Chorioretinal Coloboma

Introduction

Very rare, with an prevalence of 0.5-2.4 per 10,000
- 60% of the time, it is bilateral, with over 2/3rds being associated with systemic disorder
- Isolated anterior segment involvement in 36% (iris and ciliary body)
- Isolated posterior segment involvement in 39% (chorioretinal or ON)

Dead Giveaways

The givewaways are especially evident in normal fundus photos and OCT

Fundus:

Well captured, the coloboma is a depigmented area of yellow/white colour. This is visible sclera. Also note the numerous vessels appearing from the edges
Why this is such a big giveaway is due to the unmissable shape, but the inferonasal nature.
It is also commonly associated with a hyperpigmented border

OCT:

Evident from both the apperance, and the increased scleral transparency, there is severe asbence of RPE, PR and choroid, creating a pit

The inner retina however can still remain intact.

diagnostic features

The areas of coloboma is associated with absolute scotomas and poor VA

87% of eyes are worse than 20/200, but does depend on size and macular/ON involvement

Complications:

29% risk of retinal detachment due to changes in tissue organisation
14% risk of choroidal neovascularisation, and high risk of peripapillary CNV at edges of the optic nerve
RD and CNV both common at lesion edges or structural drop offs
Potentially new vessels, at coloboma edge