Ultraviolet radiation as a risk factor for cataract and macular degeneration

The human eye is constantly exposed to sunlight and artificial lighting. Light transmission through the eye is fundamental to its unique biological functions of directing vision and circadian rhythm, and therefore, light absorbed by the eye must be benign. However, exposure to the intense ambient radiation can pose a hazard particularly if the recipient is over 40 years of age. This radiation exposure can lead to impaired vision and transient or permanent blindness.Both ultraviolet-A (UV-A) and UV-B induce cataract formation and are not necessary for sight. Ultraviolet radiation is also a risk factor for damage to the retinas of children. The removal of these wavelengths from ocular exposure will greatly reduce the risk of early cataract and retinal damage. One way this may be easily done is by wearing sunglasses that block wavelengths below 400 nm (marked 400 on the glasses). However, because of the geometry of the eye, these glasses must be wraparound sunglasses to prevent reflective UV radiation from reaching the eye. Additional protection may be offered by contact lenses that absorb significant amounts of UV radiation.In addition to UV radiation, short blue visible light (400-440 nm) is a risk factor for the adult human retina. This wavelength of light is not essential for sight and not necessary for a circadian rhythm response. For those over 50 years old, it would be of value to remove these wavelengths of light with specially designed sunglasses or contact lenses to reduce the risk of age-related macular degeneration.     

未来人工照明:向阳光靠近——人工智能照明与视觉健康

光对于人眼的正常发育和视觉形成起到了至关重要的作用.人工照明所形成的人类新环境是现代社会发展的必然,而涉及眼健康或眼损伤的环境关联因素之一也是人工照明.在未来人工智能照明的科技发展中,如何寻求适宜眼健康的科技方向?综合光与视觉的科学研究和诸多分析观点,作者提出,未来的人工智能照明应该向"阳光"靠近,合理构建光谱组成、模拟自然光节律,并实现可调节化.     

"Glare vision". I. Physiological principles of vision change with increased test field luminance]

Clinical tests of visual acuity are an important measure of visual function. However visual acuity is usually determined only in narrow range of luminance levels between 160 and 320 cd/m2; therefore losses of visual acuity in other ranges of light intensity can not be detected. In a distance of 80 cm from the patients eyes, Landolt rings of varying sizes were presented on a small test field whose light intensity can be varied between 0.1 and 30,000 cd/m2. Thereby an acuity-luminance-function can be obtained. We studied such functions under different conditions of exposure time both with constant and with increasing luminance of the test field. We found that persons with normal vision can increase their visual acuity with increasing test field luminance up to a range of 5000 cd/m2. The maximum values of visual acuity under optimal lightening conditions lie (varying with age) between 2.2 and 0.9. Under pathological conditions visual acuity falls at high luminances accompanied by sensations of glare. Tests of glare sensitivity as a function of exposure time showed 4 sec to be a critical time of exposure since after 4 sec normal persons just reach their maximum visual acuity at high luminances. The underlying physiological mechanisms lead us to suppose that patients with neuronal light adaptation disturbances display a greater visual loss as a result of decreased time of exposure than those with disturbances in the ocular media. Visual acuity as well as the capacity to increase the patients visual acuity under optimal conditions of lighting were both found to be strongly age-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)     

Computer vision syndrome: a review

As computers become part of our everyday life, more and more people are experiencing a variety of ocular symptoms related to computer use. These include eyestrain, tired eyes, irritation, redness, blurred vision, and double vision, collectively referred to as computer vision syndrome. This article describes both the characteristics and treatment modalities that are available at this time. Computer vision syndrome symptoms may be the cause of ocular (ocular-surface abnormalities or accommodative spasms) and/or extraocular (ergonomic) etiologies. However, the major contributor to computer vision syndrome symptoms by far appears to be dry eye. The visual effects of various display characteristics such as lighting, glare, display quality, refresh rates, and radiation are also discussed. Treatment requires a multidirectional approach combining ocular therapy with adjustment of the workstation. Proper lighting, anti-glare filters, ergonomic positioning of computer monitor and regular work breaks may help improve visual comfort. Lubricating eye drops and special computer glasses help relieve ocular surface-related symptoms. More work needs to be done to specifically define the processes that cause computer vision syndrome and to develop and improve effective treatments that successfully address these causes.     

