Observations on monkey eyes exposed to light from an operating microscope

Eclipse retinopathy injury scale (ERIS): A classification of acute macular damage resulting from unprotected solar eclipse viewing

Introduction. Eclipse retinopathy occurs due to unprotected viewing of a solar eclipse. It is a long-recognized condition. The damage inflicted to the macula is due to a photochemical and photothermal effect caused by sunlight that enters the eye and is focused by the crystalline lens. Animal studies into eclipse retinopathy have been previously carried out. Retinal irradiance levels leading to macular damage have been established in rabbits. Limited data from studies on primates are also available. However, the exact values for humans have not yet been established with confidence.

Methods. Here we present a simple method for estimation of the retinal irradiance dose in humans and a classification of macular damage.

Results. As an example, the retinal irradiance dose of a theoretical patient observing the solar eclipse of March 20, 2015, is given along with the grade of macular damage according to the developed classification.

Discussion. The retinal irradiance values given in the classification are provisional for the time being. With more widespread use among ophthalmologists the developed classification should become useful for prognostic purposes.

Protective Effect of Astaxanthin on Blue Light Light-Emitting Diode-Induced Retinal Cell Damage via Free Radical Scavenging and Activation of PI3K/Akt/Nrf2 Pathway in 661W Cell Model

Light-emitting diodes (LEDs) are widely used and energy-efficient light sources in modern life that emit higher levels of short-wavelength blue light. Excessive blue light exposure may damage the photoreceptor cells in our eyes. Astaxanthin, a xanthophyll that is abundantly available in seafood, is a potent free radical scavenger and anti-inflammatory agent. We used a 661W photoreceptor cell line to investigate the protective effect of astaxanthin on blue light LED-induced retinal injury. The cells were treated with various concentrations of astaxanthin and then exposed to blue light LED. Our results showed that pretreatment with astaxanthin inhibited blue light LED-induced cell apoptosis and prevented cell death. Moreover, the protective effect was concentration dependent. Astaxanthin suppressed the production of reactive oxygen species and oxidative stress biomarkers and diminished mitochondrial damage induced by blue light exposure. Western blot analysis confirmed that astaxanthin activated the PI3K/Akt pathway, induced the nuclear translocation of Nrf2, and increased the expression of phase II antioxidant enzymes. The expression of antioxidant enzymes and the suppression of apoptosis-related proteins eventually protected the 661W cells against blue light LED-induced cell damage. Thus, our results demonstrated that astaxanthin exerted a dose-dependent protective effect on photoreceptor cells against damage mediated by blue light LED exposure.

Microscope-Induced Thermal Burns During Lymphaticovenular Anastomosis

Bright illumination sources using xenon lamps have improved microsurgical visualization under an operating microscope; however, surgeons must recognize the potential for accidental thermal damage to soft tissues.In this article, we present 2 reports of microscopic thermal burn in lymphaticovenular anastomosis (LVA).A 23-year-old woman and a 57-year-old woman with bilateral lymphedema of the legs had LVAs on both legs under local anesthesia. The burn wound in a 23-year-old woman was full thickness, and the one in a 57-year-old woman was deep dermal burn. Both of them healed without skin grafting.Working distance and high illumination intensity are important risk factor. The use of epinephrine as part the local anesthetic mixture that decreases blood flow is also a major risk factor for thermal burns. Lymphaticovenular anastomosis particularly requires high magnification, which leads to increasing the intensity and decreasing the working distance. The surgical conditions around LVA are inherently prone to microscope-induced thermal burns.

