Open angle glaucoma is the most prevalent form of glaucoma and accounts for 60% to 70% of all glaucoma. In open angle glaucoma, the aqueous humor that normally flows through the pupil into the anterior chamber cannot get through the trabecular meshwork to the normal drainage canals. This impairment of aqueous humor outflow elevates the IOP to between 25 and 35 mm Hg.

The onset of open angle glaucoma is insidious with almost no early symptoms. However, as time progresses, there is gradual loss of peripheral vision, a persistent elevation in IOP, optic-nerve degeneration, retinal nerve atrophy, and trabecular meshwork degeneration. Blindness is the outcome unless surgery or drug treatment is initiated.

Several diseases are associated with open-angle glaucoma. They include pigmentary dispersion syndrome, high myopia, retinal detachment, and diabetes mellitus.

 

Angle closure glaucoma is a rare and more severe form of glaucoma. The increase in IOP is directly related to sudden papillary blockage of aqueous humor outflow. This condition can be chronic (progressing slowly or occurring persistently) or acute (occurring suddenly). During an acute attack, the iris rotates around the cornea and blocks the outflow channels suddenly and completely. IOP over 60 is not uncommon. It can lead to severe eye pain, nausea, vomiting, blurred vision accompanied by visions of coloured halos around lights, and immediate loss of vision.

Secondary angle-closure glaucoma may develop as a result of a dislocated or swollen lens, post-operative effects, ciliary block, or post-inflammatory conditions. Ocularly instilled anticholinergics such as atropine and scopolamine can precipitate angle-closure glaucoma in patients over 30 years of age with abnormally shallow anterior chambers, and they should not be used in patients diagnosed with or predisposed to angle-closure glaucoma.

 

Both subtypes of congenital glaucoma - infant and juvenile - are rare and frequently require surgical intervention in preference to other, less effective medical treatments.

 

Open angle glaucoma does not cause any symptom until it is so advanced that control vision is threatened. It does not present with head or eye ache or with loss of acuity.

The chief signs are raised intraocular pressure, optic disc cupping and peripheral visual field loss. Since only advanced disease may be symptomatic, detection depends on chance and on examination of at-risk individuals.

 

It is not usual for patients with angle closure glaucoma, to be admitted to hospital for investigation of vomiting, until it is realised that the eye is the cause of the symptoms.

Visual loss is usual, owing to corneal edema. This is seen as a hazy cornea, which diminishes the red reflex and prevents visualisation of iris colour and structural detail. Angle closure glaucoma can be a serious emergency.

 

Several procedures are used for diagnosing glaucoma. They include the evaluation of IOP (tonometry), visual field changes (perimetry), optic-disk changes (opthalmoscopy), outflow facility and angle measurements (gonioscopy).

 

Two common tonometry techniques are used for the measurement of IOP. Applanation tonometry measures the force applied to the cornea per unit area with the use of a strain gauge. Air tonometry measures IOP by sending a "puff of air" onto the cornea to measure IOP.

 

By this technique the ophthalmologist can directly evaluate the optic nerve using an ophthalmoscope. Changes in colour/appearance of the optic disk may point to glaucomatous damage.

 

This procedure tests for visual field defects, a defining feature of glaucomatous optic nerve damage. Isolated of impaired vision, surrounded by normal areas in a vision field, are indicative of open angle glaucoma.

 

This technique allows the ophthalmologist to view the anterior chamber angle directly. Both open angles and angle closures can be detected.

To be concluded
Part - II: Management of Glaucoma

Primary Open Angle Glaucoma	Close Angle Glaucoma
Elevated intraocular pressure	People of Eskimo, Chinese or Asian Indian origin
Advanced age	Family history of disease
Being black	Age of 30 years or older
Myopia	Female sex
Diabetes mellitus	Hypermetropic eye
Migraine	-
Hypertension	-
Long-term corticosteroids	-
Previous eye injury	-

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