BRIGHT LIGHT THERAPY FOR WINTER DEPRESSION: POTENTIAL OCULAR EFFECTS AND THEORETICAL IMPLICATIONS

Techniques to Improve Photodynamic Therapy

Photodynamic therapy [dye-light therapy] is an excellent technique for use in detection and treatment of cancerous tissues. While this therapy is effective, it is limited by the phototoxic reactions that can occur in the surrounding normal tissues. These damaging side effects are of particular importance when treating neurosensory organs, such as the human eye. We report here new treatment strategies to enhance photodynamic effectiveness while limiting side effects to normal tissues.

Genetic Factors Affecting Seasonality, Mood, and the Circadian Clock

In healthy humans, seasonality has been documented in psychological variables, chronotype, sleep, feeding, metabolic and autonomic function, thermoregulation, neurotransmission, and hormonal response to stimulation, thus representing a relevant factor to account for, especially when considering the individual susceptibility to disease. Mood is largely recognized as one of the central aspects of human behavior influenced by seasonal variations. This historical notion, already mentioned in ancient medical reports, has been recently confirmed by fMRI findings, which showed that seasonality in human cognitive brain functions may influence affective control with annual variations. Thus, seasonality plays a major role in mood disorders, affecting psychopathology, and representing the behavioral correlate of a heightened sensitivity to factors influencing circannual rhythms in patients. Although the genetic basis of seasonality and seasonal affective disorder (SAD) has not been established so far, there is growing evidence that factors affecting the biological clock, such as gene polymorphisms of the core clock machinery and seasonal changes of the light-dark cycle, exert a marked influence on the behavior of patients affected by mood disorders. Here we review recent findings about the effects of individual gene variants on seasonality, mood, and psychopathological characteristics.

Light therapy: is it safe for the eyes?

OBJECTIVE

Light therapy has become an increasingly popular treatment for depression and a range of other neuropsychiatric conditions. Yet, concerns have been raised about the ocular safety of light therapy.

METHOD

We conducted the first systematic review into the ocular safety of light therapy. A PubMed search on January 4, 2017, identified 6708 articles, of which 161 were full-text reviewed. In total, 43 articles reporting on ocular complaints and ocular examinations were included in the analyses.

RESULTS

Ocular complaints, including ocular discomfort and vision problems, were reported in about 0% to 45% of the participants of studies involving light therapy. Based on individual studies, no evident relationship between the occurrence of complaints and light therapy dose was found. There was no evidence for ocular damage due to light therapy, with the exception of one case report that documented the development of a maculopathy in a person treated with the photosensitizing antidepressant clomipramine.

CONCLUSION

Results suggest that light therapy is safe for the eyes in physically healthy, unmedicated persons. The ocular safety of light therapy in persons with preexisting ocular abnormalities or increased photosensitivity warrants further study. However, theoretical considerations do not substantiate stringent ocular safety-related contraindications for light therapy.

Melanopsin-Mediated Acute Light Responses Measured in Winter and in Summer: Seasonal Variations in Adults with and without Cataracts

Seasonal adaptation is a ubiquitous behavior seen in many species on both global hemispheres and is conveyed by changing photoperiods. In humans this seasonal adaptation is less apparent, in part because changes in daylength are masked by the use of electrical lighting at night. On the other hand, cataracts which reduce light transmission, may compound seasonal changes related to the reduced daylength of winter. To better understand the effects of different photoperiod lengths in healthy adults without and with cataracts, we tested their melanopsin-mediated light responses in summer vs. winter. Fifty-two participants (mean age 67.4 years; 30 with bilateral cataracts and 22 age-matched controls with clear lenses; pseudophakes) were tested twice, once in summer and once in winter. At each test session we assessed the electroretinogram and pupil responses during daytime and we determined melatonin suppression, subjective sleepiness and mood in response to light exposure in the evening. Circadian rest-activity cycles and sleep from activity recordings were also analyzed for both seasons. Both groups had similar visual function. There were no seasonal differences in the electroretinogram. For the pupil responses to bright blue light, the post-illumination pupil response (PIPR) was greater in winter than summer in pseudophakes, but not in cataract participants, whereas melatonin suppression to acute light exposure showed no differences between both groups and seasons. Overall, intra-daily variability of rest-activity was worse in winter but participants felt sleepier and reported worse mood at the laboratory in evening time in the summer. Those with cataracts had poorer sleep quality with lower sleep efficiency, and higher activity during sleep in winter than summer. In this study, the PIPR showed a seasonal variation in which a larger response was found during winter. This variation was only detected in participants with a clear intraocular lens. In the cataract group, visual function was not impaired yet these participants showed a lack of seasonal changes in the pupil response to blue light and poorer sleep in winter. These findings raise the question for tailored lighting conditions for cataract patients in order to counter potentially deleterious effects of living with chronically lower light exposure.

