Purkinje Shift Research Articles

Are Blue-Cut Lenses Safe for Children? Potential Effects on Eye Length and Refractive Disorders

Blue-blocking lenses, including both spectacles and intraocular lenses, are designed to selectively reduce the intensity of short-wavelength visible light and UV radiation using a chromophore. Unlike standard spectacle lenses, which only offer varying degrees of UV protection, blue-blocking lenses provide additional benefits such as enhancing visual performance, reducing eye fatigue from digital screens, protecting the retina from phototoxicity, and minimizing disruption of the circadian rhythm caused by blue light-emitting devices used in the evening. Research has shown that the length of the eye tends to increase over time, especially during the first 10 months of life, indicating the importance of this period in eye development. The Purkinje shift is a phenomenon where the eye becomes more sensitive to blue light in the dark, and it is a normal physiological process. However, there is concern that prolonged use of blue-cut lenses in children may affect the development of eye length and contribute to an increase in refractive eye disorders.

Thresholds and noise limitations of colour vision in dim light.

Colour discrimination is based on opponent photoreceptor interactions, and limited by receptor noise. In dim light, photon shot noise impairs colour vision, and in vertebrates, the absolute threshold of colour vision is set by dark noise in cones. Nocturnal insects (e.g. moths and nocturnal bees) and vertebrates lacking rods (geckos) have adaptations to reduce receptor noise and use chromatic vision even in very dim light. In contrast, vertebrates with duplex retinae use colour-blind rod vision when noisy cone signals become unreliable, and their transition from cone- to rod-based vision is marked by the Purkinje shift. Rod-cone interactions have not been shown to improve colour vision in dim light, but may contribute to colour vision in mesopic light intensities. Frogs and toads that have two types of rods use opponent signals from these rods to control phototaxis even at their visual threshold. However, for tasks such as prey or mate choice, their colour discrimination abilities fail at brighter light intensities, similar to other vertebrates, probably limited by the dark noise in cones.This article is part of the themed issue 'Vision in dim light'.

Cloning of the Blue Ghost (Phausis reticulata) Luciferase Reveals a Glowing Source of Green Light.

In the southern Appalachian area of the United States, the Phausis reticulata firefly, commonly known as the "Blue Ghost," performs a unique display of bioluminescence. Adult male organisms are observed darting rapidly along paths and riverbeds in dark forests producing long-lasting and mesmerizing bluish-white luminous streaks. Starting with eighteen adult male firefly lanterns, we used a reverse transcriptase and rapid amplification of cDNA ends (RACE) approach to clone the 1635 base pair open reading frame of the P. reticulata luc gene corresponding to a 545 residue protein. Expression of the recombinant luciferase protein in Escherichia coli and characterization studies revealed the true color of the light emission to be green (λmax = 552 nm), strongly suggesting that the field observations result from a Purkinje shift. While the P. reticulata luciferase amino acid sequence is 74.3% identical to the North American Photinus pyralis luciferase, we were surprised to find that it was 88.4% and 87.7% identical to luciferases from C. ruficollis and D. axillaris both native to mainland Japan. Phylogenetic analysis confirmed the close relationship of the three enzymes that is surprising given the great distance between their natural habitats and the inability of the Japanese fireflies to produce bright bioluminescence.

Why hearts flutter: Distorted dim motions.

When a display of red spots or hearts on a blue surround is moved around under dim light, the spots appear to wobble or flutter relative to the surround (the "fluttering hearts" effect). We explain this as follows: Rods and cones both respond to the hearts. Rods are more sluggish than cones, with a latency of ∼50 ms, and they are also much more sensitive to blue than to red (the Purkinje shift; Purkinje, 1825). Thus a red spot oscillating on a blue ground produces a double image: a light spot seen by the cones, followed by a trailing dark spot seen by the rods. These interacting spots of opposite luminance polarity move like "reverse phi" (Anstis, 1970) and this generates the fluttering hearts effect. We find that hearts flutter most markedly at or near mesopic equiluminance, when the red is lighter than the blue as seen by the cones, but darker than the blue as seen by the rods. These same red/blue luminance ratios give rise to two new illusions: the ghostly twin illusion, and the reversal of red/blue grating movement.

Stereo Day-for-Night

Several approaches attempt to reproduce the appearance of a scotopic low-light night scene on a photopic display (“day-for-night”) by introducing color desaturation, loss of acuity, and the Purkinje shift toward blue colors. We argue that faithful stereo reproduction of night scenes on photopic stereo displays requires manipulation of not only color but also binocular disparity. To this end, we performed a psychophysics experiment to devise a model of disparity at scotopic luminance levels. Using this model, we can match binocular disparity of a scotopic stereo content displayed on a photopic monitor to the disparity that would be perceived if the scene was actually scotopic. The model allows for real-time computation of common stereo content as found in interactive applications such as simulators or computer games.

