Methylprednisolone therapy in laser injury of the retina

Homeostatic plasticity in the retina

Vision begins in the retina, whose intricate neural circuits extract salient features of the environment from the light entering our eyes. Neurodegenerative diseases of the retina (e.g., inherited retinal degenerations, age-related macular degeneration, and glaucoma) impair vision and cause blindness in a growing number of people worldwide. Increasing evidence indicates that homeostatic plasticity (i.e., the drive of a neural system to stabilize its function) can, in principle, preserve retinal function in the face of major perturbations, including neurodegeneration. Here, we review the circumstances and events that trigger homeostatic plasticity in the retina during development, sensory experience, and disease. We discuss the diverse mechanisms that cooperate to compensate and the set points and outcomes that homeostatic retinal plasticity stabilizes. Finally, we summarize the opportunities and challenges for unlocking the therapeutic potential of homeostatic plasticity. Homeostatic plasticity is fundamental to understanding retinal development and function and could be an important tool in the fight to preserve and restore vision.

Alexandrite Laser-Induced Choroidal Neovascularization Successfully Treated With Aflibercept

A 33-year-old female was referred to the ophthalmology department after an accidental eye injury to her right eye during a hair removal session using alexandrite laser. Although she initially experienced no symptoms, when re-examined one and a half months later the best-corrected visual acuity (BCVA) of the affected eye was 20/40 secondary to choroidal neovascularization confirmed by fluorescein angiography (FA) and optical coherence tomography (OCT). Intravitreal anti-vascular endothelial growth factor (VEGF) therapy (three monthly injections of aflibercept) led to complete regression of the neovascularization and functional recovery which was maintained at one-year follow-up post original injury.

CHOROIDAL NEOVASCULARIZATION SECONDARY TO ALEXANDRITE LASER EXPOSURE

PURPOSE

To report macular photic trauma after accidental occupational exposure to a 750-nm Alexandrite laser and management of secondary choroidal neovascularization.

METHODS

Institutional review board-approved retrospective case report.

RESULTS

A 30-year-old woman presented with immediate vision loss in her left eye after direct inadvertent exposure to a single discharge from an occupational 750-nm Alexandrite laser used for laser hair removal. Baseline Snellen visual acuity was 20/40 in the involved left eye. One week after the initial exposure, the patient experienced subjective visual decline to 20/50, was treated with oral prednisone, and then developed a subretinal hemorrhage (SRH) in the setting of choroidal neovascularization 2 weeks later, or 3 weeks after initial trauma. The patient subsequently received 5 intravitreal ranibizumab injections over 25 weeks with resolution of the SRH. Final visual acuity was 20/50.

CONCLUSION

The present case documents development and management of subretinal hemorrhage associated with choroidal neovascularization following macular photic trauma after accidental occupational to a 750-nm Alexandrite laser.

Development and recovery of laser-induced retinal lesion in rats

PURPOSE

Laser-induced retinal lesions undergo primary and secondary degeneration followed by a partial reduction of the lesion size. To evaluate treatment effects, detailed data regarding the changes of the lesion over time are essential. The purpose of the study is to describe the histologic changes in an argon laser-induced retinal lesion over a period of 60 days.

METHODS

Argon laser lesions were produced in retinas of pigmented rats. The lesions were examined by light microscopy 1 hour and 1, 2, 3, 20, and 60 days after the exposure.

RESULTS

The diameter of the lesion increased 24 hours after photocoagulation and then decreased by day 20. Most pyknotic nuclei seen in the outer nuclear layer 1 hour after lasering disappeared 3 days later. Remodeling began 3 days after lasering. By day 60, partial filling in of the empty area with sliding of adjacent nuclei was observed. Recovery was also seen in the other retinal layers.

CONCLUSION

The course of a laser-induced retinal lesion is gradual: the photoreceptors are damaged first and the damage then spreads to other layers and to the adjacent retina. By day 3, the damage spreading stops, and adjacent cells begin to fill in and remodel the area of the lesion.

