations were performed using MatLab Optimization Toolbox software (The MathWorks). RESULTS: For a given EP size, the ECRD was significantly influenced by K and slightly influenced by ACD. CONCLUSIONS: For objects on the line of sight, the ECRD was smaller than the EP in all cases. Regarding rays from objects in the periphery, the ECRD expanded rapidly as the angle of oblique incidence increased. For objects on the line of sight, the ECRD is always smaller than the clinically measured pupil (EP) because the EP is substantially magnified relative to the PP. Ablation zones larger than the EP should, in theory, prevent scattered or defocused light rays from contributing to the foveal image. When considering objects in the periphery, the increase in ECRD is sufficiently rapid that current refractive procedures cannot stop scattered light from these objects from contributing to the retinal image.