Bright light therapy in Parkinson's disease: an overview of the background and evidence

Sleep disorders are common in Parkinson's disease (PD) and seem to be strongly associated with depression. It has been suggested that sleep disorders as well as depression are caused by a disturbed circadian rhythm. Indeed, PD patients are prone to misalignment of their circadian rhythm due to various factors, and many patients with PD display a phase advance of their circadian rhythm. Current treatment options for sleep disorders and depression in patients with PD are limited and can have serious side effects; alternative treatments are therefore badly needed. Bright light therapy (BLT) restores circadian rhythmicity effectively in mood- and sleep-disturbed patients without PD. The few studies that focused on the efficacy of BLT in patients with PD demonstrated a positive effect of BLT not only on sleep and mood but also on motor function. More research on the neurobiology and efficacy of BLT in PD is warranted.

Light therapy for seasonal and nonseasonal depression: efficacy, protocol, safety, and side effects

Bright light therapy for seasonal affective disorder (SAD) has been investigated and applied for over 20 years. Physicians and clinicians are increasingly confident that bright light therapy is a potent, specifically active, nonpharmaceutical treatment modality. Indeed, the domain of light treatment is moving beyond SAD, to nonseasonal depression (unipolar and bipolar), seasonal flare-ups of bulimia nervosa, circadian sleep phase disorders, and more. Light therapy is simple to deliver to outpatients and inpatients alike, although the optimum dosing of light and treatment time of day requires individual adjustment. The side-effect profile is favorable in comparison with medications, although the clinician must remain vigilant about emergent hypomania and autonomic hyperactivation, especially during the first few days of treatment. Importantly, light therapy provides a compatible adjunct to antidepressant medication, which can result in accelerated improvement and fewer residual symptoms.

Light treatment of mood disorders

In 1981, seven patients with nonseasonal depression were treated with bright white light in 1982, bright artificial light was used to treat a manic-depressive patient with a seasonal mood cycle. In the last 20 years, a plethora of studies have further defined the depressive populations, who are responsive to light treatment; the optimal timing, intensity, spectral frequency, and duration of treatment; its comparison with other pharmacological interventions; predictors of response; side-effect profiles; viable placebo-control conditions; alternative devices and forms of administration; potential mechanisms and anatomical pathways mediating light's physiological effects; and its application to other disorders and subsyndromaI states. These studies have been conducted across multiple countries with surprisingly consistent results. Further work is needed, as highlighted in this review, to clarify the specific mechanism of action in subtypes of depressive disorders and differential age and gender effects. Although the majority of work in this area is relatively new, it behooves the reader to remember that Solomon, almost 3000 years ago, wrote in Ecclesiastes: "Truly the light is sweet and a pleasant thing it is for the eyes to behold the sun" (11:7).

Circadian rhythms and circadian rhythm disorders in children and adolescents

A clinically applicable review of circadian rhythm physiology is presented, including a detailed examination of the interaction of circadian and homeostatic systems and the maturation of the circadian system from preconception through adolescence. Emphasis is placed on the clinical evaluation gathering information through the history, sleep log, and if necessary, actigraphy and polysomnography. Circadian disorders, including advanced sleep phase syndrome, circadian disorders seen in blind children, delayed sleep phase syndrome, and non-24-hour sleep phase are described. Case descriptions of each are provided. Treatment and interventions for these disorders are described, including the importance of education, light therapy, sleep-wake schedule adjustments, and the occasional use of medications, such as sedative hypnotics and melatonin.

