Mesopic Levels Research Articles

Optical filters influence on pupil size according to their material and spectral characteristics

Abstract Purpose To evaluate pupil size variations induced by optical filter by using filters with different materials and spectral characteristics, focussing on UV and blue light transmission properties of the filters Methods 220 pupil measurements (20 eyes, 20‐55 years old) were made using the pupillometer Procyon P2000SA at high Mesopic level (4.0lux). 10 filters of varying transmittance (visible, 4%‐65%, 5 filters UV‐transmitting and 5 filters UV‐absorbing) were used in a randomised way. 5 filters (UV‐transmitting) were dye‐coated polyester films with a substrate of PET (polyethylene terephthalate) and the another 5 filters (UV‐absorbing) were Ophthalmic CR39 lenses with a tinted coating in order to get the same absorbing characteristics than the PET filters. Measurements in the absence of a filter served as control Results Significant results on pupil size variation were obtained with lower UV and blue light transmittance filters (F14, F15 and F16; p=0.00) for both materials, PET and CR39 (Mydriasis obtained: F14R=13.99%; F15R=17.57%; F16R=22.90%; F14E=23.95%; F15E=22.69%; F16E=29.87%). Also significant differences in mydriasis‐induced by the filter were obtained when materials and blue‐light transmission properties were compared for filters 14 and 16 (PET vs. CR39: F14 (p=0.006), F16 (p=0.0167) Conclusion Filters with similar visible but different UV and/or blue‐light transmission properties significantly produce variations in pupil size at high Mesopic condition (4.0lux). Differences obtained in mydriasis‐induced by the filter depend not only on the material of the filter, but also the UV and/or blue‐light transmitted by the filter

Stimulus luminance and the spatial acuity of domestic fowl ( Gallus g. domesticus)

The luminance dependence of spatial acuity in domestic fowl was measured directly over stimulus luminances ranging from 0.06 to 57.35 cd m −2. At the highest luminance, acuity was around 6.5 c deg −1, in agreement with previous studies in this species. As stimulus luminance decreased, acuity fell with increasing rate to 3.2 c deg −1 at 0.06 cd m −2, following the same shape as acuity functions for other mammalian and avian species. These findings suggest that the rod–cone transition for domestic fowl is between 0.45 and 1.79 cd m −2. Over the photopic range from 1.79 to 57.35 cd m −2 the change of acuity for fowl was 1%, compared with 32% for humans. For domestic fowl, the Rovamo–Barten MTF model of contrast sensitivity accounted for the behaviour of acuity as a function of luminance down to mesopic levels.

Sensibilidade ao contraste de crianças surdas e ouvintes para grades senoidais em condições mesópicas

The aim of this study was to compare the contrast sensitivity (CSF) of deaf children and hearing children to spatial frequency of 0.25 to 2.0 cpd (cycles per degree of visual angle) at mesopic luminance level (0.7 cd/m2), using the psychophysical forced-choice method. Twenty children (7-12 years old) participated in this research, ten with prelingual deafness and ten with normal hearing. All participants had normal or corrected visual acuity. The ANOVA showed significant difference between the two groups [F(1, 238) = 15.487; p 0.05). The results suggest alterations in CSF to sine-wave gratings stimuli of deaf children at mesopic luminance level.

Randomized Prospective Comparison of Visian Toric Implantable Collamer Lens and Conventional Photorefractive Keratectomy for Moderate to High Myopic Astigmatism

To compare the Visian Toric Implantable Collamer Lens (TICL), a toric phakic intraocular lens (IOL), and photorefractive keratectomy (PRK) in the correction of moderate to high myopic astigmatism. This prospective, randomized study consisted of 43 eyes implanted with the TICL (20 bilateral cases) and 45 eyes receiving PRK with mitomycin C (22 bilateral cases) with moderate to high myopia (-6.00 to -20.00 diopters [D] sphere) measured at the spectacle plane and 1.00 to 4.00 D of astigmatism. All patient treatment and follow-up occurred at the Naval Medical Center San Diego. Study follow-up was 1 day, 1 week, 1, 3, 6, and 12 months postoperative. Mean best spectacle-corrected visual acuity (BSCVA), change in BSCVA, proportion of cases with improvement of 1 or more lines of BSCVA, proportion of cases with BSCVA and uncorrected visual acuity (UCVA) 20/12.5 or better, proportion of cases with BSCVA and UCVA 20/16 or better (6 months, 88% vs 54%, P=.002), and predictability +/-1.00 D (6 months, 100% vs 67%, P<.001) were all significantly better in the TICL group than the PRK group at all time periods studied postoperatively. Similarly, contrast sensitivity, tested at both the 5% photopic level and the 25% mesopic level, was significantly better at all postoperative time points in the TICL group. Mean spherical equivalent refraction was closer to emmetropia (0.28+/-0.41 vs 0.76+/-0.86, P=.005), and predictability +/-0.50 D and stability of manifest refraction (+/-0.50 D and +/-1.00 D) were significantly better in the TICL group at all postoperative visits through 6 months. Mean astigmatism correction at 6 months was not significantly different between the two groups (0.52+/-0.33 vs 0.46+/-0.35, P=.450). The TICL performed better than PRK in all measures of safety (BSCVA), efficacy (UCVA), predictability, and stability in this comparison, supporting the TICL as a viable alternative to existing refractive surgical treatments.

