Atypical superior iris and chorioretinal coloboma

Non-nasal, atypical retinochoroidal coloboma in pediatric patients: Case series and review

“…Atypical colobomas are speculated to be caused by different processes because they do not originate as a defect of embryonic fissure closure, such as in the case of typical colobomas. 12 At day 22 of embryogenesis, development of the eyes commences. 13 Evagination of the neural tube from bilateral grooves in neuroectoderm forms the optic vesicles.…”

“… 14 Leading theories include: (a) defective rotation and poor closure of the fetal fissure due to errors in signaling during morphogenesis 4 ; (b) accessory embryonic fissures (as observed in sheep embryos) in atypical locations that fail to close 1 ; or (c) poor differentiation of fetal structures. 12 Transgenic mice studies have shown that the presence of RPE is required for normal morphogenesis of the retina and choroid. 4 , 15 , 16 Therefore, failure of the RPE to develop can cause poor development of the retina and choroid, appearing as an atypical coloboma.…”