Ganglion cell death in glaucoma: what do we really know?
- Nuffield Laboratory of Ophthalmology, University of Oxford, Oxford OX2 6AW
- Professor Neville Osborne, Nuffield Laboratory of Ophthalmology, University of Oxford, Walton Street, Oxford OX2 6AW.
What are the apparent characteristics of ganglion cells in glaucoma?
Glaucomatous optic neuropathy is a chronic process which progresses over many years. Data derived from clinical observations and from animal experiments suggest that the axons of the optic nerve and the retinal ganglion cell somata do not die at the same time but that death can vary between months and many years.1 2 Glaucoma patients have characteristic fields of visual loss which enlarge as the disease progresses. Thus, glaucomatous optic neuropathy may not be a chronic degeneration of the whole of the optic nerve and ganglion cell somata but rather a series of acute losses of individual, or groups of, ganglion cells. It seems therefore reasonable to assume that when a patient is diagnosed initially as having glaucoma, only some ganglion cells are dead, whereas others may range from being “unhealthy” to being “slightly sick” while others are “perfectly normal”. It seems also reasonable to argue that if a neuroprotectant (a substance which reaches the retina to elicit an effect: Table 1) can be applied at some stage before blindness occurs it could be of benefit to the glaucoma patient by either “slowing down” the death process of neurons that has already been initiated to die or perhaps by preventing the initiation of death signals to perfectly healthy ganglion cells. This argument can be made despite the lack of success in the use of neuroprotectants for a variety of other diseases (stroke, epilepsy, Parkinson’s disease, AIDS dementia) where neuronal death is a characteristic.1 3 It is the apparent nature of ganglion cell death in glaucoma, very slow and variable, that makes it more likely that the use of neuroprotectants could be successful.