Evidencefor response contraction bias in side-by-side matching tasks

A recent study of lamp spectrum effects at mesopic levels employed side-by-side matching to investigate brightness. The results revealed an unexpected effect, identified here as a response contraction bias, normally only expected when judging individual stimuli. Response contraction bias causes subjective responses to be biased toward the middle of a response range. Although the bias is small its effect on brightness matching can be significant if the test procedure does not employ appropriate counterbalancing.

Comparison of two pupillometers in determining pupil size for refractive surgery

To compare a handheld and a digital pupillometer in determining pupil size in a population of refractive surgery candidates (group 1) and after implantation of an Artisan phakic intraocular lens (PIOL) for correction of myopia (group 2). Pupil size was measured with the Colvard and Procyon pupillometers in 121 eyes in group 1 and 83 eyes in group 2. Pupil sizes measured with the Colvard device were compared with the scotopic, mesopic-low and mesopic-high measurements taken with the Procyon pupillometer in both groups. Analysis of comparison between pupil measurements was performed according to methods described by Bland and Altman. The mean Colvard scotopic pupil diameter, scotopic, mesopic-low and mesopic-high Procyon pupil diameters were 5.86 +/- 0.81 mm, 6.42 +/- 0.88 mm, 5.55 +/- 0.95 mm and 4.21 +/- 0.73 mm in group 1 and 5.32 +/- 0.67 mm, 6.14 +/- 0.81 mm, 5.33 +/- 0.78 mm and 4.02 +/- 0.55 mm in group 2, respectively. The Colvard diameter compared most favourably with the Procyon mesopic-low diameter (group 2; p = 0.78). Measurements of pupil diameter with the Colvard pupillometer correlated best with measurements taken by the Procyon pupillometer under standardized mesopic-low light conditions. We believe that digital binocular infrared pupillometry is advantageous for obtaining standardized measurements of pupil size.

Supplementation with the carotenoids lutein or zeaxanthin improves human visual performance

Macular pigment (MP) is found in diurnal primate species when vision spans a range of ambient illumination and is mediated by cone and rod photoreceptors. The exact role of MP remains to be determined. In this study we investigate two new hypotheses for possible MP functions. As MP absorption coincides partly with that of rhodopsin, MP may reduce rod signal effectiveness in the mesopic range, thus extend the usefulness of cone-mediated vision into the mesopic range. Forward light scatter in the eye can reduce retinal image contrast. If blue light contributes significantly to intraocular scatter, selective blue light absorption by MP could reduce the effects of scatter. We investigated 34 subjects from a carotenoid supplementation trial. The measurements included high mesopic contrast acuity thresholds (CATs), macular pigment optical density (MPOD), wavefront aberrations, and scattered light. The measurements were made after 6 months of daily supplementation with zeaxanthin (Z, OPTISHARP), lutein (L), a combination of the two (C), or placebo (P), and again after a further 6 months of doubled supplementation. The data reveal a trend toward lower CATs in all groups supplemented, with a statistically significant improvement in the lutein group (p = 0.001), although there was no correlation with MPOD. Light scattering in the eye and the root-mean-square wavefront aberrations show decreasing trends as a result of supplementation, but no correlation with MPOD. The results suggest that supplementation with L or Z increases MPOD at the fovea and at 2.5 degrees , and that supplementation can improve CATs at high mesopic levels and hence visual performance at low illumination.