Effects of the Emitted Light Spectrum of Liquid Crystal Displays on Light-Induced Retinal Photoreceptor Cell Damage

Liquid crystal displays (LCDs) are used as screens in consumer electronics and are indispensable in the modern era of computing. LCDs utilize light-emitting diodes (LEDs) as backlight modules and emit high levels of blue light, which may cause retinal photoreceptor cell damage. However, traditional blue light filters may decrease the luminance of light and reduce visual quality. We adjusted the emitted light spectrum of LED backlight modules in LCDs and reduced the energy emission but maintained the luminance. The 661W photoreceptor cell line was used as the model system. We established a formula of the ocular energy exposure index (OEEI), which could be used as the indicator of LCD energy emission. Cell viability decreased and apoptosis increased significantly after exposure to LCDs with higher emitted energy. Cell damage occurred through the induction of oxidative stress and mitochondrial dysfunction. The molecular mechanisms included activation of the NF-κB pathway and upregulation of the expression of proteins associated with inflammation and apoptosis. The effect was correlated with OEEI intensity. We demonstrated that LCD exposure-induced photoreceptor damage was correlated with LCD energy emission. LCDs with lower energy emission may, therefore, serve as suitable screens to prevent light-induced retinal damage and protect consumers’ eye health.

Inhibition of cell proliferation, migration and apoptosis in blue-light illuminated human retinal pigment epithelium cells by down-regulation of HtrA1

AIM

To investigate the effect of HtrA1 on the proliferation, migration and apoptosis of human retinal pigment epithelium (RPE) cells in the light injured model, as well as the expression of the apoptosis related molecules.

METHODS

The human RPE cell line ARPE-19 was exposed to blue light to establish the light injured model. The cells were transfected with HtrA1 siRNA to knockdown HtrA1 expression. Subsequent expression of HtrA1 was determined by real-time polymerase chain reaction (RT-PCR) and Western blot, respectively. Changes in cell proliferation, migration and apoptosis were assessed by cell counting kit-8 (CCK-8), Transwell assay and flow cytometry respectively, as well as changes in the mRNA and protein levels of Bax, Caspase-3 and Bcl-2 expression.

RESULTS

HtrA1 was highly expressed in ARPE-19 cells after blue light irradiation. Knockdown of HtrA1 expression inhibited the proliferation, migration and apoptosis of the blue-light-irradiated ARPE-19 cells (P<0.05). Bax and Caspase-3 expression were significantly reduced both at mRNA and protein levels (P<0.05) after siRNA treatment. Bcl-2 expression significantly increased in blue-light-irradiated ARPE-19 cells after siRNA interference (P<0.05).

CONCLUSION

Silence of HtrA1 may inhibit the proliferation, migration and apoptosis of ARPE-19 cells in light injured model. Moreover, HtrA1 suppression in blue-light-irradiated ARPE-19 cells may ameliorate cell apoptosis through down-regulation of Bax and Caspase-3, and up-regulation of Bcl-2 expression.

The illumination characteristics of operative microscopes

PURPOSE

Modern operative microscopes use light sources which possess the power to severely damage underlying tissue. Currently, manufacturers provide a safety warning of this possibility. However, they are unable to suggest specific settings due to a stated "lack of scientific publications on this topic". We aim to radiometrically evaluate multiple otologic microscopes at variables which effect irradiance in order to determine reference emissions levels and provide guidelines for improved intraoperative safety.

MATERIALS AND METHODS

The optical radiance of four otologic microscopes was evaluated at variable field illumination sizes (spot size), intensity settings and working distances. The spectral emission of each microscope was separately measured. The energy absorbed in skin with representative properties was then calculated as a function of time for each microscope by accounting for the emission spectrum of the microscope and the absorption spectrum of skin.

RESULTS

Microscopes showed a wide range of optical radiance based on model, spots size, intensity setting and working distances. Spectral emission of all four microscopes was centered in the visible spectrum with minimal ultraviolet or infrared contribution. A large amount of energy is absorbed by skin during usage of operative microscopes. The highest calculated absorption at 200 min of use was 736.26 J/cm(2).

CONCLUSIONS

Operative microscopes have the ability to cause patient morbidity secondary to the energy they impart. In an effort to decrease potential injury we recommend that physicians be aware of their microscopes properties and how to control variables which effect irradiance of the skin.

