Introduction  

A clear fluid known as aqueous humor or intraocular fluid fills the front chamber of the eye. It is produced by the ciliary body and drains out through the pupil. The humor flows into the bloodstream through the drainage system of the eye.

A network of drainage canals around the outer edge of the colored part of the eye (iris) form the drainage system. The process of production, flow and drainage of the aqueous humor is continuous and critical for the health of the eye. Proper drainage enables the eye to regulate its internal pressure or intraocular pressure (IOP).

The amount of fluid in the eye determines the intraocular pressure. In a healthy eye, the fluid system produces the right amount of the intraocular fluid. The drainage system drains it out to prevent buildup. The IOP varies throughout the day and remains within the limit the eye can handle.

Also Known As

  • Chamber angle
  • Anterior chamber angle
     

Anatomy

The drainage angle is the point in the eye where iris and sclera (the white covering over the eye) meet. It extends 360 degrees at the circumference of the iris.

Function

The drainage angle is the opening where the aqueous humor drains out into the venous system. It works like a safety valve and allows excess aqueous fluid to exit the eye’s front chamber and flow into the drainage system.

Associated symptoms & disorders

A blocked chamber angle can cause an increase in intraocular pressure. High IOP damages the optic nerve and can lead to glaucoma.

The optic nerve is a sensitive, delicate network of fibers that carry images to the brain from the retina. The threads meet at the optical head, also referred to as the optic disc. High IOP damages the optic nerve fibers and they start dying. It causes the optic disc to become hollow and develop a curved or cupped shape. Where the internal pressure is too high for an extended period, optic nerve damage can lead to the development of blind spots and even permanent loss of vision.

Glaucoma affects the optic nerve. In most forms of glaucoma, the drainage angle becomes blocked which prevents the intraocular fluid from flowing out of the anterior chamber into the drainage system. The fluid accumulates causing intraocular pressure to rise.
Glaucoma diseases include:

  • Open-angle glaucoma - Chronic open-angle glaucoma is the prevalent form of glaucoma. It’s a condition where the drainage angle gets clogged leading to a gradual increase in internal pressure and optic nerve damage. The damage and loss of vision occur slowly and painlessly. Often, the patient is not aware until the optic nerve damage is severe.
  • Angle-closure glaucoma – In this disease, the drainage angle becomes narrow and gets blocked. Acute angle-closure glaucoma occurs when a sudden blockage of the drainage angle causes the intraocular pressure to shoot up.
  • Exfoliation syndrome – This is a type of open-angle glaucoma. It occurs when whitish material accumulates in the chamber angle and on the lens. The material clogs the drainage system, causing increased IOP. 
  • Pigmentary glaucoma - A rare condition in which iris pigment particles chip off and float in the anterior chamber. These particles can clog the chamber angle and cause an increase in intraocular pressure.

Diagnosis of associated disorders

The eye care professional can diagnose a blocked drainage angle through an eye exam. 
He/she can perform: 

  • Gonioscopy to inspect the drainage angle 
  • Ophthalmoscopy to check the optic nerve 
  • Tonometry to determine the eye pressure
  • Perimetry to measure the visual field of each eye
     

Treatment of associated disorders

The eye doctor may prescribe topical eye drops to reduce the IOP. Treatment may also involve systemic medications through injections or oral medication.

Where the condition is resistant to medication some form of laser or non-laser surgery may be necessary. Often, surgery is needed because of the delay in detecting the condition. Operation attempts to open up the drainage canal and prevent future blockages. It allows the aqueous humor to drain better and lower the intraocular pressure. Exfoliation syndrome and pigmentary glaucoma respond well to laser treatment.

Where the drainage angle and the drainage system have suffered severe damage, the eye surgeon may prescribe a regime of medication which help to lower IOP after the surgery.