Acute Glaucoma: Symptoms, Causes & Emergency Treatment

What Is Acute Glaucoma?

Acute glaucoma is a sudden, severe increase in eye pressure caused by blocked fluid drainage in the eye. This creates an emergency that can cause permanent vision loss within hours if untreated. It differs from the more common open-angle glaucoma, which develops slowly over years.

Acute glaucoma, medically known as acute angle-closure glaucoma (AACG), occurs when the drainage angle in the eye suddenly becomes blocked. This angle, located where the iris meets the cornea, normally allows a clear fluid called aqueous humor to drain from the eye. When this drainage pathway closes abruptly, fluid builds up rapidly, causing a dramatic spike in intraocular pressure.

The eye constantly produces aqueous humor, which nourishes the lens and cornea and removes waste products. Under normal conditions, this fluid drains through channels in the drainage angle. In acute glaucoma, the iris can bow forward and physically block these drainage channels, causing pressure to rise from a normal 10-21 mmHg to potentially over 50 mmHg within hours.

This elevated pressure damages the optic nerve, the bundle of nerve fibers that transmits visual information from the eye to the brain. Unlike some other parts of the body, optic nerve damage cannot be repaired or regenerated. This is why acute glaucoma is considered an ophthalmic emergency requiring immediate intervention.

How Acute Glaucoma Differs from Open-Angle Glaucoma

There are two main types of glaucoma, and understanding the difference is crucial. Open-angle glaucoma is the most common form, accounting for about 90% of all glaucoma cases. It develops gradually over months or years, often without noticeable symptoms until significant vision loss has occurred. The drainage angle remains open, but the drainage channels become less efficient over time.

Acute glaucoma (angle-closure) is much less common but far more urgent. The drainage angle physically closes, pressure rises rapidly, and symptoms are dramatic and immediate. While open-angle glaucoma rarely causes pain, acute glaucoma typically causes severe pain that demands attention. Both conditions can lead to blindness, but acute glaucoma can cause permanent damage within hours rather than years.

What Are the Symptoms of Acute Glaucoma?

Acute glaucoma symptoms include sudden severe eye pain, rapidly decreasing vision, seeing rainbow-colored halos around lights, a red and irritated eye, headache, and nausea with vomiting. These symptoms typically affect one eye and develop within hours.

The symptoms of acute glaucoma are unmistakable and alarming, which actually helps ensure people seek the urgent care they need. Unlike the gradual, painless progression of open-angle glaucoma, acute glaucoma announces itself dramatically. The combination of symptoms creates a distinctive clinical picture that should prompt immediate medical attention.

The hallmark symptom is severe eye pain, often described as an intense aching or pressure sensation in or around one eye. This pain is caused by the rapid stretching of eye tissues as pressure builds. Many patients describe it as one of the most intense pains they have experienced. The pain may radiate to the forehead, temple, or even the jaw on the affected side.

Vision deteriorates rapidly during an acute attack. Patients typically notice their vision becoming increasingly blurry or hazy, as if looking through fog or a dirty window. The high pressure causes swelling in the cornea (the clear front surface of the eye), which scatters light and degrades image quality. Some patients experience near-complete vision loss in the affected eye during a severe attack.

The Distinctive Halo Sign

One of the most characteristic symptoms of acute glaucoma is seeing rainbow-colored halos around lights. This occurs because the corneal swelling acts like a prism, breaking white light into its component colors. Patients may see concentric rings of color around streetlights, headlights, or indoor lights. This symptom is highly specific to acute glaucoma and should always be taken seriously.

Associated Symptoms

The intense pain and physiological stress of acute glaucoma trigger a cascade of associated symptoms. Many patients experience nausea and vomiting, sometimes so severe that they initially believe they have a gastrointestinal problem rather than an eye condition. This occurs because the eye and digestive system share nerve pathways through the vagus nerve.

A severe headache commonly accompanies the eye pain, often concentrated on the same side as the affected eye. Some patients also report abdominal pain or chest discomfort. These systemic symptoms can occasionally mislead both patients and healthcare providers, potentially delaying the correct diagnosis.

When Should You Seek Emergency Care?

Seek immediate emergency care if you experience sudden severe eye pain with vision changes, see colored halos around lights, or have a red painful eye with nausea. Go directly to an emergency department or urgent eye care center. Acute glaucoma can cause permanent blindness within hours without treatment.

Time is critical in acute glaucoma. The longer eye pressure remains elevated, the greater the risk of permanent optic nerve damage and irreversible vision loss. Studies show that patients who receive treatment within the first few hours have significantly better visual outcomes than those whose treatment is delayed.

