The role of retinal pigment epithelium in the early stage of development of subretinal neovascularization

In order to evaluate the role of retinal pigment epithelium (RPE) in the early stage of experimental subretinal neovascularization, we severely damaged RPE cells before the development of subretinal neovascularization. Three adult rhesus monkeys were used in this study. One mol/l l-ornithine hydrochloride saline solution was injected intravitreously at 2 weeks before intense krypton laser photocoagulation on the retina at the posterior pole, and clinical and histopathological course were studied at 1 to 28 days after photocoagulation. As a result, no evidence of new vessel formation could be observed clinically throughout the entire course. Histopathologically, at 3 days after photocoagulation, slight proliferation of RPE cells was identified by electron microscopy at the margin of the laser lesions, and budding of vascular endothelial cells derived from choroidal microvessels was observed in the choroid. However, no newly-formed vessels extended into the subretinal space at 7 days or more after photocoagulation. These results confirmed our hypothesis that proliferated RPE cells had inductive effect on the growth of endothelial cells in the early stage of development of subretinal neovascularization.     

Dye laser photocoagulation treatment for experimental subretinal neovascularization. 2. Histopathological findings of unsuccess lesions

We observed the histopathological process in unhealed lesions following photocoagulation treatment for experimental subretinal neovascularization (SRN) in rhesus monkey eyes. Long-lasting SRNs were produced experimentally by the method which we previously reported. These SRNs were treated by a 590nm dye laser beam, and were examined clinically and histopathologically. Lesions in which insufficient photocoagulation treatment was performed showed serous fluid accumulation and fluorescein angiography revealed remaining neovascularization. In these lesions abundant patent neovascularization was seen with proliferation of spindle-shaped fibroblast-like retinal pigment epithelial (RPE) cells in the subretinal space. These metaplastic RPE cells produced matrix and abundant collagen fiber around the cells. The above results showed that insufficient photocoagulation induced neovascularization and proliferation of RPE cells in the subretinal space and promoted the formation of fibrovascular membrane.     

Krypton and argon laser photocoagulation effects in subretinal hemorrhage

Previous studies suggested that krypton laser photocoagulation was more effective in the treatment of macular diseases than argon laser. Furthermore, it could perform photocoagulation more effectively in some lesions with subretinal hemorrhage, because the krypton laser beam was poorly absorbed by hemoglobin. In the present experiment, hemorrhagic retinal detachment was produced in monkey eyes with Q-switched Nd-YAG laser, and 4 weeks later photocoagulation was performed with krypton and argon lasers to compare the differences in the effects of these two lasers. When the subretinal hemorrhage and a heavy coagulation effect was produced in the detached retina, but no coagulation effects were observed in the choroid. Krypton laser beam could go through the hemorrhage and certain coagulation effects were observed in the choroid and the detached retina. It is suggested that krypton laser photocoagulation is more effective in the lesions behind subretinal hemorrhages than photocoagulation with argon laser.     

A role of the retinal pigment epithelium in the involution of subretinal neovascularization]

We clarified a role of the retinal pigment epithelium (RPE) in the regression of experimentally induced subretinal neovascularization (SRN) in monkey. Eight eyes of 5 rhesus monkeys were used in this study. Two weeks after intense krypton laser photocoagulation to the posterior pole of the fundus, 0.5M l-ornithine hydrochloride solution 0.03 ml was injected intravitreously for the purpose of selective RPE damage. After ornithine injection, SRN continued without any evidence of spontaneous regression over 8 weeks following photocoagulation. Histopathologically, SRN developed with wide lumen in the subretinal space accompanied with serous detachment of the sensory retina, and new vessels were not enveloped completely by the proliferating RPE cells. We already showed that experimentally induced subretinal neovascularizations naturally regress spontaneously by envelopment of RPE cells 5 to 8 weeks after photocoagulation. Our results suggested that SRN persist actively without regression due to incomplete enclosure by RPE by selective damage of RPE at the active stage of SRN. We have confirmed that the RPE cells played an important role at the involution stage of SRN.     

