One of the most common ophthalmic complications of systemic diseases is glaucoma. Some people do not consider it as a major clinical condition due to its gradual progression but it is a fact that glaucoma is not a disease in itself. It is a bunch of disorders characterised by neural degeneration of eye in progressive manner leading to loss of vision. Increased intra-ophthalmic pressure is a non-separable component of the condition.
What Brings on Glaucoma?
Etiological factors involving in death of retinal ganglion are the main cause of these deformities which results in glaucoma. Few main factors are mentioned below in brief-
Primary Insults Leading to Glaucoma
Mechanical Theory or Retinal Intraocular Pressure-
Increased intra-ocular pressure (IOP) starts applying mechanical stress on lamina cribrosa which presents as deterioration of axons and alteration of blood flow in capillaries resulting in the necrosis of associated retinal area. All these newly formed deformities lead to inability of growth factors or neutrophins to reach the ganglionic bodies of retina in optimal amount resulting in the scarcity of essential survival elements hence, death.
Vascular Insufficiency theory-
This theory was introduced under the light that some patient shows glaucomatous symptoms even in the absence of raised intra ophthalmic pressure. According to this theory, in patients with normal intra ophthalmic pressure other factors take a lead role. This also includes factors affecting perfusion of vascular vessels of optic area.
However, some additional factors also lead to normal tension glaucoma (NTG) and even in patients with increased intra ophthalmic pressure.
Failure of Blood Flow Auto Regulation Mechanism: There is existence of a peculiar mechanism between optic nerve and retina in order to regulate flow in the vascular vessels by using auto regulatory function of central nervous system. Once this mechanism is compromised, blood flow cannot be regulated beyond a critical range of intra ophthalmic pressure.
Secondary Insults or Excitotoxicity Theory Leading to Glaucoma
It is believed that neuronal degeneration is derived by some factors that are toxic to the cell. These factors include glutamate which is an excitatory toxin and some oxygen free radicals such as molecules released during lysis of Donnan’s membrane of red blood cells because of primary insults e.g. nitric oxide. Thus, we can say that secondary insult creates a marking hazardous effect due to primary insult. This leads to repeated and progressive destruction mediated by apoptosis even when the primary insult is not there.
Clinico-Etiological Classification of Glaucoma
On the basis of above pathogenesis and age group glaucoma is classified into three different groups given below-
- Congenital or developmental glaucoma
- Primary adult glaucoma
- Secondary glaucoma
Though glaucoma is a group of disorders yet it can be managed fully in most of the patients in initial stages of progression. However, efficient treatment is not available in patient in high degree of retinal damage or blind patients. But these numbers are very less and most of the patients can be easily diagnosed with increased IOP.
Let us observe some epidemiological data for better understanding of case strength and causes of the clinical situation.
Glaucoma prevalence (worldwide)
Seen among 2 percent population of age group of 40 years and above.
Prevalence rise multiple times up to 10 percent when it comes to the age group of 80 years and above.
PACG and POAG prevalence among different ethnicities
|Urban Chinese African, European and Hispanic||3||1|
Blindness due to Glaucoma
Global complete loss of vision: 9.0%
Complete loss of vision in India: 12.6%
Patho-physiology of Glaucomatous Ocular Destruction
As it is mentioned previously, all types of glaucomatous condition are characterised by progressive optic neuropathy. It is well recognised presently, this clinical condition is a resultant of dying retinal ganglion cells in a specific pattern common to every type of glaucoma which leads to appearance of characteristic optic disc with exclusive defects in visual field.
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