Is whole eye transplantation possible?

Rarely does a day go by when a patient doesn't ask about whether eye transplantation is possible. The stock answer is "No," primarily because the optic nerve (which connects the eye to the brain) will not regenerate once it has been cut. But a review of the scientific literature in the March edition of the British Journal of Ophthalmology seems to offer some hope.

The article addresses three specific questions:

(1) Is recovery of visual function following eye transplantation greater in cold-blooded vertebrates compared with mammals? The researchers found that in a majority of the studies, recovery of visual function can occur after whole eye transplantation in cold-blooded vertebrates.

(2) Will the retinal photoreceptors continue to function after an eye has been removed from the body (a procedure known as enucleation) and then reconnected? The literature review finds that following enucleation retinal photoreceptor function is maintained from four to nine hours.

(3) The nerve cells that make up the optic nerve are known as ganglion cells. The researchers investigated whether there is a correlation between ganglion cell survival and either time after transection or proximity of optic nerve transection to the eye? The researchers found that the longer the eye is disconnected from the body, the more ganglion cells will die. Also, more nerve cells will die if the optic nerve is cut nearer the eye. However, newly developed drugs, such as neurotrophins, can increase ganglion cell survival following transection.

The researchers conclude that the use of a donor eye is feasible for whole eye transplantation. While technically feasible, it will be many years before this will be a viable treatment option. On the other hand, retinal prosthetics - sometimes referred to as "bionic eyes" - are an exciting technological advance that is projected to be commercially available by the end of 2010.