Blue LED light exposure develops intracellular reactive oxygen species, lipid peroxidation, and subsequent cellular injuries in cultured bovine retinal pigment epithelial cells

The effects of blue light emitter diode (LED) light exposure on retinal pigment epithelial cells (RPE cells) were examined to detect cellular damage or change and to clarify its mechanisms. The RPE cells were cultured and exposed by blue (470 nm) LED at 4.8 mW/cm(2). The cellular viability was determined by XTT assay and cellular injury was determined by the lactate dehydrogenase activity in medium. Intracellular reactive oxygen species (ROS) generation was determined by confocal laser microscope image analysis using dihydrorhodamine 123 and lipid peroxidation was determined by 4-hydroxy-2-nonenal protein-adducts immunofluorescent staining (HNE). At 24 h after 50 J/cm(2) exposures, cellular viability was significantly decreased to 74% and cellular injury was significantly increased to 365% of control. Immediately after the light exposure, ROS generation was significantly increased to 154%, 177%, and 395% of control and HNE intensity was increased to 211%, 359%, and 746% of control by 1, 10, and 50 J/cm(2), respectively. These results suggest, at least in part, that oxidative stress is an early step leading to cellular damage by blue LED exposure and cellular oxidative damage would be caused by the blue light exposure at even lower dose (1, 10 J/cm(2)).

Shedding light on nanomedicine

Light is an electromagnetic radiation that can convert its energy into different forms (e.g., heat, chemical energy, and acoustic waves). This property has been exploited in phototherapy (e.g., photothermal therapy and photodynamic therapy (PDT)) and optical imaging (e.g., fluorescence imaging) for therapeutic and diagnostic purposes. Light-controlled therapies can provide minimally- or noninvasive spatiotemporal control as well as deep tissue penetration. Nanotechnology provides numerous advantages, including selective targeting of tissues, prolongation of therapeutic effect, protection of active payloads, and improved therapeutic indices. This review explores the advances that nanotechnology can bring to light-based therapies and diagnostics, and vice versa, including photo-triggered systems, nanoparticles containing photoactive molecules, and nanoparticles that are themselves photoactive. Limitations of light-based therapies such as photic injury and phototoxicity are discussed.

Foveal light exposure is increased at the time of removal of silicone oil with the potential for phototoxicity

BACKGROUND

There is sudden and dramatic visual function deterioration in 1-10 % of eyes filled with silicone oil at the time of removal of silicon oil. Transmission of high-energy blue light is increased in eyes filled with silicone oil. We sought to identify if increased foveal light exposure is a potential factor in the pathophysiology of the visual loss at the time of removal of silicone oil.

METHODS

A graphic ray tracing computer program and laboratory models were used to determine the effect of the intraocular silicone oil bubble size on the foveal illuminance at the time of removal of silicone oil under direct microscope light. The graphic ray tracing computer program revealed a range of optical vignetting effects created by different sizes of silicone oil bubble within the vitreous cavity giving rise to an uneven macular illumination. The laboratory model was used to quantify the variation of illuminance at the foveal region with different sizes of silicone oil bubble with in the vitreous cavity at the time of removal of silicon oil under direct microscope light. To substantiate the hypothesis of the light toxicity during removal of silicone oil, The outcome of oil removal procedures performed under direct microscope illumination in compared to those performed under blocked illumination.

RESULTS

The computer program showed that the optical vignetting effect at the macula was dependent on the size of the intraocular silicone oil bubble. The laboratory eye model showed that the foveal illuminance followed a bell-shaped curve with 70 % greater illuminance demonstrated at with 50-60 % silicone oil fill. The clinical data identified five eyes with unexplained vision loss out of 114 eyes that had the procedure performed under direct microscope illumination compared to none out of 78 eyes that had the procedure under blocked illumination.

