A glaucoma is a group of eye illnesses that damage the optic nerve. Glaucoma is the second leading cause of blindness worldwide after cataracts. Though there is no cure, treatment and regular checkups to stop or slow down its progression. Read below to learn more about how to prevent glaucoma and potentially save your sight.
What is Glaucoma? Causes of Glaucoma
Glaucoma is a term used to describe a group of eye disorders damaging the optic nerve, which is a bundle of nerve fibers responsible for transmitting visual information from the eye’s retina to the brain for interpretation.
Normally, a fluid called aqueous humor is produced constantly in the front part of the eye. The fluid helps to nourish the eyes and maintain the eyes’ shape. This fluid is drained away through the drainage channels, called the trabecular meshwork, at the drainage angle where the iris and cornea meet. If the channels are blocked or if excessive fluid is produced, then the pressure inside the eye (intraocular pressure, IOP) rises and damages the optic nerve, possibly leading to vision loss.
Although this mechanism is likely to be the reason for glaucoma, however, the exact cause of glaucoma is not clearly understood yet. In fact, glaucoma can also develop with normal intraocular pressure. This subtype is named low-tension or normal-tension glaucoma.
Types of Glaucoma
There are many types of glaucomas which are mainly classified as either open-angle glaucoma (chronic) or angle-closure glaucoma (chronic or acute). Glaucoma can be primary or secondary, primary glaucoma refers to glaucoma without a known cause whereas secondary glaucoma refers to any glaucoma due to an identifiable cause, such as medical conditions (e.g. cataracts), medicines, injuries, tumors, etc. Major types of glaucoma include:
- Open-angle glaucoma: Primary open-angle glaucoma (POAG) is the most common type of glaucoma. It eventually leads to increased intraocular pressure and hence optic nerve damage. POAG develops slowly and many people may not notice any symptoms until vision loss.
- Angle-closure glaucoma (closed-angle glaucoma): This is a less common but serious type of glaucoma. It happens when the iris is very close to the drainage angle and eventually blocks it. When the drainage angle gets blocked, intraocular pressure increases rapidly. This is called acute angle-closure glaucoma (AACG) that requires medical attention right away. Angle-closure glaucoma can also develop gradually, which is called chronic angle-closure glaucoma (CACG) and often go unnoticed until an acute attack strikes.
- Congenital glaucoma: This is a type of open-angle glaucoma that occurs in infants. It is due to a defect in the drainage system that slows down fluid drainage during prenatal development.
- Low-tension or normal-tension glaucoma: This condition causes optic nerve damage even if your intraocular pressure is normal. Its reason and cause are unclear, but a high sensitivity of the optic nerve or decreased blood supply to the optic nerve may be related.
- Pigmentary Glaucoma: It is secondary glaucoma that happens when the pigment from the iris flakes off (Pigment dispersion syndrome). These granules may then block the trabecular meshwork and elevate intraocular pressure.
- Pseudoexfoliative (exfoliative) glaucoma: This is a type of open-angle glaucoma resulting from abnormal accumulation of flaky material detached from parts of the eye which block the drainage system.
- Neovascular glaucoma: It is a severe type of secondary glaucoma that happens when the drainage angle is blocked by extra blood vessels generated by the eyes.
- Uveitic glaucoma: This is caused by inflammation inside the eyes (uveitis).
Signs and Symptoms of Glaucoma
Though open-angle glaucoma is very common, many people do not notice any signs or symptoms until it progresses gradually to result in vision loss. That’s why glaucoma is called the “silent thief of sight”. For that reason, it is vitally important to take regular eye examinations with your ophthalmologist to prevent vision loss.
Signs and symptoms of open-angle glaucoma develop slowly, and you may not notice them until the later stages. As it progresses, the following glaucoma symptoms become obvious:
- Blind spots: As glaucoma starts damaging the optic nerve, small blind spots may begin to develop in the peripheral vision. People are usually unaware of the blind spots until the vision loss develops near or in the central vision.
- Tunnel vision: The loss of peripheral vision.
Acute angle-closure glaucoma (AACG):
Acute angle-closure glaucoma is a medical emergency and can give rise to more severe signs and symptoms suddenly. You should seek medical help immediately if you experience the following glaucoma symptoms:
Risk factors of Glaucoma
Glaucoma can affect anyone, but certain groups are at higher risk and need to be checked more frequently by an ophthalmologist. Risk factors of glaucoma include:
- Family history of glaucoma
- 60 years old or above
- Being of African descent, Hispanic/Latino, or Asian
- Having a high intraocular pressure (IOP)
- Severe nearsightedness (myopia) or farsightedness (hyperopia)
- Physical injury or trauma of the eyes, or previous eye surgery
- Medical conditions, such as diabetes, cataracts, heart diseases, hypertension, etc.
- Medications administration, such as corticosteroid eye drops
Diagnosis of Glaucoma
In order to screen or diagnose glaucoma, your ophthalmologist will take your complete medical history and perform a comprehensive eye examination. The following examinations and tests can be done to diagnose glaucoma:
- Perimetry (visual field test): This is a functional test to check your peripheral vision. To do the test, you need to look straight at the center of an instrument. Some light spots would flash in different places around the edge of your vision to check for areas of vision loss.
- Tonometry: Your doctor will instill eye drops to numb your eyes and use a device to touch the front surface of the eye to measure the intraocular pressure.