Retinal afferents to the dorsal raphe nucleus in rats and Mongolian gerbils

A direct pathway from the retina to the dorsal raphe nucleus (DRN) has been demonstrated in both albino rats and Mongolian gerbils. Following intraocular injection of cholera toxin subunit B (CTB), a diffuse stream of CTB-positive, fine-caliber optic axons emerged from the optic tract at the level of the pretectum/anterior mesencephalon. In gerbils, CTB-positive axons descended ventromedially into the periaqueductal gray, moving caudally and arborizing extensively throughout the DRN. In rats, the retinal-DRN projection comprised fewer, but larger caliber, axons, which arborized in a relatively restricted region of the lateral and ventral DRN. Following injection of CTB into the lateral DRN, retrogradely labeled ganglion cells (GCs) were observed in whole-mount retinas of both species. In gerbils, CTB-positive GCs were distributed over the entire retina, and a nearest-neighbor analysis of CTB-positive GCs showed significant regularity (nonrandomness) in their distribution. The overall distribution of gerbil GC soma diameters ranged from 8 to 22 micrometer and was skewed slightly towards the larger soma diameters. Based on an adaptive mixtures model statistical analysis, two Gaussian distributions appeared to comprise the total GC distribution, with mean soma diameters of 13 (SEM +/-1.7) micrometer, and 17 (SEM +/-1.5) micrometer, respectively. In rats, many fewer CTB-positive GCs were labeled following CTB injections into the lateral DRN, and nearly all occurred in the inferior retina. The total distribution of rat GC soma diameters was similar to that in gerbils and also was skewed towards the larger soma diameters. Major differences observed in the extent and configuration of the retinal-DRN pathway may be related to the diurnal/crepuscular vs. nocturnal habits of these two species.

Circadian oscillation of photopigment transcript levels in the mouse retina

The mammalian retina contains an autonomous circadian oscillator that can sustain rhythms in outer segment disc shedding and melatonin synthesis even in the absence of cues from the central oscillator in the suprachiasmatic nucleus (SCN). The present investigation aimed to ascertain whether the steady-state levels of rod and cone opsin mRNA exhibited a circadian oscillation in the mouse, and if so, to characterise this oscillation with regard to phase. Retinas were collected from mice free-running in constant darkness at circadian times (CT) 0, 4, 12, 16, and 20. RNA was extracted for the production of Northern blots, which were sequentially hybridised with probes for alpha-tubulin (control), ultraviolet opsin, and rhodopsin. Whereas no significant oscillation was detected in the levels of alpha-tubulin, the levels of both ultraviolet opsin and rhodopsin transcripts oscillated with an amplitude of at least 3-fold. The highest levels were found at around CT12 (which corresponds to the subjective evening, the time of activity onset in the mouse). These results show that the levels of rod and cone photopigment mRNA are under circadian control. The significance of the rhythms and their phasing is discussed. These findings have potential clinical implications both with regard to nocturnal light treatment of phase asynchrony, and in the timing of chemo- and radiotherapy.

Effects of moderately bright light on subjective evaluations in healthy elderly women

Eight healthy elderly women aged 56-72 years (mean age: 67.4 years) participated in this study. They were exposed to moderately bright light (1000 lux) for 1h in the morning every 6 days in their homes. Moderately bright light improved self evaluations for alertness, mood, motivation, happiness, refreshment, concentration and appetite after the second exposure to the light. Sleep maintenance, anxiety and integrated sleep feeling also improved after the fourth exposure to the light. The phase of rectal temperature rhythm did not change in a moderately bright light condition. These results suggest that bright light influences sleep quality and self evaluations without changing the biological rhythm phase.

Effects of short duration morning bright light in healthy elderly subjects. I: subjective feeling and ophthalmological examinations

Seven aged subjects aged 61-78 years were exposed to 6000 lx bright light for 30 min during morning hours at their homes for 1 week. Visual analog scale was recorded before bedtime and after rising to assess subjective feelings. Ophthalmological examinations were made before and after light exposure, to exclude pre-existing ocular disorders and to detect ocular damage. Furthermore, ocular fatigue was self-evaluated immediately before and after exposure. Visual analog scale results indicated that alertness reduced significantly before bedtime. Ophthalmological abnormalities were not found after exposure. These findings suggest that short duration morning bright light exposure reduces night-time vigilance.

Changes in circadian rhythms and sleep quality with aging: mechanisms and interventions

Literature is reviewed indicating that aging is characterized by changes in circadian rhythms and sleep quality. The most marked change is an attenuation of amplitude. An advance of phase, a shortening of period, and a desynchronization of rhythms are also evident. The mechanisms underlying these changes are unknown. However, age-related changes in the retina, suprachiasmatic nucleus, and pineal gland seem relevant along with behavioral changes such as a reduction in physical activity and exposure to photic stimulation. Changes in circadian rhythms are frequently associated with a reduction in nighttime sleep quality, a decrease in daytime alertness, and an attenuation in cognitive performance; reversing such changes could enhance the quality of life for a large and rapidly increasing percentage of the population. Reversal appears possible by increasing melatonin levels with either appropriately timed exposure to photic stimulation and/or appropriately timed administration of exogenous melatonin. These interventions may increase aspects of genetic expression that have changed with aging. A hypothesis concerning the potential benefits of enhanced circadian amplitude is also offered.

