Subretinal neovascularization developing after prophylactic argon laser photocoagulation of atrophic macular scars

Argon Laser Lesions of the Retina; Occurence and Origin of Macrophages

Macrophage infiltration is frequent in the early stages of various proliferative eye disorders, including subretinal neovascularization. In this study, we set out to establish the origin of macrophages found in an animal model of laser-induced subretinal neovascularization.

One primate received several intravenous injections of a colloidal carbon suspension. We then applied standard argon laser lesions to the retina of both eyes, which were enucleated eight days later and sectioned serially for histological examination. A quantitative estimate of carbon-laden and non-laden leukocytes was made based on morphological criteria. Mononuclear leukocytes accumulated in the laser lesions and the percentage of carbon-laden mononuclear leukocytes in relation to the total leukocyte number was higher in the extravascular area of the laser sites than in the systemic circulation. These findings indicate that the majority of mononuclear leukocytes that accumulate at the sites of laser lesions are derived from the systemic circulation.

Review of the ocular angiogenesis animal models

Increasing interest in developing reliable and reproducible models to study angiogenesis has emerged due to recent advances in the treatment of eye disease with pathologic angiogenesis. This review provides a summary of the principal ocular animal models for angiogenesis. Models of anterior segment neovascularization include the corneal micropocket assay, used to study the influence of specific molecules/proteins in angiogenesis, and corneal chemical and suture induced injury, which mimic more closely the complex nature of the human disease. Angiogenesis models of the posterior segment include the well-known laser-induced injury of the choroid/Bruch's membrane, as well as the oxygen induced retinopathy and models of injections of pro-angiogenic/inflammatory molecules. In addition, knockout or knock-in transgenic mice provide powerful tools in studying the role of specific proteins in angiogenesis.

Overexpression of FasL in retinal pigment epithelial cells reduces choroidal neovascularization

Choroidal neovascularization (CNV) is responsible for the severe visual loss in age-related macular degeneration. CNV formation is considered to be due to an imbalance between pro- and antiangiogenic factors that lead to neovascular growth from the choriocapillaris into the subretinal space. To define whether FasL overexpression in retinal pigment epithelial cells (RPE) can inhibit choroidal neovascularization through Fas-FasL-mediated apoptosis, we examined the role of this pathway in a mouse model of laser-induced choroidal neovascularization. FasL was expressed in the retinal pigment epithelium of transgenic mice. Polymerase chain reaction (PCR), immunoblot, and immunohistochemistry confirmed that the transgene FasL was specifically expressed in RPE. The established laser model was used to induce choroidal neovascularization (CNV) in wild-type (WT) and transgenic mice. CNV formation was compared with respect to fluorescein angiographic leakage (at days 0 and 14 after laser injury) and histological appearance. The lesions were assessed on RPE-choroidal flatmounts after CD31-labeling and with confocal microscopy after perfusion with rhodamine-labeled concanavalin A (Con A). Apoptosis was quantified by TUNEL positivity and caspase activation. FasL mRNA and protein were highly expressed in the RPE of the transgenic mice before and after laser photocoagulation. In contrast, FasL was only weakly expressed in the RPE layer of WT C57BL/6J mice. While ruptures of Bruch's membrane and CNV formation were observed histologically two weeks after laser photocoagulation in transgenic as well as control eyes, the shape and size of CNV lesions were reduced in the transgenic mice. The area of leakage was decreased by 70% in FasL transgenic mice compared with WT mice (P<0.005). The number of TUNEL-positive cells was greater in FasL-overexpressing mice and correlated with the expression of activated caspases. Th expression of other antiangiogenic factors such as PEDF remained unchanged. The specific overexpression of FasL in RPE layer reduced CNV formation in our laser model. Our results strongly point to the FasL-Fas pathway as a potential therapeutic target in controlling pathological choroidal neovascularization.

Influence of laser photocoagulation on choroidal capillary cytoarchitecture

AIM

To identify if laser photocoagulation induces morphological changes specifically related to the choroidal capillary endothelial processes that protrude into Bruch's membrane.

METHODS

Two human eyes and one adult macaque monkey eye received retinal laser photocoagulation that was just suprathreshold, before enucleation or exenteration. They were examined by electron microscopy to determine the length of the endothelial processes emanating from the choroidal capillaries in the region around the laser burn. One human and two monkey untreated eyes were used for comparison.