You should go directly to an emergency department or an emergency eye clinic if you suddenly develop severe pain in one eye, especially if accompanied by decreased vision, seeing halos around lights, or nausea. Tell the staff immediately that you suspect you may have acute glaucoma—this is a time-sensitive emergency that needs rapid evaluation.

Do not wait to see if symptoms improve. Do not try home remedies. Do not wait until the next day to see your regular eye doctor. The window for preventing permanent damage may be only a few hours. Even if you are uncertain whether your symptoms represent acute glaucoma, it is far better to seek evaluation and be reassured than to delay and suffer preventable vision loss.

What to Expect at the Emergency Department

When you arrive at the emergency department, explain your symptoms clearly. Mention the sudden onset of eye pain, vision changes, halos around lights, and any nausea. If you know you have risk factors such as farsightedness or a family history of glaucoma, mention these as well. This information helps medical staff prioritize your care appropriately.

A doctor—who may be an emergency physician initially, with an ophthalmologist consulted as needed—will examine your eye and measure the intraocular pressure. The examination may include shining a light into your eye to check pupil reactions (in acute glaucoma, the pupil often does not constrict normally), looking at the eye under magnification, and using a special instrument to measure pressure.

How Is Acute Glaucoma Diagnosed?

Acute glaucoma is diagnosed through eye examination including pressure measurement (tonometry), slit-lamp examination, pupil reaction testing, and gonioscopy to view the drainage angle. Pressure is typically markedly elevated above the normal range of 10-21 mmHg.

Diagnosing acute glaucoma requires a systematic evaluation of the eye. The classic presentation—severe eye pain, decreased vision, halos, red eye, and systemic symptoms like nausea—creates a recognizable pattern that often suggests the diagnosis before formal testing confirms it. However, objective measurements are essential to confirm the diagnosis and guide treatment.

The cornerstone of diagnosis is tonometry, the measurement of intraocular pressure. Various methods exist for measuring eye pressure, and the doctor may apply numbing drops before the measurement depending on the technique used. Normal eye pressure ranges from 10 to 21 mmHg. In acute glaucoma, pressure typically rises dramatically, often exceeding 40-50 mmHg or even higher.

Physical Examination Findings

The doctor will look for several characteristic signs. The affected eye is typically red and injected, with prominent blood vessels visible on the white of the eye. The cornea appears hazy or steamy due to swelling from the elevated pressure. The pupil is often mid-dilated and fixed, meaning it does not constrict normally when light is shined into it—a classic sign that helps distinguish acute glaucoma from other causes of red, painful eyes.

A slit-lamp examination allows the doctor to examine the eye's structures under high magnification. This reveals the corneal swelling, evaluates the depth of the anterior chamber (the space between the cornea and iris), and helps assess the drainage angle. The shallow anterior chamber typical of eyes at risk for angle closure is often apparent.

Gonioscopy

Gonioscopy is a specialized examination that directly visualizes the drainage angle. The doctor places a special contact lens with mirrors on the eye (after applying numbing drops) to see the angle where the iris meets the cornea. In acute glaucoma, this examination confirms that the angle is closed, blocking fluid drainage. Gonioscopy is typically performed once the acute attack is under control rather than during the height of the crisis.

How Is Acute Glaucoma Treated?

Acute glaucoma treatment has two phases: first, emergency medications (eye drops, oral and intravenous drugs) rapidly lower eye pressure; then, laser peripheral iridotomy creates a permanent drainage pathway to prevent recurrence. Most patients recover well with prompt treatment.

Treatment of acute glaucoma follows a logical sequence: first, rapidly reduce the dangerously elevated pressure with medications, and then perform a definitive procedure to prevent recurrence. Treatment often begins in the emergency department and continues with an ophthalmologist. Importantly, any doctor can initiate emergency treatment—waiting for a specialist should not delay the start of pressure-lowering therapy.

The urgency of treatment cannot be overstated. Every hour that pressure remains elevated causes additional damage to the optic nerve. Modern medical treatment can usually reduce pressure within a few hours, but the sooner treatment begins, the better the chance of preserving vision.

Initial Medical Treatment

Emergency treatment aims to reduce eye pressure as quickly as possible using multiple medications that work through different mechanisms. This multi-drug approach attacks the problem from several angles simultaneously:

• Beta-blocker eye drops (such as timolol) reduce the production of aqueous humor
• Carbonic anhydrase inhibitors (such as acetazolamide, given orally or intravenously, and dorzolamide drops) also decrease fluid production
• Alpha-agonist eye drops (such as brimonidine) reduce production and increase drainage through alternative pathways
• Pilocarpine eye drops constrict the pupil and can help pull the iris away from the drainage angle
• Intravenous mannitol or oral glycerol may be given in severe cases to rapidly draw fluid out of the eye

These medications work together to reduce pressure from potentially dangerous levels above 50 mmHg down toward the normal range. The combination approach is more effective than any single medication alone. Patients typically receive multiple eye drops simultaneously, along with oral or intravenous medications for faster effect.