Treatment of seasonal affective disorder: a review

OBJECTIVE

To review the status of current treatment of seasonal affective disorder (SAD).

METHOD

Treatment studies of SAD published between January 1989 and March 1995 were identified using a computerized MEDLINE literature search. Additional citations were obtained from the reference sections of these articles. Studies included in this review were selected using operational methodologic criteria.

RESULTS

Many studies support the efficacy of bright light therapy using a fluorescent light box. The best studied protocol is > 2500 lux white light for 2 hours per day, but newer protocols using 10,000 lux for 30 minutes have comparable response rates. Studies of light visors and other head-mounted devices also report similar response rates, but have not yet shown superiority over putative control conditions. There are fewer medication studies in SAD, but controlled studies suggest that fluoxetine, d-fenfluramine and propranolol are effective. Other treatments such as dawn simulation require further study. No studies of psychological treatments for SAD were found. Many studies had methodologic limitations, including brief treatment periods, small sample sizes, and lack of replication, that limit the generalizability of findings.

CONCLUSION

There are several well-studied, effective treatments for SAD, including light therapy and medications. However, further research must be done to demonstrate sustained treatment response over time, to clarify the intensity-response relationship of light therapy, to clarify the role of light therapy and medications, and to assess combination treatments.

Treatment of delayed sleep phase syndrome

Delayed sleep phase syndrome (DSPS) is a common but little reported cause of severe insomnia. Affected individuals complain of difficulty falling asleep and difficulty awaking at socially acceptable hours. It results from a dysregulation of the circadian sleep-wake cycle. DSPS presents in clinically heterogenous ways as modulated by motivation, psychopathology, drug status, and treatment compliance factors. Patients respond variably to the range of possible treatments. Bright light treatment potentially corrects the circadian abnormality of DSPS. Other treatments reported to relieve some DSPS patients include schedule shifts, drugs, and vitamin and hormone treatments. The safety and efficacy of light treatment have not been conventionally defined, but available information suggests that it is ophthalmologically safe. At present, DSPS must be managed empirically by various methods.

Visible light induced changes in the immune response through an eye-brain mechanism (photoneuroimmunology)

The immune system is susceptible to a variety of stresses. Recent work in neuroimmunology has begun to define how mood alteration, stress, the seasons, and daily rhythms can have a profound effect on immune response through hormonal modifications. Central to these factors may be light through an eye-brain hormonal modulation. In adult primates, only visible light (400-700 nm) is received by the retina. This photic energy is then transduced and delivered to the visual cortex and by an alternative pathway to the suprachiasmatic nucleus (SCN). The SCN is a part of the hypothalamic region in the brain believed to direct circadian rhythm. Visible light exposure also modulates the pituitary and pineal gland which leads to neuroendocrine changes. Melatonin, norepinephrine and acetylcholine decrease with light activation, while cortisol, serotonin, gaba and dopamine levels increase. The synthesis of vasoactive intestinal polypeptide (VIP), gastrin releasing peptide (GRP) and neuropeptide Y (NPY) in rat SCN has been shown to be modified by light. These induced neuroendocrine changes can lead to alterations in mood and circadian rhythm. All of these neuroendocrine changes can lead to immune modulation. An alternative pathway for immune modulation by light is through the skin. Visible light (400-700 nm) can penetrate epidermal and dermal layers of the skin and may directly interact with circulating lymphocytes to modulate immune function. However, even in the presence of phototoxic agents such as eosin and rose bengal, visible light did not produce suppression of contact hypersensitivity with suppresser cells. In contrast to visible light, in vivo exposure to UV-B (280-320 nm) and UV-A (320-400 nm) radiation can only alter normal human immune function by a skin mediated response. Each UV subgroup (B, A) induces an immunosuppressive response but by differing mechanisms involving the regulation of differing interleukins and growth factors. Some effects observed in humans are: inhibition of allergic contact dermatitis; inhibition of delayed hypersensitivity to an injected antigen; prolongation of skin-graft survival and induction of a tumor-susceptible state. The following article will review much of the progress in this field and explore possible areas of future research.

