Glaucoma

Glaucoma Symptoms & Treatment

Glaucoma is the term used to describe a group of eye diseases that result in cell death of the optic nerve. In many cases of undiagnosed disease, patients with glaucoma will have already reached the point of advanced eye disease by the time they experience symptoms: for this reason, glaucoma is known as the “silent thief of sight.”

Contrary to popular belief, glaucoma is not always associated with high intraocular pressure (although high IOP is a risk factor for glaucoma). Individuals with normal or even below normal eye pressure (ie. below 21 mmHg) may still have glaucoma, and alternatively, people with high eye pressure may have a perfectly healthy optic nerve.

An estimated 3 million Americans suffer from glaucoma, 120,000 of which have lost their sight because of it. Elsewhere in the world, where glaucoma treatment is not as readily available, prevalence is even higher and glaucoma is the leading cause of blindness.

How High Intraocular Pressure Causes Glaucoma

In cases where glaucoma is associated with high intraocular pressure, the disease process that is occurring is has to do with an imbalance in the inflow and outflow of aqueous humor through the eye. Aqueous is normally produced in the ciliary body (directly behind the iris) and flows between the iris and the crystalline lens into the anterior chamber. Once in the anterior chamber, the aqueous makes its way to the anterior angle (located at the point where the cornea meets the iris) and is drained through the trabecular meshwork. In most cases, there is either a problem with the production of aqueous (too much is produced) or with the drainage (something is blocking the drainage system). A subsequent rise in intraocular pressure results in damage to the optic nerve which sends information from the retina to the brain. As optic nerve fibers die off, information gathered by the light-sensitive cells in the retina cannot be transmitted to the brain and are therefore not seen (producing a blind spot in vision). Optic nerve fibers that are associated with peripheral retinal cells are damaged first and so peripheral vision is the first to be affected.

Types of Glaucoma

There are two major categories of glaucoma: primary open angle glaucoma (chronic) and acute closed angle glaucoma (aka. angle closure glaucoma). These two types make up the vast majority of glaucoma cases (POAG being the most common of the two), but there are still other less common types as well, including congenital glaucoma, secondary glaucoma, and pigmentary glaucoma.

1. Primary Open Angle Glaucoma (POAG)

   Primary open angle glaucoma is by far the most common type of glaucoma. It is the type of glaucoma that provides no warning signs that something is wrong, until permanent damage has occurred. In primary open angle glaucoma, the anterior angle, which is located at the point where the cornea meets the iris, is wide open (hence “open angle”). This is the location where aqueous humour drains from the eye.



2. Angle Closure Glaucoma (ACG)

   Angle closure glaucoma presents itself as an acute attack in which eye pressure suddenly rises to an alarming level. Associated symptoms of angle closure glaucoma include sudden onset eye pain, headache, haloes around lights, dilated pupils, red eyes, and vision loss. Such acute symptoms may even lead to nausea and vomiting. An angle closure glaucoma attack can last as long as a few hours and often recurs. Each attack causes damage to the optic nerve and subsequent permanent vision loss. For anyone who has any or all of the risk factors and experiences these symptoms should immediately visit their optometrist.

   
   

   In angle closure glaucoma, the drainage system of the eye becomes completely blocked so that aqueous cannot drain. Meanwhile, as aqueous continues to be produced, the pressure inside the eye builds.



3. Normal Tension Glaucoma

   Also known as low-pressure glaucoma or low-tension glaucoma, normal tension glaucoma is similar to primary open angle glaucoma, but without the characteristic high IOP.



4. Congenital Glaucoma

   Congenital glaucoma is an eye condition in which the eye pressure is raised. It is present at or near birth and is particularly difficult to spot simply because children cannot know better. Congenital glaucoma can result from any malformation of the aqueous drainage system or it could be a secondary complication of another eye disease. Congenital glaucoma occurs more often in males (65%) than in females. Symptoms of congenital glaucoma include clouding of the cornea, light sensitivity, and bulging or protrusion of the eye. The musical genius Ray Charles was an unfortunate victim of congenital glaucoma and without treatment, he lost his sight by the age of seven.



