Glaucoma occupies an important place among the causes of vision loss in the world. The incidence is related to age and the existence of other diseases in those who suffer from this condition. Many of its clinical forms are asymptomatic, so that the optic nerve deteriorates slowly and causes patients to go to the ophthalmologist in advanced stages of the process. Damage to the optic nerve substantially limits the patient's ability to act and fully enjoy life, in addition to its enormous socio-economic impact, which is why it now represents a medical priority in many countries. In the healthy eye, a clear liquid called aqueous humor circulates within the front of the eye. To maintain a constant and normal pressure in the eye, the eye continuously produces a small amount of aqueous humor, while an equal amount of the liquid leaves the eye. In the glaucoma patient, the aqueous humor does not flow out of the eye properly. The pressure of the fluid left in the eye increases and, over time, damages the fibers of the optic nerve. Only half of the estimated three million Americans who have glaucoma are aware that they have the condition.
Types and Causes of Glaucoma:
Causes of glaucoma include elevated pressure in the eye (called intraocular pressure or IOP) due to the eye's inability to drain fluid efficiently.
When you have glaucoma, the aqueous humor does not flow through the trabecular meshwork properly. If the drainage angle becomes less efficient at draining fluid, as in common open-angle glaucoma, the excess fluid cannot flow out of the eye properly, causing the intraocular pressure (IOP) to rise. Over time, a high IOP causes damage to nerve fibers. If the drainage angle is totally blocked, the pressure in the eye rises rapidly, resulting in an attack of angle-closure glaucoma which leads to pain in the eyes and forehead, nausea, and vomiting. An attack of angle-closure glaucoma is a medical emergency and must be treated immediately.
In some cases, optic nerve damage between different patients can occur at a different eye pressure level. Your ophthalmologist sets the ideal pressure your eye should have to prevent further damage to the optic nerve. Each patient has a different ideal pressure.
Some people have normal-tension glaucoma, or low-tension glaucoma. Eye pressure is always less than 21 mm Hg, but optic nerve damage and visual field loss can still occur.
Congenital glaucoma is a rare type of glaucoma that develops in infants and young children. It can be hereditary, and occurs when the eye's drainage system does not develop fully or properly before birth.
Glaucoma can often be caused by other eye conditions or diseases. This condition is known as secondary glaucoma. For example, someone who has a tumor, or people who have been on steroid therapy for a long period of time, can develop secondary glaucoma. Other causes of secondary glaucoma include: Injury to the eye, Inflammation of the eyes, Formation of abnormal blood vessels due to diabetes or retinal blood vessel obstruction, Use of steroid medications (pills, drops, sprays).
Glaucoma symptoms
In the early stages, open-angle glaucoma has no obvious symptoms. As the disease progresses, it causes more damage, blind spots develop in peripheral (side) vision. These points may go undetected until the optic nerve has been severely damaged, or until it is detected by an ophthalmologist during a comprehensive eye exam.
People at risk of developing angle-closure glaucoma (also called narrow-angle glaucoma) usually have no symptoms before an attack, although some initial symptoms may include blurred vision, halos, headache, or mild eye pain. An attack of angle-closure glaucoma includes the following symptoms:
- Severe pain in the eyes or forehead, redness of the eye, decreased or blurred vision, headache, nausea, vomiting.
People with "normal-tension glaucoma" may have eye pressure within normal ranges, but have signs and symptoms of glaucoma, such as blind spots in the field of vision and damage to the optic nerve.
Some people may not have symptoms of glaucoma, but they may have higher than normal pressure in the eye (called ocular hypertension). These patients are considered "glaucoma suspects" and should be carefully evaluated by an ophthalmologist.
Who is at risk of developing Glaucoma?
Some people are at increased risk of developing glaucoma and should see an ophthalmologist regularly, especially for glaucoma testing.
Glaucoma Diagnosis
One of the problems with glaucoma, especially open-angle glaucoma, is that there are usually no symptoms in the early stages. Many people who have the disease are not aware that they have it. This is why it is important to undergo eye exams by an Eye Doctor, especially as you age.
Eye pressure measurement (tonometry) The doctor measures eye pressure using tonometry. The eye pressure test is an important part of the glaucoma evaluation. A high pressure reading is often the first sign that you have glaucoma. During this test, the eye is numbed with eye drops. Normal pressure in the eye generally ranges from 10 to 21 mm Hg. However, people with normal-tension glaucoma may have damage to their optic nerve and visual field loss, even though their eye pressure continues to be consistently below 21.
Inspection of the drainage angle of the eye (gonioscopy) A gonioscopy allows your ophthalmologist to get a clear picture of the drainage angle to determine the type of glaucoma you may have. Your ophthalmologist, using a mirror lens, can examine the drainage angle and determine if you have open-angle glaucoma (in which the drainage angle is not working effectively), closed-angle glaucoma (in which the drainage angle is at least partially blocked), or a narrow angle (dangerously narrow, in which the iris is so close to the drainage of the eye that it can become blocked).