Night-shift work in Antarctica: sleep characteristics and bright light treatment

Changes in sleep parameters during and after night-shift and the effects of bright white (2500-3000 1x) and dim red (> 500 1x) light treatment on re adaptation after night-shift during winter were studied in 14 men on the British Antarctic Survey Base of Halley (75 degrees south). Subjects kept daily sleep diaries and mood ratings from one week before to three weeks after night-shift and received either full-spectrum white or dim red light treatment from 1100 to 1300 h daily during the first week after night-shift. Plasma melatonin (for 24 h at the end of weeks 1, 2 and 4), and urinary 6-sulfatoxymelatonin (aMT6s, for 48 h weekly) were measured. A significant (MANOVA; p < 0.05) improvement in sleep was seen during night shift (latency and duration) and with bright light treatment (latency). Melatonin and aMT6s rhythms delayed by 7-8 h during night-shift. The white light group readapted slowly, apparently by phase delay, as assessed by aMT6s measurement. The red light group readapted slightly, but significantly (ANOVA, p < 0.01) faster than the white light group.

Light therapy for seasonal affective disorder. The effects of timing

BACKGROUND

Sixty-eight patients with seasonal affective disorder participated in a 10,000-lux light treatment study in which two questions were addressed: do response rates differ when the light is applied at different times of the day and does short-term rank ordering of morning and evening light influence response rates?

METHOD

Three groups of patients received a 4-day light treatment: (I) in the morning (8.00-8.30 a.m., n = 14), (II) in the afternoon (1.00-1.30 p.m., n = 15) or (III) in the evening (8.00-8.30 p.m., n = 12). Two additional groups of patients received two days of morning light treatment followed by two days of evening light (IV, n = 13) or vice versa (V, n = 14).

RESULTS

Response rates for groups I, II and III were 69, 57 and 80% respectively, with no significant differences between them. Response rates for groups IV and V were 67 and 50% respectively; this difference was not significant and these percentages did not differ significantly from those of groups I and III.

CONCLUSIONS

The results indicate that the timing of light treatment is not critical and that short-term rank ordering of morning and evening light does not influence therapeutic outcome.

Ophthalmologic examination of patients with seasonal affective disorder, before and after bright light therapy

PURPOSE

We assessed the potential ocular hazards of bright light therapy for patients with seasonal affective disorder, after both short- and long-term treatment, and identified prospective patients with pre-existing ocular abnormalities.

METHODS

Fifty patients with seasonal affective disorder received daily exposure to artificial light in the morning or evening for 30 minutes at an illuminance level of 10,000 lux (irradiant dose, 0.016 J/cm2). Ophthalmologic examinations were performed before and after short-term treatment (two to eight weeks) and after three to six years of use during the fall and winter months. Over the four years of patient intake, the eye examination included subsets of the following tests: visual acuity, intraocular pressure, slit-lamp biomicroscopy, direct and indirect ophthalmoscopy, color vision, visual field, fundus photography, Amsler grid, ocular motility, pupillary reactions, contrast sensitivity, stereopsis, and the macular stress test.

RESULTS

No ocular changes were detected after short-term treatment. Long-term treatment (three to six years) of 17 patients, with cumulative exposure durations of 60 to 1,250 hours, also resulted in no ocular abnormalities.

CONCLUSIONS

Light therapy yields about 75% clinical remissions. It is effective as an antidepressant and appears safe for the eyes. Current knowledge is insufficient to specify any definite ocular contraindications for bright light therapy, although we recommend that patients with preexisting ocular abnormalities and those using photosensitizing drugs undergo treatment only with periodic ophthalmologic examination.

Seasonal affective disorder

The authors claim psychiatric mental health nurses, particularly those in private practice, must recognize symptom patterns of Seasonal Affective Disorder (SAD) so that appropriate treatment, including holistic modalities, can be instigated. Using a case study presentation, the authors describe the disorder and atypical phototherapy treatment.

Phototherapy with broad spectrum white fluorescent light: a comparative study

The principles of photobiology suggest that the antidepressant effect of phototherapy depends on the dose and spectrum of light. We investigated the effect of spectrum by comparing two broad spectrum fluorescent light sources with different spectral distributions. In a crossover design, 11 patients with seasonal affective disorder (SAD) were treated with broad spectrum fluorescent and cool white light for 7 days. Scores on the Hamilton Rating Scale for Depression were reduced from 22.5 to 8.1 with broad spectrum fluorescent light and from 23.5 to 8.8 with cool white light. The results suggest that both light sources are effective treatments.

