What is Glaucoma?
Glaucoma is a leading cause of blindness worldwide.
Glaucoma is a disease of the optic nerve in the eye. The optic nerve is made up of millions of nerve fibres and is the part of the eye that transmits images from the eye to the brain so that we can see. When these nerve fibres are damaged by glaucoma, irreversible visual loss ensues.
What causes glaucoma?
Raised eye pressure is the main causative factor for glaucoma. The aqueous humor is a clear fluid circulating within the front part of the eyeball. The pressure in the eye is maintained at 10-21mmHg by the constant production and drainage of this fluid. If the drainage facility of the eye is compromised, this fluid will accumulate in the eye over time with resultant increased eye pressure. Prolonged raised eye pressure leads to irreversible optic nerve damage.
Other factors that may contribute to optic nerve damage are reduced blood circulation and oxidative damage.
Risk factors for glaucoma
Important risk factors include: older age, familiy history of glaucoma, near-sightedness, far-sightedness, steroid use, previous eye trauma, systemic dieases such as diabetes, and migraine.
The risk of developing glaucoma is higher if you have any of the above risk factors. If you or your family member have any of the above risk factors, it is advisable to have an eye examination to screen for glaucoma.
What are the types of glaucoma?
There are 2 categories of glaucoma: Primary and Secondary glaucoma.
Primary glaucoma is more common and is not associated with any pre-existing eye disease. There are 2 types of primary glaucoma – Primary open angle glaucoma and Primary closed angle glaucoma.
Primary open angle glaucoma occurs as a result of age-related changes in the drainage facility of the eye, resulting in suboptimal drainage and fluid accumulation within the eyeball over time. The persistent raised eye pressure causes irreversible optic nerve damage.
Primary closed angle glaucoma is associated with a blocked drainage facility, which is due to the presence of a narrowed drainage angle in the eye. This is common in middle-aged to elderly Asian females as well as farsighted eyes. The pressure in these eyes can rise rapidly with symptoms of headache, nausea, blurred vision, eye pain and redness and visual haloes. This is a condition called acute angle closure and is an ocular emergency requiring immediate medical attention.
Secondary glaucoma is associated with pre-existing eye conditions such as diabetic eye disease, previous eye trauma, inflammation, steroid-induced ophthalmopathy, previous eye surgery, etc. The drainage facility is compromised as a result of the pre-existing eye disease and glaucoma ensues.
Glaucoma can also occur in childhood but this is uncommon.
How is glaucoma detected?
Prevention of irreversible visual loss to glaucoma with early detection and treatment is key. A comprehensive eye examination is necessary to determine whether you have glaucoma.
During your glaucoma evaluation, your doctor will:
– assess your vision
– measure your eye pressure
– examine the drainage angle of your eye to determine the type of glaucoma
– evaluate for any optic nerve damage (ophthalmoscopy, stereodisc photography and structural evaluation using optical coherence tomography)
– test your periheral visual field using a visual field perimetry test
– measure your central corneal thickness
– evaluate your risk factors for glaucoma
How can glaucoma affect my vision?
In the early to moderate stage, glaucoma affects only your peripheral visual field. This is often subtle and you will still maintain good vision. A visual field test is necessary to demonstrate the loss of peripheral vision at this stage.
In advanced glaucoma, your central vision is likely to be affected. You may also notice a reduction in contrast and brightness sensitivity.
What are the treatment options?
Medications: Glaucoma is usually treated with the daily use of eyedrops. There are five classes of eyedrops which aim to either reduce the production of aqueous fluid produced and/or enhance the drainage of aqueous fluid out of the eye. Good control of your eye pressure depends on your compliance with the use of these eyedrops – daily use at the frequency as advised by your doctor. As all medications can have side effects, it is important that you notify your doctor if you experience them.
Laser treatment: Laser procedures may be recommended for the treatemnt of glaucoma. The drainage facility can be lasered to improve aqueous fluid outflow in open angle glaucoma (Trabeculoplasty). The laser can also be used to create a hole in the iris (Iridotomy) to improve aqueous fluid outflow in closed angle glaucoma. As a laser procedure is associated with potential risks, your doctor should discuss them with you.
Surgery: Filtration surgery is necessary when medical therapy fails to control the eyes pressure. A drainage route is surgically created, which then leads to increased fluid outflow and reduced eye pressure. This is usually performed under regional anesthesia. As a surgical procedure is associated with potential risks, your doctor should discuss them with you.
