Rare – 0.14% general population.
40% leads to RD.
Due to defective closure of the embryonic fisure
Typically inferonasal quadrant
Genetic associations – PAX6 gene (AD); Sonic HedgeHog (SHH) gene; CHARGE syndrome
Environmental causes – teratogenic drugs (thalidomide, alcohol, LSD, carbamazine); Maternal Vitamin A & E deficiency; radiation; hyperthermia; infection (CMV, toxoplasmosis).
85% has iris colonoma.
Parents noticed child cannot follow objects
Leukocoria or squint may be present
40% RD with high risk of PVR (8%)
Rare – CNV
Long term – cataract and glaucoma
Poor visual prognosis long-term if macular involved
Macular coloboma – also similar like toxoplasmosis scar
Prophylactic laser barrage retinopexy with gentle laser burns – debatable.
RD – break usually in the intercalary membrane (60%) from round atrophic holes and difficult to find due to absent choroid. Treat with encirclement band + PPV + 360 degrees endolaser + 5000 Cs SiO.
Other colobomas of interest:
Optic nerve coloboma – AD; bilateral (60%); may have microphthalmia and non-RRD; may have associated CNS abnormalities; can be confused with optic disc pit maculopathy.
Morning glory syndrome – associated with transsphenoidal basal encephalocele; RD due to small slit-lke reak at edge of anomalous disc (peripapillary break); exudative RD can happen as well; treat with PPV or peripapillary laser.
Optic nerve hypoplasia – similar enviromental risk factors to coloboma; double ring sign (classical); associated with De Morsier syndrome (septo-optic hypoplasia) – which also has absent septum pellucidum and pituitary gland dysfunction.