Eye pressure: All you need to know about this silent thief of sight

You could be going blind—and never feel a thing. That's the silent danger of rising eye pressure. It creeps in quietly, damaging your vision without warning. By the time you notice something is wrong, the damage is often permanent and irreversible.

Dr Alain M'bongo, Assistant Professor of Ophthalmology and Vitreo-Retinal Surgeon at Aga Khan University Hospital, shares that dangerously high pressure inside the eye often develops without any symptoms.

"The eye is in a closed setup called the orbit—there is a bone surrounding it," he explains. In children, the eye is still developing, so when pressure builds up, the volume of the eye can increase, meaning it takes longer for the optic nerve to get damaged.

"But for an adult, the volume is fixed. So, when the pressure builds up, there is no room."

In normal conditions, excess fluid is supposed to drain out of the eye, maintaining safe pressure levels.

But when it doesn't drain properly, pressure builds inside the eyeball, putting tension on the delicate structures. Over time, the optic nerves are damaged, gradually leading to vision loss.

What causes eye pressure?

The pressure inside the eye, known as intraocular pressure, plays a crucial role in keeping your eye functioning properly. This pressure is created by the production of a special fluid called aqueous humor, which nourishes the eye with nutrients and maintains its shape.

"In a normal situation, it doesn't cause any harm to the eye," says Dr M'bongo. But when things go wrong, conditions like glaucoma can cause that pressure to rise dangerously, silently damaging your vision.

To help visualise this, he uses a simple analogy: a tap. "You open your water and it flows to the sink, then to the drainage." The same happens in your eye—aqueous humor is produced from inside, and it flows out through the blood supply. But for it to leave the eye properly, it follows specific drainage pathways, tiny net-like channels.

"Now, when you have glaucoma, be it congenital—a baby being born with glaucoma—or the one we call primary open glaucoma, the net channel narrows and there is accumulation of that fluid in the eye, and it puts pressure inside the eye," he shares. That pressure builds gradually, damaging the eye from the edges of your vision before it creeps toward the centre.

Glaucoma is no small threat. After cataracts, it is the second leading cause of blindness globally. What makes it particularly dangerous, according to Dr M'bongo, is how quietly it progresses. "It's a dangerous eye disease because patients do not feel any pain or discomfort until they lose their eye."

How is eye pressure tested?

A trained eye care specialist uses a small, flat-tipped instrument called a tonometer, which gently comes into contact with your cornea—the clear front surface of your eye. Within seconds, the device measures your eye pressure.

Dr M'bongo explains that the process is quick and usually painless, though some people may feel slight discomfort. "Some people's eyes water a little, but it clears up right after the test."

The ideal pressure should be between 10mmHg to 21mmHg. But in a few cases, with normal pressure, you can still have glaucoma—which is called normal tensile glaucoma.

Are there more vulnerable people? "If you are black and 40 years old, you are susceptible to eye pressure. Four to eight people out of 100 in that age group—40 years and above—are likely to have glaucoma."

However, eye pressure is not constant throughout the day. Dr M'bongo says, "For people who don’t have glaucoma, even though the eye pressure fluctuates, it remains in the normal range."

Does food, lifestyle, or stress lower or raise eye pressure?

"No. Only medicine can affect."

In most cases, people with raised eye pressure—known medically as ocular hypertension—don't feel anything unusual.

Symptoms only appear when the pressure is dangerously high. That's why Dr M'bongo says glaucoma, particularly among Africans, is such a silent threat. "The pressure is never too high," he explains, making it easy for the disease to sneak in unnoticed until damage is done.

But there's another, more aggressive type known as acute lunar glaucoma, where the pressure spikes so suddenly and severely that immediate medical attention becomes non-negotiable.

"The pressure goes too high that you are forced to seek treatment the same day," he explains. The danger? If you don't receive treatment within 48 hours, the result is permanent blindness.

Do digital devices affect eye pressure?

Dr M'bongo explains, having a digital device close to the eye in a dark room makes the pupil dilate, and then the pressure builds up.

So, is it harmful to scroll through your phone in bed with the lights off? "It is not good, even for the sake of the eye itself."

Can eye pressure be lowered without surgery? "Yes. Most of the time, it can be controlled with medicine. We use tablets for a short period, but eye drops have to be used every day for life."

For some, surgery is an option. Dr M'bongo says sometimes surgery works and the person can remain without using medicine for even 5 to 10 years—but that rarely happens for that long.

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