CONCLUSIONS

Foveal light exposure, and therefore the potential for phototoxicity, is transiently increased at the time of removal of silicone oil. This is due to uneven macular illumination resulting from the optical vignetting effect of different silicone oil bubble sizes. The increase in foveal light exposure may be significant when the procedure is performed under bright operating microscope light on already stressed photoreceptors of an eye filled with silicon oil. We advocate the use of precautions, such as central shadow filter on the operating microscope light source to reduce foveal light exposure and the risk of phototoxicity at the time of removal of silicone oil. The graphic ray tracing computer program used in this study shows promise in eye modeling for future studies.

Retinal light toxicity

The ability of light to enact damage on the neurosensory retina and underlying structures has been well understood for hundreds of years. While the eye has adapted several mechanisms to protect itself from such damage, certain exposures to light can still result in temporal or permanent damage. Both clinical observations and laboratory studies have enabled us to understand the various ways by which the eye can protect itself from such damage. Light or electromagnetic radiation can result in damage through photothermal, photomechanical, and photochemical mechanisms. The following review seeks to describe these various processes of injury and many of the variables, which can mitigate these modes of injury.

Sub-lethal photodynamic damage to ARPE-19 cells transiently inhibits their phagocytic activity

Efficient phagocytosis of photoreceptor outer segments (POS) membranes by retinal pigment epithelium (RPE) plays a key role in biological renewal of these highly peroxidizable structures. Here, we tested whether photodynamic treatment, mediated by merocyanine 540 (MC 540), rose Bengal or a zinc-substituted chlorophyllide inhibited phagocytic activity of ARPE-19 cells in vitro. Specific phagocytosis of fluorescein-5-isothiocyanate-labeled POS isolated from cow retinas and nonspecific phagocytosis of fluorescent polystyrene beads were measured by flow cytometry. Photodynamic treatment, mediated by all three photosensitizers with sub-threshold doses, induced significant inhibition of the cell-specific phagocytosis. The nonspecific phagocytosis was inhibited by photodynamic treatment mediated only by MC 540. The inhibition of phagocytosis was a reversible phenomenon and after 24 h, the photodynamically treated cells exhibited phagocytic activity that was comparable with that of untreated cells. This study provides proof of principle that sub-threshold photodynamic treatment of ARPE-19 cells with appropriate photosensitizers is a convenient experimental approach for in vitro study of the effects of oxidative stress on specific phagocytic activity of RPE cells. We postulate that oxidative damage to key components of the cell phagocytic machinery may be responsible for severe impairment of its activity, which can lead to retinal degeneration.

Light-induced damage to the retina: role of rhodopsin chromophore revisited

The presence of the regenerable visual pigment rhodopsin has been shown to be primarily responsible for the acute photodamage to the retina. The photoexcitation of rhodopsin leads to isomerization of its chromophore 11-cis-retinal to all-trans-retinal (ATR). ATR is a potent photosensitizer and its role in mediating photodamage has been suspected for over two decades. However, there was lack of experimental evidence that free ATR exists in the retina in sufficient concentrations to impose a risk of photosensitized damage. Identification in the retina of a retinal dimer and a pyridinium bisretinoid, so called A2E, and determination of its biosynthetic pathway indicate that substantial amounts of ATR do accumulate in the retina. Both light damage and A2E accumulation are facilitated under conditions where efficient retinoid cycle operates. Efficient retinoid cycle leads to rapid regeneration of rhodopsin, which may result in ATR release from the opsin "exit site" before its enzymatic reduction to all-trans-retinol. Here we discuss photodamage to the retina where ATR could play a role as the main toxic and/or phototoxic agent. Moreover, we discuss secondary products of (photo)toxic properties accumulating within retinal lipofuscin as a result of ATR accumulation.