RESULTS

In human eyes, there was no increase in the number of processes 15 hours after laser treatment but at 5 days the processes were more numerous and longer within 400-500 microm of the burn than in the untreated half of the same eye. The processes were longer 9 days after photocoagulation in the monkey, when compared with untreated monkeys, and some breached the elastic lamina, a phenomenon not seen in the untreated eyes. Qualitative differences were also noted in the endothelial cell processes following photocoagulation. Neovascularisation was not observed.

CONCLUSIONS

Protrusion of choroidal endothelial cell processes into Bruch's membrane is a normal anatomical feature but the number, length, and morphology of the processes change following mild photocoagulation. It is plausible that these processes may play a part in the clearance of debris from Bruch's membrane, and represent an early stage of angiogenesis. If the latter is true prophylactic laser photocoagulation at just suprathreshold levels may carry a risk of inducing choroidal neovascularisation.

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.

Iatrogenic choroidal neovascularization

Iatrogenic choroidal neovascularization is an uncommon complication of laser photocoagulation and other ocular surgical procedures. It appears to be the result of a number of conditions, including damaged Bruch's membrane and/or retinal pigment epithelium, whose reparative processes trigger the release of angiogenic factors. Inflammatory cells and choroidal ischemia may also play a role. The prognosis varies depending on the underlying disease and the type of choroidal neovascularization (subretinal, chorioretinal, or choriovitreal). Minimizing the amount of laser energy used during laser procedures, avoiding repeat laser treatment to the same retinal area, and minimizing direct mechanical trauma to the retinal pigment epithelium and choroid decrease the chance of inducing iatrogenic choroidal neovascularization.

Laser-induced chorioretinal venous anastomosis for nonischemic central retinal vein occlusion: evaluation of the complications and their risk factors

PURPOSE

To evaluate the complications of laser-induced chorioretinal venous anastomosis in nonischemic central retinal vein occlusion (CRVO) and to identify the associated risks.

METHODS

A retrospective consecutive series of 91 eyes (91 patients) with nonischemic CRVO with a mean +/- SD duration of 15.0 +/- 15.2 weeks (range, 3 to 72 weeks )and corrected visual acuity reduced to 20/100 or less because of perfused macular edema were reviewed. All eyes had one or more anastomotic attempts using argon laser (combined with Nd-YAG laser in 46 eyes) and a minimum of 12 months of follow-up.

RESULTS

Successful chorioretinal venous anastomoses were created in 49 eyes (54%). Eighteen eyes (20%) had neovascular complications. These consisted of intravitreal, intraretinal, and subretinal neovascular membranes and were significantly associated with retinal ischemia (P < .001). There was avascular fibrous tissue proliferation at the anastomotic site in eight eyes (9%), and it was not associated with retinal ischemia (P = .727). No eye developed further capillary nonperfusion once an anastomosis became functional. A chorioretinal venous anastomosis was associated with improved vision (P < .001); 84% of eyes had an average +/- SD improvement of 4.3 +/- 3.8 lines (range, 2 to 20 lines), with the remaining 16% having no improvement or reduced vision.

CONCLUSION

The major vision-threatening complication of laser-induced chorioretinal venous anastomosis for nonischemic CRVO is neovascular membranes occurring at the anastomotic site; these are associated with retinal ischemia. Prompt laser photocoagulation to areas of retinal ischemia that develop after the anastomotic attempt has been made may reduce the risk and severity of this complication.

Choroidal neovascularization after laser photocoagulation for diabetic macular edema

Choroidal neovascular membranes (CNVMs) developed in eight patients after photocoagulation for clinically significant diabetic macular edema (DME). The CNVMs developed in areas where Bruch's membrane was ruptured and were diagnosed 2 weeks to 5 months after treatment. Only six patients had symptoms. The CNVMs were treated in four patients; final visual acuity was poor in all eight patients. This serious complication that follows laser treatment for DME may be related to the use of repeated small-size, short-duration laser or intense laser burns, or both.

Complications of endodrainage retinotomies created during vitreous surgery for complicated retinal detachment

The authors report nine cases of endodrainage retinotomy site complications that occurred after vitreous surgery for complicated retinal detachments (RDs). Postoperative subretinal neovascularization developed in four eyes at the retinotomy drainage site. In two eyes, postoperative proliferation at a posteriorly placed endodrainage site created traction macular detachments. Redetachment due to retinotomy opening caused by postoperative drainage site proliferation developed in three eyes. The retinas of all nine eyes were eventually reattached, and vision improved from the preoperative level. These complications are related to retinal pigment epithelium and/or Bruch's membrane damage during internal subretinal fluid drainage and retinotomy endolaser photocoagulation. Careful evaluation of extrusion instruments, drainage techniques, retinotomy placement, and subsequent endolaser treatment is necessary to minimize these complications.