Retinal laser burn disrupts immune privilege in the eye

Immune privilege allows for the immune protection of the eye in the absence of inflammation. Very few events are capable of overcoming the immune-privileged mechanisms in the eye. In this study, we report that retinal laser burn (RLB) abrogates immune privilege in both the burned and nonburned eye. As early as 6 hours after RLB, and as late as 56 days after RLB, antigen inoculation into the anterior chamber of the burned eye failed to induce peripheral tolerance. After RLB, aqueous humor samples harvested from nontreated eyes but not from either the burned or the contralateral eye, down-regulated the expression of CD40 and up-regulated interleukin-10 mRNA in peritoneal exudate cells, and converted peritoneal exudate cells into tolerogenic antigen-presenting cells (APCs). Unlike F4/80(+) APCs from nontreated mice, F4/80(+) APCs from RLB mice were unable to transfer tolerance after anterior chamber inoculation of antigen into naïve mice. The increased use of lasers in both the industrial and medical fields raises the risk of RLB-associated loss of immune regulation and an increased risk of immune inflammation in the eye.

Steroidal and Nonsteroidal Antiinflammatory Medications Can Improve Photoreceptor Survival after Laser Retinal Photocoagulation

OBJECTIVE

To determine whether methylprednisolone or indomethacin can enhance photoreceptor survival after laser retinal injury in an animal model.

DESIGN

Experimental study.

PARTICIPANTS

Twenty rhesus monkeys.

METHODS

Twenty rhesus monkeys (Macaca mulatta) received a grid of argon green (514.5 nm, 10 ms) laser lesions in the macula of the right eye and a grid of neodymium:yttrium-aluminum-garnet (Nd:YAG; 1064 nm, 10 ns) lesions in the macula of the left eye, followed by randomization to 2 weeks of treatment in 1 of 4 treatment groups: high-dose methylprednisolone, moderate-dose methylprednisolone, indomethacin, or control. The lesions were assessed at day 1, day 14, 2 months, and 4 months. The authors were masked to the treatment group. This report discusses the histologic results of ocular tissue harvested at 4 months.

MAIN OUTCOME MEASURE

The number of surviving photoreceptor cell nuclei within each lesion was compared with the number of photoreceptor nuclei in surrounding unaffected retina. The proportion of surviving photoreceptor nuclei was compared between each treatment group.

RESULTS

Argon retinal lesions in the high-dose steroid treatment group and the indomethacin treatment group demonstrated improved photoreceptor survival compared with the control group (P = 0.004). Hemorrhagic Nd:YAG lesions demonstrated improved survivability with indomethacin treatment compared with controls (P = 0.003). In nonhemorrhagic Nd:YAG laser retinal lesions, the lesions treated with moderate-dose steroids demonstrated improved photoreceptor survival compared with the control group (P = 0.004).

CONCLUSIONS

Based on histologic samples of retinal laser lesions 4 months after injury, treatment with indomethacin resulted in improved photoreceptor survival in argon laser lesions and hemorrhagic Nd:YAG laser lesions. Treatment with systemic methylprednisolone demonstrated improved photoreceptor survival in argon retinal lesions and in nonhemorrhagic Nd:YAG lesions.

Neuroprotection in ophthalmology: a review

Evidence has accumulated that damaged neural cells may not inevitably degenerate, and that in vivo cells which are not directly injured by an insult may be adversely affected by adjacent dying cells. Neuroprotection is a strategy which aims to maximize recovery of injured neural cells and minimize secondary damage to neighboring cells. In this work, we review the current knowledge from neuroprotection research using in vitro and animal models of eye diseases, and clinical data.

Laser eye injuries

Laser instruments are used in many spheres of human activity, including medicine, industry, laboratory research, entertainment, and, notably, the military. This widespread use of lasers has resulted in many accidental injuries. Injuries are almost always retinal, because of the concentration of visible and near-infrared radiation on the retina. The retina is therefore the body tissue most vulnerable to laser radiation. The nature and severity of this type of retinal injury is determined by multiple laser-related and eye-related factors, the most important being the duration and amount of energy delivered and the retinal location of the lesion. The clinical course of significant retinal laser injuries is characterized by sudden loss of vision, often followed by marked improvement over a few weeks, and occasionally severe late complications. Medical and surgical treatment is limited. Laser devices hazardous to the human eye are currently in widespread use by armed forces. Furthermore, lasers may be employed specifically for visual incapacitation on future battlefields. Adherence to safety practices effectively prevents accidental laser-induced ocular injuries. However, there is no practical way to prevent injuries that are maliciously inflicted, as expected from laser weapons.

Methylprednisolone therapy for retinal laser injury

OBJECTIVE

Laser photocoagulation treatment of the posterior pole of the retina is often complicated by immediate visual impairment, which is caused by the unavoidable laser-induced destruction of the normal tissue adjacent to the lesion. A neuroprotective therapy aimed at salvaging this normal tissue might enhance the benefit obtained from treatment and permit safe perifoveal photocoagulation. To determine whether corticosteroids can provide neuroprotection during photocoagulation, we examined the effect of methylprednisolone on laser-induced retinal injury in a rat model.

