tamponade, leaving a relative milder scotoma arising from the persistent inner layer separation, which does not respond much to the tamponade effect [74].

isolated finding or as part of a complex malformation syndrome. Optic disc colobomas can have associated retinal and iris defects (Fig. 5.9a).

5.3.10  Complications and Associations

Congenital pits of the optic nerve have been associated with retinochoroidal colobomas [30], supporting the concept that some congenital optic disc pits develop secondary to incomplete closure of the superior end of the embryonic fissure. Larger pit size has been shown to predispose to retinal detachment. Pit depth may vary, and increased depth is not associated with increased risk of retinal detachment [30]. Macular holes developing in the serous retinal detachment have been described with optic pits [36, 75]. Unlike the common inner lamellar macular holes, these holes are outer retinal holes. The preference to the outer retinal layers is yet unclear but may exclude the role of vitreous traction as an etiological agent in these cases.

5.4  Optic Disc Coloboma

5.4.2  Genetics

Colobomas of the optic nerve head transmitted in a pedigree as an autosomal dominant defect was first reported by Weyert [77] in 1890. Two reports have linked optic nerve colobomas to mutations of the PAX2 gene located at 10q24–q25 [78]. Savell and Cook [79] studied a large family with an isolated autosomal dominant optic disc anomaly, which they termed “atypical coloboma.” Slusher et al. reported a wide spectrum of cavitary disc anomalies in a single family [80]. They described peripapillary pigment rings, large irregular cups, and large cilioretinal vessels, which occurred both in conjunction with cavitary defects of the disc or in the fellow eye as isolated findings. Within the kindred, which included five generations, patients with all possible combinations of colobomas, pits, anomalous optic nerve, and normal disc were seen. The pattern was consistent with autosomal dominant inheritance of a single genetic trait but with variable expressivity.

Optic disc coloboma is a common ocular malformation, which refers to a developmental defect in the internal structure of the eye [76]. It can occur as an

Ocular colobomas result from failure of the embryonic fissure to properly close. The embryonic fissure is the opening along the inferior aspect of the developing eye through

which mesodermal tissue enters the globe. Closure normally begins at the midpoint of the fissure at approximately 5–6 weeks and extends proximally and distally. Failure of the proximal end to close results in optic disc coloboma. Multiple secondary ocular malformations may accompany colobomas presumably due to neuroectodermal induction anomalies. The peripapillary retina may be dysplastic, and there may be ectopic choroidal development with cartilage, bone, muscle, or fat formation.

5.4.4  Natural History and Prognosis

When the coloboma is isolated to the disc, vision may be normal unless the defect involves the macula or microophthalmia is present. Serous macular detachments can occur from isolated optic disc colobomas. An important systemic syndrome associated with optic disc colobomas is the CHARGE association [81] (Table 5.4). A chromosomal abnormality should be considered when colobomas occur in patients with multiple congenital anomalies, mental retardation, or growth failure. Associated central nervous system abnormalities such as basal encephalocele can occur, and neuroimaging should be considered especially in bilateral cases.

Fig. 5.10  Optic disc coloboma. Note bridging vessels across the excation

a

Table 5.4  Optic disc coloboma CHARGE syndrome

C – coloboma

H – heart defects

A – coanal atresia

R – retarded growth, mental retardation

G – genitourinary anamolies (hypoplasia)

E – ear abnormalites

Fig. 5.11  Bilateral optic disc and retinal coloboma. (a) Right eye: large inferior coloboma involvin the disc and retina. Note macular area is spared. Visual acuity was normal. (b) Left eye: more extensive involvement including macular area. Visual acuity was poor