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Editor,—We describe a patient presenting with a choroidal neovascular membrane (CNVM) at the demarcation line of a longstanding rhegmatogenous retinal detachment (RRD), and characterise its immunopathological features following surgical removal.
A 46 year old myopic woman attended the vitreoretinal service with a 3 month history of a shadow in the superior half of her left visual field. Her visual acuity was 6/9 right and 6/12 left, with a refractive error of −13.0D and −9.50D effective spheres respectively.
Examination of the left fundus revealed longstanding detached and thinned retina inferiorly and a broad heavily pigmented demarcation line passing through the macula with associated retinal pigment epithelial (RPE) hypertrophy. An area of parafoveal retina adjacent to the tide mark appeared elevated and a fundus fluorescein angiogram (FFA) revealed a juxtafoveal CNVM emerging from the edge of RPE hypertrophy. Three months later she reported decreased vision and metamorphopsia in her left eye, with a best corrected left visual acuity reduced to counting fingers. A subfoveal extension of the CNVM with bordering haemorrhage was present, confirmed by FFA (Fig 1A, B). She subsequently underwent pars plana vitrectomy, parafoveal retinotomy, and removal of subfoveal CNVM, together with external scleral buckling, argon laser retinopexy, and 20% sulphur hexafluoride gas tamponade.
Postoperatively, an area of inferior retinal detachment persisted and further surgery with silicone oil tamponade was undertaken. Subsequently, a posterior subcapsular cataract developed and she underwent left phacoemulsification with intraocular lens implantation and removal of silicone oil. Postoperatively, visual acuity improved to 6/18 and the retina remained flat with no clinically apparent CNVM (Fig1C). Four months later, her visual acuity was reduced to 6/36. Fundal examination showed an elevated area at her fovea and FFA confirmed a recurrent CNVM. We are treating this conservatively as the patient is asymptomatic and has declined further surgery.
The CNVM specimen was fixed in 10% formol saline, processed through ascending concentrations of alcohol into xylene and embedded with paraffin wax. Tissue sections 5 μm thick were freshly cut for this study, dewaxed, and rehydrated before use.
The distribution of basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), macrophages (PGM1), and von Willebrand factor (vWF) were investigated using a standard biotin-streptavidin-biotin, alkaline phosphatase complex method (Dako Ltd). The alkaline phosphatase label was visualised as a red final reaction product (Vector Ltd). Nuclei were weakly stained with Mayer's haematoxylin. A normal human donor eye was used as a positive control, while the negative control used was normal rabbit serum diluted to give a final protein concentration equivalent to that of the primary antibody used.
Histopathological examination revealed a CNVM consisting of numerous endothelial lined vascular channels and chronic inflammatory cells. The CNVM was lined by an incomplete layer of RPE cells on its posterior aspect, as determined by the clinical orientation of the membrane at the time of removal (Fig 2A).
A large portion of the CNVM consisted of vascular channels lined by endothelial cells displaying immunoreactivity for von Willebrand antigens (Fig 2B). There was staining for VEGF (Fig 2C) and bFGF (Fig2D) in the extracellular matrix, with a similar distribution of immunoreactivity.
Choroidal neovascularisation occurs in a wide spectrum of conditions, including degenerative, inflammatory, traumatic, and hereditary disorders—all characterised by breaks in Bruch's membrane.1 A few cases of CNVM developing at the edge of a demarcation line have been reported in both chronic rhegmatogenous and tractional retinal detachments; however, the immunopathology does not appear to have been previously described.2 3
A demarcation line (“high watermark”) is characteristically found in longstanding retinal detachments that either progress very slowly or remain static.4 In this setting, RPE cells may detach from Bruch's membrane to proliferate and undergo metaplasia in the subretinal space at the junction of attached and detached retina. Clinically, a demarcation line appears as a line of increased pigmentation in this area and may form a sufficiently firm adhesion to prevent progression of a retinal detachment. The local wound healing response at the edge of the detached retina may also lead to excessive RPE proliferation. In our patient, such chorioretinal adhesion may have allowed the transmission of mechanical vitreoretinal traction forces to Bruch's membrane.3 This could potentially have compromised the integrity of Bruch's membrane, allowing the formation of a CNVM. High myopia was a further predisposing factor for choroidal neovascularisation in this patient, making Bruch's membrane more susceptible to disruption.1
Grossniklaus and Gass have described two fundamentally different types of choroidal neovascular growth patterns—type 1, with growth of new vessels beneath the retinal pigment epithelium, and type 2, with growth of new vessels in the subsensory retinal space.5
In our patient, the presence of RPE cells on the posterior surface of the CNVM indicates that it represented a type 2 membrane, as determined by its clinical orientation at the time of removal.
Experimentally detached retina in cats has been shown to possess higher angiogenic activity than normal attached retina.6 Indeed, peripheral retinal neovascularisation has been described in chronic rhegmatogenous retinal detachment.7 Retinal detachment is likely to lead to compromised metabolism and hypoxia of the outer retinal layers due to elevation of the retina from the choroid.6 RPE cells may secrete VEGF in response to this hypoxic insult and also secondary to mechanical stress incurred at the edge of the demarcation line.8 9 VEGF may then stimulate the recruitment and activation of monocytes, which in turn could promote mediators of angiogenesis.10 It is therefore possible that the liberation of neovascular growth factors in this setting may have contributed further to the development of CNVM in our patient.
RHY Asaria is supported by the June Sutor Fellowship.
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