METHODS

Argon laser lesions were inflicted on the retinas of 36 rats and were followed immediately by intraperitoneal injections of high-dose methylprednisolone or saline. The animals were sacrificed after 3, 20, or 60 days, and their retinal lesions were evaluated histologically and morphometrically.

RESULTS

No histopathologic differences were observed between the treated and control animals. Methylprednisolone treatment was demonstrated to posses some neuroprotective effect for a short time after laser exposure, but was ineffective in ameliorating the long-term results of retinal laser injury.

CONCLUSIONS

On the basis of our results, we suggest that high-dose methylprednisolone treatment is ineffective in ameliorating laser-induced retinal injury. Other drugs should be investigated for their potential role as neuroprotective agents to prevent the spread of retinal laser damage.

The effect of high-dose methylprednisolone on laser-induced retinal injury in primates: an electron microscopic study

BACKGROUND

Previously we reported an ameliorative effect of high-dose methylprednisolone in laser injury to monkey retinas. The ultrastructural modification by methyl-prednisolone has not been examined.

METHODS

Cynomolgus monkeys were given severe (grade III) retinal laser burns and treated with an intravenous megadose of methylprednisolone. Pathologic features of the retinal lesions with or without methylprednisolone treatment were evaluated by light and electron microscopy.

RESULTS

Ultrastructurally, the treated lesions showed rapid recanalization of choriocapillaris; proliferation of retinal pigment epithelium to replace the necrotic and damaged cells, resulting in rapid re-establishment of blood retinal barrier; mild macrophagic activity; and rapid reformation of the outer limiting membrane by Mueller cells.

CONCLUSION

A high dose of methylprednisolone affected the responses of the choriocapillaris, retinal pigment epithelium, photoreceptor cells and Mueller cells to laser injury, showing an overall beneficial effect. These modifications might be ascribed to methylprednisolone's anti-inflammatory action, protection of the microcirculation and anti-lipid peroxidation effect.

Neuroprotective therapy for argon-laser induced retinal injury

Laser photocoagulation treatment of the central retina is often complicated by an immediate side effect of visual impairment, caused by the unavoidable laser-induced destruction of the normal tissue lying adjacent to the lesion and not affected directly by the laser beam. Furthermore, accidental laser injuries are at present untreatable. A neuroprotective therapy for salvaging the normal tissue might enhance the benefit obtained from treatment and allow safe perifoveal photocoagulation. We have developed a rat model for studying the efficacy of putative neuroprotective compounds in ameliorating laser-induced retinal damage. Four compounds were evaluated: the corticosteroid methylprednisolone, the glutamate-receptor blocker MK-801, the anti-oxidant enzyme superoxide dismutase, and the calcium-overload antagonist flunarizine. The study was carried out in two steps: in the first, the histopathological development of retinal laser injuries was studied. Argon laser lesions were inflicted in the retinas of 18 pigmented rats. The animals were killed after 3, 20 or 60 days and their retinal lesions were evaluated under the light microscope. The laser injury mainly involved the outer layers of the retina, where it destroyed significant numbers of photoreceptor cells. Over time, evidence of two major histopathological processes was observed: traction of adjacent normal retinal cells into the central area of the lesion forming an internal retinal bulging, and a retinal pigmented epithelial proliferative reaction associated with subretinal neovascularization and invasion of the retinal lesion site by phagocytes. The neuroprotective effects of each of the four compounds were verified in a second step of the study. For each drug tested, 12 rats were irradiated with argon laser inflictions: six of them received the tested agent while the other six were treated with the corresponding vehicle. Twenty days after laser exposure, the rats were killed and their lesions were subjected to image-analysis morphometry. The extent of retinal destruction was assessed by measuring the lesion diameter and the amount of photoreceptor cell loss in the outer nuclear layer. Methylprednisolone and MK-801 were shown to ameliorate laser-induced retinal damage, whereas both superoxide dismutase and flunarizine were ineffective. Furthermore, MK-801 diminished the proliferative reaction of the retinal pigment epithelial cells. On the basis of our results we suggest that the pigmented rat model is suitable for studying and screening various compounds for their neuroprotective efficacy in treating retinal laser injury. We further suggest that glutamate might play a key role in mediating retinal injury induced by laser irradiation.