Glaucoma: Why Can Vision Be Lost Before You Notice Anything?

Glaucoma is a group of eye conditions that damage the optic nerve, the cable that carries images from the eye to the brain. In its common form, glaucoma can cause no pain and no early change in sharp central vision, so side vision may shrink slowly before you notice. Sudden eye pain with nausea, a red eye and halos around lights is an emergency. This article covers types, risk factors, eye exams, treatment and warning signs.

What is glaucoma and why can it go unnoticed?

MedlinePlus (NIH) describes glaucoma as a group of diseases that damage the optic nerve, and it notes that vision loss can occur without early symptoms in many people. You can read its overview in MedlinePlus: Glaucoma.

Several features of how we see help explain why it goes unnoticed:

• Damage often starts at the edges. In many people with open-angle glaucoma, peripheral (side) vision is affected first, while central vision stays sharp for a long time.
• Your two eyes cover for each other. If one eye has a blind patch, the other eye can fill in much of the gap.
• Your brain fills in gaps. The brain can smooth over small missing areas in the visual field, so a patch may not feel like a hole.
• There is usually no pain. Pressure inside the eye can rise slowly without any sensation.

Lost nerve fibers generally do not grow back. That is why treatment focuses on protecting the vision you still have, and why eye exams matter even when everything looks fine to you.

What is happening inside the eye

The front of the eye is filled with a clear fluid called aqueous humor. It is made continuously and drains out through a mesh-like channel near the edge of the iris. When drainage is reduced, pressure inside the eye (intraocular pressure) can rise. Higher pressure is one important factor that can injure the optic nerve.

The picture is more complicated than pressure alone. Some people develop glaucoma damage with pressure in the statistically typical range, and some people have higher-than-typical pressure without nerve damage. Blood flow to the nerve, the structure of the nerve head and genetics may all contribute, and the mechanism is not fully understood. A review of the condition, The glaucomas - a review, discusses these overlapping factors.

Types of glaucoma

Primary open-angle glaucoma

This is a common form. The drainage angle looks open, but fluid drains too slowly. It usually progresses gradually and painlessly, which is why it can go unnoticed for years.

Angle-closure glaucoma

In angle-closure glaucoma, the iris can block the drainage angle. This may happen slowly, with few symptoms, or suddenly. A sudden (acute) attack can cause severe eye pain, headache, nausea or vomiting, blurred vision, halos around lights and a red eye. This is an emergency because a sudden pressure rise can damage the optic nerve.

Normal-tension glaucoma

Here the optic nerve is damaged although measured eye pressure falls in the typical range. Eye doctors look closely at the nerve and the visual field to make this diagnosis.

Secondary glaucoma

Another condition or exposure can cause pressure to rise. Examples include eye injury, inflammation inside the eye (uveitis), abnormal blood vessel growth related to diabetic eye disease, and long-term use of corticosteroids in some people. See MedlinePlus: Diabetic Eye Problems for how diabetes can affect the eye.

Congenital and childhood glaucoma

Some babies are born with drainage structures that did not develop normally. Signs in an infant can include cloudy or enlarged-looking eyes, excessive tearing and light sensitivity. These need prompt evaluation by an eye specialist.

Who may be at higher risk

Risk factors are associations, not predictions. Many people with risk factors never develop glaucoma, and some people with none do. Factors that MedlinePlus (NIH) and other eye organizations commonly list include:

• Older age
• A parent or sibling with glaucoma
• Higher eye pressure
• African, Hispanic/Latino or Asian ancestry, with different glaucoma types being more common in different groups
• Thin corneas and significant nearsightedness or farsightedness
• Past eye injury or eye surgery
• Long-term corticosteroid use, including eye drops, pills and inhalers in some cases
• Diabetes and high blood pressure, which have been linked to glaucoma risk in some studies

If you have diabetes or high blood pressure, our pages on Type 2 diabetes and hypertension cover those conditions in detail. Tell your clinician about any steroid medicine you take so they can decide whether eye monitoring is appropriate.