Updating on intraoperative light-induced retinal injury

We are presenting the state of knowledge concerning intraoperative light-induced retinal injury, considered to be a combination of photic retinopathy and retinal photocoagulation. It may arise from retinal light exposure to the operating microscope or to the fiberoptic endoilluminator. Ultraviolet and short-wavelength visible light are more dangerous than longer wavelength light. Many risk factors may facilitate the onset of this iatrogenic disease following surgery. Many aspects of the retinal damage are still poorly understood. Many mid light-induced retinal injuries probably remain undiagnosed in routine postoperative examination. Current appropriate light filters are not the definitive solution. Appropriate precautions should be taken during both anterior segment and vitreoretinal surgery.

In vivo effect of visible light on feline cortical microcirculation

The present study was designed to test the hypothesis that prolonged illumination of the cerebral cortex, for instance during neurosurgical interventions, may affect the pial microcirculation. Experiments were performed with the closed window technique in cats. The cortical surface below the window was exposed to visible, cold light of 61,000 lumens/m2 (lux) over a period of 1 to 5 hours. Pial arterioles reacted with a slight initial dilatation to 106.8 +/- 2.6% of their resting diameter after switching to the high intensity light. Measurements of the cortical surface temperature showed an average temperature increase of 1.5 +/- 0.34 degrees C within the first 10 minutes of illumination. For assessment of pial vascular function, the responses to topical application of acetylcholine (ACh) were tested before and during the illumination period. The effect of sustained illumination on the cortical microcirculation consisted of abolition of the endothelium dependent relaxation due to ACh, and of intravascular thrombus formation, the latter, however, only in the presence of topically applied ACh. The suspected mechanism responsible for these functional alterations is light-induced generation of free oxygen radicals which are known to inactivate or destroy the endothelium-derived relaxing factor (EDRF). Further studies are recommended to elucidate the practical and clinical relevance of these findings to neurosurgical procedures.

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 hazards to the patient's retina from ophthalmic instruments

The spectral radiance and irradiance of several common ophthalmic instruments were measured. The respective spectral retinal irradiance a patient might receive was calculated. To evaluate the potential light hazard to the patient's retina, we calculated the temperature rise resulting from light absorption at the fundus, compared retinal irradiance with threshold values for photochemical retinal damage, and correlated them with safety guidelines. A thermal hazard to the patient's retina can result from operation microscopes if light output is maximal and exposure prolonged. Comparison of light exposures from different ophthalmic instruments with thresholds for photochemical-induced lesions showed that one has to be more concerned about the actinic effect of light exposure. At maximum lamp voltage, the light exposure from operation microscopes reaches thresholds for photochemical damage even after a few minutes. Other ophthalmic instruments present no particular hazard if they are used at common exposure durations. Application of laser safety guidelines confirm these results. In some cases, light from operation microscopes exceeds the safety margin in <1 min.

Fluorophotometric assessment of blood-retinal barrier function after white light exposure in the rabbit eye

Fluorophotometry was performed in 14 rabbits after exposure of one eye to white light with an energy insufficient to cause visible phototoxic retinal damage as determined by ophthalmoscopy and fundus photography. Fluorescence measurements in the vitreous were performed before and 1 hr after i.v. injection of fluorescein. Ratios between the fluorescein concentrations in the exposed and in the non-exposed fellow eye were calculated after correction for the autofluorescence. The average ratio directly after light exposure had significantly increased (P = 0.005) as compared to pre-exposure values and was maximal one day after exposure (P less than 0.005). Four days after exposure the ratios had returned to pre-exposure values (P greater than 0.05). A significant linear correlation between age and the ratios directly after exposure was found (r = -0.67; P less than 0.01). Signs of phototoxic retinal damage were not found on ophthalmoscopy and fundus photography, nor on light and electron microscopic examination of the retinal pigment epithelium, neuro-retina or retinal capillaries 1 and 4 days after light exposure. A fluorophotometric assessment of the blood-retinal barrier (BRB) function after white light exposure appeared to be a more sensitive parameter of light-induced damage than morphological examination since light exposures at retinal irradiance levels below the threshold for ultrastructural damage resulted in a temporary BRB dysfunction that could be detected by fluorophotometry but not by the other methods.

