Blurry vision: the causes, when glasses are enough, and when to go to the emergency room right away

Blurry vision, when things look hazy and details lose their sharpness, usually has a simple cause: glasses that need updating, a dry eye surface, or fatigue after long reading or screen time. It comes on gradually or clears when you blink and rest, and an eye exam soon sorts it out. Sudden blurriness is different: the American Academy of Ophthalmology advises seeing an ophthalmologist immediately for any sudden blurriness, and the Saudi Ministry of Health lists difficulty seeing in one or both eyes among the signs that call for immediate emergency care. The practical rule: blur that is gradual or clears when you blink means an exam soon, while sudden blur, or blur with severe eye pain, a curtain over part of your vision, or weakness on one side of the body, means the emergency room the same day.

Blur that creeps in slowly: usually glasses, or a cataract

The World Health Organization says at least 2.2 billion people worldwide have a near or distance vision impairment, and for at least 1 billion of them it could have been prevented or has yet to be addressed. Among that billion, cataract causes distance vision impairment or blindness for about 94 million people and refractive error, meaning the eye needs glasses, for about 88.4 million, while presbyopia is behind near vision impairment for about 826 million. The Organization ranks glasses for refractive error and cataract surgery among the most cost-effective of all health-care interventions. The kind of gradual blur often points to its cause:

• Distant things blur, such as road signs or the screen in a classroom, while close things stay clear: usually nearsightedness.
• Trouble reading paper and your phone after 40, so you have to hold it farther away to see it: presbyopia, fixed with reading glasses or a multifocal lens.
• Blur at every distance with lights that look stretched at night: possibly astigmatism.
• Haziness that slowly gets worse, with glare from car headlights, faded or yellowish colors and a need for brighter light to read: these are cataract symptoms listed by the American Academy of Ophthalmology, which compares seeing with a cataract to looking through a foggy or dusty car windshield.

None of these is a reason to panic, but do not put off the exam. The Academy recommends that adults with no symptoms or risk factors get a baseline eye disease screening at age 40, and that anyone with symptoms or risk factors, at any age, see an ophthalmologist to decide how often they need to be examined.

Blur that clears when you blink or rest: dry eye and reading or screen fatigue

If your vision blurs at the end of the working day or after a stretch of reading, then clears when you blink or rest, the cause is usually the surface of the eye, not your prescription. The American Academy of Ophthalmology explains that tears spread over the eye with every blink and keep its surface smooth and clear, which is why they matter for good vision, and it lists blurred vision, especially when reading, as a symptom of dry eye, naming long screen time, reading and any activity that reduces blinking among its causes. Answering a question about blur that appears after 30 minutes of reading, one of its ophthalmologists notes that the pupils get smaller when we read, so poor lighting can make it hard to see; that a nearsighted person's focusing muscles may tire after a while; and that blinking slows while reading, so someone with dry eye may notice symptoms. What helps:

• Good lighting when you read, and good posture on a comfortable, well-designed chair.
• Do not sit with the air conditioner, fan or heater blowing straight at your face, advice worth taking seriously in homes and offices where the air conditioning runs most of the year.
• Artificial tears used regularly are a great help, as the Academy's ophthalmologist says; ask a pharmacist or doctor which type suits you.
• See a doctor if dry eye symptoms persist or get worse, affect your daily activities, are not relieved by over-the-counter lubricating drops, or come with significant redness, pain or a change in vision, as the Academy advises.
• If your vision blurs with both eyes open and clears when you close one, the problem may be in how the two eyes work together rather than in either eye alone, as one of the Academy's ophthalmologists explains, and it needs an ophthalmologist's assessment.

Blur that comes and goes: blood sugar and migraine

The American Academy of Ophthalmology says changes in blood sugar levels can affect your vision, which is why it advises people with diabetes to have their blood sugar under control for at least a week before an eyeglasses exam, because glasses prescribed when blood sugar is stable work best. But blurry vision in someone with diabetes can also be a sign of diabetic retinopathy, a disease that often has no symptoms in its early stages and, as it gets worse, shows up as blurry vision or vision that changes from blurry to clear. So the Academy advises people with diabetes to see their ophthalmologist regularly for dilated eye exams, since the exam may find the disease before you notice any change in your vision, and it says controlling blood sugar and blood pressure can stop vision loss.

As for migraine, the Academy explains that many people with migraine have visual symptoms before the pain, such as zigzag lines or shimmering, colored or flickering lights in one side of their vision, which can last up to 30 minutes and sometimes come without any headache. It adds that a temporary dimming or loss of vision during a migraine episode is rare, but if it happens, or your symptoms last longer than 60 minutes, see an ophthalmologist right away to rule out a transient ischemic attack (a mini-stroke), which can be serious.

When blurry vision is an emergency: one sign is enough

Sudden blur is not the same as gradual blur. The American Academy of Ophthalmology advises seeing an ophthalmologist immediately for any sudden blurriness, and says sudden loss of vision should be checked right away: even if your vision darkens for a few seconds and then comes back, you may need to go to the emergency room or get an urgent appointment with your ophthalmologist. Go to the emergency room or call an ambulance right away if any one of these signs appears; they do not have to come together:

• Sudden blur with severe pain in the eye or forehead, a red eye, nausea or vomiting, or rainbow-colored halos around lights: the Academy lists these as signs of an angle-closure glaucoma attack, and calls the attack a true eye emergency that can cause blindness if not treated right away. Even the milder early symptoms that can come before an attack, such as blur with a mild headache or slight eye pain, call for a check by an ophthalmologist as soon as possible, according to the Academy.
• Sudden flashes of light, new spots or lines floating across your vision, or a dark shadow or grey curtain covering part of your vision: the Ministry of Health lists these as symptoms of retinal detachment and treats it as an emergency that means going to an eye doctor or the emergency room immediately, because delayed treatment can let more of the retina detach and raises the risk of permanent vision loss.
• Sudden difficulty seeing in one or both eyes, numbness or weakness of the face, arm or leg especially on one side of the body, difficulty speaking or understanding, dizziness and loss of balance, or a sudden severe headache: the Ministry of Health lists these as signs of a transient ischemic attack, which can come before a stroke, and says emergency care should be sought immediately. Even if the symptoms pass within minutes, the Ministry calls a transient attack a serious warning sign that should not be ignored.

Do not drive yourself if your vision suddenly blurs; ask someone to take you or call an ambulance, and do not wait until morning to see whether your vision improves.

Before your appointment: what to notice to help the doctor

When the blur is not an emergency, a few simple notes help the doctor reach the cause faster. Write them down before your appointment:

• Is the blur in one eye or both? Cover each eye with your palm in turn and compare.
• Is it at a distance, up close, or both?
• Did it start suddenly or gradually? Is it constant or does it come and go, and when is it worse: late in the day, after screen time, or at night?
• Does it improve when you blink, with lubricating drops, or when you close one eye?
• Which medicines do you take, and do you have diabetes or high blood pressure? Bring your current glasses and your latest prescription if you have one.