Laser treatment of macular subretinal neovascularization in angioid streaks

The authors examined 17 eyes with macular subretinal neovascularization in angioid streaks treated by direct laser photocoagulation. Two eyes were treated with dye laser (590 nm), two with blue-green argon, three with green argon and ten with red krypton laser. At twelve-month follow-up, the visual acuity was of 0.21, a statistically significant decrease respect to the presenting vision. Poor functional results are due to the frequent recurrences of neovascularization.     

Hereditary hemorrhagic macular dystrophy

We treated two brothers who had a hemorrhagic macular lesion in one eye; a similar problem affected the fellow eye of both patients within eight months. Generalized fine granularity of the retinal pigment epithelium and peripheral iris transillumination defects were observed in both siblings. A study of the family suggested that the disorder was dominantly inherited and probably was Sorsby's pseudoinflammatory macular dystrophy. The macular lesions in one brother were treated by argon green laser photocoagulation and in the other brother by krypton red laser photocoagulation. Although the brother treated by krypton red laser photocoagulation attained better final visual function, additional differences in treatment methods also may have contributed to the final outcome.     

Photocoagulation in Eales' disease

Between 1970 and 1991 the authors examined 466 cases with Eales' disease. 359 eyes of 295 of these 466 cases received photocoagulation treatment. The mean age was 30.4, ranging between 14 and 55 years. Ten eyes with persistent vitreous hemorrhage underwent pars plana vitrectomy before photocoagulation. 210 eyes were treated with xenon arc, 135 with argon laser, 12 with krypton laser and two with yellow dye laser. Hypoxic areas and retinal neovascularizations were closed completely in 298 eyes. In 21 eyes with elevated neovascularizations intruding into the vitreous cavity feeder vessel photocoagulation was used. 24 eyes with disc neovascularization were treated with panretinal photocoagulation. 12 eyes with branch vein occlusion and four eyes with central vein occlusion received photocoagulation treatment to areas of non-perfusion and retinal neovascularization. At a mean follow-up of 43 months, seven new retinal neovascularizations and three new disc neovascularizations developed in eyes which previously had received photocoagulation for retinal neovascularization and hypoxia. Nine out of 21 eyes with elevated neovascularizations developed vitreous hemorrhage. Disc neovascularization resolved completely in 13 out of 24 eyes, it partially regressed in eight eyes and did not respond to treatment in three eyes. The visual acuities were improved in 12.3%, maintained in 77.4% and deteriorated in 10.3% of the eyes after treatment. Periodic follow-up and early photocoagulation treatment is useful in stabilizing the retinal lesions and in maintaining functional levels of vision in Eales' disease.     

Photocoagulation with free-running mode Nd: YAG laser on neovascular maculopathy

Seventeen eyes in 14 cases of early neovascular maculopathy were treated with free-running mode Nd: YAG laser and followed up for 7 to 56 months by examination of visual acuity, fluorescein angiography and static perimetry. Obliteration of subretinal neovascularization could be achieved with both mild and moderate photocoagulation. Retinal sensitivity after moderate photocoagulation decreased moderately. Damaged retinal sensitivity after mild photocoagulation recovered one month later. Two out of 11 eyes in which only the neovascular membrane was treated showed recurrent neovascularization adjacent to the treated lesion 6 months and 9 months after photocoagulation. One out of 6 eyes received mild photocoagulation on the neovascular membrane and the surrounding area showed recurrent neovascularization adjacent to the treated lesion 6 months after photocoagulation. Retinal hemorrhage occurred in one out of 14 eyes that received mild photocoagulation and in one out of three moderately photocoagulated eyes. The recurrent neovascularization occurred in two eyes with retinal hemorrhage and in one mild burned eye without retinal hemorrhage. Recurrent neovascularization may correlate with retinal hemorrhage.     