Toward a CIE supplementary system of photometry: brightness at any level including mesopic vision

Photometry for brightness at any level including mesopic vision is described on the basis of the work conducted towards the development of a Commission Internationale de l'Eclairage (CIE) supplementary system of photometry in CIE technical committees. Several critical items in developing such a system are discussed: (1) how to scale brightness using the concept of equivalent luminance; (2) the basic vision model of brightness perception; (3) a description of the chromatic contribution to brightness at the photopic as well as at the mesopic level; (4) formulation of an adaptation coefficient for rod-cone interaction. A possible photometric model for brightness is described based on these considerations, together with a quantitative evaluation of the model using experimental data.

Visual performance in night‐time driving conditions

This paper introduces an experimental multitechnique method which was developed to establish a basis for a task performance-based mesopic photometry. This approach considers night-time driving by dividing visual performance into three visual tasks, of which achromatic threshold and reaction time are presented. The performance of both visual tasks decreased with decreasing luminance level from 1 to 0.01 cd m(-2), showing the strong effect of light level on visual performance in driving. The behaviour of the achromatic contrast threshold and reaction time for low-contrast targets was similar in terms of spectral effects, the strongest effects occurring at the lower mesopic levels. Both measures showed the Purkinje shift with decreasing luminance levels. The experimental data were used to calculate mesopic performance measures with the new mesopic model. The results imply that compared with V(lambda), spectral sensitivity in night-time driving can be better described with a mesopic model based on visual performance measures.

The Role of Retinal Adaptation in Night Driving

Driving is essentially a visuomotor task, and there is now compelling evidence that the disproportionate number of road accidents under night driving conditions is linked to changes in visual performance resulting from reduced lighting. The objective of this article is to establish the extent to which vision is either rod-or cone-dominated under night driving conditions. Visual thresholds are measured under lighting conditions that simulate urban lighting. Dark adaptation curves are obtained under three ambient lighting conditions ranging from low (0.1 cd/m) to high (5 cd/m) mesopic levels of retinal adaptation using circular discs of different sizes (1 degree, 2 degrees, 3 degrees, and 5 degrees) presented at retinal eccentricities of 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 40 degrees. The dark adaptation curves exhibit the classic inflection point between rod and cone activity for the lower levels of ambient illumination but a simple monophasic function for the high mesopic levels (>0.5 lux). Adaptation rates are four times faster for the higher compared with the lower illumination level and twice as fast for central compared with peripheral presentation. The data suggest that vision is mediated by cone pathways at 5 lux and by rod pathways at 0.5/0.1 lux. This shift does not profoundly affect sensitivity, but because rod pathways are known to be slower than cone pathways, it will certainly affect observers' ability to respond to rapidly changing viewing conditions such as are encountered when driving at night.

The significance of mesopic visual performance and its use in developing a mesopic photometry system

In this research work detection rate was measured to evaluate the visual performance of human eyes at three mesopic light levels: 0.01, 0.1 and 1 cd m - 2 . Effects on visual performance at mesopic levels were analysed and spectral sensitivity curves were indirectly drawn based on the visual performance values. A comparison between the research results of the brightness-matching method and the performance-based method proves that the results from the latter method are in essence compatible with the results from the bright-matching method, since they are both in accordance with the Purkinje shift. Furthermore, the results of the performance-based method reflect the contribution of the colour channel in the visual information processing system.

Change of Color Appearance in Photopic, Mesopic and Scotopic Vision

Mesopic vision describes a range of light levels where vision is mediated by both cones and rods. The appearance of color in mesopic vision differs drastically from that in photopic vision, where only cones mediate visual information. We used a haploscopic color matching technique to investigate the color appearance under various illuminance levels, ranging from photopic to scotopic via mesopic levels. The observers did color matching between a test color chip under various illuminance levels and a matching color stimulus presented on the Cathode-Ray Tube (CRT) display under the photopic illuminance condition. The results showed that not only chroma and lightness but hue of most color chips changed with illuminance. The manner of the hue changed depended on the color of the test chip, while matching points approached a neutral gray with decrease in illuminance level for all test chips. Chroma reduced continuously with decrease of the illuminance level until 0.1 lx for reddish and yellowish color chips or until 1 lx for greenish and bluish ones. Beyond those illuminance levels, chroma was approximately constant. Lightness decreased with decreasing illuminance level for all test chips except bluish color chips, for which lightness did not decrease much in general and even increased in some cases as predicted by the Purkinje shift. The experimental results obtained in the present study provide critical features that should be considered in predicting the appearance of color at low light levels.

