What is Glaucoma?

Glaucoma is one of the leading causes of irreversible blindness in the eyes in Singapore. It is a disease characterized by pressure in your eye or progressive damage to the optic nerve, which are made up of the fibers that connect our eyes to our brain. Optic nerve damage leads to eye problems like irreversible loss of our visual field, starting from peripheral field and progressing centrally to cause ‘tunnel-like’ or blurred vision. In severe cases, total vision loss and blindness may occur.

There are many different types of glaucoma with different causative mechanisms. Broadly, the types of glaucoma can be divided into: Open-angle glaucoma and Angle-closure glaucoma. Simply explained, the angle of our eye is the drainage site of the fluid in our eyeball. Any compromise to the drainage system at our angles will lead to a build-up in eye pressure and consequently, glaucoma.

Glaucoma is frequently associated with high pressures in your eye, although it can occur even in people with seemingly normal eye pressures, due to a state of poor oxygen perfusion to their optics. In most early cases, there are no symptoms of high eye pressures; which means most people are unaware that they even have eye problems. That is why it is important to maintain good eye health or to get your eyes checked annually to detect any signs of early glaucoma or damage. This is especially so in people who have risk factors for glaucoma.

Development of glaucoma

Risk factors for Glaucoma:

  • Family history of glaucoma: We know that there is a genetic predisposition for glaucoma and the disease tends to run in families. Those with family members with glaucoma such as acute angle closure glaucoma should get checked annually for eye conditions from the age of 40 years.
  • Systemic Hypertension: It has been shown that individuals with high blood pressure may be more likely to have high eye pressure, hence may be at higher risk for glaucoma.
  • Diseases with poor blood circulation such as diabetes mellitus, previous stroke, heart disease, migraine: When blood circulation to the nerve at our optic is poor, the millions of tiny fibres within it start to get starved of oxygen. Some of the fibres will eventually die and blind spots in vision will appear. It is when all the fibres die, that all vision will be lost.
  • Obstructive Sleep Apnea: It is well-established that there is increased prevalence of glaucoma in obstructive sleep apnea. The mechanisms by which obstructive sleep apnea causes glaucoma are complex and are a combination of hypoxia, vascular and mechanical factors. It has also been shown that glaucoma progression is related to the severity of obstructive sleep apnea.
  • High Myopia: It is well-known that individuals with a high degree of short-sightedness are at higher risk of glaucoma. This could be due to the fact that myopic optic nerves are structurally weaker and hence more susceptible to nerve fibre loss than non-myopic optic nerves.
  • Thin corneas: Those who have thin corneas (less than 500 micrometres) will show artificially low-pressure readings. This is dangerous because if there are discrepancies in their readings, such people are at risk of developing vision sight-threatening glaucoma without them or their eye doctor or ophthalmologist knowing. Without realizing it, a large percentage of our population have such thin corneas. These are the people who have had prior LASIK treatment because LASIK is a procedure which uses laser to cut and shave down the thickness of cornea in order to correct refractive vision errors like myopia. Hence, people with prior LASIK treatment would need continuous monitoring with a competent eye doctor or ophthalmologist who is meticulous about adjusting measured pressure readings accordingly to prevent glaucoma.
  • Prolonged use of steroid medication in any form: There is evidence that links steroid use to glaucoma. Prolonged use of steroid in the form of oral medication, nasal sprays, inhalers or eye drops can lead to side effects including an increase in the intraocular pressure. It is well-known that approximately 40% of our population are termed as ‘steroid-responders’, which means that they will develop a high response in the eyes to the use of steroids.
  • Advanced cataracts: When the cataractous lens thickens, it tends to narrow the angles and compromise our eye’s drainage system. People who have very thick cataracts are more likely to suffer from a type of glaucoma known as angle-closure glaucoma. They are advised to find a doctor or ophthalmologist to monitor any symptoms.
Normal eye and eye with glaucoma

Glaucoma could be related to Severe Snoring

Snoring is such a common phenomenon and yet did you know that people with severe snoring could really have obstructive sleep apnea? That means that in your state of deep sleep and muscle relaxation, your airway could get so narrowed that it becomes difficult to get enough air in – this commonly manifests as snoring. A lack of air leads to oxygen deprivation in many organs – hence obstructive sleep apnea is commonly related to early-onset hypertension, heart disease and even stroke.

