Mesopic Levels Research Articles

Effect of changing mesopic and photopic light conditions on visual functions.

To determine the effects of change in light conditions on refractive error and visual functions including visual acuity, stereopsis and contrast sensitivity. This cross-sectional study was conducted in the optometry clinic of the Shahid Beheshti School of Rehabilitation on 48 students in 2021-2022. All of them had eye health and normal visual function and could have refractive errors or not. Light intensity of 4 lx was considered equivalent to photopic light condition and light intensity of 1 lx was considered to be equivalent to mesopic light condition. The amount of refractive error was checked by auto refractometer and its changes in mesopic light condition were subjectively measured. Also, visual acuity, stereopsis and contrast sensitivity (in five spatial frequencies of 1.5, 3, 6, 12, and 18 cycles per degree), were measured first in photopic light condition and then in mesopic light condition, by Snellen control vision chart, stereo butterfly test and the M&S technology monitor test respectively. In the 48 student subjects with an average age of 22.69±3.56y, mean of refractive error as sphere equivalent, visual acuity and stereopsis were -1.25±1.74 diopters, 0 logMAR, 44.37±13.03 seconds of arc, respectively in photopic light condition while in mesopic light was equal to -1.56±1.75 diopters, 0.12±0.09 logMAR and 50.62±33.35 seconds of arc, respectively. The mean of contrast sensitivity measured at spatial frequencies of 1.5, 3, 6, 12, and 18 cycles per degree in photopic condition was equal to 2.38±0.04, 2.37±0.07, 2.04±0.21, 1.27±0.32, 0.82±0.27 logarithm of contrast sensitivity, respectively and in mesopic lighting condition was equal to 2.34±0.12, 2.30±0.16, 1.84±0.28, 1.02±0.28, 0.63±0.24 logarithm of contrast sensitivity, respectively. Statistical analysis showed a significant difference between the two lighting conditions in all evaluated variables [refractive error (P<0.001), visual acuity (P<0.001), stereopsis (P=0.008) and contrast sensitivity (P<0.001)]. The refractive error of the student subjects in mesopic light condition change towards myopia, and its amount is clinically significant. Also, the examination and comparison of the factors of visual acuity, stereopsis and contrast sensitivity in these two lighting conditions show that the decrease in brightness level to the mesopic level causes a decrease in the aforementioned visual functions.

Divergent outer retinal circuits drive image and non-image visual behaviors.

SUMMARYImage- and non-image-forming vision are essential for animal behavior. Here we use genetically modified mouse lines to examine retinal circuits driving image- and non-image-functions. We describe the outer retinal circuits underlying the pupillary light response (PLR) and circadian photoentrainment, two non-image-forming behaviors. Rods and cones signal light increments and decrements through the ON and OFF pathways, respectively. We find that the OFF pathway drives image-forming vision but cannot drive circadian photoentrainment or the PLR. Cone light responses drive image formation but fail to drive the PLR. At photopic levels, rods use the primary and secondary rod pathways to drive the PLR, whereas at the scotopic and mesopic levels, rods use the primary pathway to drive the PLR, and the secondary pathway is insufficient. Circuit dynamics allow rod ON pathways to drive two non-image-forming behaviors across a wide range of light intensities, whereas the OFF pathway is potentially restricted to image formation.

Efficiency in Street Lighting Projects by Employing LED Luminaires and Mesopic Photometry

