Glaucoma

Glaucoma is a disorder affecting the eye. It involves damage to the optic nerve, affecting vision and thus it can cause permanent damage to the affected eye. Without treatment, it can lead to blindness.

Background
The ciliary body is attached to the iris. It is composed of ciliary muscle and ciliary processes, coated by ciliary epithelium.

The ciliary body is covered by non-pigmented epithelium and it produces aqueous humour.

The anterior portion of the eye is divided into the anterior and posterior chambers. Aqueous humour, produced from the ciliary body is released into the posterior chamber. It later flows via the pupil into the anterior chamber. From there, it drains into the trabecular tissue and enters into the canal of Schlemm. This is then drained into the episcleral vein and into the other veins of the orbit.

The angle of drainage (irido-corneal angle) is normally approximately 45 degrees which allows for sufficient drainage.

The amount of fluid production and the amount of fluid drainage must maintain a balance. An imbalance in this will lead to Glaucoma.

Signs & Symptoms
An imbalance in fluid drainage leads to an increased intraocular pressure (IOP). This increased pressure pushes on the optic nerve and the retina.

This continuous pressure leads to eventual ‘cupping’ of the nerve, leading to loss of vision. It starts with loss of peripheral vision, and then loss of central vision and eventual blindness.

If the drain remains closed, the pressure accumulates giving the eye the appearance of frosted glass along with intense pain, nausea and vomiting.

Closed-angle attacks are present in the Acute type of Glaucoma. They can occur where the drainage is completely closed off causing spikes in IOP and mild degrees of damage. However, repeated attacks cumulate to cause extensive damage. A sign of this attack is headache around the eyebrow.

Types
Primary Open-Angle Glaucoma (Chronic Glaucoma)

It is the most common type of glaucoma. It is painless and slow-progressing.

During chronic glaucoma, the angle of drainage is wide and open, however the trabecular tissue and the canal of Schlemm becomes clogged and thus allows less fluid to leave the eye.

The drainage of the fluid is backed up, however the production of aqueous humour in the eye continues, resulting in an increasing intraocular pressure (IOP).

Acute Closed-Angle Glaucoma

During acute glaucoma, the angle of drainage is narrow and is ≤ 25 degrees. It is very painful and causes permanent damage to sight.

There is a sudden and greater blockage to the flow of aqueous fluid from the eye, causing a steep and immediate rise in the intraocular pressure due to the contact between the edge of the iris and cornea. This type of glaucoma presents itself in closed-angle attacks (see Signs & Symptoms).

Secondary Glaucoma

Secondary glaucoma is when an increase in IOP occurs as a secondary effect of:
 * another eye condition (e.g. uveitis)
 * operations
 * injuries
 * medications (e.g. corticosteroids).

Developmental Glaucoma

Developmental (congenital) glaucoma is present at birth and results from the abnormal development of the fluid outflow channels in the eye. It affects young babies and is very rare.

Treatment
Primary Open-Angle Glaucoma (Chronic Glaucoma)

Treatment can only prevent further damage. It cannot fix any damage already caused. Treatments are used in order to lower the IOP and some improve the blood supply to the optic nerve (II).

Treatments begin with eye drops which either reduce the amount of fluid produced in the eye or open the drainage channels to drain excess fluid. In the case that the patient is not satisfied/dislikes eye drops, IOP can also be reduced via:

Laser Trabeculoplasty makes very small evenly spaced burns in the trabecular meshwork, using a laser, to stimulate the draining of fluid.

Trabeculotomy & Goniotomy involves removing part of the trabecular meshwork to allow drainage. Goniotomy usually requires a clear cornea while trabeculotomy does not.

Acute Closed-Angle Glaucoma

If diagnosed and treated early, there may be almost complete recovery of vision and closed-angle attacks can be avoided.

Closed-angle attacks are an eye emergency and need to be treated immediately.

Laser Peripheral Iridotomy (LPI) is recommended in both eyes (even if only one eye is affected as risk to the second eye is high). LPI consists of making a microscopic opening in the periphery of the iris creating an area of outflow. It is a safe and easy way to prevent an eye attack.

Secondary Glaucoma

The treatment is aimed at reducing the pressure, and treating the underlying cause.

Developmental Glaucoma

The initial treatment is a drainage-angle surgery, e.g. goniotomy and trabeculotomy.

Related articles
Eye