Retinochoroidal coloboma is a congenital abnormality caused by faulty closure of the embryonic fissure. Choroidal neovascularization (CNV) secondary to retinochoroidal coloboma is an uncommon complication.

The treatment option in vision-threatening cases may be laser photocoagulation.1, 2, 3, 4 However, no reports about long term outcome of this therapy has been reported so far. This may be of interest in the era of new therapeutic options such as photodynamic therapy or subretinal surgery. Herein we present a case of CNV associated with retinochoroidal coloboma with a follow-up of 12 years after thermal laser treatment.

Case report

A 28-year-old woman presented complaining of decreased vision and metamorphopsia in the left eye in October 1993. The left eye reportedly had had poor central vision since childhood. The best-corrected visual acuity was 20/20 OD and 20/400 OS. Refractive errors were −0.75 −1.0 × 160° OD, and −0.25 −2.0 × 175° OS. Slit-lamp biomicroscopy showed bilateral iris coloboma. Funduscopic examination of the right eye revealed an inferior retinochoroidal coloboma that did not involve macula or disc. Indirect ophthalmoscopy of the left eye revealed a large inferior retinochoroidal coloboma involving macula and optic disc. Subretinal and intraretinal haemorrhage, and a subretinal, greyish, partly pigmented lesion at the border between coloboma and normal retina (Figure 1a) was noted. Fluorescein angiography of the left eye showed subretinal leakage at the foveal edge of the retinochoroidal coloboma, consistent with an extrafoveal CNV (Figure 1b and c).

Figure 1
figure 1

(a) Fundus photograph of the left eye shows subretinal and intraretinal haemorrhage and subretinal fluid at the border of the coloboma at the time of first presentation (November 1993). (b) Fluorescein angiogram (early phase) of the left eye demonstrates hyperfluorescence at the margin of the coloboma (November 1993). (c) Fluorescein angiogram (late phase) of the left eye showing increased hyperfluorescence consistent with choroidal neovascularisation (November 1993). The inferior part of the CNV was not considered for the laser treatment (arrow). (d) Fundus photograph of the left eye 12 years after the last photocoagulation shows a dry macula and subretinal fibrosis.

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After obtaining written informed consent, the CNV was treated with argon green laser photocoagulation. The visual acuity of the left eye improved to 20/160. In November 1994, the patient again complained of blurred vision, which started a few days ago. A fluorescein angiogram performed at this time showed recurrent extrafoveal CNV. The patient subsequently underwent a second laser photocoagulation. Follow-up angiographies obtained during the following years showed subretinal staining and a dry macula. At the last follow-up visit, 12 years after the initial laser treatment, atrophy and fibrosis were noted at the border of the coloboma (Figure 1d). The macula was dry. The visual acuity of the left eye remained stable at 20/160.

Comment

Retinochoroidal coloboma is a developmental abnormality of the eye. At the border of a coloboma there is a disruption of the normal anatomy. The marginal retina splits into the intercalary membrane, which bridges the base of the coloboma, and a retinal duplication, which represents the eversion of the optic cup that originally caused the coloboma.8 Complications of this malformation are retinal detachment, cataract, microphthalmia with cyst, and rarely CNV. To the author's knowledge, the case presented is the ninth case of CNV associated with retinochoroidal coloboma in the literature.1, 2, 3, 4, 5, 6, 7 In all of these cases, the CNV developed at the margin between the coloboma and the normal retina. Discontinuities of Bruch's membrane are present at the border of a coloboma where Bruch's membrane abruptly terminates and the retinal pigment epithelium is laterally displaced. Subpigmentepithelial and choroidal vessels may enter the subretinal space at this junction (the locus minoris resistentiae).

Two of the previously reported patients were 65 and 70-years-old. Age related degenerative changes may have contributed to the development of CNV in these cases. One of these patients reportedly had scattered macular drusen in both the eyes.6

Five of the nine cases reported in the literature received thermal laser treatment. In two cases no treatment was considered because the membrane did not threaten visual acuity,6 one patient refused to undergo photocoagulation,7 and in another case the lesion was located subfoveally and observational management was chosen.5 Four previously reported patients who underwent photocoagulation retained stable or improved visual acuity (follow-up 0–33 months) (Table 1).

Table 1 Patients with retinochoroidal coloboma associated with choroidal neovascularization—review of the literature
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CNV secondary to retinochoroidal coloboma can be a vision threatening disorder. The visual acuity of the presented patient remained stable for 12 years after laser treatment. Patients with retinochoroidal coloboma may be at risk for developing CNV throughout life. Thus, regular monitoring of such patients is advisable as early detection and laser photocoagulation may permanently prevent visual loss.