Glaucoma is a common eye disease that damages the optic nerve, also known as the retina, which leads to blindness. The retina is a vital channel that provides visual information from the eyes to the brain. This disease occurs due to high pressure inside the eye. It is known as intraocular pressure or IOP. The increased pressure also known as ocular hypertension is an imbalance in the production and drainage of fluid inside the eye known as aqueous humour on the front part of the eye. Pressure begins to build when the channel that drains aqueous humour called trabecular meshwork is obstructed and damaged while new fluid is constantly created. This, however, does not rule out others without IOP from developing glaucoma. There is no specific level of pressure that would lead someone to develop glaucoma or to be free from it. Pressure can also build due to eye injury.
Types, Causes and Symptoms
Glaucoma is divided into two types. Primary glaucoma is glaucomas that occur for reasons unknown and secondary glaucoma are glaucoma that is caused by medical conditions.
Open-angle glaucoma (OAG) is the most common type of primary glaucoma. There are no symptoms and you would only realise it when you begin to lose their sight. Individuals diagnosed with hypertension are more likely to have this type of glaucoma.
Normal-tension glaucoma (NTG) is a variant of open-angle glaucoma. The major difference is it occurs in people with normal eye pressure.
Angle-closure glaucoma (ACG) is a medical emergency disease. It is also known as narrow-angled or acute glaucoma. The symptoms are intense pain in the eye, nausea, red eyes and blurred vision. This form of glaucoma happens when the iris blocks fluid from draining out of the front of the eye. A rapid fluid build-up would lead to a spike in the eye pressure.
Congenital glaucoma happens when babies are born with glaucoma. Young children who have this medical condition have cloudy eyes, are sensitive to light, have extra tears and their eyes may be larger than normal. Glaucomas that affect babies and children are considered pediatric glaucoma types.
Neovascular glaucoma is secondary glaucoma caused by hypertension and diabetes. It happens when the eye makes extra blood vessels that cover the part where the fluid is supposed to be drained. Pain, redness in the eye and vision loss are its symptoms.
Exfoliation glaucoma is another variant of open-angle glaucoma. It is also known as pseudoexfoliation. It is a condition where extra materials detach from parts of the eye and block fluid from draining.
Pigmentary glaucoma occurs when pigments from the iris flake off and disperse throughout the eye. When loose pigments build up and block fluid from draining out, it results in heightened pressure. Blurry vision and seeing rainbow-coloured visions around lights are its symptoms.
People who have uveitis can develop uveitic glaucoma. Uveitis is a medical condition that causes inflammation in the eye. Experts believe that the inflammation scars tissues in the middle of the eye. Subsequently, the path where fluid drains out is damaged or blocked. Pressure is heightened causing uveitic glaucoma. Corticosteroids – steroid hormones – consumption would also cause uveitic glaucoma as a side effect.
Glaucoma Stages and Classifications
The stage is vital in measuring the progress of patients having this condition. There are three classification systems used to measure the severity of glaucoma and determine its stages. The following table displays the different classifications and stages.
Glaucoma Risk Factors
The risk factors may differ for different types of glaucoma. For open-angle glaucoma the risk factors are older age which is consistent in raising the IOP, family history, thinner central corneal thickness (CCT), lower ocular perfusion pressures. There is also suspicious optic nerve appearance with increased cupping
Those with a family history are 2.1 times more likely to have open-angle glaucoma. Immediate family members of patients are 9 times more likely to inherit them.
Ocular hypertension is another risk factor but this is also the only risk factor manageable through medication and surgery.
If we are considering gender as a risk factor, men are likely to have open-angle glaucoma whereas women have a higher risk of having angle-closure glaucoma.
People from certain races are also more likely to have glaucoma. Black Americans are six times more likely to contract this condition compared to white Americans. There are a higher number of ACG cases among Asians compared to Caucasians.
Myopia (nearsightedness) is a prevalent risk factor among Asians in the progress towards glaucoma. Myopia and hyperopia (farsightedness) are risk factors for ACG and OAG.
The risk factors for pigmentary glaucoma are severe myopia, male, black and Krukenberg spindles. The spindles are patterns formed on the inner surface of the cornea by pigmented iris cells that are shed during the mechanical rubbing of the posterior pigment layer of the iris.