Present status of eyelid phototherapy. Clinical efficacy and transmittance of ultraviolet and visible radiation through human eyelids

BACKGROUND

Phototherapy for the eyelid has not previously been recognized as a safe and effective treatment of photoresponsive dermatoses of the eyelid, such as atopic dermatitis, vitiligo, psoriasis, lymphomatoid papulosis, and parapsoriasis.

OBJECTIVE

The purpose of this study was to demonstrate the efficacy and safety of this treatment.

METHODS

Two cases are presented to demonstrate clinical efficacy. In addition, a retrospective eye evaluation of seven patients receiving a combined total of greater than 1300 eyelid phototherapy treatments was performed. To determine whether potentially harmful UV radiation is significantly transmitted through eyelid skin, an in vitro study was conducted to measure the percentage transmittance of ultraviolet-visible radiation through five excised eyelids.

RESULTS

In the two cases presented, remarkable improvement occurred without adverse side effects, suggesting that it is possible to deliver incremental UV dosages to eyelid skin to achieve clearing of skin disease. Retrospective analysis of patients' records revealed no ocular disease from the phototherapy. In vitro eyelid examination produced data that indicated negligible quantities of UV radiation were transmitted through eyelid skin compared with the visible spectrum, in which up to 77% of the radiation was transmitted through the tissue.

CONCLUSION

The combined clinical experience and transmittance data suggest that eyelid phototherapy is a safe and effective treatment in selected patients.

Properties and function of the ocular melanin--a photobiophysical view

This paper reviews the biosynthesis and physicochemical properties of the ocular melanin. Age-related changes of melanin granules and the corresponding formation of lipofuscin pigments in the retinal pigment epithelium (RPE) are also described. Adverse photoreactions of the eye and, in particular, light-induced damage to the RPE-retina are reviewed in relation to the ocular pigmentation. A hypothesis on the photoprotective role of the RPE melanin is presented that is based on the ability of the cellular melanin to bind redoxactive metal ions. Since bound-to-melanin metal ions are expected to be less damaging to the pigment cells, it is proposed that sequestration of heavy metal ions by the RPE melanin is an efficient detoxifying mechanism. It is postulated that oxidative degradation of RPE melanin may lower its metal-binding capability and decrease its anti-oxidant efficiency. Cellular and environmental factors that may contribute to possible oxidative damage of the RPE melanin are discussed in connection with the etiology of age-related macular degeneration.

Light damage in the rat retina: the effect of dietary deprivation of N-3 fatty acids on acute structural alterations

We investigated the effect of depleting membrane docosahexaenoic acid (DHA, 22:6n-3) content through dietary deprivation of n-3 fatty acids on the susceptibility of the photoreceptors and pigment epithelium cells to acute light-induced changes. Male Sprague-Dawley rats were raised throughout gestation, lactation and up to the age of 8 weeks on semi-purified diets containing either safflower oil (SFO, n-3 deficient diet) or soybean oil (SO) as the sole source of lipids. A third group was switched at weaning from safflower oil to soybean oil (SFO/SO). Rats were maintained on a 12 hr/12 hr light/dark cycle in which the light level at the front of the cages was 5-10 lx. Light damage was produced by exposing dark-adapted animals to diffuse white fluorescent light of 700-800 lx for 30 min followed by 90 min of darkness. In order to study recovery from light damage, additional groups of SFO and SO rats were returned to dim cyclic light for 27 hr following bright light exposure. DHA content in retinal phosphatidylethanolamine and phosphatidylcholine was 65-75% lower in rats fed SFO than in rats fed SO. The decrease was compensated for by an increase in 22:5n-6, the total content of polyunsaturated fatty acids (PUFA) being similar in both the SFO and SO groups. The SFO/SO rats had DHA levels similar to SO animals, but 22:5n-6 remained elevated resulting in a slightly higher level of total PUFA. Severe rod outer segment (ROS) membrane disruptions were seen following bright light exposure in rats on the SO and SFO/SO diets. The appearance of these disruptions did not change significantly during more than 24 hr in dim cyclic light. In contrast, there were virtually no acute ROS lesions in the SFO group. Furthermore, there was a strong light-elicited disk-shedding response in the SO rats but not in the other two groups. The pigment epithelium of the DHA deficient retinas showed a significantly greater accumulation of large lipid droplets in the dark-adapted state. Notably, whole retina rhodopsin levels were 15% higher in the SFO than in the SO group. These results indicate that depletion of retinal DHA reduces the susceptibility of the rod outer segments to acute light damage and at the same time may alter visual pigment photochemistry and other photoreceptor and pigment epithelium functions.

