Optic Disc Coloboma
●It is a bowl shaped excavation often inferiorly with sharp borders
●Unlike the morning glory disc, the ODC has no central glial tuft and the disc vasculature is usually normal
●It can mimic glaucomatous cupping but the excavation in ●ODC is normally decentered inferiorly and is non-progressive
●Microphthalmia can be present if the ODC related excavation includes the retina or choroid
●Visual acuity in ODC can be difficult to predict from the appearance of the disc alone and can range from mild to severely affected vision
●ODC can be unilateral/ bilateral
●No racial predilection
●The defect may extend to include the retina, choroid, or iris (iris coloboma)
ETIOLOGY:
●Incomplete closure of the proximal part of the embryonal fissure during the sixth week of gestation
●PAX2 genes, expressed in astrocytic cells, are also expressed in adult retinal cells located on the optic nerve head
●Precursor astrocytes are found on the edge of the optic nerve during early development – forming the theory that abnormal astrocyte differentiation or migration during development may play a role in optic nerve coloboma formation
DIAGNOSIS:
●SS-OCT: sparse and irregularly oriented scleral fibers and openings of the subarachnoid space just posterior to the bottom of the excavation and to assess the depth and extent of the excavation and to monitor for secondary issues like macular retinoschisis
●B-Scan USG: to identify the optic nerve and nerve-insertion anatomy when the anterior segment or the media is opacified
ASSOCIATIONS:
●PAX gene mutations
●Walker-Walburg syndrome
●Aicardi syndrome
●Papillorenal syndrome
●Tuberous sclerosis (isolated cases)
●Serous maculopathy
MANAGEMENT:
●While the coloboma itself cannot be repaired, management focuses on managing complications like retinal detachment, which can occur, particularly in children
Image from Rajan Eye Care Hospital
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