By the light of the silvery Moon: fact and fiction

Is moonlight ‘silver’ or ‘cold’? In this paper we discuss the interesting combination of factors that contribute to the common descriptions of moonlight. Sunlight is reflected from the lunar surface and red-shifted. When traversing the atmosphere, moonlight is further depleted of short wavelength content by Rayleigh scattering. We measured the spectra of the moonlight to show these effects and compared them with sunlight. All measurements, including spectral reflectance, suggest that moonlight is redder than sunlight. The silvery Moon is just an illusion due to the properties and behaviour of our own eyes, including the responses of rods and cones and the physiological perceptive phenomenon called Purkinje shift.

Is UV and blue-green egg colouration a signal in cavity-nesting birds?

We analysed the eggs of the European starling Sturnus vulgaris for variability of UV and blue-green colouration. We noted the calcium deposition in eggshells, egg measurements, light conditions in nests and starling eye properties. Egg colouration shows high within-clutch similarity. Intensity of the blue-green egg colour neither depends on Ca deposition in the eggshell nor correlates with egg measurements, clutch size and laying date. This suggests that the intensity of the blue-green colour of starling eggs does not reflect female condition, which is reported to affect egg and clutch parameters. Low light intensity in cavities enables only mesopic vision, which is characterised by degraded visual acuity and colour sense, as well as Purkinje shift. As a consequence, the probability of precise assessment of the differences in eggs colour by starling males, crucial for the signalling hypothesis (Moreno & Osorno2003), is not high. On the other hand, irrespective of its intensity, blue-green is the last colour visible under decreased illumination. Thus such coloured eggs may attract higher parental attention in dark cavities. We also demonstrated a strong negative correlation between intensity of blue-green and UV colouration of starling eggs, as well as constrained sensitivity of the starling eye to the range of eggs' maximum UV reflectance. Our study indicates that it is blue-green, not the UV component of the egg's spectral characteristics, which seems to increase the perception of eggs by adults in dark cavities. We suggest that it might have been the most important pressure towards evolution of blue-green colouration of eggs in cavity-nesting birds.

Mesopic visual efficiency II: reaction time experiments

Reaction times are recorded to chromatic, mesopic stimuli to investigate mesopic reaction time spectral sensitivity. Measurements are made using three laboratory setups and a driving simulator. The chromatic stimuli have spectral distributions that range from quasi-monochromatic to broadband. Reaction time spectral sensitivity for small (0.29°) foveal stimuli changes little with luminance and is described adequately by V (λ). Reaction time spectral sensitivity for peripheral stimuli exhibits a Purkinje shift, and approaches V ' (λ) at 0.01 cd m-2. In the periphery, the results for medium-sized stimuli (2°) reflect the activity of colour-opponent neurons in addition to rod and cone-based achromatic activity, resulting in three-peaked spectral sensitivity functions.

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 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.

ROD AND CONE SIGNALING TRANSMISSION IN THE RETINA OF ZEBRAFISH: AN ERG STUDY

It has been suggested that in lower vertebrates, visual signals are propagated in the retina using mixed bipolar cell pathways. In this article, we examined rod and cone signaling transmission in the retina of teleost zebrafish. Full-field electroretinograms (ERGs) were recorded from the cornea of control or 2-amino-4-phosphonobutyric acid (APB)-treated zebrafish. During dark adaptation following bright light adaptation, the intensity-response (V-log I) curve for both the ERG b- and d-waves shifted. In control animals, the b-wave response displayed a typical visual Purkinje shift and became more sensitive. By contrast, the d-wave- became less sensitive. In the early dark adaptation, cone-dominant signals were readily recorded in both b- and d-waves. In the late dark adaptation, rod signals became dominant. However, no obvious d-wave was recorded. Intraocular injections of APB selectively blocked the b-wave, but revealed the d-wave in both early and late dark adaptation

The Purkinje rod-cone shift as a function of luminance and retinal eccentricity

In the Purkinje shift, the dark adapted eye becomes more sensitive to blue than to red as the retinal rods take over from the cones. A striking demonstration of the Purkinje shift, suitable for classroom use, is described in which a small change in viewing distance can reverse the perceived direction of a rotating annulus. We measured this shift with a minimum-motion stimulus (Anstis & Cavanagh, Color Vision: Physiology & Psychophysics, Academic Press, London, 1983) that converts apparent lightness of blue versus red into apparent motion. We filled an iso-eccentric annulus with radial red/blue sectors, and arranged that if the blue sectors looked darker (lighter) than the red sectors, the annulus would appear to rotate to the left (right). At equiluminance the motion appeared to vanish. Our observers established these motion null points while viewing the pattern at various retinal eccentricities through various neutral density filters. Results: The luminous efficiency of blue (relative to red) increased linearly with eccentricity at all adaptation levels, and the more the dark-adaptation, the steeper the slope of the eccentricity function. Thus blue sensitivity was a linear function of eccentricity and an exponential function of filter factor. Blue sensitivity increased linearly with eccentricity, and each additional log 10 unit of dark adaptation changed the slope threefold.