Photocoagulation in Eales' disease

Between 1970 and 1991 the authors examined 466 cases with Eales' disease. 359 eyes of 295 of these 466 cases received photocoagulation treatment. The mean age was 30.4, ranging between 14 and 55 years. Ten eyes with persistent vitreous hemorrhage underwent pars plana vitrectomy before photocoagulation. 210 eyes were treated with xenon arc, 135 with argon laser, 12 with krypton laser and two with yellow dye laser. Hypoxic areas and retinal neovascularizations were closed completely in 298 eyes. In 21 eyes with elevated neovascularizations intruding into the vitreous cavity feeder vessel photocoagulation was used. 24 eyes with disc neovascularization were treated with panretinal photocoagulation. 12 eyes with branch vein occlusion and four eyes with central vein occlusion received photocoagulation treatment to areas of non-perfusion and retinal neovascularization. At a mean follow-up of 43 months, seven new retinal neovascularizations and three new disc neovascularizations developed in eyes which previously had received photocoagulation for retinal neovascularization and hypoxia. Nine out of 21 eyes with elevated neovascularizations developed vitreous hemorrhage. Disc neovascularization resolved completely in 13 out of 24 eyes, it partially regressed in eight eyes and did not respond to treatment in three eyes. The visual acuities were improved in 12.3%, maintained in 77.4% and deteriorated in 10.3% of the eyes after treatment. Periodic follow-up and early photocoagulation treatment is useful in stabilizing the retinal lesions and in maintaining functional levels of vision in Eales' disease.     

Clinicopathologic studies of treated choroidal neovascular membranes. A review and report of two cases.

The previously reported and two additional clinicopathologic studies of treated choroidal neovascular membranes were reviewed. Laser photocoagulation can obliterate choroidal neovascular membranes, but persistent and recurrent neovascularization contiguous with the treated area or the development of a new area of neovascularization contiguous or not contiguous with the treated area was seen histopathologically in nine of 12 (75%) lesions of 10 eyes. The scar that ensues after photocoagulation resembles the naturally occurring scar associated with choroidal neovascularization. Portions of the scar are comprised of hyperplastic retinal pigment epithelium. The inner retinal layers are more likely to be preserved after krypton red photocoagulation. Full-thickness destruction of the retina occurs with argon blue-green and argon green photocoagulation at levels of energy in which the end point is a uniform, white lesion.     

Expression of FLK-1 in laser-induced choroidal neovascularization in mouse

AIM: To investigate the expression of vascular endothelial growth factor receptor 2 (VEGFR-2, also known as FLK-1) in laser-induced choroidal neovascularization (CNV) in mouse. METHODS: CNV was induced in C57BL/6 mouse eyes by krypton laser photocoagulation. Choroidal fluorescein angiography and histopathological examination were used to assess the development of experimental CNV. Cryostat sections from lesions on day 10 after laser treatment and normal eyes were prepared for immunohistochemistry for FLK-1. RESULTS: Laser-induced CNV developed in all lesions on day 10. The expression of FLK-1 was detected in endothelial cells, retinal pigmented epithelium (RPE)-like cells and fibroblast-like cells in neovascular lesions. In normal adult mouse retinas, FLK-1 expression was mainly observed in RPE cells, inner nuclear and ganglion cell layers. CONCLUSION: Our findings demonstrate that expression of FLK-1 may play a role in the formation of laser-induced CNV in mice, which suggests that FLK-1 may be a promising potential target for antiangiogenesis therapy for CNV.     