Spectral sensitivity of the pupillary system

Background: The spectral sensitivity of the pupillary mechanism is reported to be greater in the blue part of the visible spectrum compared to the sensitivity of the visual system as defined by V(Λ) for a twodegree field. This means that blue light gives rise to smaller pupils compared to those that occur with light of other colours of the same luminance. This has been interpreted as indicating that there may be a rod input to pupil response even at photopic levels of illumination. An alternative explanation is that the smaller pupil size for blue light is an artefact arising from the use of the CIE V(Λ) function which is based on the spectral sensitivity of the eye to a twodegree field. In most investigations of pupil response, the adapting luminous field is much larger than two degrees. Method: The size of the static pupil was measured using an entoptic method when the eye was adapted to a large ‘Ganzfeld’ field of wavelengths of 624, 580, 521, 467 and 429 nm and luminances ranging from mesopic to photopic. Results: The pupil is smaller for light of shorter wavelengths compared to that for light of longer wavelengths of the same luminance. This effect disappears at photopic luminances when luminance is calculated using the V10° (Λ) function instead of the V2° (Λ) function but is still evident at mesopic levels. When pupil size is plotted against equivalent luminance for a lodegree field V10° (Λ, Leq) pupil size is independent of wavelength. Conclusion: The apparent enhanced sensitivity of the pupil to blue light at photopic levels is an artefact arising from the inappropriate use of the V2° (Λ) for the measurement of luminance when the adapting field in pupil response measurements is a large field. Pupil size is a simple linear function of the log of equivalent luminance calculated for large fields for adapting luminances from photopic to mesopic and is independent of the wavelength of the adapting field for the whole range of adapting luminances.

Color identification data obtained from photopic to mesopic illuminance levels

AbstractTo use colors properly as an aid in visual tasks, it is necessary to know how colors are identified under various illuminating environments. In this study color identification was examined under a wide range of illuminances, from photopic to mesopic levels. Fifteen subjects named a color chip using one of the preselected color terms: red, orange, yellow, yellow‐green, green, blue‐green, blue, purple, pink, brown, white, gray, and black. The 256 color chips were selected from value planes of 4, 6, and 8 of the Munsell color space. The illuminance levels tested were 1000, 10, 1, and 0.1 lx. At 1000 lx the color chips were identified consistently by each of the color terms. At 10 lx the pattern of color identification was very similar to that at 1000 lx, though the consistency of the identification evidently declined. At 1 lx great changes in color identification occurred. By 0.1 lx reliable color identification was completely lost, though blue and red responses remained. At the lower illuminances green was replaced with blue, and red, orange, and pink were frequently confused with each other. However, the border between blue and purple was almost constant. These results provide a scientific basis for the appropriate use of colors in various illuminating environments. Also, they are useful for studies in color appearance modeling. © 2002 Wiley Periodicals, Inc. Col Res Appl, 27, 252–259, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.10065

Design and optimization of aretinal flux density meter

We present the design and calibration of a retinal fluxdensity (RFD) meter. This device can serve as a standard illuminancemeter or can measure flux density on the retina, using both photopicand scotopic spectral responses. In addition, through postprocessing, the instrument can determine standard illuminances andRFDs at mesopic levels. This device is an extension of an earlierinstrument, reported on by us, which replicated the spatialefficiency function of the human eye to determine retinal exposure.In this paper we describe the need for such a measurement device,detail its design, and report on its performance.

Night myopia and driving

Current knowledge of the refractive shifts (twilight myopia, night myopia, dark focus) that occur as the luminance is progressively lowered from photopic levels is reviewed. In complete darkness, myopic changes of the order of 1 dioptre are typical in young adult subjects. These gradually diminish as presbyopia is approached. The possible role of these refractive changes in causing visual difficulties for young drivers on the road at night is considered. It is concluded that high mesopic levels (about 1 cd/m2) of road luminance produced by street and vehicle lighting are normally too great to allow significant refractive shifts to occur, although acuity will be reduced due to light-dependent neural changes. Under these circumstances it appears unlikely that specific night-driving prescriptions will be beneficial: the accurate correction of normal refractive errors is, however, more important during night than day driving due to the greater blur associated with the larger night-time pupil. Suggestions are made for further experimental work in this area.

Night myopia and driving

Current knowledge of the refractive shifts (twilight myopia, night myopia, dark focus) that occur as the luminance is progressively lowered from photopic levels is reviewed. In complete darkness, myopic changes of the order of 1 dioptre are typical in young adult subjects. These gradually diminish as presbyopia is approached. The possible role of these refractive changes in causing visual difficulties for young drivers on the road at night is considered. It is concluded that high mesopic levels (about 1 cd/m2) of road luminance produced by street and vehicle lighting are normally too great to allow significant refractive shifts to occur, although acuity will be reduced due to light-dependent neural changes. Under these circumstances it appears unlikely that specific night-driving prescriptions will be beneficial: the accurate correction of normal refractive errors is, however, more important during night than day driving due to the greater blur associated with the larger night-time pupil. Suggestions are made for further experimental work in this area.