Images of Purkinje’s Vision

Purkinje images can be seen reflected from the surfaces of the cornea and lens. There are many other images that Purkinje presented in his two books on subjective visual phenomena, some of which bear his name. The first hook was his doctoral dissertation, published in 1819 and reprinted in 1823. Among the phenomena described in it was the Purkinje tree (the visibility of shadows of the retinal blood vessels). The book was well received and widely reviewed; one review was by Goethe. The second book was published in 1825 and the contents had appeared initially as three long articles in the same year. The Purkinje shift (the differential brightness of colours before and after sunrise) was described in the book, as were the colour zones of the eye and distortions that can be seen in geometrical patterns. By contrast to the reception of the first book, we have not been able to find any reviews of the second volume. This was so despite the fact that perhaps more novel phenomena were described in it than in the first book. The contents of the two books are briefly outlined, and we speculate on the basis for the differences in the receptions of the two books.

Simulation of Night Myopia in Pseudophakic Eyes

Purpose: Eyes with an intraocular lens (IOL) implanted that have no accommodative ability are likely to have night myopia caused by Purkinje's shift and chromatic aberration. We evaluated the changes in retinal images caused by night myopia in various IOL-implanted eyes by simulation using model eyes. Methods: A polymethylmethacrylate (PMMA) IOL, soft acrylic IOLs, and high-refractive-index silicone IOLs were prepared, and inserted into the model eye. The image plane of the model eye was determined as the line image at which a slit light of 560 nm was best focused, which was regarded as emmetropic condition under photopic vision. A slit light of 505 nm was then directed into the model eye. Its line image on the image plane was blurred, which was regarded as myopic condition under scotopic vision. Under each condition. The modulation transfer functions (MTF) were calculated and the line images were photographed. Results: The degree of reduction of MTF and blurring of the line image under the night myopic condition was in the order of PMMA<soft acrylic<high refractive index silicone IOL. Conclusion: Eyes with a soft acrylic or high-refractive-index silicone IOL may have more intense night myopia caused by chromatic aberration.

Spectral sensitivity in hemianopic macaque monkeys.

We measured the increment threshold sensitivity to 2 degrees, 200-ms targets presented at a lateral and radial eccentricity of approximately 20-26 degrees in both visual hemifields of three macaque monkeys whose left striate cortex had been removed 5 years earlier, and in one normal control. As in patients with blindsight, sensitivity of the hemianopic field for blue, green and red stimuli was reduced by as little as 0.5 log units. With increasing light adaptation from scotopic to mesopic to photopic levels, there was a progressive increase in the sensitivity to long wavelengths relative to that for short and medium wavelengths. This shift in relative sensitivity ('Purkinje shift') shows that rod and cone mechanisms operate in both the normal and hemianopic fields and that the sensitivity that remains following removal of striate cortex is not mediated exclusively by rods.

The electroretinogram of the rhodopsin knockout mouse.

The electroretinogram (ERG) of the rhodopsin knockout (rho-/-) mouse of Humphries et al. (1997) (Humphries et al., 1997) was studied for evidence of light-evoked rod activity and to describe the cone function. The rho-/- retina develops normal numbers of rod and cone nuclei, but the rods have no outer segments, and no rhodopsin is found by immunohistochemistry. The dark-adapted ERG threshold was elevated 4.7 log units above wild-type (WT) control mice, indicating that any residual rod responses were reduced >50,000-fold, consistent with a complete functional knockout. The dark-adapted rho-/- ERG had a cone waveform, and the spectral sensitivity peaked near 510 nm for both dark-adapted and light-adapted conditions, without evidence of a Purkinje shift. The light-adapted ERG b-wave amplitude of young rho-/- mice was the same as WT. The amplitude remained steady up to postnatal day P47, but thereafter it declined to only 1-2% by P80 when no cone outer segments remained. Cone b-wave threshold of dark-adapted rho-/- mice was -1.07 +/- 0.39 log cd-s/m2 (n = 17), which is 1.27 log units more sensitive than light-adapted thresholds against a rod-suppressing Ganzfeld background of 1.61 log scotopic cd/m2. This indicates that dark-adapted WT responses to still dimmer stimuli are exclusively rod driven with minimal cone intrusion. Above this cone threshold intensity, the dark-adapted b-wave of WT will be a summation of rod and cone responses. Threshold versus intensity (TVI) studies gave no evidence of a rod influence on the mouse cone b-wave.

