PRIMARY OPEN ANGLE GLAUCOMA

In angle glaucoma the structure of the trabecular meshwork appears normal but offers an increased resistance to the outflow of aqueous which results in an elevated ocular pressure.

Clinical features:

Ø  The disease is insidious and usually asymptomatic, until it has caused a significant loss of visual field.

Ø  Patients may experience mild headache, eye ache and visual field defect in late cases.

Ø  Reading and close work often present increasing difficulties owing to accommodative failure due to constant pressure on the ciliary muscle and its nerve supply. Therefore, patients usually complain of frequent changes in presbyopic glasses.

Ø  Ocular examination including slit-lamp biomicroscopy may reveal normal anterior segment.

Ø  In late stages pupil reflex becomes sluggish and cornea may show slight haze.

Ø  In the initial stages the IOP may not be raised permanently, but there is an exaggeration of the normal diurnal variation. Therefore, repeated observations of IOP (every 3-4hour), for 24 hours is required during this stage (Diurnal variation test). Applanation tonometry should be preferred over Schiotz tonometry.

Ø  Gonioscopy reveals open angles.

Ø  Optic disc changes are typically progressive, asymmetric and present a variety of characteristic clinical patterns. It is essential, therefore, to record the appearance of the nerve head in such a way that will accurately reveal subtle glaucomatous changes over the course of follow-up period.

Investigations:

l  Perimetry to detect the visual field defects.

l  Nerve fibre layer analysis and disc topography analysis to detect early damage and for progression analysis.

Pharmacological treatment:

1.  Identification of target pressure. From the baseline evaluation data a ‘target pressure’ should be identified for each patient. Progression of disease is uncommon if IOP is maintained at less than 16 to 18 mm of Hg in patients having mild to moderate damage and 10 to 12 mmHg in patients with severe damage.

2.  Single drug therapy. One topical antiglaucoma drug should be chosen after due consideration to the patient’s personal and medical factors. If the initial drug chosen is ineffective or intolerable, it should be replaced by the drug of second choice.

3.  Combination therapy. If one drug is not sufficient to control IOP then a combination therapy with two or more drugs should be tried.

Monitoring of therapy by disc changes, field changes and tonometry is most essential on regular follow-up. In the event of progression of glaucomatous damage, the target pressure should be reset at a lower level and any risk factors should be evaluated

3.  Laser treatment.

Argon laser trabeculoplasty (ALT) or selective laser trabeculoplasty (SLT) are indicated in patients intolerant to topical medication, failure of medical therapy or non compliance to treatment. Since IOP reduction with laser is seldom greater than 30%, an IOP higher than 28 mmHg is unlikely to be adequately controlled by laser alone.

4.  Surgical treatment

Uncontrolled glaucoma despite maximal medical therapy and laser trabeculoplasty. Non-compliance of medical therapy and

Intolerance to medical therapy

Eyes with advanced disease i.e., having very high IOP, advanced cupping and advanced field loss should be treated with filtration surgery as a primary line of management.

Types of surgeries- trabeculectomy, shunt & valve surgeries, non penetrating glaucoma.

Patient education:

Treatment of glaucoma whether medical or surgical is aimed to decrease further damage to optic nerve. Once damage has occurred, it is irreversible.