What is glaucoma?
Glaucoma is an eye disease that affects the health of the nerve at the back of the eye. Many people do not realize they have glaucoma, as it can be painless and tends to affect side vision first.
There are many types of glaucoma, but most fall into 2 general groups.
- Open angle glaucoma - the eye has natural drainage channels inside that allow the fluid in the eye (aqueous) to leave the eye. How easily this fluid in the eye leaves the eye determines the pressure inside the eye (intraocular pressure). With open angle glaucoma, these drainage channels are open, but the aqueous cannot pass through the channels as easily as normal.
- Closed angle glaucoma - the drainage channels of the eye are physically closed in this type of glaucoma, so there is nowhere for the fluid in the eye (aqueous) to go. The fluid is continually produced in the eye, and therefore the pressure in the eye increases quickly.
What causes glaucoma?
The most common type of glaucoma (primary open angle glaucoma) does not have a known cause.
It is a nerve disease that does not have a cure; however, if intraocular pressure is reduced, this improves the long term prognosis.
Angle closure glaucoma is a different type of sudden glaucoma seen in small crowded eyes, where the drainage channels inside the eye can become blocked suddenly, when the pupil dilates. This causes a severe sudden headache, and nausea/vomiting. Sometimes this can be caused by dilating eye drops, or certain medications by mouth that dilate the pupil (cold medicines, psychiatric medications, etc…)
There is a group of glaucomas called “secondary glaucomas” that do have other specific causes, but these tend to be less common (abnormal blood vessels growing at the front of the eye, trauma, inflammation, etc…)
How is glaucoma diagnosed?
Glaucoma is diagnosed by an optometrist or ophthalmologist using specialized equipment. Generally, the following tests are needed.
- Examination of the optic nerve - this is best done using an “OCT” (ocular coherence tomography). This is a special machine that takes a high resolution scan of the optic nerve and measures any change or progression of disease from appointment to appointment.
- Visual field testing - this is a machine that measures side vision formally, and compares each visit to see if there is loss of side vision. In glaucoma, side vision is slowly damaged.
- Intraocular pressure - there are several ways to measure this. Most types of glaucoma can be stabilized by lowering intraocular pressure. A normal pressure is usually less than 21mmHg.
- Corneal thickness - the thickness of the cornea is a measurement that is only taken once, and generally does not change. Thicker corneas are associated with a good prognosis, while thinner corneas are associated with progression of glaucoma. Your doctor may decide to treat your glaucoma more aggressively if you have thin corneas.
How is glaucoma treated?
Open angle glaucoma - usually there is a stepwise approach to treating open angle glaucoma, from more conservative (least risk) to most invasive (most risk). Most people start with eye drops to lower intraocular pressure. If this does not work, a laser treatment (selective laser trabeculoplasty) can be done. Surgery is a last resort to lower pressure. Surgery can involve putting “stents” inside the eye to allow fluid to leave the eye more easily, or a “trabeculectomy” can be done. A trabeculectomy involves making a “trap door” in the upper white of the eye, and covering it with the surface eye tissues (conjunctiva) to allow fluid to leave the eye more easily.
Closed angle glaucoma - a laser iridotomy (making a small hole in the colored part of the eye) is performed in the clinic to correct this problem. Sometimes eye drops are also needed long term.