| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York |
| Transcript |
"Sometimes we can see a problem in the back of the eye, which is a lack of the fusion of the elements of the optic nerve (the retina or anteriorly into the iris and the lens), and that thing we call a coloboma. It can be in the front of the eye which means we can get a coloboma in the iris from the lack of fusion there. That iris thing can be in the lens also, so you can see a sector loss in the lens, or in the back of the eye, it can be the optic nerve, and it can take on this kind of configuration, or extend into the retina. The colobomas are usually inferior because of the embryology of the formation of the eye, so you need to know a little bit about embryology. Basically, when we have the primitive forebrain which is going to become the optic nerve and the eye, we have two pieces in the anterior portion - that's the surface ectoderm which is going to form the front of the eye, and in the back of the eye the neuro ectoderm, and then we have mesenchymal elements that are going to be the blood vessels. So, these three embryologic tissues are going to interact somewhere in the sixth or so week of gestational age. The first thing that happens is you get this stalk that comes out, and that stalk is going to have a cup at the end. The name of this stalk is the optic stalk, and the name of this cup is the optic cup. At the front, it's going to meet the surface ectoderm, and there is going to be simultaneous invagination from the surface ectoderm side which is going to be the lens placode and the anterior segment of the eye is going to form from that, and the part that matters to us is this back part which is the cup. Inside this stalk is a fissure - the choroidal fissure, and basically we need this fissure because the primitive hyaloid artery, the primitive supply to the front of the eye during this part of development has to go up inside that, and so in a cross-sectional view we can see that the choroidal fissure and the optic nerve is starting to close that hole, and because this inferior portion is the last part to close embryologically it might get stuck open. If it gets stuck open, you can get an iris keyhole coloboma; you can get a coloboma on the optic nerve; or the coloboma can be in the retina because it didn't close properly and that's why it's usually inferior. You need to know that it can be associated with other conditions including problems in your kidney (you can look up the PAX genes and all the genes that are associated with that); as well as imaging this kind of patient because we want to look at their hypothalamic pituitary axis. So, in patients who have midline deficits like coloboma, they might have hypothalamic pituitary axis dysfunction, and that means they're going to have hormonal abnormalities and pan-hypopituitarism. In addition, if there's a problem with the skull base, there might be a basal encephalocele. So, we really have to image the coloboma and what you're looking for is hypothalamic pituitary axis abnormalities, and the basal encephalocele. Some of the patients also have hydrocephalus for which they might have to have a shunting procedure. It can be unilateral or bilateral (I image either of those), and it can come to us in adulthood because the coloboma produces risk for retinal detachment and glaucoma and other eye diseases way downstream even though they were born with this. So, you need to know a little bit about coloboma in the front of the eye, the back of the eye, and a little bit about the embryology of the eye that got us there." |