Laser Peripheral Iridotomy (LPI)

Once eye pressure has been controlled with medications—usually within a few hours—definitive treatment with laser peripheral iridotomy is performed. This procedure creates a small hole in the peripheral iris, providing an alternative pathway for aqueous humor to flow from behind the iris to the front of the eye and into the drainage angle.

The procedure is performed in a clinic setting and takes only one to three minutes. The patient sits at a slit-lamp microscope. After applying numbing eye drops, the doctor places a special contact lens on the eye to focus the laser. Brief pulses of laser energy create a tiny opening (about 0.5mm) in the iris. Most patients feel only minimal discomfort, perhaps a brief pinch sensation with each laser pulse.

After the iridotomy, aqueous humor can flow freely through the new opening, equalizing pressure on both sides of the iris and preventing future angle closure. The opening is permanent and does not affect vision or appearance (it is hidden under the upper eyelid). The fellow (unaffected) eye is usually treated prophylactically as well, since it shares the same anatomical risk factors.

After Treatment

Recovery after acute glaucoma treatment is typically rapid. Once pressure normalizes, pain resolves and vision begins to improve. The corneal swelling clears over hours to days. Some patients may need to continue pressure-lowering eye drops for a period after the acute episode, though many can eventually discontinue them if the iridotomy successfully resolves the underlying problem.

Patients can usually leave the hospital the same day or after an overnight stay for observation. Some inflammation is normal after laser treatment, and anti-inflammatory eye drops may be prescribed for several days. Follow-up appointments monitor pressure and ensure the iridotomy remains open and effective.

What Causes Acute Glaucoma?

Acute glaucoma occurs when the iris blocks the drainage angle in the eye, preventing aqueous humor from flowing out. This is more likely in eyes with naturally shallow anterior chambers, which is common in farsighted people. The blockage causes rapid pressure buildup that damages the optic nerve.

Understanding the anatomy of the eye helps explain why acute glaucoma occurs. The front part of the eye contains a clear fluid called aqueous humor, which is continuously produced by a structure called the ciliary body behind the iris. This fluid flows through the pupil, fills the anterior chamber (the space between the cornea and iris), and drains through the trabecular meshwork in the drainage angle where the iris meets the cornea.

In eyes predisposed to angle closure, the anterior chamber is naturally shallow—there is less space between the iris and cornea than usual. This anatomy creates a situation where the iris can easily contact and block the drainage angle. When the pupil dilates (in dim light, with certain medications, or due to emotional stress), the iris bunches up at its periphery and can suddenly occlude the drainage pathway.

Pupillary Block Mechanism

The most common trigger for acute glaucoma is called pupillary block. In this mechanism, the aqueous humor has difficulty passing through the pupil from behind the iris to in front of it. This creates a pressure difference that bows the iris forward, like a sail catching wind, pushing it against the drainage angle and sealing it shut.

Several situations can precipitate an acute attack in susceptible individuals:

• Dim lighting causes natural pupil dilation that can trigger angle closure
• Emotional stress or excitement activates the sympathetic nervous system, dilating pupils
• Medications that dilate pupils, including certain antihistamines, decongestants, antidepressants, and medications used during medical procedures
• Eye drops used during eye examinations that dilate the pupil can occasionally trigger attacks in predisposed individuals

Why Farsightedness Increases Risk

People with farsightedness (hyperopia) have shorter-than-average eyes. This means all the internal structures are proportionally smaller, including a shallower anterior chamber. The shortened distance between the iris and cornea makes angle closure much more likely. This is why farsighted individuals, particularly those over age 50, are at significantly elevated risk for acute glaucoma.

Who Is at Risk for Acute Glaucoma?

Risk factors for acute glaucoma include age over 50, farsightedness (hyperopia), being female, Asian ethnicity, family history of angle-closure glaucoma, and use of medications that dilate pupils. People with these risk factors should have regular eye examinations.

While acute glaucoma can theoretically occur in anyone, certain factors significantly increase the risk. Understanding these risk factors allows for appropriate screening and, in some cases, preventive treatment before an acute attack ever occurs.

Age is the most important risk factor. Acute glaucoma is rare before age 40 and becomes increasingly common after age 50. This is because the lens of the eye thickens with age, pushing the iris forward and making the anterior chamber progressively shallower. Most cases occur in people between 55 and 75 years old.