Light damage in the rat retina: effect of a radioprotective agent (WR-77913) on acute rod outer segment disk disruptions

Primary events in the course of light induced retinal lesions are still not fully elucidated. Under chronic conditions, lipid peroxidation in the retina and death of photoreceptor cells are observed. The radioprotective agent WR-77913 scavenges singlet oxygen, hydrated electrons and free radicals. WR-77913 was used to protect against acute light induced photoreceptor outer segment membrane disruptions in the rat retina. There was a partial but not complete protection at higher illuminance levels (800 lx for 30 min), whereas threshold lesions (400 lx for 30 min) were almost completely prevented. These observations indicate an involvement of photodynamic reactions in causing acute photoreceptor lesions.

The photophysics and photobiology of the eye

The eye consists of three major segments: the cornea, lens and retina. The main function of the anterior ocular tissue, the cornea and the lens is to transmit and focus light on the retina without distortion. They also filter out UV light (less than 400 nm) and prevent it from reaching the retina. Much of the light reaching the retina is used for sight. However, light can have numerous other effects on the constituents of the eye, both beneficial and deleterious. This article reviews the interaction of light with the eye, various protective mechanisms, the possible role of light in aging and disease states and the role of light in biological processes other than sight such as mood, hormonal secretions and the cyclic growth and phagocytosis of the rods and cones.

The visual input stage of the mammalian circadian pacemaking system: II. The effect of light and drugs on retinal function

Acute light pulses as well as long-term light exposure may not only modulate photoreceptive properties, but also induce reversible or irreversible damage to the retina, depending on exposure conditions. Illuminance levels in laboratory animal colonies and manipulations of lighting regimens in circadian rhythm research can threaten retinal structure and physiology, and may therefore modify zeitgeber input to the central circadian system. Given the opportunity to escape light at any time, the nocturnal rat self-selects a seasonally varying "naturalistic skeleton photoperiod" that protects the eyes from potential damage by nonphysiological light exposures. Both rod rod-segment disk shedding and behavioral circadian phase shifts are elicited by low levels of twilight stimulation. From this vantage point, we hypothesize that certain basic properties of circadian rhythms (e.g., Aschoff's rule and splitting) may reflect modulation of retinal physiology by light. Pharmacological manipulations with or without the addition of lighting strategies have been used to analyze the neurochemistry of circadian timekeeping. Drug modulation of light input at the level of the retina may add to or interact with direct drug modulation of the central circadian pacemaking system.

The visual input stage of the mammalian circadian pacemaking system: I. Is there a clock in the mammalian eye?

Threads of evidence from recent experimentation in retinal morphology, neurochemistry, electrophysiology, and visual perception point toward rhythmic ocular processes that may be integral components of circadian entrainment in mammals. Components of retinal cell biology (rod outer-segment disk shedding, inner-segment degradation, melatonin and dopamine synthesis, electrophysiological responses) show self-sustaining circadian oscillations whose phase can be controlled by light-dark cycles. A complete phase response curve in visual sensitivity can be generated from light-pulse-induced phase shifting. Following lesions of the suprachiasmatic nuclei, circadian rhythms of visual detectability and rod outer-segment disk shedding persist, even though behavioral activity becomes arrhythmic. We discuss the converging evidence for an ocular circadian timing system in terms of interactions between rhythmic retinal processes and the central suprachiasmatic pacemaker, and propose that retinal phase shifts to light provide a critical input signal.

Adaptation to dim light in depressed patients with seasonal affective disorder

Supersensitivity to light has been suggested as a possible trait marker for manic-depressive illness. Because winter seasonal affective disorder (SAD) is associated with depressive episodes during dark winter days, the authors postulated that SAD patients would show diminished sensitivity to dim light. Dark-adaptation curves were obtained in 10 medication-free, depressed SAD patients and in 10 age- and sex-matched drug-free healthy controls. Contrary to the hypothesis, patients adapted to dim light more rapidly than controls.