Operating microscope-induced retinal phototoxicity: pathophysiology, clinical manifestations and prevention

Retinal light damage is a poorly understood phenomenon, due to its multifactorial etiology and relatively infrequent recognition. It has been increasingly identified following ocular surgery involving the intense light of the operating microscope. The authors describe the clinical entity, review salient features of its pathophysiology and provide guidelines for prevention of retinal phototoxicity.

Reversible changes of visual acuity and pattern-electroretinograms after blue-green argon laser photocoagulation of diabetic patients

Visual acuity, color vision, pattern-visual-evoked-potentials (P-VEPs) and pattern-electroretinograms (P-ERGs) were measured in 13 diabetic subjects before, and 24 hours and 5 weeks after blue-green argon laser treatment. As control, the same examinations were performed in 7 normal subjects and 7 diabetic patients before and after slit lamp examination with the Goldman three mirror contact lens. Visual acuity and P-ERG amplitudes were significantly reduced one day after the laser treatment, while 5 weeks after the laser coagulation, visual acuity and P-ERG amplitudes recovered to pretreatment values. The control group showed no significant changes after slit lamp examination. Since fluorescein angiography revealed no macular changes after laser treatment, the possibility of a reversible functional light damage after blue-green argon laser coagulation (ALC) is discussed.

The site of operating microscope light-induced injury on the human retina

We determined the site of the focal illumination from the Zeiss OPMI-6 operating microscope on the retina of the phakic and aphakic human cadaver eye by directly observing the illuminating element image on the posterior scleral surface of the globe. With the eye straight ahead and the operating microscope level, the focal oval area of retinal illumination was located superior to the foveola in both the phakic and aphakic eye. Tilting the operating microscope 10 degrees toward the surgeon displaced the entire illuminating element image 0.50 mm below the foveola in the phakic eye and 0.25 mm below the foveola in the aphakic eye. Rotating the eye inferiorly 10 degrees displaced the entire illuminating element image 1.0 mm below the foveola in the phakic eye and 1.25 mm below the foveola in the aphakic eye. Centering the field of view superiorly (viewing the superior limbus) paradoxically displaced the illuminating element image inferiorly, resulting in central foveal illumination. Foveal light exposure was avoided in most eye positions by tilting the microscope at least 10 degrees toward the surgeon.

Microscope light-induced maculopathy in combined penetrating keratoplasty, extracapsular cataract extraction, and intraocular lens implantation

A characteristic retinal phototoxicity reaction was noted in four patients who underwent penetrating keratoplasty, extracapsular cataract extraction (ECCE), and intraocular lens (IOL) implantation. This complication has been well documented in association with other ocular procedures, but only one previous similar case has been reported. The authors bring this potential complication to the attention of corneal surgeons, discuss the risk factors, and offer suggestions on prevention.

Three cases with light-induced retinopathy

Three patients presented a characteristic retinopathy presumably induced by light arising from operating microscope during extracapsular cataract extraction combined with intraocular lens insertion. The operating microscope was equipped with video-recorder. Light sources were tungsten bulb. All cases were asymptomatic and an inspection at the post-operative control examination led to the detection of this type of retinopathy.