5. Pigmentary Glaucoma

   In pigmentary glaucoma, pigment from the iris rubs off and flows along the route of aqueous humour into the anterior angle and becomes trapped in the drainage system (trabecular meshwork). Often there are no symptoms associated with pigmentary glaucoma besides transient pain and blurred vision following exercise. Pigmentary glaucoma occurs most often in white males between the ages of 20 and 50.

Symptoms of Glaucoma

Symptoms of glaucoma are extremely variable across the different types of glaucoma and across individuals affected by glaucoma. The following list offers a general outline of the more common symptoms of glaucoma:

• Primary Open Angle Glaucoma:
  No symptoms at first. The first symptom may occur with a permanent loss of peripheral vision. Regular eye examinations may help to detect POAG before permanent damage occurs.


• Acute Angle Closure Glaucoma:
  Severe pain, nausea, vomiting, blurred vision, & haloes around lights. This is a medical emergency: without treatment, blindness is imminent within days.


• Normal Tension Glaucoma:
  No symptoms at first. Like POAG, first symptoms may occur with permanent vision loss.


• Congenital Glaucoma:
  Enlarged eyes, cloudy corneas, and infant may be very fussy (due to ocular discomfort).


• Pigmentary Glaucoma:
  May produce no symptoms initially. Possible symptoms include haloes, blurred vision, & eye pain.

Detection & Diagnosis of Glaucoma

Glaucoma is detected and diagnosed using a collection of screening tests by an optometrist. The four basic tests for glaucoma include tonometry (to measure eye pressure), ophthalmoscopy (to examine the optic nerve at the back of the eye), perimetry (to determine if there has been any loss of peripheral vision), and gonioscopy (to examine the size of the anterior angle).

Figure: Glaucomatous Cupping. Courtesy of EyeAtlas.com.

In the case of glaucoma, the optic nerve head shows damage. The normal appearance of the optic nerve is that of a sort of "cup" at the back of the eye, with a healthy, good-sized rim out of which blood vessels travel out into the retina. During the progression of glaucoma, the rim of this cup begins to narrow and form a sort of bowed-out bowl. The narrowing of the rim is referring to as glaucomatous cupping and is measured by eye care professionals to evaluate progression of the disease. See the Figure for an idea of what the optic nerve looks like in a person with fairly advanced glaucoma.

Glaucoma does run in the family, making it all that much more important for people who have a family history of glaucoma to maintain regular eye examinations.

Glaucoma Risk Factors

The following is a list of groups of individuals who tend to be at higher risk for developing glaucoma:

• African Americans
• Family history of glaucoma
• Diabetes
• High blood pressure
• High IOP in one or both eyes
• Prolonged corticosteroid use
• Previous eye injury
• Myopia (nearsightedness)

Glaucoma Treatment

Despite its prevalence, glaucoma treatment is still really only satisfactory at best. Glaucoma treatment is most effective when the eye disease is caught early. Current glaucoma treatment targets eye pressure: use of eye drops to lower pressure inside the eye. Such eye drops function either to reduce production of aqueous or to improve drainage of aqueous through the trabecular meshwork. A list of the most important types of glaucoma medications is as follows:

• Beta blockers: reduce the amount of aqueous produced; not recommended for anyone with heart of lung problems
• Alpha-2 Agonists: reduce aqueous production; some also improve drainage
• Prostaglandin Analogs: improve aqueous flow through a secondary drainage route

Although there are more glaucoma medications, the above list comprises the vast majority of the most effective glaucoma treatments. Most ophthalmologists start a patient on one glaucoma medication, but often within a couple years, a secondary glaucoma medication is also needed. Glaucoma treatment with eye drops is a lifelong commitment.

Although increasingly less popular, surgical options for glaucoma treatment are also available. Surgery is often used as a last resort when eye drops are no longer effective. In an Argon Laser Trabeculoplasty, a laser is used to make tiny holes in the trabecular meshwork, which improves drainage of the aqueous humour and lowers IOP. A trabeculoplasty is used to treat primary open angle glaucoma.

Prevention of Glaucoma

While glaucoma itself cannot be prevented, vision loss resulting from glaucoma can be significantly reduced or even prevented if the disease is caught early and controlled. Visit your optometrist every two years for a regular eye examination. For individuals at high risk, glaucoma testing should be performed every 1-2 years in individuals aged 35 and over.

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