Modified grid pattern treatment of diabetic perifoveal edema by orange dye laser photocoagulation

Diabetic perifoveal edema is a potentially dangerous condition. A consecutive series of 58 diabetic eyes with fluorescein angiographically verified perifoveal edema and decreasing visual acuity and/or metamorphopsia was treated by orange dye laser photocoagulation in a perifoveal grid pattern. Observation periods ranged from 3 to 74 weeks (median 23.5 weeks). Post-treatment fluorescein angiography showed 51 dry foveas, 5 had discrete residual edemata and 2 were not controlled by fluorescein angiography, but were clinically dry. Metamorphopsia decreased simultaneously in most patients. Two eyes deteriorated more than 2 lines on the Snellen chart. Both developed chronic maculopathy, maybe induced by treatment. Except for these two, we found only minor changes in visual acuities and central visual fields. We find the method to be a relatively safe procedure to dry up diabetic foveal edema.

Subretinal neovascularization after focal argon laser for diabetic macular edema

The authors reviewed four cases of iatrogenic subretinal neovascularization after focal argon green photocoagulation for clinically significant diabetic macular edema. An inappropriate combination of small spot size with a high-power setting is the common feature in each case of iatrogenic subretinal neovascularization. Close follow-up with fluorescein angiography is used to identify iatrogenic subretinal neovascularization at an early, treatable stage. All four patients responded favorably to laser photocoagulation of the subretinal neovascular membrane.

Choroidal neovascularization in children: report of five cases and literature review

Choroidal neovascularization is rare in the pediatric population. It has been associated in this age group with a variety of conditions. Increasing ability to treat these neovascular lesions with laser photocoagulation makes early recognition very important for visual preservation. An overview is presented, including an updated list of conditions associated with choroidal neovascularization in children and adolescents. Guidelines to recognition, parent and patient instructions, and the selective use of fluorescein angiography are emphasized. Five illustrative cases are highlighted, including a 10-year-old boy successfully treated with krypton laser photocoagulation near the fovea.

Idiopathic sub-retinal neovascular membranes in the macula (hemorrhagic macular choroidopathy of young adults). Clinical report and effectiveness of laser treatment

Twenty-six patients with idiopathic sub-retinal neovascular membranes (INVMs) located within the posterior pole were examined. Clinical and fluorescein angiographic features of these patients are described. Follow-up ranged from 2 to 96 months (mean 16.5 months). Laser treatment was performed according to the location of the neovascular membrane: 7 out of 9 eyes (77%) increased their final visual acuity or stabilized after Argon blue-green laser photocoagulation (INVMs further than 200 microns from the center of the fovea). Krypton red light laser treatment was performed in 13 eyes with juxta-foveal and sub-foveal INVMs: following treatment 10 eyes (77%) improved by 2 or more Snellen lines or maintained their pre-treatment visual acuity. Because of the fact that the Krypton laser was not yet available, 5 patients were not treated: all of them had sub-foveal (3) or juxta-foveal INVMs (2). The natural history of 4 cases (80%) showed an increase in the final visual acuity in 3 eyes and a steady state in one eye. Pathogenesis and treatment outcome of the disease are finally discussed.

Choroidal neovascularization

Choroidal neovascularization is now considered to be a most important feature in the pathogenesis and treatment of a number of chorioretinal disorders. Since the recognition of its importance, choroidal neovascularization has been described in clinical and pathologic studies of a variety of different ophthalmologic conditions. We have summarized the diseases in which choroidal neovascularization occurs and have reviewed studies on the natural history, clinical findings, and therapy of choroidal neovascularization that provide the basis for the current management of this condition.

Cellular processes causing defects in Bruch's membrane following krypton laser photocoagulation

Krypton laser photocoagulation of the posterior fundus of the rat created white retinal lesions comparable with therapeutic burns in the human. Twenty-four hours after injury, the retinal pigment epithelium was destroyed and the majority of the endothelial cells survived. The choriocapillary lumen was occluded. Bruch's membrane was not fractured nor had it undergone thermal lysis in any area studied but choriocapillary endothelial cell buds invaded the choroidal side of Bruch's membrane. After seven days, cellular protrusions arising from retinal pigment epithelial cells traversed Bruch's membrane through full-thickness defects and entered the choroid. Although intense laser burns may destroy Bruch's membrane, we conclude from this data that many so-called "breaks" in Bruch's membrane following laser therapy are formed by cellular processes and are not caused primarily by laser coagulation.

