If you’re like me, the world is quite blurry before putting on a pair of glasses or contact lenses in the morning. Why is this?
In a perfect world, all of us would have eyes shaped nearly like perfect spheres. When looking at an object, the light it gives off would hit the front of our eyes and be focused perfectly to a single spot on each retina. This would give us a sharp image with good depth perception as our two eyes work together.
In the real world, not all of us have perfectly shaped eyes! When our eyes can’t provide us with crystal clear vision without glasses or contacts, the term we use is “refractive error.” Refractive error can also be treated with LASIK or other forms of laser vision correction.
Myopia
The most common type of refractive error is “myopia,” or near-sightedness. You probably have myopia if you can see up close but struggle to see across the room without glasses.
Myopia usually occurs for a couple of reasons:
- If the eye is longer than “normal,” the focusing parts of the eye will create an image in front of the retina. This usually results as the eye grows from its child to adult size. Sometimes, it is hereditary.
- High myopes beware! If the eye gets too long, the risk of retinal tears or detachments increases significantly. This occurs because the retina is stretched along the entire contour of a long, myopic eye. Generally, I advise patients with a glasses prescription of -6.00 or stronger to avoid contact sports and be cautious of new symptoms including floaters, flashes of light, or a shade in the vision.
- If the eye’s focusing parts are stronger than usual, this will also lead images to be created in front of the retina. This might happen in the following examples:
- advancing cataract
- swings in the blood sugar related to diabetes
- pregnancy
Usually, myopia is corrected simply with a pair of minus-powered glasses or contact lenses that move the image backwards onto the retina. Myopia tends to be a benign condition that is easily treated.
Hyperopia
Hyperopia refers to another common condition where a person’s eyes see well for distance but struggle to focus on objects that are near. The common term for this is “far-sightedness.”
Usually, hyperopia occurs when the eye is shorter or smaller than “normal.” This causes the focusing parts of the eye to place an image behind the retina. We generally treat this with plus-powered glasses or contact lenses that move the image forward.
You may recall that plus-powered glasses are often sold at the drug store in the form of OTC readers. Some hyperopes are lucky – if your prescription is mild and similar between the two eyes, some people can use OTC readers to improve their distance vision instead of prescription glasses. In the long run, this can save a lot of money!
High hyperopes beware! As the eye gets smaller and shorter, its different anatomical structures must fit into a tighter space. This means that far-sighted patients may be at higher risk of an eye emergency called acute angle closure. In this condition, the eye’s own structures may block the “filters” that typically allow fluid to exit the eye. As a result, the pressure inside the eye may rise significantly – even to double or triple what is normal. The symptoms of acute angle closure include severe eye pain, decreased vision, redness, haziness of the front part of the eye, and change in the size of the pupil. If you suspect this condition, visit your ophthalmologist or local emergency room immediately!
Astigmatism
The final common cause of refractive error is astigmatism. This is often combined with myopia or hyperopia. Astigmatism causes multiple images to be formed on or around the retina. As you might have guessed, this can cause vision to be blurry at both distance and near.
Astigmatism occurs when the eye’s contour is curved more in one direction than the other. A common way to think about astigmatism is to consider the difference between a basketball and a football:
- A basketball is a perfect sphere. Therefore, it is equally curved in all directions.
- A football, on the other hand, is more curved in one direction than the other.
When a person has astigmatism, the eyes are generally shaped more like footballs than basketballs. This causes the uncorrected vision to be blurred.
Fortunately, simple astigmatism is also usually easy to correct with glasses or contact lenses. When contact lenses are prescribed to correct astigmatism, the word we use is “toric.” There are even toric intraocular lenses that can be used to correct astigmatism during cataract surgery!
Sometimes, astigmatism is not so simple. This can occur after eye injuries or because of other medical conditions. Your ophthalmologist can help explain your options if this pertains to you.