Ocular optics, electroretinography and primary open angle glaucoma

Advancing the knowledge of ocular image quality is important in the development of new tests for the earlier detection of primary open angle glaucoma (POAG). Loss of blue sensitivity is an important feature of POAG; however, it is difficult to separate this loss from the effects of wavelength related intraocular light scatter and media absorption. A technique for recording the S-cone electroretinogram is described which may solve these problems. The effect of scattered light is avoided by a Ganzfeld stimulus and the absorption of short wavelength light is compensated by a photometric balancing of blue and green stimuli using the M-cone response. The modulation transfer function of the eye has enabled the true spatial tuning function of the retina to be determined by pattern electroretinography (PERG). This has demonstrated the role of retinal ganglion cells in the generation of the PERG. These techniques are shown to be highly sensitive tests in the early stages of POAG.     

Effects of chromatic adaptation on saturation discrimination in goldfish

Saturation discrimination for the goldfish is better at short wavelengths with short wavelength adaptation and at long wavelengths with long wavelength adaptation. These results are accounted for by a model of color vision that predicts the appearance of the diluting light for different states of adaptation. The analysis also accounts for the results from a human subject in the same procedure.     

Red light increment threshold as a measure of deficient color vision.

PURPOSE: People with deficient red/green color vision have both poor color discrimination and are also insensitive to colored lights, especially red, in an increment threshold situation. In this study we compare detection thresholds for a long wavelength increment to two standard color discrimination tests. METHODS: Forty-five color normal subjects and 19 color-deficient subjects (CDs) (12 deutans, 4 protans, and 3 unclassified) were tested with the Hardy-Rand-Rittler (HRR) plate test (4th edition), Farnsworth D-15 arrangement test and a long wavelength increment threshold test, i.e., the red test. RESULTS: All CDs were less sensitive to the red increment than any of the normal subjects. The red test identified all CDs. There were no significant correlations between the red test results and the HRR test or the Farnsworth D-15 test. CONCLUSIONS: The red test measures red light increment threshold, a characteristic of color vision not assessed by conventional tests of color vision which are based upon measuring loss of color discrimination. All CD observers have raised red light increment thresholds and the test clearly differentiates CD observers from those with normal color vision.     

Potential ultraviolet vision in pre-settlement larvae and settled reef fish--a comparison across 23 families

After hatching, larvae of coral reef fishes experience a pelagic phase during which they are diurnal planktivores. It has been suggested that ultraviolet (UV) vision is beneficial for the detection of planktonic prey. Aims were therefore to investigate whether ocular media of pre-settlement reef fish differ from those of respective adults, and whether larvae have UV-transparent ocular media required for UV vision. The ocular media of 84 pre-settlement and 98 adult species belonging to the same families were measured and compared. We suggest that adult lifestyle rather than planktivory in general shapes the ocular media properties of pre-settlement larvae.     

The Role of Dopamine in Emmetropization Modulated by Wavelength and Temporal Frequency in Guinea Pigs

PurposeWavelength and temporal frequency have been found to influence refractive development. This study investigated whether retinal dopamine (DA) plays a role in these processes.MethodsGuinea pigs were randomly divided into nine groups that received different lighting conditions for 4 weeks, as follows: white, green, or blue light at 0, 0.5, or 20.0 Hz. Refractions and axial lengths were measured using streak retinoscopy and A-scan ultrasound imaging. DA and its metabolites were measured by high-pressure liquid chromatography-electrochemical detection.ResultsAt 0 Hz, green and blue light produced myopic and hyperopic shifts compared with that of white light. At 0.5 Hz, no significant changes were observed compared with those of green or blue light at 0 Hz, whereas white light at 0.5 Hz induced a myopic shift compared with white light at 0 or 20 Hz. At 20 Hz, green and blue light acted like white light. Among all levels of DA and its metabolites, only vitreous 3, 4-dihydroxyphenylacetic acid (DOPAC) levels and retinal DOPAC/DA ratios were dependent on wavelength, frequency, and their interaction. Specifically, retinal DOPAC/DA ratios were positively correlated with refractions in white and green light conditions. However, blue light (0, 0.5, and 20.0 Hz) produced hyperopic shifts but decreased vitreous DOPAC levels and retinal DOPAC/DA ratios.ConclusionsThe retinal DOPAC/DA ratio, indicating the metabolic efficiency of DA, is correlated with ocular growth. It may underlie myopic shifts from light exposure with a long wavelength and low temporal frequency. However, different biochemical pathways may contribute to the hyperopic shifts from short wavelength light.     