What a glaucoma eye exam includes

No single test settles the question. Eye doctors combine your history, examination and several tests:

• Tonometry measures eye pressure.
• Dilated eye exam lets the doctor look at the optic nerve for changes in its shape or color.
• Visual field testing maps your side vision and can detect blind spots you have not noticed.
• Gonioscopy checks whether the drainage angle is open or narrow.
• Pachymetry measures corneal thickness, which can affect how pressure readings are interpreted.
• Optical coherence tomography (OCT) creates cross-section images of the nerve fiber layer and may detect thinning.

Eye doctors often repeat these tests over time, because changes between visits can be more informative than a single result. Ask your eye doctor how often you should be examined based on your own risk factors, since no single schedule fits everyone. General guidance on exams is at MedlinePlus: Eye Care.

Treatment options

Treatment aims to lower eye pressure to a level that helps protect the optic nerve. It can slow progression, and outcomes vary from person to person. It generally cannot restore vision that has already been lost.

Prescription eye drops

Drops are often the first step. Several classes exist, including prostaglandin analogs, beta blockers, alpha agonists and carbonic anhydrase inhibitors. Each has label cautions.

Beta-blocker drops need particular care. Timolol and other beta-blocker eye drops are absorbed into the bloodstream through the eye and nose, and they can cause breathing and heart-rate problems in some people. Product labeling for timolol eye drops lists contraindications that include bronchial asthma, severe COPD (chronic obstructive pulmonary disease), a slow heart rate and second- or third-degree heart block (a disorder of the heart's electrical signals). Your eye doctor will decide whether another drop class is safer for you. Tell every prescriber and pharmacist you see that you use these drops, and report any history of lung or heart rhythm problems to your eye doctor before starting them. Severe wheezing, trouble breathing, chest pain or fainting after using any glaucoma drop needs emergency care; do not use another dose until you have spoken to a clinician.

Check the product label and ask your eye doctor or pharmacist before changing how you use any drop. If drops sting, cause mild redness or are hard to use, tell your clinician so they can consider options rather than stopping on your own.

Laser treatment

Laser procedures can improve fluid drainage or, in some cases, reduce fluid production. Laser trabeculoplasty targets the drainage channel and is sometimes used early. Cyclophotocoagulation, which reduces fluid production, is generally considered when other treatments have not controlled pressure sufficiently. Your eye doctor can explain which option fits your type of glaucoma.

Surgery

Surgical options create a new drainage path or place a small drainage device. Combined glaucoma and cataract surgery is one option your surgeon may discuss. If you also have clouded lenses, see our article on cataracts and when surgery is considered.

Treatment for angle-closure

A narrow angle may be treated with a laser peripheral iridotomy, which makes a small opening in the iris to improve fluid flow. An acute attack is treated urgently in an emergency setting.

Living with glaucoma

• Keep follow-up visits, since visual field and nerve changes are tracked over time.
• Use prescribed drops as directed, and ask your eye doctor about a routine that fits your day if you often forget doses.
• Tell every clinician and pharmacist that you have glaucoma. Some medicines, including certain decongestants and anticholinergic drugs, carry label cautions for people with narrow angles. Ask your pharmacist before starting a new one.
• If you notice trouble with night driving, bumping into objects on one side or missing steps, mention it to your eye doctor.
• Cost can be a barrier to care. A review of the economic burden of glaucoma on patients describes how expenses may affect treatment, and your eye clinic or pharmacist may know of assistance options.

Some people ask about cannabis for glaucoma. MedlinePlus has general information on cannabis, and discuss any such use with your eye doctor, since it is not a substitute for prescribed treatment.

How glaucoma differs from other causes of vision change

Cataracts cloud the lens and tend to blur or dim vision gradually. Retinal conditions and optic nerve disorders have their own patterns; see MedlinePlus: Retinal Disorders and Optic Nerve Disorders. Our page on blurry vision that comes and goes covers that symptom. Because glaucoma can occur with few symptoms, a pair of glasses that seems to work well does not rule it out, and only an eye exam can sort these causes apart.

When to Seek Medical Care