Biomedical Engineering Reference
In-Depth Information
Fig. 1 Scanning electron micrographs of trypsin-digested optic nerve heads from normal (left) and advanced
glaucoma (right) human eyes. The lamina cribrosa is distorted (cupped) in the glaucomatous eye, resulting in
damage to the optic nerve fibers which pass through this region. From Downs JC, Roberts MD, Sigel IA (2011)
Glaucomatous cupping of the lamina cribrosa: A review of the evidence for active progressive remodeling as a
mechanism. Exp Eye Res 93(2):133-140
perfusion of the optic nerve despite increased IOP. Alternatively, up
to 1/3 of humans may show glaucomatous damages and vision loss
despite having IOPs that are considered to be within the normal
range for the population as a whole (so-called
normotensive glau-
coma
), presumably due to a more flexible lamina cribrosa or more
tenuous perfusion of the optic nerve [
4
]. Other factors involved in
RGC cell death may include deprivation of neuronal growth factors
due to impaired axoplasmic flow, peroxynitrile toxicity from increased
nitric oxide synthase activity, immune-mediated nerve damage and
oxidative stress [
3
]. Additionally, dying RGCs may release mediators
that can lead to vicious cycle of programmed cell death (apoptosis) of
previously healthy adjacent RGCs [
3
]. Because IOP is the only clinical
risk factor that can be therapeutically manipulated to date, the over-
whelming majority of anti-glaucoma drug studies involve drugs
which alter IOP. As our understanding of the pathogenicmechanisms
behind glaucomatous optic neuropathy improves, however, numer-
ous other drug targets aimed at preventing RGC cell death or stimu-
lating the regeneration of RGCs will emerge.
Glaucoma occurs in two main forms: primary and secondary [
2
].
Secondary glaucoma
, which is infrequently a target of anti-
glaucoma drug studies, results when there is another structural
abnormality in the eye that leads to impaired outflow from the
eye. Examples include obstruction of the outflow pathways by
inflammatory debris, red blood cells, or tumor cells; displacement
of the lens, occlusion of the pupil, and many others.
Primary
glaucoma
occurs when the abnormality lies in the iridocorneal
angle or trabecular meshwork. In both forms of glaucoma the
iridocorneal angle can be further classified as “open” or “closed”
angle by use of a specialized goniolens.
Primary open angle glaucoma (POAG) in humans is the target
disorder for most anti-glaucoma drugs [
2
]. It is a chronic life-long
1.1 Forms
of Glaucoma
