Glaucoma is a group of ocular diseases, which leads to optic nerve damage resulting in loss of vision and blindness. During the early stages of glaucoma, there are no symptoms, no pain, and vision is normal.
Slowly, people with glaucoma start losing their side (peripheral) vision. They miss objects to the side and out of the corner of their eye. Their vision seems to be like looking through a tunnel. As the disease progresses, they start losing their straight vision, until no vision remains. Glaucoma can occur in one or both the eyes.
Different types of glaucoma
Open-angle glaucoma: Open-angle glaucoma is the most common type of glaucoma and accounts for 90% glaucoma cases. It is caused due to slow blockage of the drainage canals leading to increased pressure in the eye. It is asymptomatic and is a life-long condition.
Angle-closure glaucoma: It is less common as compared to open-angle glaucoma. It is caused due to clogging of drainage canals which results in increased intraocular pressure. There is the closed angle between the iris (the colored part of the eye) and the cornea. It develops very rapidly and has symptoms that are very visible.
Normal-Tension glaucoma: It is also known as low-tension or normal-pressure glaucoma. In this type of glaucoma, there is damage to the optic nerve even though the pressure in the eye is not very high. The normal pressure range in the eyes is between 12-22 mmHg. The causes of normal-tension glaucoma are unknown. Researchers are examining the causes of the damage to an optic nerve in spite of relatively low eye pressures.
Congenital glaucoma: Also known as childhood glaucoma, this type of glaucoma develops in babies when there is incomplete development of the drainage canals in the eyes during fetal development. This is a rare type of glaucoma and may be inherited. It is mostly diagnosed in the first year of life. Babies with congenital glaucoma develop enlarged eyes, cloudiness of the cornea, and sensitivity to light.
Secondary glaucoma: It is a glaucoma condition that develops because of other medical problems. There is a recognizable cause of increased eye pressure, resulting in damage to the optic nerve and loss of vision. Secondary glaucoma can be open-angle or angle-closure glaucoma. Secondary glaucoma can be caused due to an injury of the eye, inflammation, due to the certain type of medications like steroids, advanced cases of cataract and diabetes.
How is glaucoma diagnosed?
Glaucoma is diagnosed through a complete dilated eye exam which includes:
Visual acuity test: This test measures how well the patient is able to see at various distances.
Visual field test: This test examines the peripheral or side vision of the patient.
Dilated eye exam: In this test, drops are placed into the patient’s eyes to widen or dilate the pupils and then the eyes are examined with a magnifying glass for any retina or optic nerve damage.
Tonometry: This exam measures the pressure inside the eyes by use of an instrument called the tonometer.
Pachymetry: This test measures the thickness of the patient’s cornea. Numbing drops are applied to the eye and an ultrasonic wave instrument is used to measure the thickness of the cornea.
Although there is no cure for glaucoma, it can be controlled with proper care and management. The main focus of the glaucoma treatments is to lower the eye pressure to a level that is less likely to cause further damage to the optic nerve. The main goals of the glaucoma treatments include:
- Prevention or slow down the progression of vision loss
- Preservation of the structure and function of the optic nerve
- Reduction in pain and improvement of the vision in acute forms
- Improvement in the quality of life and functional vision
The different approaches to glaucoma treatment include aerobic exercise (to lower the intraocular pressure), medications, and laser or surgical procedures in case drug therapy is unsuccessful or patient cannot tolerate the medications.
Below, we list the current glaucoma treatments.
Glaucoma treatments
1. Beta-blockers
Also called as beta-adrenergic antagonists, beta-blockers are used to lower the intraocular pressure. They work by decreasing the production of fluid in the eye called as aqueous humor. There are two types of beta-blockers: selective and non-selective.
Non-selective beta-blockers: Non-selective beta-blockers have a wider range of effects on the body and are associated with a greater number of side effects. However, they are more effective in lowering eye pressure. Examples of non-selective beta-blockers include timolol, levobunolol.