Clinical advantages of colorimetric exploration in the early diagnosis of glaucomatous neuropathy

AIM: The purpose of this investigation was to evaluate acquired color vision defects in the early stages of primary glaucoma and in patients at risk for glaucoma. MATERIAL AND METHODS: Patients with primary open-angle glaucoma, normal-tension glaucoma and ocular hypertension were examined with the IF-2 anomaloscope. The Rayleigh equation and the Moreland equation were tested. We studied the relationships between color vision defects and the other tested variables. RESULTS: We found the mean value of the setting range of the Moreland equation significantly increased in all tested groups. Color vision disturbances were found in 57% of eyes with glaucoma and in 31% of eyes with ocular hypertension. We found a positive correlation between the blue-green colour vision defects and the perimetric changes in the glaucomatous eyes. These results indicate a decrease in color discriminating sensitivity in the short wavelength part of the visible spectrum in patients with glaucoma as well as in patients with ocular hypertension. CONCLUSION: Blue-yellow color vision testing with the anomaloscope may serve as an additional test in the early diagnosis of glaucoma but the absence of dyschromatopsia does not exclude the disease.     

计算机视觉综合征的发展和现状

计算机正逐步成为我们日常生活的一部分内容,越来越多的人体验到各种各样与计算机使用密切相关的视觉症状,包括眼睛疲乏、易激惹、赤红、视觉模糊、双重视觉等症状,即计算机视觉综合征。本文描述视觉综合征的特征和治疗方法。计算机视觉综合征症状也许是视觉表面反常性或适应性痉挛造成的,同时,各种外在因素譬如照明设备、强光、显示颜色和分辨率以及光照时间等都会对视觉综合征造成不同程度的影响。     

Color vision in glaucoma

This article is a general view of evaluated acquired color vision defects in the early stages of primary glaucoma and in patients at risk for glaucoma. The articles published until now indicates a decrease in color discriminating sensitivity in the short wavelength part of the visible spectrum in patients with glaucoma as well as in patients with ocular hypertension. It has been found a positive correlation between the blue-yellow color vision defects and the perimetric changes in the glaucomatous eyes. Blue-yellow color vision testing with the anomaloscope may serve as an additional test in the early diagnosis of glaucoma but the absence of dyschromatopsia does not exclude the disease.     

The effect of light scattering on multifocal electroretinography

PURPOSE: Unclear ocular media is a very common condition of older eyes characterized by significant light scattering and image degradation. The multifocal electroretinography (MERG) is a useful objective technique to measure retinal activity but its validity in the presence of cloudy ocular media remains unclear. We tested the MERG under controlled light scattering conditions using a liquid crystal diffuser (LCD) that simulated different degrees of image degradation. METHODS: The MERG were taken from 13 normal young subjects seated behind a LCD set under two conditions: scatter (visual acuity approximately 6/18) and non-scatter (visual acuity approximately6/6). The pupils had been dilated and the eyes were optically corrected for the working distance. The first-order kernel MERG response was analysed. Three subjects underwent MERG measurement with two additional intermediate light scattering levels (i.e. visual acuity approximately 6/9 and 6/12). RESULTS: The macular MERG response density was reduced (p < 0.001), but the peripheral MERG response densities were increased (p < 0.001) under the scattering condition. A similar trend was also observed with intermediate degrees of light scattering. Comparing the MERG waveforms without light scattering, a new retinal response was identified with a characteristic latency of about 60 ms (P60), but it was diminished in size under the scattering conditions. CONCLUSIONS: The veiling luminance might have caused the reduction in the macular MERG response and an elevation in the peripheral retina with light scatter. The functional suppression of P60 observed under the influence of light scatter may be related to retinal adaptation. Unclear optical media will affect the interpretation of MERG results.     