Sex also plays a role: women are two to four times more likely than men to develop acute glaucoma. This is largely because women tend to have smaller eyes with shallower anterior chambers. The hormonal changes of menopause may also contribute to changes in eye anatomy that increase risk.

Ethnic and Genetic Factors

Asian ethnicity confers significantly increased risk. Acute angle-closure glaucoma is considerably more common in East Asian and Southeast Asian populations than in people of European or African descent. This reflects anatomical differences in eye structure, with naturally shallower anterior chambers being more common in Asian populations.

Family history of angle-closure glaucoma increases risk, suggesting genetic factors that influence eye anatomy. First-degree relatives of someone who has had acute glaucoma should inform their eye care provider and consider screening examinations.

Medications That Can Trigger Attacks

Certain medications can precipitate acute glaucoma in susceptible individuals by causing pupil dilation:

• Antihistamines (commonly used for allergies and colds)
• Decongestants (including over-the-counter cold medications)
• Tricyclic antidepressants
• Some medications for urinary symptoms (anticholinergics)
• Topiramate (used for epilepsy and migraines, through a different mechanism)
• Pupil-dilating eye drops used during eye examinations

If you have risk factors for acute glaucoma, inform your healthcare providers before starting new medications or having procedures that involve pupil dilation. This does not necessarily mean avoiding these medications entirely, but allows for appropriate precautions and monitoring.

Can Acute Glaucoma Cause Permanent Damage?

Yes, acute glaucoma can cause permanent vision loss if not treated promptly. The elevated pressure damages the optic nerve, which cannot regenerate. However, with rapid treatment, most patients retain good vision. The prognosis depends primarily on how quickly treatment is initiated.

The potential for permanent damage is what makes acute glaucoma a true emergency. The optic nerve, which carries visual information from the eye to the brain, is exquisitely sensitive to pressure. When intraocular pressure rises dramatically, the nerve fibers in the optic nerve begin to die. Unlike many other body tissues, these nerve cells cannot regenerate or be replaced.

The amount of permanent damage depends on two main factors: how high the pressure rises and how long it remains elevated. Brief episodes of moderately elevated pressure may cause minimal lasting harm, while prolonged severe elevation can result in significant, irreversible vision loss. This is why the speed of treatment is so critical.

Prognosis with Treatment

The good news is that most patients who receive prompt treatment recover with good visual outcomes. Studies show that patients treated within the first six to twelve hours of symptom onset generally retain excellent vision. The key is recognizing the symptoms and seeking care immediately rather than waiting to see if things improve.

Even in cases where some permanent damage occurs, the affected individual often maintains functional vision. The visual field (peripheral vision) may be somewhat reduced, but central vision typically remains intact. Most patients treated for acute glaucoma continue to live normal lives with adequate vision.

If vision loss does occur from a delayed presentation, various adaptive strategies and visual aids can help. Low vision specialists can provide devices and training to maximize remaining vision. However, preventing damage through early treatment is always far preferable to managing the consequences of delay.

Prevention of Recurrence

After successful treatment with laser iridotomy, recurrent acute attacks are rare. The permanent opening in the iris prevents the pupillary block mechanism from occurring again. However, the underlying anatomy that predisposed to angle closure remains, so continued monitoring with regular eye examinations is important.

Can Acute Glaucoma Be Prevented?

In people at high risk, acute glaucoma can often be prevented with prophylactic laser iridotomy performed before an attack occurs. Regular eye examinations can identify those at risk. If you have risk factors, discuss preventive options with your eye care provider.

While it may not be possible to prevent the anatomical features that predispose someone to acute glaucoma, it is often possible to prevent the acute attack itself through prophylactic treatment. The same laser peripheral iridotomy used to treat acute glaucoma can be performed preventively in people identified as high-risk during routine eye examinations.

During a comprehensive eye examination, the eye care provider can identify narrow drainage angles that suggest elevated risk for angle closure. Specialized techniques including gonioscopy and anterior segment imaging can precisely measure angle width and identify those who would benefit from preventive treatment.

Who Should Consider Preventive Treatment

Prophylactic iridotomy is generally recommended for people who have:

• Extremely narrow or nearly closed drainage angles on examination
• Had an acute attack in one eye (the fellow eye should be treated)
• Signs of previous partial angle closure (peripheral anterior synechiae)
• Strong family history combined with narrow angles

The decision involves weighing the small risks of the laser procedure against the potential benefits of preventing an acute attack. For most people with clearly narrow angles, preventive iridotomy is a reasonable choice that provides lasting protection.