Selective beta-blockers: Selective beta-blockers are safer, however, their effect on reducing the eye pressure is less as compared to non-selective beta-blockers. Selective beta-blockers should be used with caution in patients with respiratory problems. Example of a selective beta-blocker used to treat glaucoma is betaxolol. Some side effects of beta-blockers include:
- Wheezing or difficulty in breathing
- Slow or irregular heartbeat
- Increased risk for heart failure
- Depression
- Impotence
- Difficulty measuring blood glucose changes in diabetes patients
- Eye irritation or allergy in the eye
- Headache, dizziness, and weakness
2. Prostaglandin analogs or Prostamides
These medications work by decreasing the intraocular pressure. The decrease in the eye pressure is due to the increased outflow of the aqueous humor. Examples of these medications include latanoprost, bimatoprost, and travoprost. These medications should be used with caution in patients with a history of inflammation of the eye, herpes infection of the eye or selling of retina. Prostaglandin analogs are slightly more effective glaucoma treatments as compared to non-selective beta-blockers. Some side effects of these medications include
- Redness of the eye
- Darkening of the iris and eyelid skin
- Increased growth, thickness, and pigmentation of the eyelashes
- Blurred vision
- Muscle aches
- Eye irritation or itching
- Headache
3. Carbonic Anhydrase inhibitors (CAIs)
These agents have remarkable eye pressure-lowering ability. They act by decreasing the production of aqueous humor in the eye. These medications may be considered as adjunct therapy or primary therapy for patients with cardiopulmonary contraindications to beta-blockers. However, since these medications are sulphonamides, patients with allergy to sulfa antibiotics should not take these for glaucoma treatment. Examples of topical CAIs include dorzolamide and brinzolamide. Oral medications are also available such as acetazolamide, methazolamide. Some side effects of these medications include:
- Dry eyes
- Blurred vision
- Eye irritation or allergy
- Headache or dizziness
- Bitter taste in the mouth
- Stomach upset
Oral medications have more side effects such as an increased urge to urinate, tingling sensation in fingers and toes, severe allergic reactions, unusual tiredness or weakness.
4. Alpha-agonists
Alpha-agonists lower the intraocular pressure by decreasing the production of aqueous humor in the eye. The prototype of alpha-agonists, called as epinephrine is not available in Canada because of its unacceptable adverse effects in the eyes. The other available alpha-agonists for glaucoma treatment include apraclonidine, brimonidine, and dipivefrin. Possible side effects of these agents include:
- Eye allergy with a red eye
- Dry mouth
- Blurred vision
- Sensitivity to bright light
- Headache
- Tiredness or fatigue
- Low or high blood pressure
5. Cholinergic agonists
These medications cause direct stimulation of the muscarinic receptors resulting in contraction of ciliary muscles and increased trabecular outflow. Example of a topical cholinergic agonist used to treat glaucoma is pilocarpine. However, these drugs are poorly tolerated by children and youngsters. Side effects include:
- Excessive constriction of the pupil with reduced night vision
- Myopia (when eyes can see close objects clearly but distant objects are blurred)
- Brow ache
- Abdominal cramping or diarrhea
6. Combination treatments
Several eye drops are available as a combination of two different drugs. The combination glaucoma treatments are more convenient for patients to use and thus improve patient compliance. These agents also reduce cumulative exposure to the preservatives. In Canada, the combination treatments available for glaucoma are brimonidine/timolol, brinzolamide/timolol, dorzolamide/timolol, latanoprost/timolol, travoprost/timolol and brimonidine/brinzolamide. All these combination treatments are more effective than individual drugs.
7. Surgery
The surgery options for glaucoma treatment include selective laser trabeculoplasty and laser peripheral iridotomy. In selective laser trabeculoplasty, the surgeon uses a laser to create microscopic bursts of energy in the drainage canals of the eyes. These burns open the drainage holes and allow the fluid to drain better through them. This helps to lower the eye pressure and prevent further damage to the optic nerve and loss of vision. Some risks involved with this type of surgery are inflammation, and bleeding inside the eye.
The surgeon may suggest further treatment with medications after the surgery. The other surgery option is laser peripheral iridotomy, in which a laser is used to create an opening in the iris so that the fluid can leave the angle of the eye more easily. It is performed in patients with narrow-angle glaucoma. This is also a successful procedure but can cause inflammation and bleeding inside the eyes.
Successful glaucoma treatment is a joint effort between the patient and the doctor. The doctor can prescribe the glaucoma treatment but it is up to the patient to follow the doctor’s instructions. Once the treatment is started, the patients are expected to visit their doctors every three to six months. Proper use of glaucoma medication can improve its effectiveness and reduce the side effects.
Written by Pratibha Duggal
References:
- Eye Conditions, Disorders & Treatments – Vision Health Information from The Canadian Ophthalmological Society (COS). http://www.cos-sco.ca/vision-health-information/conditions-disorders-treatments/glaucoma/glaucoma-treatment/
- Glaucoma Treatment. https://www.aao.org/eye-health/diseases/glaucoma-treatment
- Facts About Glaucoma | National Eye Institute. https://nei.nih.gov/health/glaucoma/glaucoma_facts
- Types of Glaucoma. https://www.glaucoma.org/glaucoma/types-of-glaucoma.php
- CPS [Internet]. Ottawa (ON): Canadian Pharmacists Association; c2018. Glaucoma. Available from: http://www.e-cps.ca