Optic nerve inspection (ophthalmoscopy) The pupils are dilated (widened) with eye drops to allow the doctor a better view of the optic nerve. A normal optic nerve is made up of more than a million small nerve fibers. Glaucoma damages the optic nerve, causing the death of some of these nerve fibers and as a result, the appearance of the optic nerve changes. This is known as cupping. As the suction cups increase, black spots begin to develop in the field of vision.
Side or peripheral vision test (visual field test) This is a visual field test to look for blind spots in the patient's vision, including spots that you may not even notice.
The test is done with a bowl-shaped instrument called a perimeter. During the exam, a patch is temporarily placed on one of the eyes so that only one eye is tested at a time. Random points of light appear suddenly, flashing around the perimeter, and the patient must press a button each time the light flashes. Visual field tests are generally done every 6 to 12 months to monitor changes.
Measurement of the thickness of the cornea, the clear window in the front of the eye (pachymetry) A probe called a pachymeter is gently placed over the cornea to measure its thickness.
Glaucoma medications
Medicated drops are the most common way to treat glaucoma. These medications reduce eye pressure in two ways: 1. by decreasing the production of aqueous humor; or 2. Improving flow through the drain angle. The eye drops should be applied every day. Like any other medication, it is important that you apply the eye drops regularly, as prescribed by your ophthalmologist.
Never change or stop taking your medications without consulting a doctor. If the medicine is running low, ask the doctor if it should be reordered.
If you suffer from glaucoma, it is important to tell your ophthalmologist your medical history and the medications you are currently taking. Also inform your primary care physician and other doctors you are consulting about the medications you are taking for glaucoma.
Glaucoma Surgery
Surgery is recommended for some glaucoma patients. Glaucoma surgery improves fluid flow out of the eye, resulting in low pressure in the eye.
Laser trabeculoplasty There are two types of surgery: argon laser trabeculoplasty (TLA, or ALT) and selective laser trabeculoplasty (TSL, or SLT).
During TLA surgery, a laser beam makes small, evenly spaced burns in the trabecular meshwork. The laser does not create new drainage holes, but instead stimulates drainage to work more efficiently.
During TSL surgery, a low-energy laser beam is aimed at specific cells in the drainage channels (similar to a mesh or net), using very short light applications. Treatment has shown drops in eye pressure, comparable to an TLA. After laser trabeculoplasty, most patients continue to take glaucoma medications. For many, this surgery is not a permanent solution.
About half of those who receive this type of surgery develop increased pressure in the eye again within five years.
Laser trabeculoplasty can also be used as a first line of treatment for patients who are unwilling or unable to use glaucoma drops.
Laser iridotomy During this surgery, a laser creates a small hole the size of the head of a pin through the upper part of the iris to improve the flow of aqueous humor to the drainage angle.
Peripheral iridectomy Peripheral iridectomy is done in an operating room. During surgery, a small part of the iris is removed, allowing fluid to access the drainage angle again. Because most cases of angle-closure glaucoma can be treated with glaucoma medications and laser iridectomy, a peripheral iridectomy is rarely necessary.
Trabeculectomy During a trabeculectomy, a small cap or flap is made on the sclera (the white outer layer of the eye). A leaking blister, or reservoir, is created under the conjunctiva (the thin, transparent membrane that covers the white of the eye). Once created, the blister looks like a small bump on the white of the eye above the iris, usually covered by the upper eyelid. The aqueous humor can drain back through the flap made in the sclera and collect in the blister, where the fluid is absorbed into the blood vessels around the eyes.
During surgery, the ladder flap is closed with tiny stitches. Some of these stitches may be removed after surgery to increase drainage. Medications to reduce scars are often used during and after surgery.
Eye pressure is effectively controlled in three out of four people who have a trabeculectomy.
Aqueous bypass surgery If trabeculectomy cannot be performed, aqueous bypass surgery is very effective in reducing eye pressure.
An aqueous bypass is a small plastic tube or valve connected to one end of a reservoir or reservoir (a round or oval plate). The shunt is an artificial drainage device that is implanted into the eye through a small incision. The shunt changes the direction of the aqueous humor to an area below the conjunctiva (the thin membrane that covers the inside of the eyelids and the white of the eye). The liquid is absorbed by the blood vessels. When the patient has healed, the reservoir is not easily seen unless you look down and lift the eyelid.
It is important to follow the doctor's instructions to the letter and keep a regular appointment schedule to avoid further damage to vision.
Bibliography:
American Academy of Ophthalmology, 2016.
