To see clearly, the cornea and the lens of the eye must bend (refract) light rays so they focus on the retina. The retina, a layer of light-sensing cells that line the back of the eye, converts the light rays into impulses that are sent to the brain where they are recognized as images. If the light rays don’t focus on the retina, the image you see will be blurry. This is called a refractive error. Glasses, contact lenses and refractive surgery such as LASIK try to reduce these errors by making light rays focus on the retina.
Any part of the eye that is not perfectly shaped, such as the cornea, lens or eyeball, can cause refractive errors and make your vision blurry. The result is a difference between the curvature of the cornea and the length of an eye. This may occur in only one eye, while the other eye might have near-perfect vision, or it can happen in both eyes in different manners. The basic types of refractive errors are:
Myopia is another word for nearsightedness and affects the ability to clearly see objects far away. Individuals with myopia have abnormally long eyeballs which cause light entering the eye to focus in front of the retina instead of on its surface. Because of this abnormality, objects up close may appear clearly and in fine detail, but distant objects may appear to be blurry or distorted. This makes tasks such as driving and reading signs difficult. Other symptoms can include squinting, eyestrain, headaches and fatigue when driving or playing sports.
Hyperopia is another word for farsightedness, this condition is where distant objects may appear clear, but objects that are nearby look blurry or distorted. Hyperopia occurs when the eyeball is shorter than normal and light entering the eye is focused behind the retina.
Astigmatism is typically caused by an irregularly shaped cornea and causes blurred vision, regardless of distance. A healthy cornea is symmetrical and round (think of a basketball) but a cornea with astigmatism has an oblong shape (like a football). The abnormal shape causes light to focus on the retina in multiple points instead of a single focus. Astigmatism can occur alone or in combination with myopia and hyperopia.
Presbyopia is a condition that typically develops between ages 40 and 50 and makes it more difficult to see very close. It can be corrected with bifocals or reading glasses, but usually can’t be corrected by LASIK or some other refractive surgery.
If you are experiencing blurry vision, please contact Harvard Eye Associates to schedule an appointment with one of our doctors. We can help diagnose your refractive error and explore treatment options.