Most of us are now aware that obstructive sleep apnea results in a state of hypoperfusion (or insufficient oxygen) to our tissues while asleep. However, many of us are NOT aware that such hypoperfusion states in our eye tissues could lead to various eye diseases and even vision loss. There has been increasing evidence that obstructive sleep apnea is associated with glaucoma, ischemic optic neuropathy, central serous chorioretinopathy and other retinal diseases that affect our vision. Since glaucoma is one of the most serious sight-threatening diseases common to our ageing population, let us look at the determinants of glaucoma, how it is related to obstructive sleep apnea and why we should get checked early.

Although complex, we now know that these various factors are responsible for the development of glaucoma in obstructive sleep apnea:

  1. Hypoxia: Oxygen is important for the proper functioning of all cells. Hypoxia describes the lack of oxygen and subsequent oxidative stress which takes place in cells. Prolonged episodes of hypoxia, which is what happens in obstructive sleep apnea, directly damages the optic fibres, results in glaucoma and thus affects vision.
  2. Vascular factors: Obstructive sleep apnea is well-known to be associated with various vascular changes including hypertension, atherosclerosis of carotid artery and increase in intracranial pressure. This is also related to definite vascular changes and dysregulation of the optic nerve. Such vascular changes disturb the blood flow and is exacerbated by states of nocturnal hypotension in obstructive sleep apnea.
  3. Mechanical factors: Apart from the supine position that is adopted at night to sleep, obesity is also another risk factor for high eye pressures due to excessive intraorbital fatty tissue and increased episcleral venous pressure. 
Eye examination

What are the Symptoms of Glaucoma?

Very often, there are little to no glaucoma symptoms. This is because elevated pressure in your eye (more than 21mmHg) is insidious and undetectable by patients. Even vision loss which takes place from peripheral vision goes unnoticed until too late. It is only when eye pressure is extremely high above 35 or visual field is severely narrowed, that patients are alerted of such symptoms. At that stage, glaucoma may be too advanced and visual loss damage may be irreversible for treatment.

How is Glaucoma Detected?

At risk patients should have the following assessed by their eye specialist for potential glaucoma diagnosis:

  1. Eye pressure: An eye pressure above 21 mmHg is considered high and at risk of glaucoma. Patients with a thin cornea should have an even lower threshold than 21 mmHg.
  2. Cornea thickness: A person’s actual eye pressure must be adjusted according to his/her cornea thickness.
  3. Angle assessment: How open or narrow a person’s angles will contribute to his/her risk.
  4. Optic nerve appearance: By looking at the optic nerve, most well-trained eye specialists or eye doctors will be able to assess the risk of glaucoma. A healthy optic nerve has optimal color and thickness; while a glaucomatous one has pallor and thinning of the nerve rims.
  5. Retinal Nerve Fiber Layer Thickness: With advanced eye imaging technology, we are able to measure the exact thickness of the retinal nerve fiber layer thickness and compare this to the normal population data to a determine whether there is glaucoma risk. This measurement is also useful for subsequent follow-up visits and eye exams because the machine is able to track the thickness progression over years.
  6. Visual Field assessment: Patients with glaucoma will have areas of their visual field that are affected and appear diminished to them. By performing a visual field test, we are able to map out the area of visual field defects that are present and determine whether the disease is progressively deteriorating.
Eye examination

How is Glaucoma Treated?

Treatment of glaucoma is targeted at treating the underlying cause and reducing the eye pressure. It is thought that with a decrease in eye pressure, blood perfusion to the optic nerve can be improved.

The first line of treatment is usage of glaucoma medications like eye pressure-lowering eye drops. There are a multitude of glaucoma treatment eye drops, each with its own specific benefits and side effects. Treatment eye drops should be individualized and customized according to the individual’s characteristics and needs.

When glaucoma cannot be adequately controlled by eye drops, it is then prudent to consider glaucoma laser therapy or glaucoma surgery for better control and treatment of the condition. Laser and surgery are not without risks, hence the decision to proceed should be made after detailed discussion with your eye specialist or doctor.

Since there is no cure for glaucoma and visual loss is irreversible, the importance of early glaucoma detection by a doctor cannot be further emphasized. In fact, it is recommended that patients with obstructive sleep apnea should get screened for glaucoma and other eye diseases by an eye specialist or doctor.

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