10-Glaucoma

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GLAUCOMA

Definition:

It is an increase of intraocular pressure (IOP). It is one of the most frequent causes of blindness. The elevated IOP eventually involves all tissues of the eye.

Types:

1-Primary glaucoma-No overt cause (absence of concurrent ocular disease).

2-Secondary glaucoma -Due to iridocyclitis, intraocular neoplasms, and luxated lens.

3-Congenital glaucoma-Congenital malformation at the anterior chamber angle. Anterior segment anomaly usually present at birth (gonio-dysgenesis)

Effect of elevated IOP on the tissues of the eye:

Glaucoma may be due to impairment of the outflow of aqueous humour from the anterior chamber angle. The exit of this fluid occurs through the trabicular meshwork at the anterior chamber and uveoscleral outflow to the suprachoroid space. The effect of elevated IOP varies with the age of the animal, duration, and levels of IOP. In young animals, evaluated  IOP rapidly leads to buphthalmia (enlargement of the globe).

1-Cornea: -

With acute elevation of IOOP, the cornea becomes edematous. Vascularization and pigmentation resulted with buphthalmia (megaloglobus). The cornea may enlarge (megalocornea). At later stages, rupture of Descemet's membrane may occur, and ulceration and perforation may result. Corneal edema in acute glaucoma disappears within hours if IOP has been normalized.

2-Sclera: -

Buphthalmia and elevated IOP result in enlargement of the sclera. It -becomes thin and atrophied. At the scleral canals (emissaria-seat of entrance of blood vessels and nerves), staphylomas will occur. Cupping of optic nerve with its atrophy occurs later on.

3-Iris: -

It undergoes progressive atrophy, and iris stroma becomes thin, and pigments become dispersed into the anterior chamber. The pupil becomes enlarged and less responsive to cholinergic miotics.

4-Ciliary Body: -

The ciliary body becomes progressively atrophied, and aqueous humour formation becomes impaired with resultant hypotony

5-Anterior Chamber: -

It exhibits closure, and extensive numbers of peripheral anterior synechiae resulted.

6-Choroid: -

Thinning and atrophy

7-Lens: -

It exhibits changes in morphology and position. Cataract with displacement is usually evident

8-Vitreous humour: -

Undergoes degeneration with formation of distinct strands and extensive liquefaction (syneresis).

9-Retina and optic disc: -

Loss of retinal ganglion cells and thinning of nerve fiber layer, cupping of the optic disc with loss of myelin, loss of vasculature, and atrophy of the disc.

Methods of Diagnosis:

1-Tonometry:

It is the estimation of the IOP

2-Gonioscopy:

It is a diagnostic procedure to examine the angle of the anterior chamber. Direct goniolenses and indirect gonioprisms are useful for examinations. Open anterior chamber angles in giaucomatous eyes usually respond to medical treatment, while narrow or closed angles are usually candidates for antiglaucoma surgical procedures

3-Tonography:

Is a tonometry for an extended period of time, usually 4 minutes. This is to estimate the coefficient of aqueous humour outflow

4-Ophthalmoscopy:

It is essential for evaluation of the condition of the fundus and optic disc.

Treatment:1-Medical Treatment: -

The purpose of this treatment is the maintenance of IOP within the range of normality.

a-Miotics as 1 to 2% pilocarpine.

b-Adrenergics to reduce IOP by stimulating the alpha and beta receptors. The alpha receptors increase the outflow of aqueous, and beta receptors decrease the aqueous production (1 to 2% epinephrine).

c-Osmotic diuretics as mannitol, intravenously, 1-2 gram/Kg and glycerol orally, .1-2 ml/Kg.

d-Carbonic anhydrase inhibitors are useful (acetazolamide oral 10 to 25 ing/Kg). These drugs reduce active aqueous humour formation by inhibiting enzymatic processes within the ciliary body.

2-Surgical treatment: -

a-Iridencleisis: -

A radical section of the iris is permanently positioned through a limbal incision into the subconjuctival space beneath the bulbar conjunctiva.

Technique:

-Limbal-based conjunctival flap.

-Limbal incision.

-Pupillary border of iris grasped and retracted into the limbal incision.

-Iris torn into 2 separate iridal pillars.

-Iridal pillars are secured at the ends of limbal wound.

-The conjuctival flap is opposed.

b-Cyclodialysis: -

It is an artificial fistula between the anterior chamber and subconjunctival space through the sclera.

Technique:

-Fornix-based conjunctival flap

-Excision of a full thickness block of the sclera 4 to 5 mm from the limbus

-Cyclodialysis spatula is introduced through the subscleral space to the anterior chamber

-The conjunctival flap is opposed.

c-Iridectomy: -

It is the removal of a complete section of the iris.

Technique:

-Limbal-based conjunctival flap

-Limbal incision

-Iris grasped through the incision

-A section of iris is excised

-Conjunctival flap is opposed (pupil appears like keyhole).

d-Iridencleisis and Cyclodialysis: -

e-Corneoscleral trephination: -

f-Exl»ernal fistulation under scleral flap: -

g-Removal of subluxated lens for treatment of glaucoma: -