Glaucoma occurs when the intraocular pressure exceeds the ability of the affected eye to tolerate it. This is as a result of aqueous humor, a clear fluid that is continually produced within the eye to bathe and nourish it. In a healthy eye, this fluid flows and drains out at the same rate. This maintains a steady pressure within the eye referred to as Intraocular Pressure (IOP).
In patients with Glaucoma, the eye continues to produce the aqueous humor, but it is unable to drain at the normal rate. The result is an increase in IOP. This high intraocular pressure results in visual loss by damaging the optic nerve and retina.
Glaucoma usually affects both eyes. Visual loss from Glaucoma is irreversible; no medical treatment or surgical operation can restore vision that has been lost as a result of Glaucoma.
Visual loss first occurs in the peripheral portion of the visual field if the disease is not controlled. A patient with Glaucoma may have good central vision but very restricted peripheral (side) vision.
The normal intraocular pressure is 10-21 mmHg. This is considered normal because the intraocular pressure of 95 percent of eyes measured falls within this range.
Glaucoma may occasionally occur in any eye with intraocular pressure within the normal range. Such a case is called “Low Tension” Glaucoma. An intraocular pressure above 21mmHg does not necessarily mean that Glaucoma is present, but it should be suspected. Until Glaucoma is proven, such a patient is considered to be a “Glaucoma Suspect” or “Ocular Hypertensive”. The presence of ocular hypertension alone does not establish the diagnosis of Glaucoma; two out of the following three criteria usually are required to establish diagnosis of Glaucoma:
- Elevated intra ocular pressure
- Visual field loss
- Damage to the optic disc
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