Rod temporal channels

Mechanisms underlying rod temporal contrast sensitivity have been considered in terms of a fast retinal signal predominating at mesopic levels and a slower retinal signal predominating at scotopic levels. Here we use a small signal masking method, which has previously been used to delineate the cone-mediated cortical temporal channels, to investigate their rod-mediated cortical counterparts. The results suggest that there are three different rod-mediated cortical temporal channels, one which is lowpass and two which are bandpass. These mechanisms co-exist at all light levels and their relative sensitivity depend on the stimulus spatio-temporal frequency.

Polyaxonal amacrine cells of rabbit retina: PA2, PA3, and PA4 cells. Light and electron microscopic studies with a functional interpretation.

Polyaxonal (PA) amacrine cells are a new class of amacrine cell bearing one to six branching, axon-like processes that emerge from the cell body or dendritic trees within 50 microns of the cell body. These slender processes of uniform caliber branch at right angles and in many respects closely resemble the axons of Golgi type II cells found elsewhere in the brain. Of the four types of polyaxonal amacrine cell that we have recognized in rabbit retina, two have been described previously in brief communications. One of these, the PA1 amacrine cell with its interstitially displaced cell body, located in the inner plexiform layer (IPL), has been analyzed extensively in two preceding reports. This paper concerns PA2, PA3, and PA4 amacrine cells. Type 2 polyaxonal (PA2) amacrine cells, identified in Golgi preparations of whole-mounted rabbit retinas, have smaller cell bodies (9-14 microns) than the other three types and these are always displaced to the ganglion cell layer (GCL) or the inner border of the inner plexiform layer (IPL). The dendritic fields of PA2 cells are also smaller than those of other PA amacrine cells, and most of their sparse dendritic branching is narrowly stratified at the border of strata (S) 4 and 5. Some members of this more heterogeneous amacrine cell "type" are bistratified, however, and more highly branched with terminal branches rising to end in S1. PA2 amacrine cells bear a scattering of small dendritic spines and may also exhibit complex dendritic appendages arising at the ends of terminal branches in proximal regions of the dendritic tree. PA2 cells emit one to three axons from the proximal dendritic tree, and about half of the cells bear a single axon. Type 3 polyaxonal (PA3) amacrine cells resemble PA1 cells in the large size of their cells bodies (11-16 microns) and dendritic fields, but differ from the latter in placement of cell bodies, which is in the GCL, and dendritic and axonal stratification, which is multistratified, ranging from S4 to S1, with a concentration in S3 or S4 and a variable contribution to S1. PA3 cells differ from PA1 cells in several other respects, including dendritic branching which occurs at higher frequency and is biased toward temporal retina, and in characteristic bristling dendritic spines, clustered in the intermediate regions of the dendritic tree, that are longer, more variable in appearance and more tightly clustered than the small, uniform spines of PA1 cells that are clustered on proximal dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)

Rod and cone contribution to adaptation processes in cat retinal ganglion cells

Extracellular ganglion cell responses were recorded to investigate mechanisms of light adaptation. Monochromatic test spots (575 nm) were projected onto the receptive field center of off-center cells and superimposed on a steady blue-green Ganzfeld background (Schott Filter BG 28), the strength of which was increased in steps of 0.5 log units to adapt rods. Response vs. log intensity functions were determined over a range of 7 log units of test light irradiance at each background level. At higher adaptation levels response thresholds followed the typical Weber function. Surprisingly at lower adaptation levels the sensitivity of the cell increased by about 0.7 log units, most markedly in a range of 1 log unit of moderate light adaptation when the background was changed from dark to the dimmest detectable background (10(-5) lm/m2). In the dark-adapted state a small off-response of long latency (40-100 ms at 10(2) quanta.s-1.microns-2) is observed at low rod stimulating test light irradiances. A transition to a cone-dominated transient response of 2 to 5 ms duration occurred at high intensities (10(5) quanta.s-1.microns-2). At mesopic levels the two responses seem to cancel each other, rendering a delayed off-response that is probably the result of rod-cone interaction. As in psychophysics, saturation can be observed at very high background intensities (10(6) quanta.s-1 microns-2). These data suggest interactions between rods and cones that determine the sensitivity of cat retinal ganglion cells at low levels of adaptation for suprathreshold stimuli.