Eye Health Central

What Causes Blurred Vision?

What Causes Blurry Vision?

Hazy, unfocused vision can be caused by a litany of different diseases or conditions. People with blurry vision often have to squint in order to see clearly, and even then it may only make their sight slightly better than it is without squinting. In many cases corrective lenses are needed to fully correct blurry vision, such as contacts or eye glasses.What Causes Blurry Vision?Other times, the cause of the blur may not be refractory in nature, and might require medicine or surgery, or may not be correctable at all. No matter the cause of blurry vision, it may not affect both eyes equally, with one eye being more in focus than the other. In fact, each eye may experience blurred vision for two totally different reasons, and may need to be corrected with different methods.

Refractive Errors

For a large majority of people with blurry vision, the issue is a refractive error, meaning that the lenses in the front of the eye aren't accurately focusing light on the retina in the back of the eye. This is similar to holding a magnifying glass too close or too far away from an object or text. Finding the sweet spot brings everything into focus, which is what happens during squinting. The muscles around the eye squeeze and reshape the eye to bring the lens closer to or farther from the retina. A routine eye exam is the best way of diagnosing these types of vision problems.

There are several different kinds of refractive errors, each with similar but distinct symptoms, as well as their own means of correction.

  • Myopia – Commonly called nearsightedness, and occurs when light is focused in front of the retina. With this condition, things near by appear clear and in focus, but become increasingly blurry as distance between the object and the eye increases. Corrective lenses can be used to refract light and move its focal point backwards, placing it directly on the retina.
  • Hyperopia – Also known as farsightedness, which is just the opposite of nearsightedness. Vision becomes blurry the closer an object gets to the eyes, as the light's focal point is behind the retina. This is less common, but just as easily solved with corrective lenses.
  • Astigmatism – This issue can be had in conjunction with myopia and hyperopia. It is a condition in which the eye is shaped irregularly, similar to an egg, rather than a sphere. By itself it can cause mild double vision, but this may be hard to notice along side other refractive errors. This can also be corrected with contact or glasses, but they need to be specially designed to treat astigmatism, as regular lenses won't do.
  • Presbyopia – A condition that affects many people as they age, usually starting in the 40s or 50s. Like astigmatism, this can occur on its own or along side other vision problems. However, unlike the issues listed above, this is not caused by an irregular shape of the eye or its lens, but by the weakening of the muscles around the eye that are responsible for focusing light. Simple reading glasses can correct the issue, but when other refractory problems exists simultaneously, multifocal lenses may be needed to correct them all at once.

Temporary Causes

Other causes of blurry vision may not be as chronic as refractory errors, and may only last several months, weeks, days, or even moments. Corrective lenses aren't effective as treatment, however that doesn't mean that no treatment is available. Below are some of the varied non-refractive error causes of blurred vision, and the best way of addressing them.

  • Dry Eyes – Some people suffer chronically from dry eyes, others only experience it for brief periods. In either scenario, the eyes aren't well lubricated, which can lead to irritation and discomfort, as well as blurred vision. If the surface of the cornea becomes too dry, it may not allow light to pass through cleanly, and might cause a blurring effect. Simple wetting eye drops are usually enough to solve this issue.

  • Pregnancy – There are many changes that happen throughout the body during pregnancy, and a change in visual acuity is only one of them, as is double vision. They are both causes by shifts in hormone levels, which then affect the shape of the cornea. While they aren't usually anything to worry about, it's important to bring changes in visual acuity to your doctors attention, as there is a small change they could be signs of gestational diabetes or high blood pressure.

  • Headaches – Even brief headaches or migraines can affect the muscles that focus the eyes, as well as cause serious and debilitating sensitivity to light. They usually don't last very long, but if they persist or happen frequently, you should see a doctor.

  • Floaters – Caused by microscopic bits of tissue or microbes moving within the gel-like fluid within the eye, floaters momentarily block light from passing through the eye, and cast a very tiny shadow on the retina. They typically only last a few seconds at a time, and can be moved by quickly looking right and left, or up and down. If they begin to happen frequently, or in abundance, they may be early signs of a detached retina, which requires immediate medical treatment to avoid blindness.

  • Medications – Some pills and medicated eye drops can affect the vision, either by weakening the muscles that focus the eye, or by depositing chemicals or substances on the surface of the cornea. This can sometimes be treated with eye drops, but consult with your doctor first to make sure they won't interfere with the medication.

  • Laser Eye Surgery – You may experience blurred vision immediately following any type of eye surgery as the eye begins to heal. This is common and nothing to worry about unless it persists for more than a few days. Consults with your eye doctor if you still have blurred vision longer than that.

  • Allergies – Seasonal or environmental allergies can affect the eyes, making them feel itchy, watery, and appear red. Taking allergy medications can be helpful, or simply removing the allergen from the environment. For pollen that may be difficult to achieve, but allergies to food, animals, or hygiene products are far more manageable.

  • Foreign Objects – Simply getting a bit of dust, dirt, or sand in your eye can cause not just blurred vision, but serious discomfort as well. Never rub your eye if it feels like there's something in it, as they may press it into the surface and cause serious scratching, as well as infection. Attempt to flush it out with eye wash, or clean water if none is available. If the feeling persists, seek medical attention quickly.

  • Contact Lenses – Under normal circumstances, contact lenses should only make vision clearer, not blurry. However if they aren't seated properly, haven't been cleaned well, or have been worn for too long, they may indeed make it more difficult to see. Either washing the lenses with cleaning solution, or changing them out for new ones should solve the problem, as well as giving your eyes a rest for several hours.

A Symptom Of A More Serious Issue

In rare cases blurry vision may be a symptom of a more serious underlying condition. If you are experiencing any of the symptoms below, you should make an appointment with your doctor quickly, as some of these problems can be very serious, and potentially lead to either blindness, or even death.

  • Cataracts – If blurred vision begins to appear cloudy, along with glare or night halos, then you may be developing cataracts. They can be treated, usually with artificial lenses, but can severely limit vision if left unchecked. Cataracts are very common in senior citizens, but can occur as early as birth.

  • Glaucoma – Blurry tunnel vision may indicate the onset of glaucoma. These symptoms may develop slowly over time, or may occur suddenly. Without treatment, glaucoma will only continue to worsen until all vision is lost, but can be alleviated with proper medical treatment.

  • Macular Degeneration – One of the most common causes of blindness in senior citizens around the world, this condition causes not only blurred vision, but distortion of lines and images, and primarily affects the center of the field of view, spreading outward over time.

  • Diabetic Retinopathy – Diabetes can lead to many other problems and conditions, one of which affects the eyes. Any diabetics that begin to have blurred vision should see a doctor immediately in order to avoid complete and total blindness.

  • Systemic Issues – Strokes, heart disease, brain hemorrhages, and even multiple sclerosis all share a common symptom, which is blurred vision. While each of these has many other symptoms that appear along side diminished visual acuity, it's important to seek emergency medical attention should any of them arise. These can be life threatening conditions, where just minutes can make the difference between life and death.

Author: John Dreyer Optometrist Bsc(Hons), MCOPTOM, DipCLP
Created: 3 Jul 2016, Last modified: 11 Sep 2020