Circadian Rhythms of Rod–Cone Dominance in the Japanese Quail Retina

When the Japanese quail is held in constant darkness, retinal responses (ERG b-waves) increase during the animal's subjective night and decrease during its subjective day. Rod photoreceptors dominate the b-wave responses (lambdamax = 506 nm) to all stimulus intensities at night but only to those intensities below the cone threshold during the day. Above the cone threshold, cones dominate b-wave responses (lambdamax, approximately 550-600 nm) during the day regardless of the state of retinal adaptation. Apparently a circadian oscillator enables cone signals to block rod signals during the day but not at night. The ERG b-wave reflects the activity of bipolar cells that are postsynaptic to rods and cones. The ERG a-wave reflects the activity of both rods and cones. The amplitude of the isolated a-wave (PIII) changes with time of day, as does that of the b-wave, but its spectral sensitivity does not. The PIII responses are maximal at approximately 520 nm both day and night and may reflect multiple receptor mechanisms. The shift in rod-cone dominance detected with the ERG b-wave resembles the Purkinje shift of human vision but, unlike the Purkinje shift, does not require a change in ambient light intensity. The shift occurs in constant darkness, with a period of approximately 24 hr indicative of a circadian rhythm in the functional organization of the retina.

Photic Environment, Visual Pigments, and the Limits of the Visible Spectrum

The limits of the visible spectrum are set by the light available for vision, and by the visual pigment absorbance. The hundreds of visual pigments studied to the present day have absorbance maxima spread within the range from 350 to 620 nm. Yet this diversity is used for vision quite nonuniformly: rod and cone visual pigments are tightly clustered around a few preferred positions in the spectrum, eg near 500 nm in the rods of land animals. The so-called ‘sensitivity hypothesis’ assumes that the clustering is to maximise the number of absorbed photons available in the animals' light environment. In most cases, however, visual pigments are substantially more short-wave (blue-shifted) than is necessary for maximum quantal absorption. Examples of the ‘blue shift’ are the Purkinje shift during cone - rod transition in dark adaptation, the hypsochromic shift of rod visual pigments in deep-water fish, and a similar shift in the cone pigments of geckos and some snakes as a result of evolutionary adaptation to nocturnal habits. It is argued that an important limiting factor in vision is the dark noise produced by thermal isomerisation of the chromophore. Measurements of the dark noise in rods with different visual pigments show that the noise increases steeply when the absorbance maximum is shifted to longer wavelengths, thus precluding the use of long-wave pigments for vision at low intensities. The optimum spectral position of a pigment may be that which ensures a maximum light-to-noise ratio in a particular photic environment.

Doparninergic control of light-adaptive synaptic plasticity and role in goldfish visual behavior

Dopamine has been implicated in processes of retinal light and dark adaptation. In goldfish retina, horizontal cell dendrites elaborate neurite processes (spinules) into cone terminals, in a light- and dopamine-dependent manner. However, the functions of retinal dopamine and the horizontal cell spinules in visual behavior are unknown. These issues were addressed in behavioral, electroretinographic, and anatomical studies of normal fish and those with unilateral depletion of retinal dopamine induced by intraocular (i.o.) injections with 6-hydroxydopamine (6-OHDA). Dopamine interplexiform cells (DA-IPC) disappear within 2 weeks after 6-OHDA injection; cell bodies appear at the marginal zone within 6 weeks at which time neurites slowly reinnervate the retina with a sparse plexus over the next 12 months. We found that dopamine depletion increased light sensitivity at photopic but not scotopic backgrounds by 2.5 log units, an effect mimicked by i.o. injections of dopamine DI and D2 antagonists. The ERG b-wave increment thresholds were the same for control and dopamine depleted eyes, indicating a normal transition from rod to cone systems in the ON pathway. Light-dependent spinule formation was reduced by about 60% in dopamine-depleted retinas, but returned to normal by 3 months and 9 months after injection in the entire retina, even areas not directly innervated with DA-PC processes. Spinule formation in vivo was inhibited 50% with i.o. injection of SCH 23390 in control retinas as well as throughout 3 month 6-OHDA injected retinas, including DA-IPC free areas. This latter result indicates a volume effect of dopamine, diffusing laterally through the retina over several millimeters, in regulating spinules. We conclude that DA-IPCs regulate sensitivity to background at photopic levels not via the ON pathway, but perhaps the OFF pathway. Goldfish display both increased sensitivity to light and a normal Purkinje shift in the ERG b-wave whether or not horizontal cell spinules are present, indicating that dopamine control of photopic vision in fish is not mediated through light-induced spinule formation of horizontal cell dendrites.