Health Corner

What is glaucoma?
Glaucoma is a leading cause of blindness in Hong Kong. About 3 out of every 100 adults over the age of 40 are at risk of developing glaucoma. Early diagnosis can prevent vision loss and blindness.

In the early stages, glaucoma may not show obvious symptoms, so patients often overlook it. By the time vision problems are noticed, the disease is usually advanced. This is why glaucoma is known as the “silent thief of sight.” It can cause permanent blindness, but early detection and treatment can help preserve vision. People over 40 or those with high-risk factors should have an eye examination every year to detect early glaucoma and prevent deterioration.

Why does glaucoma occur?

Inside the eye, there is a clear, watery fluid called aqueous humor. It supplies oxygen and nutrients to eye tissues, removes waste products, and maintains the shape of the eyeball. If the drainage of aqueous humor is blocked, pressure builds up inside the eye (intraocular pressure). High intraocular pressure can damage the optic nerve, leading to glaucoma. Therefore, measuring eye pressure is an important part of glaucoma screening.

What types of glaucoma are there?

Glaucoma can be categorized in different ways depending on cause and disease progression:

• Acute glaucoma
  This form develops suddenly, causing blurred vision, seeing halos or rainbow rings around lights, red and painful eyes, and possibly headache, nausea, or vomiting. It is a medical emergency that requires immediate treatment with oral or injected medications and eye drops to lower eye pressure, followed by laser or surgical treatment.
• Chronic glaucoma
  This type develops gradually with no obvious early symptoms. Vision narrows slowly, and by the time patients notice serious vision loss, much of the damage is irreversible. This is why it’s also called the “thief of sight.”
• Congenital and acquired glaucoma
  Although most glaucoma patients are over 40, some infants are born with abnormal drainage structures in the eyes, leading to congenital glaucoma. These babies may be sensitive to light, have excessive tearing, and have larger-than-normal eyeballs.
• Primary and secondary glaucoma
  Primary glaucoma is not caused by another disease. Secondary glaucoma results from other eye or systemic conditions such as advanced cataracts, uveitis, eye tumors, diabetic eye disease, or prolonged use of steroid eye drops. Treatment for secondary glaucoma must address the underlying condition first.
• Normal-tension glaucoma
  In some patients, eye pressure is within the normal range, but the optic nerve is still damaged due to its lower tolerance to pressure. Such cases require detailed examination to diagnose.
• High-tension glaucoma
  This is the most common type where increased intraocular pressure damages the optic nerve, leading to progressive vision loss and narrowed visual fields.

What are the common symptoms of glaucoma? 

• Gradual narrowing of the visual field

• Nausea or vomiting

• Eye pain with or without headache or migraine

• Sudden blurred vision

• Red or swollen eyes

• Seeing halos or rainbow rings around lights

How is glaucoma diagnosed?

Diagnosis involves a series of clinical tests based on the patient’s condition and medical history. Common tests include:

• Intraocular pressure measurement

• Visual field test

• Fundus (retinal) examination

• Slit-lamp examination

• Gonioscopy (to examine the drainage angle)

• Assessment of optic nerve damage

• Checking aqueous humor drainage function

How is glaucoma treated?

The goal of glaucoma treatment is to control eye pressure, prevent or slow disease progression, protect the optic nerve, and preserve vision. Treatments include medications (eye drops or oral drugs), laser therapy, or surgery. Today, there are also minimally invasive surgical options. With early detection, 90% of patients can avoid blindness.

Surgery is usually performed under local anesthesia, where the eye is numbed but the patient remains awake. General anesthesia is reserved for specific cases.

Surgical options to lower intraocular pressure:

1. Glaucoma filtration surgery – A small incision is made in the eye wall to create a tiny drainage channel for aqueous humor to exit and reduce eye pressure.

2. Non-penetrating filtration surgery – Similar to traditional filtration surgery but preserves certain corneal layers and may use implants.

3. Tube (shunt) implantation surgery – A drainage tube is inserted into the eye to divert excess fluid out.

4. Minimally invasive glaucoma surgery (MIGS) – Techniques that either enhance drainage or reduce aqueous humor production with less tissue disruption.

5. Ciliary body laser or cryotherapy – Laser or freezing treatment to reduce aqueous humor production by partially destroying the fluid-producing tissue.

In some surgeries, anti-scarring drugs (such as mitomycin C or 5-fluorouracil) may be applied to increase success rates. After surgery, an eye shield is used to protect the surgical site.