Adaptive plasticity during the development of colour vision

Colour vision greatly enhances the discriminatory and cognitive capabilities of visual systems and is found in a great majority of vertebrates and many invertebrates. However, colour coding visual systems are confronted with the fact that the external stimuli are ambiguous because they are subject to constant variations of luminance and spectral composition. Furthermore, the transmittance of the ocular media, the spectral sensitivity of visual pigments and the ratio of spectral cone types are also variable. This results in a situation where there is no fixed relationship between a stimulus and a colour percept. Colour constancy has been identified as a powerful mechanism to deal with this set of problems; however, it is active only in a short-term time range. Changes covering longer periods of time require additional tuning mechanisms at the photoreceptor level or at postreceptoral stages of chromatic processing. We have used the trichromatic blue acara (Aequidens pulcher, Cichlidae) as a model system and studied retinal morphology and physiology, and visually evoked behaviour after rearing fish for 1-2 years under various conditions including near monochromatic lights (spectral deprivation) and two intensities of white light (controls). In general, long-term exposure to long wavelengths light had lesser effects than light of middle and short wavelengths. Within the cone photoreceptors, spectral deprivation did not change the absorption characteristics of the visual pigments. By contrast, the outer segment length of middle and long-wave-sensitive cones was markedly increased in the blue rearing group. Furthermore, in the same group, we observed a loss of 65% short-wave-sensitive cones after 2 years. These changes may be interpreted as manifestations of compensatory mechanisms aimed at restoring the balance between the chromatic channels. At the horizontal cell level, the connectivity between short-wave-sensitive cones and the H2 cone horizontal cells, and the spinule dynamics were both affected in the blue light group. This observation rules out the role of spinules as sites of chromatic feedback synapses. The light-evoked responses of H2 horizontal cells were also sensitive to spectral deprivation showing a shift of the neutral point towards short wavelengths in the blue rearing group. Interestingly, we also found an intensity effect because in the group reared in bright white light the neutral point was more towards longer wavelength than in the dim light group. Like the changes in the cones, the reactions of horizontal cells to spectral deprivation in the long wave domain can be characterised as compensatory. We also tested the spectral sensitivity of the various experimental groups of blue acara in visually evoked behaviour using the optomotor response paradigm. In this case, the changes in the relative spectral sensitivity were more complex and could not be explained by a simple extrapolation of the adaptive and compensatory processes in the outer retina. We conclude that the inner retina, and/or the optic tectum are also involved and react to the changes of the spectral environment. In summary, we have shown a considerable developmental plasticity in the colour vision system of the blue acara, where epigenetic adaptive processes at various levels of the visual system respond to the specific spectral composition of the surroundings and provide a powerful mechanism to ensure functional colour vision in different visual environments. We suggest that processes involving an active fine-tuning of the photoreceptors and the postreceptoral processing of chromatic information during ontogenetic development are a general feature of all colour vision systems. Such mechanisms would establish a functional balance between the various chromatic channels. This appears to be an essential condition for the cognitive systems to extract the relevant and stable information from the unstable and changing stimulus situation.     

Continuous ambient lighting and lens compensation in infant monkeys.

PURPOSE: Protracted daily lighting cycles do not promote abnormal ocular enlargement in infant monkeys as they do in a variety of avian species. However, observations in humans suggest that ambient lighting at night may reduce the efficiency of the emmetropization process in primates. To test this idea, we investigated the ability of infant monkeys reared with continuous light to compensate for optically imposed changes in refractive error. METHODS: Beginning at about 3 weeks of age, a hyperopic or myopic anisometropia was imposed on 12 infant rhesus monkeys by securing either a -3 D or +3 D lenses in front of one eye and a zero-powered lens in front of the fellow eye. Six of these monkeys were reared with the normal vivarium lights on continuously, whereas the other six lens-reared monkeys were maintained on a 12-h-light/12-h-dark lighting cycle. The ocular effects of the lens-rearing procedures were assessed periodically during the treatment period by cycloplegic retinoscopy, keratometry, and A-scan ultrasonography. RESULTS: Five of six animals in each of the lighting groups demonstrated clear evidence for compensating anisometropic growth. In both lighting groups, eyes that experienced optically imposed hyperopic defocus (-3 D lenses) exhibited faster axial growth rates and became more myopic than their fellow eyes. In contrast, eyes treated with +3 D lenses showed relatively slower axial growth rates and developed more hyperopic refractive errors. The average amount of compensating anisometropia (continuous light, 1.6 +/- 0.5 D vs. control, 2.3 +/- 0.5 D), the structural basis for the refractive errors, and the ability to recover from the induced refractive errors were also not altered by continuous light exposure. CONCLUSION: Ambient lighting at night does not appear to overtly compromise the functional integrity of the vision-dependent mechanisms that regulate emmetropization in higher primates.     