This paper discusses the importance of adapting conventional photometric quantities when lighting systems with low luminance levels are under analysis, as public lighting or external lighting in general. In this sense, it is presented an alternative methodology for lighting projects in street lighting, considering the mesopic photometry. The CIE recommendation 191:2010 proposes correc-tion factors that convert conventional photometric quantities (photopic) into quantities adapted to the corresponding mesopic level. However, a necessary parameter to obtain these correction factors is the relationship between the scotopic and photopic light fluxes of a light source (S/P ratio), which requires special equip-ment that it is not easily available to engineers, technicians and lighting designers. Thus, this paper proposes a general equation that provides the S/P ratio as a function of the correlative color temperature and the color rendering index of the light source, which are information provided in the manufacturers’ catalogs or electric lamp packages. To illustrate the application of the exper-imentally derived relationship, a typical street lighting project is considered, specifically a retrofit from HPS lamps to modern LED luminaires. In this case, the conventional routine must be changed, allowing the adaptation of conventional quantities to mesopic quantities without need for specialized equipment. The case study evidences that the use of mesopic photometry in con-junction with more appropriate technologies, such as LED lumi-naires, lead to a higher energy efficiency of the system.

Non-linearities in the Rod and Cone Photoreceptor Inputs to the Afferent Pupil Light Response.

Purpose: To assess the nature and extent of non-linear processes in pupil responses using rod- and cone-isolating visual beat stimuli.Methods: A four-primary photostimulating method based on the principle of silent substitution was implemented to generate rod or cone isolating and combined sinusoidal stimuli at a single component frequency (1, 4, 5, 8, or 9 Hz) or a 1 Hz beat frequency (frequency pairs: 4 + 5, 8 + 9 Hz). The component frequencies were chosen to minimize the melanopsin photoresponse of intrinsically photosensitive retinal ganglion cells (ipRGCs) such that the pupil response was primarily driven by outer retinal photoreceptor inputs. Full-field (Ganzfeld) pupil responses and electroretinograms (ERGs) were recorded to the same stimuli at two mesopic light levels (−0.9 and 0 log cd/m2). Fourier analysis was used to derive the amplitudes and phases of the pupil and ERG responses.Results: For the beat frequency condition, when modulation was restricted to the same photoreceptor type at the higher mesopic level (0 log cd/m2), there was a pronounced pupil response to the 1 Hz beat frequency with the 4 + 5 Hz frequency pair and rare beat responses for the 8 + 9 Hz frequency pair. At the lower mesopic level there were few and inconsistent beat responses. When one component modulated the rod excitation and the other component modulated the cone excitation, responses to the beat frequency were rare and lower than the 1 Hz component frequency condition responses. These results were confirmed by ERG recordings.Conclusions: There is non-linearity in both the pupil response and electroretinogram to rod and cone inputs at mesopic light levels. The presence of a beat response for modulation components restricted to a single photoreceptor type, but not for components with cross-photoreceptor types, indicates that the location of a non-linear process in the pupil pathway occurs at a retinal site earlier than where the rod and cone signals are combined, that is, at the photoreceptor level.

Spectral characteristics of road surfaces and eye transmittance: Effects on energy efficiency of road lighting at mesopic levels

In 2010, the CIE published a recommended system for mesopic photometry based on visual performance. According to this system, scenes illuminated at mesopic levels with light sources of high S/P ratio, will produce better visual performance than those illuminated with light sources of a lower S/P ratio at equal photopic luminance. However, there could be other factors affected by SPD that, when quantified, could lead to a contradictory final effect. The scope of this paper was to evaluate how road lighting is affected by the spectral road surface reflectance and by the human eye transmittance as people get older. Our results suggest that the benefits of considering the mesopic vision effect for light sources with high S/P ratios are totally counteracted by the other two effects at mesopic luminances between 0.75 cd/m2 and 1.73 cd/m2 for people between 20 and 60 years of age, depending on the light source and the age of observers.

Mesopic increment detection sensitivity, Part I: Phenomenological analysis

Mesopic threshold detection sensitivity was investigated by projecting quasi-monochromatic incremental targets with 22 centroid wavelengths between 422 nm and 652 nm onto different backgrounds. Every detection target was observed by at least nine subjects under eight different viewing conditions: two mesopic luminance levels (0.1 cd/m2; 1 cd/m2) and four eccentricities of target appearance off the visual axis (0°, 2.65°, 10° and 20°). Results were expressed in terms of absolute detection sensitivity values, i.e. inverse increment radiance values for each target at the detection threshold in sr·m2·W−1 units. In this part, the experimental method is described, and the dataset is analysed in terms of retinal mechanisms.