Medical therapy for Glaucoma
Aim of Medical Therapy
The aim of medical therapy is to control the eye pressure at an individualized target level and retard the risk of glaucoma progression. A good control of eye pressure is essential in maintaining your vision in the long term. Glaucoma is a treatable disease. There is no cure for glaucoma.
Classes of Glaucoma Eye Drops
There are five classes of eyedrops which aim to reduce the production of aqueous fluid produced and/or enhance the drainage of aqueous fluid out of the eye. As all medications may have side effects, it is important that you notify your doctor if you experience them. Some common side effects of these eye drops include blurred vision, eye redness, itch, discomfort and localized skin irritation. You may still continue to instill these eye drops if these symptoms are very mild and transient.
Prostaglandin Analogs: Xalatan, Travatan, Taflotan, Lumigan
These eye drops help lower your eye pressure by enhancing aqueous fluid drainage via an alternative pathway within the eye. This is a once a day instillation at bedtime. Potential side effects specific to this group of eye drops include growth of thicker and longer eye lashes, eyelid pigmentation, change of iris colour and ocular inflammation. Most of these side effects are reversible after discontinuation of the eye drop.
Beta-Blockers: Timolol, Timabak (preservative free)
These eye drops help lower your eye pressure by reducing the production of aqueous fluid within the eye. This eye drop needs to be instilled twice a day. Potential side effects specific to this group of eye drops include low blood pressure, shortness of breath, reduced pulse rate, fatigue, depression, insomnia, hair loss, dizziness and reduced libido. Most of these side effects are reversible after discontinuation of the eye drop.
Alpha-Agonists: Alphagan P
This eye drop helps lower your eye pressure by reducing the production of aqueous fluid as well as increasing the fluid drainage capability within the eye. This eye drop may be instilled twice or thrice a day as prescribed by your doctor. Potential side effects specific to this eye drop include fatigue, headache, dizziness, depression, dry mouth and nose, photophobia and slight elevation of upper eyelid. Most of these side effects are reversible after discontinuation of the eye drop.
Carbonic Anhydrase Inhibitors: Trusopt, Azopt
These eye drops help lower your eye pressure by reducing the production of aqueous fluid within the eye. This eye drop may be instilled twice or thrice a day as prescribed by your doctor. Potential side effects specific to this group of eye drops include fatigue, loss of appetite as well as tingling sensation of the hands and feet. Most of these side effects are reversible after discontinuation of the eye drop.
Cholinergics: Pilocarpine 2% and Pilocarpine 4%
These eye drops help lower your eye pressure by increasing fluid drainage through the conventional pathway (trabecular meshwork situated in the angle between the iris and cornea) within the eye. This eye drop is usually instilled four times a day. Potential side effects specific to this group of eye drops include headache, brow ache and dim vision. Most of these side effects are reversible after discontinuation of the eye drop. Rarely, retinal detachment may occur with prolonged use.
Combination 2-in-1 Eye Drops: Combigan, Xalacom, Duotrav, Ganfort, Cosopt, Azarga
Each of these eye drops contain 2 medications within a bottle. The benefits of using these combination eye drops include the convenience and ease of application as well as reduced preservative exposure. The frequency of instillation depends on the type of eye drop that is prescribed by your doctor. The mechanism(s) of action and potential side effects are similar to each individual drug component.
Oral Medication: Diamox
Diamox (also known medically as Acetazolamide) is an oral form of the carbonic anhydrase inhibitor class of medication. It is only prescribed by your doctor when your eye pressure is very high and needs to be rapidly reduced to a safe level. Potential side effects specific to Diamox include fatigue, skin rash, loss of appetite as well as tingling sensation of hands and feet and frequent urination. Rarely, patients develop kidney stones and blood abnormalities. Most of these side effects are reversible after discontinuation of the medication. As some of the rarer side effects may be life-threatening, long term intake of Diamox is not advisable.
How do I know that my glaucoma condition is stable?
As glaucoma does not cause any symptoms, you will not know whether your eye pressure is controlled. This highlights the importance of a regular follow-up with your doctor. At each follow-up, your eye pressure will be measured. Visual field tests will also be performed to evaluate the stability of your condition. A stable glaucoma condition is essential to prevention of further vision loss.
Importance of glaucoma screening
Glaucoma is a prevalent eye disease and prompt treatment can prevent visual loss. If you or your family member have any of the above risk factors stated above, a comprehensive eye examination is advisable.