Ocular Hypotony Secondary to Spontaneously Ruptured Sclera in ChoroidalColoboma

We describe a patient who developed unilateral optic disc edema dueto ocular hypotony secondary to spontaneous rupture of the thin sclera formingthe floor of a chorioretinal coloboma. B-scan ultrasonography was useful inconfirming the diagnosis of a posterior filtering site. The scleral defectwas successfully treated with implantation of a meridional silicone buckle.

A 63-year-old white woman complained of a 3-month history of painlessblurred vision in her left eye. Her medical and ocular history was unremarkable.Her best-corrected visual acuity was 20/20 OD and 20/50 OS, with intraocularpressure of 15 mm Hg OD and 4 mm Hg OS. Biomicroscopic fundus examinationof the patient's left eye was remarkable for fully developed optic disc edemawith gross elevation of the optic nerve head, blurred disc margins, and choroidalfolds consistent with hypotony (Figure 1,A). The peripheral fundus examination showed a chorioretinal coloboma in theinferonasal equatorial retina, with an oval retinal break and a subclinicalretinal detachment restricted to the colobomatous area. The size of the colobomawas about 6 disc diameters, while the size of the break was 1.5 disc diameters.The disc and the macula were not involved in the coloboma. Results of examinationof the right eye were normal.

Fluorescein angiography showed dye leakage from the optic nerve in theleft eye, staining at the edge of the coloboma, and a dark area caused bythe absence of the choroid and of the retinal pigment epithelium (Figure 1, B). Indocyanine green angiographyconfirmed the absence of choroid (Figure 1, C). B-scan ultrasound examination showed a diffuse swollen choroidand a hypoechoic region posterior to the sclerochoroidal defect in the markedlythin and deformed sclera that formed the floor of the coloboma, consistentwith fluid (Figure 1, D).

On the basis of findings from the clinical examination and supportingimaging studies, a diagnosis of ocular hypotony secondary to spontaneous posteriorrupture of the thin sclera, forming the floor of the coloboma, was made.

Treatment options were evaluated; the day before surgery, the retinalbreak was treated with laser photocoagulation along the border of the colobomaas a prophylactic procedure. During the surgery, limited prolapsed vitreouswas excised, 2 vertical mattress sutures were placed between the scleral colobomato create a deep buckle, and a meridional solid silicone buckle was fittedto cover the scleral defect, with the goal of sealing the posterior filteringsite.

One year postoperatively, examination of the left eye was remarkablefor a visual acuity of 20/25 and intraocular pressure of 13 mm Hg; fundusview showed the retina attached with a mildly swollen optic nerve head andsome choroidal folds still present.

Typical coloboma is a congenital defect caused by the improper closureof the embryonal fissure. The reported incidence of retinochoroidal colobomais 0.14%, and in 40% of these patients rhegmatogenous retinal detachment maydevelop sometime during their lifetime.¹

Unilateral optic disc edema secondary to ocular hypotony after a spontaneousrupture of the thin sclera, forming the floor of the posterior chorioretinalcoloboma, has not yet been described, to our knowledge. We preoperativelyidentified an oval retinal break that occurred within the intercalary membraneof the coloboma, with a subclinical retinal detachment restricted to the colobomatousarea (type IIA according to the classification by Gopal et al¹).No vitreal traction or operculum could be identified in front of the break,suggesting the atrophic origin of the break within the atavistic retinal tissue.This type of break, occurring in the retinal tissue within the coloboma, correspondsto the second type of breaks identified by Gopal et al.¹

Most likely the asymptomatic retinal detachment, restricted to the colobomatousarea, was caused by the break in the diaphanous tissue that is continuousanatomically with the neurosensory retina. The posterior bulging of the sclerain the affected area, forming a staphyloma, has been reported in the literature.^2,3 The retinal break and the asymptomaticretinal detachment could have been present for a long time, and the spontaneousrupture of the thin sclera could have occurred afterward. A similar case ofocular hypotony secondary to spontaneous ruptured posterior staphyloma inhigh myopia has been described recently.⁴

In the present case, we believe the healing of the posterior filteringsite was caused by mechanical action and by the formation of a fibrotic scarsecondary to the external silicone buckle that was fitted to cover the scleraldefect.

Although ocular hypotony caused by spontaneous rupture of thin scleraforming the floor of a chorioretinal coloboma is an uncommon event, an externalscleral buckling technique was beneficial in this case and provides a therapeuticoption.

Correspondence: Dr Staurenghi, Department of Ophthalmology, Universityof Brescia, Via Tiraboschi 8, 20135 Milan, Italy (giovanni.staurenghi@unimi.it).