FMRI activation of LGN and visual cortex under photopic, mesopic and scotopic luminance levels

fMRI activation of LGN and visual cortex under photopic, mesopic and scotopic luminance levels

Determinants and standardization of mesopic visual acuity.

It is well established that visual acuity (VA) decreases with luminance but the specific factors that are responsible remain unclear. The purpose of this study was to quantify the contributions of accommodative error, pupil size, and higher-order aberrations to the decrease in VA when transitioning from photopic to mesopic light levels. Additionally, repeatability of VA at photopic and mesopic levels was measured to derive a luminance recommendation for mesopic VA testing, which can provide the standardization needed for future translational clinical studies and the widespread adoption of mesopic VA testing. Monocular VAs were assessed at one photopic and three mesopic light levels: 94, 3, 0.75, and 0.38 cd/m, with an E-ETDRS testing system in 43 normal subjects. Accommodative error, pupil size, and higher-order aberrations were obtained. Twenty subjects were retested at another visit to assess VA repeatability. The mean (±SD) logMAR (logarithm of the minimum angle of resolution) VA was -0.08 (±0.06) at 94 cd/m, 0.05 (±0.07) at 3 cd/m, 0.16 (±0.06) at 0.75 cd/m, and 0.27 (±0.09) at 0.38 cd/m. Light level and accommodative error were significantly associated with VA, and light level explained 75% of the variance. The mean differences in VAs between two visits were not significantly different from zero (p > 0.05). The coefficients of repeatability for 94, 3, 0.75, and 0.38 cd/m were 0.08, 0.11, 0.14, and 0.14 logMAR, respectively. Light level, among all other factors studied, contributes the most to the reduction in VA tested under mesopic conditions. Testing mesopic VA at 0.75 cd/m, or about 2.0 log units less than photopic testing, provides a significant and repeatable decrease in VA similar to standardized low-contrast VA testing, and therefore this level is recommended.

Dark versus bright equilibrium hues: rod and cone biases

Equilibrium (unique) red, green, blue, and yellow stimuli look bright in a black surround, but they look dark in a bright white surround, and yellow changes to brown. We investigated differences in equilibrium-hue chromaticity between bright and dark hues to reveal changes in weighting of cone and rod signals. The largest, most consistent shifts were found between yellow and brown, with equilibrium-brown chromaticity shifted toward red compared to equilibrium yellow at both photopic and mesopic levels. Also, at mesopic levels, rod influence reversed for most observers from a green bias for yellow to a red bias for brown. Bright/dark differences for blue, green, and red were much smaller and/or less consistent. Thus, shifts of cone and rod hue biases between bright and dark hues are most prominent in L-M-cone pathways, especially those activated by yellow and brown stimuli.

Violation of Bloch's Law that specifies reciprocity of intensity and duration with brief light flashes.

For more than a century researchers have been reporting that the visual impact of a very brief flash is determined by the quantity of photons that the flash delivers. This has been variously described as the Bunsen-Roscoe Law or Bloch's Law, often specified as reciprocity of intensity × duration. Prior research found no evidence for such reciprocity when microsecond-duration flashes from a light-emitting diode array were used to display the major contours of nameable shapes. The present work tested with flash durations ranging up to 100 ms and also found no reciprocity. This departure from classic principles might be due to the specific range of wavelengths of the light-emitting diodes and to a mesopic level of ambient light, which together would preclude activation of rods. The reciprocity of intensity and duration may only be valid with full dark adaptation and very dim flashes that activate rods.

