The coloboma of the choroid simulating optic nerve duplication

Abstract

In the article, a coloboma of the choroid is described simulating optic disc duplicaton as well as modern possibilities of instrumental work-up methods, which allowed to make a diagnosis. A coloboma (from the Greek koloboma, meaning defect) — is a defect of lid tissues, iris, choroid or optic nerve. A coloboma may be сongenital or acquired. A typical coloboma of the choroid is localized in the lower part of the eye fundus. At times, it comes down to the optic disc, and sometimes involves it as well. The white color of the defect is due to the show-through of the sclera, because the choroid here is completely absent. Corresponding to the coloboma of the choroid, the retina is hypoplastic or absent at times. An optic disc duplication — at this anomaly there are two optic discs on the eye fundus. Sometimes, both may be phtitical and hypoplastic, but more often one of them is hypoplastic, and the second one is performing its function. A true optic disc duplication comes out of the optic nerve partition into 2 or more fascicles. The duplicated optic nerve is pointed out by two optic foramens in one orbit by radiographic analysis, two blind spots in the visual field of one eye, simultaneous central retinal artery pulsation on both optic discs. Ultrasonic B-scanning or OCT and MRI may confirm the existence of a true optic nerve and optic disc duplication. A pseudo-duplication of the optic disc is also very rare and represents a well delineated defect, close to the normal optic disc and simulating an ancillary optic disc with an adjoining area of chorioretinal atrophy.