小鼠脉络膜血管新生模型中FLK-1的表达

目的:探讨小鼠脉络膜血管新生(choroidal neovascu larization, CNV)模型中FLK-1的表达.方法:采用激光击射的方法诱导成年C57BL/6小鼠CNV模型,术后行脉络膜灌流铺片及组织病理学检查观察CNV的发展.应用免疫组织化学染色探讨正常视网膜以及激光术后10d CNV模型中FLK-1的表达.结果:术后10d所有激光光斑均发展为实验性CNV,其中血管内皮细胞,类视网膜色素上皮细胞(retinal pigmented epithelium,RPE)及类成纤维细胞FLK-1表达强烈;在正常视网膜中,FLK-1仅在RPE、内核层及神经节细胞层有微弱的表达.结论:FLK-1参与了实验性CNV的发病过程,提示拮抗FLK-1可能成为防治CNV有效的生物学方法之一.     

Early retinal adhesion from laser photocoagulation

Histopathologic examination of eight cynomolgus monkey eyes and one human eye revealed that both argon and krypton laser photocoagulation cause adhesion between the neurosensory retina and the retinal pigment epithelium (RPE) within 24 hours of treatment. The neurosensory retina remained attached at the sites of laser burns despite surrounding retinal detachment in untreated areas. This early adhesion with the laser is useful for the treatment of eyes in which the retina has been recently reattached such as at the end of a vitrectomy for a retinal detachment with proliferative vitreoretinopathy (PVR) or after a pneumatic retinopexy. It is also useful for the treatment of retinal breaks without detachment.     

Effective transfection of a cis element "decoy" of the nuclear factor-kappaB binding site into the experimental choroidal neovascularization

PURPOSE: To evaluate the efficacy of the gene transfer of a double-stranded phosphorothioate oligonucleotides (ODNs), called a "decoy", against the NF-kappaB binding site into cells of an experimentally-induced choroidal neovascularization. METHODS: FITC-labeled decoy was injected into the subretinal space of rat eyes by the HVJ-liposome delivery system, and 3 days later, choroidal neovascularization was induced by laser photocoagulation. The eyes were removed and the transfected cells were detected by fluorescence microscopy and also detected by immunohistochemistry. The degree of neovascularization was evaluated by fluorescein angiography. RESULTS: The decoy was transfected into the retinal pigment epithelial (RPE) cells, inner and outer segment of the photoreceptors at 3 days after the injection. When choroidal neovascularization was induced, highly effective transfection of the decoy was observed 3 to 14 days after photocoagulation, after which the level decreased. Decoys were transfected into the RPE cells and macrophages in the choroidal neovascularization. The eyes transfected with NF-kappaB decoy showed a weaker leakage in fluorescein angiograms than that of the control eyes transfected with scrambled decoy. CONCLUSIONS: A decoy can be transfected into retinal cells and cells within a choroidal neovascularization by the HVJ-liposome method. The transferred NF-kappaB decoy reduced the degree of choroidal neovascularization. Decoy targeted against NF-kappaB may be considered as a potential therapy for neovascularization.     

Repair of retinal pigment epithelium and its relationship with capillary endothelium after krypton laser photocoagulation

The regeneration of the retinal pigment epithelial (RPE) cells and their relationship with the vascular endothelium were studied during the healing of laser burns produced by krypton laser photocoagulation in rats. During the healing process the epithelial sheet was reformed by a morphologically heterogeneous population of RPE cells, some of which resembled macrophages. There seems to be a correlation between the specific phenotype of the regenerated RPE cell and the state of vitality of the adjacent endothelium. This was particularly evident in the scattered foci of choroidal subretinal neovascularization surrounded by RPE cells. One possible explanation for this apparent correlation is that the cytologic variations of the RPE cells reflect the multiple functions of a single cell which is expressed differently in different situations and in the course of interaction with other cells. This presumed ability of RPE cells may explain an intriguing aspect of cell-cell interaction, namely, the dual stimulatory and inhibitory effects of RPE cells on the vascular endothelium.     