The Research of LED Lights Model Based on Road Lighting in Mesopic Vision

This paper analyzes the structural features of the human eye in the middle of the road lighting visual state of the visual request of road lighting in the Mesopic range of lighting, road lighting standards to build a white and green LED light source distribution model and defines the sharpness of the image according to the model function. In the Matlab7.1 environment, high pressure sodium yellow light LED white light and LED white and green background light, the model simulation analysis of the image clarity, results show that, in the Mesopic same brightness level state road lighting selection white and green the LED light source has better clarity and sensitivity.

Comparison of Higher Order Aberrations After Implantable Collamer Lens Implantation and Wavefront-guided LASEK in High Myopia

To compare changes in ocular higher order aberrations (HOAs) after Visian Implantable Collamer Lens (ICL, STAAR Surgical Co) implantation and wavefront-guided laser epithelial keratomileusis (WFG-LASEK) to correct high myopia. This prospective case series comprised 30 eyes (18 patients) that underwent ICL implantation (ICL group) and 33 eyes (18 patients) that underwent WFG-LASEK (WFG-LASEK group). All eyes had spherical equivalent of -6.00 to -9.00 diopters. Entire ocular, internal optic, and corneal HOAs were measured before surgery and 3 months after surgery using a laser ray tracing aberrometer. Contrast sensitivity testing was performed in 10 eyes from each group at a photopic light level of 85 cd/m(2) and a mesopic level of 3 cd/m(2) 3 months after surgery. In the ICL group, HOAs changed for the entire ocular trefoil-y, spherical aberration, internal optic spherical aberration, and corneal trefoil-y. In the WFG-LASEK group, increased HOAs were observed for total HOAs, entire ocular and corneal spherical aberration, secondary astigmatism, and tetrafoil. The ICL group had lower induced aberration values of entire ocular and corneal HOAs compared with the WFG-LASEK group. No significant differences in contrast sensitivity values between groups at the photopic level were noted; however, contrast sensitivity values were significantly lower for 3 (P=.01) and 6 cycles per degree (P<.001) in the WFG-LASEK group at the mesopic level. At the mesopic level, total HOAs, trefoil-y, spherical aberration, and secondary astigmatism were higher in the WFG-LASEK group. Implantable Collamer Lens implantation induced fewer ocular and corneal HOAs and resulted in better contrast sensitivity at mesopic levels than WFG-LASEK in eyes with high myopia.

Mesopic luminance assessed with minimum motion photometry

We measured the relative contribution of rods and cones to luminance across a range of photopic, mesopic, and scotopic adaptation levels and at various retinal eccentricities. We isolated the luminance channel by setting motion-based luminance nulls (minimum motion photometry) using annular stimuli. Luminance nulls between differently colored stimuli require equality in a weighted sum of rod and cone excitations. The relative cone weight increases smoothly from the scotopic range, where rods dominate, to photopic levels, where rod influence becomes negligible. The change from rod to cone vision does not occur uniformly over the visual field. The more peripheral the stimulus location, the higher is the light level required for cones to participate strongly. The relative cone contribution can be described by a sigmoid function of intensity, with two parameters that each depend on the eccentricity and spatial frequency of the stimulus. One parameter determines the "meso-mesopic" luminance--the center of the mesopic range, at which rod and cone contributions are balanced. This increases with eccentricity, reflecting an increase in the meso-mesopic luminance from 0.04 scotopic cd/m(2) at 2° eccentricity to 0.44 scotopic cd/m(2) at 18°. The second parameter represents the slope of the log-log threshold-versus-intensity curve (TVI curve) for rod vision. This parameter inversely scales the width of the mesopic range and increases only slightly with eccentricity (from 0.73 at 2° to 0.78 for vision at 18° off-axis).