Solar radiation and age-related macular degeneration

Age-related macular degeneration (AMD) involves a progressive impairment of the outer layers in the center of the retina. Experimental studies have demonstrated that bright light preferentially damages precisely the region that degenerates in AMD. The evidence that solar radiation is responsible for some of the deteriorative changes that lead to AMD is examined in this review. In the primate eye, the high-energy portion of the solar spectrum is most hazardous to retinal molecules, with damaging effects increasing as photon energy rises. This action spectrum is explicable by the quantum laws which describe the interaction of radiation with matter. High-energy visible and ultraviolet photons can produce molecular damage by a photochemical mechanism. The lesion is exacerbated by oxygen, which initiates free-radical chain reactions (photodynamic effects). Melanin exerts a protective effect against damage from sunlight. In the human retina, documented lesions from solar radiation range from the acute effects of sun-gazing to injuries resulting from prolonged periods of exposure in brightly illuminated environments. The damage occurs in the same region that degenerates in AMD. A cataractous lens and ocular melanin both protect the retina against AMD, as predicted by the radiation hypothesis. Identification of an environmental factor that evidently plays a role in the etiology of AMD provides the basis for a program of preventive medicine.

The spectra, classification, and rationale of ultraviolet-protective intraocular lenses

I measured the spectral transmittance of 16 implantable intraocular lenses from 12 manufacturers and examined the rationale for using ultraviolet-absorptive intraocular lenses to protect pseudophakic individuals from photic retinopathy. Each ultraviolet-protective lens was classified by the wavelength at which its spectral transmittance fell to 10% in the blue or ultraviolet region of the spectrum. Current ultraviolet-protective intraocular lenses differ in the effectiveness of their protection against photic retinopathy, and product descriptions may be misleading.

Temperature-dependent light damage to the retina

We examined the ability of hypothermic infusion fluid to reduce the risk of light damage to the retina from the intraocular fiberoptic probe during vitreous surgery. Following vitrectomy, we exposed the retina of rabbits to light from an intraocular fiberoptic probe during infusion of fluid at body temperature (39 C) and compared this with exposures during infusion of room temperature fluid (22 C). Retinal irradiance was 0.33 W/cm2. Damage was determined ophthalmoscopically and histologically. Cooling the infusion fluid from body to room temperature extended the damage threshold from approximately 25 to 60 minutes. A 35-minute exposure to body temperature fluid was compared with the same exposure during infusion of room temperature fluid. While retinal and retinal pigment epithelium damage was present after the body temperature exposure, no damage was detected after the room temperature exposure. Vitreoretinal surgeons should avoid warming intraocular infusion fluids to levels above room temperature.

Photic retinopathy from the operating room microscope

Photic retinopathy was produced in two patients after a 60-minute exposure to light from an operating room microscope (Zeiss OpMi 6). The first patient had a blind eye with clear (phakic) media and a normal-appearing retina. A 60-minute exposure produced an oval gray lesion in the posterior pole at the level of the pigment epithelium. With an ultraviolet-400 filter added for a second exposure, a second lesion was produced. The second patient received a 60-minute exposure (without an ultraviolet filter) 72 hours before enucleation for a malignant melanoma. This produced photic retinopathy that resulted in a slight decrease in central visual acuity and a dense paracentral scotoma. This conclusively establishes a cause-and-effect relationship between exposure to the light from an operating room microscope and a retinal lesion in the human eye.

Light-induced maculopathy

Photochemical retinal damage can result from the light of the operating microscope during cataract extraction with implantation of intraocular lenses. Three patients (a 47-year-old woman, a 73-year-old woman, and a 69-year-old man) who underwent cataract extraction with the Zeiss OMNI-6 operating microscope with internal incandescent coaxial illumination developed phototoxic retinal damage in the macular region. A posterior chamber lens was used in the first case, an anterior chamber lens in the second, and an iris-supported lens in the third. The photochemical damage was most evident in fluorescein angiographic studies, and Goldmann visual field studies documented scotomas in the affected areas. Final visual acuities were 20/40 in Case 1, 20/30 in Case 2, and 20/30 in Case 3.

Operating microscope light-induced retinal injury: mechanisms, clinical manifestations, and preventive measures

Experimental and clinical evidence of light-induced retinal injury associated with the operating microscope is reviewed. The mechanism of photochemical injury is discussed, as well as the concept of reversible phototoxic insults. Factors that influence retinal recovery and measures that can be taken by the surgeon to reduce light exposure to the retina are also discussed.