This patient had a large inferior chorioretinal coloboma in the right eye, which evidently was related to the amblyopia in that eye, and myelinated nerve fiber layer in the left eye. In the right eye, the inferior view is directly onto the white sclera due to the absence of retinal and choroidal tissues. Because the white sclera is brighter, it appears elevated in the two-dimensional image. However, one can appreciate that the retina is flat by noting that the retinal blood vessels coursing over the coloboma are not out of focus.
Colobomas can be anterior, posterior, or both. Iris colobomas often have the appearance of a keyhole, and lens colobomas typically include localized absence of zonules. Anterior, posterior, and complete colobomas can be unilateral or bilateral, and they are often associated with microphthalmia. They are caused by incomplete or failed closure of the embryonic fissure during the second month of embryonic development. The incidence is 0.5 to 2.2 cases per 10,000 live births. Though many cases are sporadic, chorioretinal colobomas are associated with many syndromic and chromosomal abnormalities. Retinal detachment occurs in 23-42% of patients with chorioretinal colobomas.
Myelinated nerve fiber layer (MNFL) has a characteristic feathery appearance that corresponds to the pathways of the nerve fiber layer. There is partial or complete obscuration of underlying retinal blood vessels. The incidence is about 0.57-1% of the population, and about 7% of cases are bilateral. Most cases are asymptomatic, but the condition can be associated with axial myopia, amblyopia, and strabismus. It is rarely associated with systemic syndromes, and familial cases have been reported. The condition is generally static, but acquired or progressive MNFL has been described. MNFL can disappear after surgery or optic nerve damage.