Coloboma : The Retina's Missing Chapter

I looked at the optic disc twice. Optic Disc was unusually large and deeply excavated. It was the kind of finding that immediately made me think of glaucoma. Focusing only in the optic disc (upper circle), Rim was lost in the inferior part, blood vessels was in bayonetting shape and peripapillary changes was seen at the side of rim loss which resembled sever glaucomatous cupping.

But something didn't quite fit. And that was shape !

When the retina (fundus) picture presents as a puzzle, developmental anatomy is the culprit. As optic disc is a familiar landmark with pale pink in structure where all the retinal vessels emerge. First I looked at the patient anterior segment . That is Cornea, Lens, Anterior chamber and Iris. Developmental defect could have been present in anterior segment also, but all the structures were in Normal Limit

Dilated Pupil Examination (Collage maker from pixlr.com)

Anterior Segment Examination

Eye had been born this way

Double Disc appearance was fascinating observation. The more closely I lookes at it, the clearer the answer became. In my observation, the fundus had a colobomatous defect that has been challenging our mind. Apparent second disc or disc like structure requires careful assessment to distinguish true duplication from a colobomatous defect or another congenital anomaly.

• Right Eye was in normal condition*

Left Eye

We can observe a second disc in fundus photo with some swelling of macula. The foveal reflex was dull (Right arrow head). I conducted a Optical Coherence Tomography of the patient macula to visualize the swelling and retinal vessels. Patient complained of gradual vision loss with present visual acuity 6/36 unaided and 6/18 with pinhole.

Comparing OCT picture of Right and Left eye

Normal Right Eye OCT with intact retina and choroidal structure. Clear and attached subretinal space

Left Eye macula was the culprit of gradual loss of vision

Above picture shows elevated retina from subretinal space. Subretinal fluid was present. Macular thickness was 440um which abnormal. There was some leakage from the colobomatous disc area that had caused the swelling. I planned the patient to treat with Double Neodymium - doped Yttrium Aluminium Garnet (Nd:YAG) green laser around the colobomatous disc.

With 50nm spot size, I used these following parameters to apply laser around the colobomatous area that will stop the leakage points.
For me, as a lesson for today in ophthalmology is that before naming an unusual disc, we should understand its anatomy and should begins with one simple question : What am I really looking at ?

Image Source - Embryology.med

Simply, coloboma develops due to incomplete closure of the embryonic fissure (choroidal fissure) present in the above image. Usually it closes around 5th- 7th week of gestation during the early fetal eye development to form the structure of eye. If this closure fails, then there is a congenital gap or defect present in the iris, retina, choroid or optic nerve.

You can go through the Ida Manns Coloboma classification as a reference as this was my first time observing and treating type 5 Coloboma .

Thanks for looking into my today's giant cup, but not glaucoma. Like and follow for more interesting ophthalmology blogs.
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