- Pachymetry: After the eye has been numbed, a device placed on the front of the eye is used to measure the thickness of the eye’s cornea.
- Gonioscopy: After numbing the eye with drops, a special contact lens with mirrors is placed onto the surface of the eye. The mirror allows the doctor to see if the drainage angle is opened or closed and find any other abnormalities.
- Dilated eye exam: Eye drops will be instilled to dilate the pupil. It is used to check the optic nerve at the back of the eyes.
- Ophthalmoscopy: This is an examination of the back part of the eye (fundus) using a beam of light and lens.
- Optical coherence tomography (OCT): This test uses light waves to measure the anatomy of the optic nerve and layers of the retina, such as the ganglion cells. OCT renders high-definition images of the eye with measurements expressed in microns. The test assists in diagnostic precision and in monitoring for disease progression.
Treatments of Glaucoma
There is no cure for glaucoma and vision loss cannot be reversed, but it can be treated in several ways to slow down the disease progression and prevent further damage. The main treatment for glaucoma is medication (eye drops). If it fails, your doctor may recommend laser therapy and surgery.
Medication is used to lower intraocular pressure (IOP) as a means to reduce the progression of visual field loss. Treatment can either increase the outflow of aqueous humor or decrease the production of aqueous humor. Based on your response and severity, more than one of the following eye drops may be prescribed:
- Prostaglandins: Prostaglandins are the first-line agents used in glaucoma to increase the outflow of aqueous humor in the eye. Examples include latanoprost, bimatoprost, travoprost, tafluprost, and latanoprostene bunod.
- Beta-blockers: Topical beta-blockers are also regarded as the first-line treatment of glaucoma. Unlike prostaglandins, beta-blockers decrease aqueous humor production and cause more systemic side effects, such as bradycardia. Examples include timolol, betaxolol, and carteolol.
- Alpha-adrenergic agonists: Brimonidine, a second-line agent, is often used to reduce intraocular pressure by both reducing aqueous humor production and stimulating its outflow.
- Carbonic anhydrase inhibitors (CAI): Brinzolamide and dorzolamide are CAIs that can decrease aqueous production to lower intraocular pressure.
- Miotics / cholinergic agents: Cholinergic agonists, such as pilocarpine, are not commonly used nowadays due to their side effects and frequent dosing regimens.
- Rho kinase inhibitor: Rho kinase inhibitor is a relatively new drug class that is believed to be able to increase the outflow of aqueous humor through the trabecular meshwork. Examples include netarsudil and ripasudil, but they are not available in Hong Kong yet.
- Oral carbonic anhydrase inhibitors (CAI): Acetazolamide can be used when eye drops are not effective. It is commonly used in combination with other topical agents in a short term.
- Osmotic agents: Mannitol is an intravenous treatment for acute glaucoma. It is used when other treatments fail to reduce intraocular pressure.
If medication is not effective or tolerable, laser therapy is an alternative treatment option for glaucoma. It aims to help aqueous humor drain from the eyes. There are several types of laser treatments, including:
- Laser trabeculoplasty: Trabeculoplasty is indicated for open-angle glaucoma. It uses a beam of light to open the drainage angle of the eye which makes it easier for aqueous humor to drain and hence decreases intraocular pressure. There are argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT) available.
- Iridotomy (laser peripheral iridotomy): This is the first-line treatment for angle-closure glaucoma. It involves making a tiny hole in the iris to help fluid flow to the drainage angle.
- Cyclophotocoagulation: Cyclophotocoagulation is a laser surgery that can alter the ciliary body of the eye responsible for fluid production.
If medication and laser therapy do not relieve glaucoma’s conditions, several surgical procedures can be recommended:
- Trabeculectomy: Surgeons remove a part of the trabecular meshwork to create a new drainage system. The fluid can drain with relative ease through the new opening into a reservoir called bleb, to reduce intraocular pressure.
- Drainage implant: A small drainage tube is inserted into the eye which sends fluid to a reservoir. The fluid is then absorbed into nearby blood vessels.
- Minimally-invasive glaucoma surgery (MIGS): There are different types of MIGS procedures used to lower intraocular pressure and prevent damage to the optic nerve. These kinds of surgery are relatively safer than other surgeries but may not be as effective as them.
Prevention of Glaucoma
Although glaucoma can be treated to relieve its signs and symptoms, there is no way to cure or prevent it yet. Therefore, it is crucial to take comprehensive eye examinations regularly to catch glaucoma as early as possible to prevent its progression and vision loss.
According to the American Academy of Ophthalmology, adults are recommended to get a complete eye examination at age 40. You should discuss with your ophthalmologist how often you should undergo an eye test, especially if you are at high risk of glaucoma because of diabetes, high blood pressure or a family history of eye disease. Find an ophthalmologist in Hong Kong here.
If you suffer from open-angle glaucoma, you may not notice any symptoms at first. As it progresses, you will start to see small blind spots in your peripheral vision and gradually experience tunnel vision. At that point, complete vision loss can occur if glaucoma is untreated.
Dr. Marcus Marcet is a Specialist in Ophthalmology in Hong Kong and a Diplomate of the American Board of Ophthalmology. Dr. Marcet's particular area of interest is in conditions of the eyelid and oculoplastic surgery.
This article was independently written by Healthy Matters and is not sponsored. It is informative only and not intended to be a substitute for professional medical advice, diagnosis or treatment. It should not be relied upon for specific medical advice.