Ischemic Optic Nerve Disease
In Ischemic Optic
Neuropathy (ION) visual loss occurs when the optic nerve
fails to receive a continuous, sufficient blood supply.
The most common risk factors associated with ION
are older age, diabetes, hypertension, and arteriosclerosis.
ION is the most common cause of visual loss in persons over 50 years of age,
affecting millions of persons in the United States. Ophthalmologists are therefore quite familiar
with the clinical picture of a patient with reduced blood supply (ischemia)
to the optic nerve. Urgent treatment is necessary to save vision
if the cause is inflammatory blockage of
arteries, but no treatment is yet available for the non inflammatory type.
Current studies, however,
offer the hope of future drug treatment. Recently researchers have begun
to study what happens between the loss of blood flow (perfusion) into the
optic nerve, and the onset of irreversible visual loss. It is now known that
a complex sequence of chemical events leading to a loss of oxygen and glucose
in cells of the optic nerve ultimately results in a toxic overload of calcium
(Ca) which leads to the destruction of optic nerve axons and the resultant
visual loss. The chemical complexity of this process means that there is
not just one, but a number of steps along the way before ischemia sets in,
where different drugs might be able to prevent the ultimate destruction of
optic nerve cells. Several laboratories are already working on therapeutic
methods aimed at preventing visual loss in ION.