Retinal pigment epithelium decompensation. II. Laser treatment

Forty-one of 97 eyes with retinal pigment epithelium decompensation (RPED) were treated with monochromatic green argon laser photocoagulation to the focal area of RPE staining detected in the late fluorescein transit. Nineteen eyes were treated because of progressive visual deterioration. The other 22 eyes already had visual acuities of 20/50 or worse. Vision stabilized or improved in 34 eyes (82.9%) after an average of 1.6 years following treatment, compared with improvement in only 5 of 56 untreated eyes after an average follow-up period of 2.1 years. After an average follow-up of 7.1 years, 12 of 97 eyes with RPED developed choroidal neovascularization (9 spontaneously and 3 after photocoagulation) in the area where late RPE staining had been observed.     

Expression of pigment epithelium-derived factor in normal adult rat eye and experimental choroidal neovascularization

PURPOSE: Pigment epithelium-derived factor (PEDF) is a protein produced by the retinal pigment epithelial (RPE) cells. Recent studies have implicated PEDF in activities that are inhibitory to angiogenesis. In this study, the expression of PEDF was investigated in normal rat eyes and in eyes with experimentally induced choroidal neovascularization and compared with the expression of vascular endothelial growth factor (VEGF). METHODS: Choroidal neovascularization was induced by laser photocoagulation in rat eyes. At intervals of up to 2 weeks after photocoagulation, the eyes were removed and prepared for in situ hybridization and immunohistochemical study. In situ hybridization was performed with digoxigenin-labeled PEDF riboprobes. Protein expression of PEDF and VEGF was studied immunohistochemically. RESULTS: In normal adult rat eyes, PEDF mRNA was observed mainly in the corneal epithelial and endothelial cells, lens epithelial cells, ciliary epithelial cells, retinal ganglion cells, and the RPE cells. During the development of choroidal neovascularization, PEDF mRNA, PEDF protein, and VEGF protein were strongly detected in many cells within the laser lesions at 3 days after photocoagulation, after which levels gradually declined. However, PEDF was still expressed in the RPE cells that proliferated and covered the neovascular tissues at 2 weeks, whereas VEGF protein was weakly expressed in endothelial cells in choroidal neovascularization. CONCLUSIONS: PEDF is expressed in different cell types of normal rat eyes. The expression of PEDF was detected in the choroidal neovascular tissues induced by photocoagulation, and these findings suggest that PEDF may modulate the process of choroidal neovascularization.     

氪激光治疗视网膜静脉阻塞的新生血管

目的探讨氪激光治疗视网膜静脉阻塞新生血管的方法和疗效 。方法对27例视网膜静脉阻塞伴有新生血管的28只患 眼采用氪绿、氪红激光进行光凝治疗。光凝后经6个月～2．５年随访,对比分析光凝前后的 荧光素眼底血管造影及视力变化情况。结果新生血管 萎缩20只眼,占71.4％,好转6只眼,占21.4%,无效2只眼,占7.2%。 视力进步17只眼,占60.7%。结论氪激光光凝术对视网膜静脉阻塞新生血管的消退及预防其玻璃体积血具有显著疗效。(中华眼底病杂志,2001,17:12-14)     

Comparative electroretinograms in argon laser and xenon arc panretinal photocoagulation.

We performed electroretinograms (ERG) on both eyes of 11 diabetic patients before and one month after panretinal photocoagulation for diabetic retinopathy. Each patient had one eye treated with argon laser and the fellow eye treated with the xenon arc photocoagulator. After photocoagulation the ERG was symmetrically reduced unless the retinal area burned with xenon arc was greater than twice the retinal area burned in the fellow eye by the argon laser photocoagulator.     

A comparative study of argon and krypton laser. Photocoagulation in the treatment of presumed ocular histoplasmosis syndrome

Ninety eyes from 88 patients with active macular subretinal neovascular membranes of presumed ocular histoplasmosis were treated with photocoagulation: 45 eyes with blue-green argon laser and 45 with red krypton laser. Final visual results are compared between these two series and natural course of the disease. The krypton laser photocoagulated eyes obtained better final visual results when compared with both the argon laser treated series and natural course.