Systemic high and acute low blood pressures are also seen as possible risk factors based on findings of clinical studies. Glaucoma is prevalent when diastolic pressure is low and lower ocular perfusion pressure.
There are four risk factors for NTG – cardiovascular disease, low eye pressure, family history and Japanese ethnicity.
There are a total of 5 tests that you would go through in the process of diagnosing a case of glaucoma. Out of that, two are required routine checkups. The two are tonometry and ophthalmoscopy
Tonometry measures inner eye pressure. Normal eye pressure ranges from 12 to 22 mm Hg. Pressures exceeding 20 mm Hg would be classified as glaucoma. NTG involves pressure ranging from 12 to 22 mm Hg.
Ophthalmoscopy is the procedure to examine the retina for glaucoma damage. Eye drops are utilised to dilute the pupil so that the shape and colour of the retina can be examined. If the retina looks unusual, you would need to go for two other tests – perimetry and gonioscopy.
Perimetry is a visual field test that maps out your complete field of vision. If you undergo the test, you would be required to look straight ahead as light is repeatedly flashed from different positions towards the periphery vision. This visual field test is conducted one to two times annually.
Gonioscopy is the medical examination that determines whether the angle where the iris meets the cornea is open and wide or narrow and closed. This test helps determine whether you have acute ACG or chronic OAG.
Pachymetry is used to measure the thickness of the cornea as the thickness influences the intraocular pressure.
The only available treatment for glaucoma is reducing the intraocular pressure aka IOP. There are three medical treatment options – medicine, laser and surgery.
The most common medicine dispensed are eye drops. Some eye drops help fluid drain from your eyes. Examples include prostaglandins, rho kinase inhibitor and nitric oxide. Eye drops that lower the fluid amount in the eyes include alpha-adrenergic agonists, beta-blockers and carbonic anhydrase inhibitors.
Laser treatment or trabeculoplasty drains away fluid in the eyes and is used to treat OAG. You may experience soreness and swelling as side effects of the treatment but it is only a temporary effect.
There are three surgical procedure options for those who opt for surgery. Trabeculectomy is a procedure used to treat OAG. Glaucoma implant surgery is used to treat congenital glaucoma, neovascular glaucoma and glaucoma caused by an injury. Minimally invasive glaucoma surgery (MIGS) is a group of surgical procedures that can be divided into four:-
Microtrabeculectomies – This procedure drains fluid from underneath the outer membrane of the eye.
Trabecular bypass surgery – This removes trabecular meshwork that restricts fluid drainage.
Suprachoroidal shunts – This reduces the pressure between the retina and the wall of the eye.
Laser cyclophotocoagulation – Procedure for advanced glaucoma that could not be treated via trabeculectomy or shunts.
While outright prevention may be impossible it is possible to reduce the risks of glaucoma through a healthy lifestyle and diet. There is a general view which includes the following:
- Maintain a healthy weight.
- Maintain a normal blood pressure level and keep other medical conditions in check.
- Keep away from smoking.
- Limit coffee intake since high caffeine levels can raise eye pressure.
- Exercise daily.
- Prevent overexposure to sunlight when outdoors.
- Get regular comprehensive eye checkups.
- Use prescription eye drops.
In terms of diet, you should consume more dark green, yellow and orange vegetables and fruits as these contain carotenoids that counter several medical conditions including glaucoma.
Yellow carotenoid antioxidants known as macular pigments such as lutein and zeaxanthin are vital for positive vision health. These can be found in dark, leafy greens such as spinach, collard greens and kale, as well as in yellow corn, okra, broccoli, Brussels sprouts, mango, green beans, sweet potatoes, lima beans, squash, green, yellow and orange bell pepper and egg yolks.
Vitamin C rich fruits and vegetables, food with vitamins E, A and D, zinc and omega – 3 fatty acids are also highly recommended for eye health.
- Ng, M. et al. (2012) “Comparison of visual field severity classification systems for glaucoma,” Journal of glaucoma, 21(8), pp. 551–561.
- (No date) Researchgate.net. Available at: https://www.researchgate.net/profile/Stefano-Miglior/publication/51435094_Risk_Factors_for_Glaucoma_Onset_and_Progression/links/5b0fd5dd4585157f87251f6c/Risk-Factors-for-Glaucoma-Onset-and-Progression.pdf (Accessed: July 20, 2021).