Visual and optical performance with the ReZoom multifocal intraocular lens

This study evaluated visual acuity, contrast sensitivity, and wavefront aberrations after refractive multifocal intraocular lens (IOL) implantation. A prospective study comprising 174 eyes of 87 patients who had bilateral implantation of a multifocal IOL was carried out. A control group of 100 eyes of 50 age-matched patients with a monofocal IOL was used for comparison. Uncorrected and corrected distance and near visual acuity, contrast sensitivity (CS), and wavefront analysis (Hartmann-Shack) was performed 6 months after surgery. Contrast sensitivity was tested for distance and near under mesopic (2 cd/m2) and photopic conditions (90 cd/m2). Distance photopic CS was not significantly different from the monofocal group, while distant mesopic CS and near photopic and mesopic CS were significantly lower. Mean aberration root mean square (RMS) values for the multifocal IOL group were 0.229 ± 0.103 µm for coma, 0.137 ± 0.067 µm for spherical aberration (SA), and 0.301 ± 0.133 µm for higher order aberrations (HOAs). Strehl ratio averaged 0.096 ± 0.045. Distant visual performance with the multifocal IOL was excellent under photopic conditions, but was reduced under mesopic levels. Near vision showed suboptimal results in both photopic and mesopic conditions. Coma, SA, and HOAs with the multifocal IOL were higher than those reported previously, with a lower Strehl ratio.

Predicting lamp spectrum effects at mesopic levels. Part 1: Spatial brightness

This paper reports on experimental work carried out to test metrics for predicting spatial brightness at mesopic levels under lamps of different spectral power distribution. The side-by-side matching technique was used following an extensive review of experimental design. Five different types of lamps were presented in all 10 possible pairs, these being selected to compare brightness predictions based on established characteristics of lamp spectrum such as colour rendering index, correlated colour temperature and the scotopic/photopic ratio. The results were also used to test proposed systems for predicting brightness and visual performance at mesopic levels. Of the lamp characteristics examined the scotopic/photopic ratio exhibited the highest correlation with the test results. The new CIE recommended system for visual performance based mesopic photometry was found to give an acceptable prediction of the brightness results.

Predicting lamp spectrum effects at mesopic levels. Part 2: Preferred appearance and visual acuity

Laboratory tests were carried out to investigate lighting for pedestrians at mesopic levels under lamps of different spectral power distribution. This paper reports an evaluation of lamp spectrum effects on visual acuity, using Landolt ring charts of high and low luminance contrast, and forced choice judgements of the preferred appearance of human hands, a colour array and an illuminated space. These were carried out alongside judgements of brightness reported in a previous paper. Five types of lamp were used, including standard high pressure sodium, two metal halide and a fluorescent lamp of broader spectral distribution and a two-colour solid state device (LED). It was found that lamp spectrum affected judgements of preferred appearance, with the high pressure sodium and LED lamps being considered poor compared with the two metal halide lamps; these results correlated better with the CIE General Colour Rendering Index than other metrics of lamp spectral characteristics. It was also found that acuity was affected by lamp spectral power distribution, with the high pressure sodium (HPS) lamp enabling more Landolt rings to be correctly read than lamps of higher S/P ratio.

Differences in Visual Performance of Acrysof ReSTOR IOL in High and Low Myopic Eyes

To determine the differences in refractive and visual results obtained in eyes with high and low myopia after multifocal intraocular lens (IOL) implantation. Monocular visual acuity for distance and near, with and without distance correction, and photopic and mesopic contrast sensitivity were measured at 6 months after surgery in 152 myopic eyes implanted with the AcrySof ReSTOR Natural (SN60D3) IOL. Two groups were created: high and low myopia (76 eyes in each). Monocular best distance-corrected visual acuity was 0.02+/-0.06 logMAR for low myopes and 0.05+/-0.09 logMAR for high myopes. Monocular best distance-corrected near visual acuity was 0.04+/-0.05 and 0.07+/-0.08 logMAR for low and high myopes, respectively. Contrast sensitivity for high myopic eyes under photopic conditions was lower, primarily at high spatial frequencies, in relation to low hyperopic. Differences between both groups were statistically significant for 6 and 18 cycles per degree (cpd) spatial frequencies (p<0.006). At mesopic level, high myopic eyes showed lower values compared to low myopic eyes for all spatial frequencies. However, these differences were only statistically significant for 3, 6, and 12 cpd (p<0.003). The AcrySof ReSTOR IOL provided good visual acuity and contrast sensitivity for both distance and near, with and without distance correction; however, better results were found in low myopic eyes compared to those obtained in eyes with high levels of myopia.

