COMMON REFRACTIVE REASONS FOR BLURRED VISION
Normal Eye
"Doc, I see great, I only came for the free candy out front..."In the normal eye, incoming light is focused by the cornea (front layer) and then again by the lens (inside the eye) which brings it to a sharp focus on the retina (back of the eye). In the normal eye then, objects will be in focus and the brain will get a clear image. In some cases this does not occur as in the examples below. A refraction is the portion of the eye examination that determines the following most common reasons for blurred vision. The conditions described below are referred to as Refractive Errors and include Myopia, Hyperopia and Astigmatism.
Myopia
"Doc, My distance is blurry..."Generally in myopia (nearsighted) the distance vision is blurred but the close vision is still good. However, in very high degrees of myopia even the average near vision can be blurred. Myopia is caused by the front of the eye (cornea) having too much curvature or the eye being too long or a combination of the two. A small percentage of people have myopia caused by a spasm of the eyes focusing system. The unit value used to measure the degree of myopia is called Diopters which relates to the power of the spectacle lenses used to correct it. For comparison purposes the average myopic person in the USA is approximately -3.00 diopters (minus refers to myopia). The higher this negative number the higher the degree of myopia. There are many treatment options for myopia including spectacles, contact lenses and surgical procedures.
Hyperopia
"Doc, Reading books makes my eyes get tired..."Generally in hyperopia (farsighted) the near vision is blurred but the distance vision is still good. However, in very high degrees of hyperopia even the distance vision can be blurred. Hyperopia can be a common reason that a young child's eye crosses inward when not wearing their glasses. Hyperopia is caused by the front of the eye (cornea) having too little curvature or the eye being too short or a combination of the two. The treatment options for hyperopia include spectacles and contact lenses. The unit value to describe the degree of Hyperopia is called Diopters and is noted as positive (plus) value. There are many treatment options for hyperopia including spectacles, contact lenses and surgical procedures.
Astigmatism
"Doc, Everything is kinda fuzzy ..."Typically both the distance and the near vision is blurred with astigmatism. The front of the eye (cornea) has basically two different curvatures and in essence is warped. In some cases astimatism can be caused by the lens inside the eye having two different curvatures. Any incoming light will not be clearly focused and thus the blured vision. The treatment options for astigmatism include spectacles, contact lenses (usually a toric lens or rigid gas permeable, or bitoric lens) and surgical procedures.
Presbyopia
"Doc, I have to hold my books further back now and never had to when I was younger..."Almost all of us will notice a decrease in our reading (near) vision over time. This is a very normal condition called presbyopia which affects the lens inside the eye losing flexibility. Presbyopia is technically not a refractive error but is included here simply as another common reason for blurred vision. Please refer to the section entitled Presbyopia for a more detailed explanation and treatment options which include spectacles, contact lenses and surgical treatments.
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Dr. Daniel L. Mason, Optometrist
(619)656-1081