What Is Open angle glaucoma?
Glaucoma is an ophthalmic term that refers to a variety of conditions cause degeneration of the nerve that supplies visual impulses from the retina to the optic centres in the brain. This nerve is called the optic nerve.
There is two main types of glaucoma namely narrow (closed) and wide (open) angle glaucoma. Wide angle glaucoma is the commonest form of glaucoma and is present in up to ninety percent of cases. Up to 50 million people are affected by wide angle glaucoma worldwide.
The “angel” referred to in these conditions is the angle between the cornea and iris in the eye. The aqueous fluid of the eye drains through this angle. In wide angle glaucoma, the angle is open and not blocked, in contrast to closed angle glaucoma. Wide angle glaucoma causes a progressive decline in vision, often without any symptoms.
The eye has a specific pathway by which the aqueous humour (normal eye fluid) drains and circulates in the eye. Aqueous humour is produced by the ciliary processes around the lens of the eye. The humour is present between the anterior and posterior chambers of the eye, while vitreous humour fills the posterior chamber of the eye.
Aqueous humour is responsible for the intra-ocular pressure (IOP), and to give the eye its typical spherical shape. The humour also contains nutritional and immunological structures to assist the anterior structures of the eye in maintaining healthy functioning.
The ciliary processes continually produce aqueous fluid. Aqueous fluid exits the eye via a trabecular meshwork that is located between the lens and the cornea of the eye. From this meshwork, it enters a canal called Schlimm’s canal, and then enters the body’s bloodstream.
Any small effect on ciliary fluid production or outflow of fluid can have a large impact on the pressure in the eye. The balance of production versus outflow is an important aspect of the cause and treatment of glaucoma.
Diagnosis of glaucoma is made with ophthalmic examinations. Tonometry is used to measure the pressure in the eye. A slit lamp examination will show changes to the optic nerve on the retina, called cupping. Cupping is characteristic of nerve damage due to glaucoma. Gonioscopy is used to assess the angle where aqueous fluid drains between the iris and cornea. Visual field testing is done to determine the areas where vision is affected.
Wide-angle glaucoma will show an open angle between the cornea and iris on gonioscopy.
What Are The Symptoms Of Open angle glaucoma?
In contrast to narrow-angle glaucoma, wide-angle glaucoma may be asymptomatic until later stages of the disease, when the visual impairment is already advanced. Symptoms include:
- Gradual decrease in vision over time
- Peripheral vision affected before central vision
- Painless vision loss
- May go unnoticed by the patient until visual loss is quite severe
What Are The Causes Of Open angle glaucoma?
The exact mechanism by which open angle glaucoma is caused is still uncertain. Ocular hypertension is thought to be the biggest reason. Ocular hypertension means there is increased pressure in the eye. The increased pressure leads to damage of the optic nerve due to direct pressure effects and possible ischaemia (reduced blood flow to the nerve). Wide angle glaucoma may also occur without the presence of raised ocular pressure, in about fifty percent of cases.
Wide angle glaucoma is caused by a reduced drainage of aqueous humour through the trabecular meshwork. This is thought to be due to damage of the meshwork.
Certain factors may predispose to wide-angle glaucoma. These include systemic hypertension, diabetes and previous trauma to the eye or head. Medications such as systemic corticosteroids and hypertensive medications may also affect the flow of aqueous fluid.
Advanced age (above fifty years), family history (first-degree relative increases the chance by two to four times) and ethnicity (African Americans) are also associated risk factors for wide-angle glaucoma.
What Are The Things One Should Do To Manage Open angle glaucoma?
- Have any visual disturbance or visual loss treated promptly. Glaucoma’s damage is progressive and irreversible.
- Exercise. Cardiovascular exercise has shown to decrease IOP by between 1 to 5 mmHg.
- Lose weight. Some studies suggest that a lower BMI may have a lowering effect on IOP.
What Are The Things One Should Avoid To Manage Open angle glaucoma?
Do not smoke. Smoking has been shown to moderately increase IOP and predisposes to atherosclerotic disease of the ophthalmic vessels, which may have an additive effect on vision loss.
What Are The Best Foods For Open angle glaucoma?
Antioxidants have shown to have a beneficial effect on vision and glaucoma. These include foods rich in:
- Vitamin C: Oranges, berries, tomatoes, peppers
- Vitamin E: Butter, milk, nuts, avocados
- Vitamin A: Sweet potato, egg yolks, papaya, grapefruit
Lutein in green leafy vegetables such as spinach, kale, broccoli, lettuce, pumpkin
Zinc-rich foods: Seafood, beans, grain cereals, eggs, meat
What Are The Worst Foods For Open angle glaucoma?
- Caffeine containing foods. Caffeine increases the IOP in the eye.
- Studies have shown that consuming large amounts of fluid such as water at one point in time may increase IOP. It is advisable for to have smaller amounts of fluid, more frequently during the day.
What Are The Medicines For Open angle glaucoma?
Although not all types of wide angle glaucoma are caused by raised intraocular pressure, reduction of ocular pressure remains the mainstay of treatment.
Medicated eye drops are used. Combinations of alpha-agonists, beta blockers, prostaglandin analogues and carbonic anhydrase inhibitors are used in wide angle glaucoma.
Surgical procedures are indicated when the visual loss due to wide angle glaucoma is expected to be severe or if the patient is unable to tolerate the side effects and dosing schedule of topical medications.
Argon laser trabeculoplasty and selective laser trabeculoplasty is used to increases aqueous flow through the trabecular meshwork.
Surgical trabeculectomy may be done if medical and laser procedures have failed. Part of the trabecular meshwork is removed surgically, and an alternate aqueous fluid outflow path is created. Drainage implants may be done if trabeculectomy fails.
What Are The Tips To Manage Open angle glaucoma?
Recommended 3-5 yearly screening for wide angle glaucoma is suggested in patients who are at risk above the age of forty years.