Choroidal neovascular membrane

Early macular changes are often called age-related macu-lopathy and are characterized by large drusen and pigmentary abnormalities in the macula.20 Age-related maculopathy accounts for 85% to 90% of all age-related macular changes. Ten to fifteen percent of these patients will develop advanced atrophy and/or develop abnormal blood vessels in and under the retina called choroidal neovascular membranes. Patients are then classified as having AMD.23... 

Drusen ablation may help patients with multiple large drusen in both eyes that have not progressed to neovascular macular degeneration. These laser treatments may lead to resolution of the drusen and improved visual acuity. However, it is not clear if progression to choroidal neovascular membranes and neovascular macular degeneration is reduced.23 There is a possibility that the laser treatments may induce choroidal neovascularization and retinal atrophy.22... 

Choroidal neovascular membranes Development of abnormal blood vessels in and under the retina. 

Frank RN, Amin RH, Eliott D, Puklin JE, Abrams GW. 1996. Basic fibroblast growth factor and vascular endothelial growth factor are present in epiretinal and choroidal neovascular membranes. Am J Ophthalmol 122 393-403. 

Lopez PF, Sippy BD, Lambert HM, Thach AB, Hinton DR. Transdifferentiated retinal pigment epithelial cells are immunoreactive for vascular endothelial growth factor in surgically excised age-related macular degeneration-related choroidal neovascular membranes. Invest Ophthalmol Vis Sci 1996 37 855-868. 

Asrani S, Zou S, D Anna S, Phelan A, Goldberg MF, Zeimer R. Selective visualization of choroidal neovascular membranes. Invest Ophthalmol Visual Sci 1996 37 1642-1650. 

Ninomiya Y, Lewis JM, Hasegawa T, Tano Y. Retinotomy and foveal translocation for surgical management of subfoveal choroidal neovascular membranes. Am J Ophthalmol 1996 122 613-621. 

Chan CK, Kempin SJ, Noble SK, Palmer GA. The treatment of choroidal neovascular membranes by alpha interferon. An efficacy and toxicity study. Ophthalmology 1994 101 289-300. 

Choroidal neovascularization associated with age-related macular degeneration is difficult to treat with conventional laser procedures because normal retinal tissues can be destroyed, which results in loss of central vision. Photodynamic therapy offers the opportimity to selectively eradicate neovascular membranes while producing minimal damage to normal retinal and choroidal tissues. 

Inspection of the posterior pole may be hindered by vitreous debris however, it is vitally important to evaluate for CME, a primary cause of visual deficit. Another notable finding in the posterior pole is papillitis, which may occur in a variety of etiologies such as syphilis, herpetic infection, and sympathetic ophthalmia. Chronic long-term complications involving the fundus may include choroidal neovascularization, chorioretinal scarring, epiretinal membrane formation, neovascularization, and retinal detachment. 

As already pointed out, deposits of waste products (presumably derived from RPE) on the Bruch s membrane were an early finding in cases of AMD. There is evidence that the transport across Bruch s membrane is impaired due to these deposits, resulting in more deposits (Feeney-Burns and Ellersieck, 1985). It is not clear if choriocapillary dysfunction and dropout is the cause, or the result, of these deposits (Bird, 1992). Dropout of choriocapillaris could cause ischemia in RPE, changing their gene expression and perhaps causing them to produce growth factors responsible for choroidal neovascularization. 

Figure 3 Light micrograph of experimental CNV four weeks after PDT. A layer of proliferated RPE (arrow) surrounds the CNV (C) with pigment-laden cells overlying the RPE. The outer nuclear layer, photoreceptor inner segments, and a few rudimentary outer segments remain in the area of CNV. The CNV extends through Bruch s membrane (arrow head) and contains few capillaries. The spaces seen are acinar structures in RPE cells. Bar = 50 pm. Abbreviations PDT, photodynamic therapy RPE, retinal pigment epithelium CNV, choroidal neovascularization. Source From Ref. 24.

Lutetium texaphyrin (Lu-tex) is a water-soluble, porphyrin-related molecule which has been studied as a photosensitizer in experimental models of atherosclerosis and various tumors (29). In vitro work in our laboratory revealed preferential uptake of Lu-Tex by bovine capillary endothelial cells when compared with retinal pigment epithelial cells, suggesting the possibility of increased selectivity (R. Z. Renno and J. W. Miller, unpublished data). When Lu-Tex PDT was applied to the monkey model of experimental CNV, closure of the neovascular membranes was achieved at doses of l-2mg/kg with irradiation 10-40 minutes after injection using 732nm light at 50-100 J/cm2 (30). Limited toxicity to retinal and choroidal structures, similar to that seen with verteporfin was observed. 

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