Avian colour vision: Effects of variation in receptor sensitivity and noise data on model predictions as compared to behavioural results

Colour vision models require measurement of receptor noise and the absorbance of visual pigments, oil droplets, and ocular media. We have studied how variation in these parameters influences colour matching, spectral sensitivity, and colour discrimination predictions in four bird species. While colour match predictions are sensitive to variation in visual pigment and oil droplet absorbance data, discrimination predictions are mostly sensitive to variation in receptor noise. Ocular media transmittance influences only modelled spectral sensitivities at short wavelengths. A comparison between predicted and measured spectral sensitivities in domestic fowl and duck revealed large discrepancies, likely because of influences from achromatic mechanisms.     

Vision enhancement using a short wavelength light-absorbing filter

This report illustrates photographically the adverse influence of short wavelength-induced light-scattering and autofluorescence on image quality, and the improvement of image quality that results by filtering out light wavelengths shorter than 480 nm. It provides additional data on the improvement in human vision (under conditions of excessive intraocular light-scattering and fluorescence) by filters that prevent short wavelength radiant energy from entering the eye.     

Latitude-of-birth and season-of-birth effects on human color vision in the Arctic

Extreme natural ambient light reduction, in both energy and range of wavelength spectrum, occurs during the winter season at very high latitudes (above the Arctic Circle or 66 degrees 32' North) that in turn results in increased exposure to artificial lighting. In contrast, during the summer months, the sun remains above the horizon and there is no darkness or night. Little is known about these extreme changes in light exposure on human visual perception. Measuring color discriminations with the FM100 Test revealed that Norwegians born above the Arctic Circle were less sensitive to yellow-green, green, and green-blue spectrum differences whereas they were more sensitive to hue variations in the purple range than individuals born below the Arctic Circle. Additionally, it was found that the Norwegian individuals born above the Arctic Circle and during autumn showed an overall decrease in color sensitivity, whereas those born in the summer showed a relative increase. All participants were adults and their color vision was tested in the same location (i.e., in Troms? at 69.7 degrees North). These findings are consistent with the idea that there is a measurable impact on colour vision as adults of the photic environment that individuals born above the Arctic Circle and in the autumn experienced during infancy, namely a reduction in exposure to direct sunlight and an increase in exposure to twilight and artificial lighting.     

Incidence and prevalence of short wavelength automated perimetry deficits in ocular hypertensive patients

PURPOSE: To determine the prevalence and incidence of short wavelength automated perimetry deficits in comparison to standard automated perimetry deficits in patients with ocular hypertension. METHODS: Five hundred eyes of 250 patients with ocular hypertension were recruited into a prospective, longitudinal study and tested with standard automated perimetry and short wavelength automated perimetry annually for 5 years. Both eyes of 60 normal subjects, 21 to 85 years of age, were used to establish normative data for short wavelength automated perimetry and standard automated perimetry. This allowed independent evaluation of left and right eyes of patients. All normal data were corrected for age, and short wavelength automated perimetry results were corrected for lens transmission. The lowest fifth and first percentiles for the normal observers were derived for the 10 glaucoma hemifield test zones for short wavelength automated perimetry and standard automated perimetry. Visual fields were considered outside normal limits if two glaucoma hemifield test zones were below the normal fifth percentile or one glaucoma hemifield test zone was below the normal first percentile. RESULTS: Baseline prevalence of short wavelength automated perimetry and standard automated perimetry deficits were 9.4% and 1.4%, respectively. During the study, incident rates of field loss were 6.2% (1.23% per year) for short wavelength automated perimetry and 5.9% (1.18% per year) for standard automated perimetry. Once abnormal, 80% of short wavelength automated perimetry fields remained abnormal on the next examination, whereas only 45% of abnormal standard automated perimetry fields remained abnormal. New short wavelength automated perimetry deficits in ocular hypertensives were more prominent and more persistent than new standard automated perimetry deficits. CONCLUSIONS: Our findings are consistent with the interpretation that short wavelength automated perimetry deficits occur before standard automated perimetry deficits in glaucoma. The similar incidence rates suggest that both standard automated perimetry and short wavelength automated perimetry are monitoring the same underlying glaucomatous disease process.