Birdshot retinochoroidopathy and subretinal new vessels

Decrease of visual acuity in birdshot retinochoroidopathy is due either to optic atrophy or to 3 types of macular involvement: cystoid macular oedema, geographic atrophy, or macular serous detachment. We describe 3 cases of juxtapapillary subretinal neovascularisation occurring in long-standing birdshot retinochoroidopathy. The mechanism of the formation of the new vessels is discussed.

Argon and krypton laser photocoagulation of senile exudative macular degeneration

Senile exudative macular degeneration can be divided into two stages: the pre-exudative stage of drusen and pigment-epithelial degeneration and the exudative stage of pigment-epithelial detachment (PED) and the disciform lesion. Patients with PED may retain useful vision for many years but finally subretinal neovascularisation develops resulting in a disciform scar with loss of central vision. Photocoagulation has no favourable therapeutic effect. The disciform lesion has a poor visual outcome. In part of the patients the subretinal neovascularisation can successfully be treated by laser coagulation. The prognosis depends on duration of symptoms, visual acuity and the distance between neovascularisation and the foveal area. As the newly formed vessels will grow rapidly towards the posterior pole, patients with a senile disciform lesion must be considered as emergency cases. The krypton laser has advantages over the argon laser but to what degree is still to be assessed.

The disciform response: an historical perspective

This paper is a survey of the literature in an attempt to provide the basis for our current understanding of the disciform process. Particular emphasis is placed on its pathogenesis and the role of subretinal neovascularization. No two lesions appear exactly alike because of the many stages and combinations possible. Gass (1967) has delineated the broad spectrum with the many different clinical manifestations of this disease process. Verhoeff and Grossman (1937) provided the histopathologic basis for our understanding of the disciform process. The histologic correlation of the clinical "predisciform" state would seem to offer the most promising information for understanding the pathogenesis of the disciform process (Frank et al. 1973; Green and Key 1977; Kornweig 1967; Sarks 1973 and 1976; Small et al. 1976; Zauberman 1970). It is hoped that this literature review has sufficiently emphasized the inherent deficiencies of strictly clinical studies and the need for an appropriate experimental animal model (Ryan 1979).

Subretinal neovascularization after argon laser photocoagulation

An investigation has been conducted to test different theories relating to the pathogenesis of the disciform response. Considered an important first step in this systematic study, a reproducible model of subretinal neovascularization in an experimental primate model has been developed. The following report describes the methodology, clinical appearances, and results including histopathologic and electron microscopic correlation. This experimental model has served as a useful mechanism for testing the roles of breaks in Bruch's membrane, ischemia, hemorrhage, the inflammatory response, and position in relation to the center of the vascular free zone as important factors in the development and evolution of subretinal neovascularization.

Follow-up study of presumed ocular histoplasmosis syndrome

One hundred and sixty-two patients with presumed ocular histoplasmosis syndrome were evaluated. New macular scars not present on initial angiogram developed in 9% of eyes. The risk of developing a symptomatic macular lesion in eyes with asymptomatic macular scars was 23%. In eyes with peripapillary scarring, 3.8% developed a peripapillary neovascular membrane. Follow-up was 5.5 years. When the neovascular membrane was touching or outside the foveal avascular zone, the difference between photocoagulated and control eyes was not statistically significant. When only adequately photocoagulated eyes (20) were compared with control eyes (40), the difference was statistically significant (P = 0.04).

Choriovitreal and subretinal proliferations: complications of photocoagulation

Ten choriovitreal and three subretinal fibrovascular proliferations were seen after heavy focal photocoagulation of diabetic retinopathy. These complications were believed to be caused by the use of a small spot size with high energy.

Choroidal neovascularization associated with choroidal nevi

We observed choroidal neovascularization with associated macular detachment in three cases of benign choroidal nevi. Successful obliteration of the neovascular membranes was performed with argon laser photocoagulation with maintenance of good central visual acuity.

Rubella retinopathy and subretinal neovascularization

Diseases that primarily affect the pigment epithelium, Bruch's membrane, or the choroid may lead to secondary subretinal neovascularization and its sequelae of hemorrhage and scarring. We studied three cases of presumed congenital rubella retinopathy with congenital deafness, which developed unilateral subretinal neovascularization, hemorrhage, and scarring.