A comparison of simultaneous and sequential brightness judgements

This paper presents the results of brightness matching and brightness discrimination tests carried out using sequential evaluation (temporal juxtaposition) to compare brightness under lamps of different spectral power distribution at mesopic levels of illumination. These data are compared with the results of previous tests, which used simultaneous evaluations (spatial juxtaposition) to enable comparison of these different modes of evaluation. It is concluded that sequential and simultaneous evaluations yield similar estimates of illuminances required for equal spatial brightness and similar levels of precision in this task.

The virtual pupil

Stiles and Crawford showed over 75 years ago that the sensitivity of the retina varies with the place of entry of the light into the pupil, and thus with the direction of incidence of light upon the retina. The effect is a property of the cones. Rods have a very limited directional sensitivity with a common centre of symmetry with the photopic SC-function. One reason, amongst others, for the existence of the Stiles–Crawford effect is supposed to be the suppression of stray light in the ocular media. The light from, for example, the sun or the bright sky, will be scattered in the ocular media, and cause a haze over the visual scene, thereby decreasing contrast. Thanks to the Stiles–Crawford effect, this scattered light will not be perceived. In order to judge the weight, with respect to other reasons, of this stray light theory, a quantitative study of the amount of stray light is required. This suggestion is based on indications that the scattering in the ocular media is mainly forward scattering, and that stray light coming from the retina seems not to contribute much either. Indirect evidence in favour of the stray light hypothesis is that in nighttime conditions, the visual surround is dark, disturbing stray light does not exist, and the rods therefore do not need directional sensitivity. This is indeed the case, and therefore the pupil size is fully used for the few incoming light quanta. At mesopic levels, the disturbing effects of a large pupil, such as spherical and chromatic aberrations, will be limited for the cones by their directional sensitivity, in the same way as a small pupil does at high luminance levels. It is therefore proposed to consider the directional sensitivity of cones as a virtual pupil.

Refractive and Visual Results after Implantation of the AcrySof ReSTOR IOL in High and Low Hyperopic Eyes

To assess the differences in refractive and visual results obtained in eyes with high and low hyperopia after implantation of a multifocal intraocular lens (IOL). A prospective study was performed on 172 hyperopic eyes implanted with the AcrySof Re-STOR Natural (SN60D3) IOL. Two groups were created, high and low hyperopes (86 eyes in both cases). We analyzed monocular visual acuity for distance and near, with and without distance correction. Photopic and mesopic contrast sensitivity (CS) were also assessed. All measurements were performed at 6 months after surgery. Monocular best distance-corrected visual acuity was 0.01+/-0.03 logMAR for low hyperopes and 0.04+/-0.10 logMAR for high hyperopes. Monocular best distance-corrected near visual acuity was 0.02+/-0.04 and 0.05+/-0.06 logMAR for low and high hyperopes, respectively. CS for high hyperopic eyes under photopic conditions was lower, primarily at high spatial frequencies, in relation to low hyperopic eyes. Differences between both groups were statistically significant for all spatial frequencies (p<0.004). At the mesopic level, high hyperopic eyes showed lower values compared to low hyperopic eyes for all spatial frequencies. However, these differences were only statistically significant for 1.5, 12, and 18 cpd (p<0.002). The visual acuity and CS for both distance and near, with and without distance correction, were statistically better in eyes with low hyperopia compared to those obtained in eyes with high levels of hyperopia.