What is the difference between myopia (near-sightedness), hyperopia (far-sightedness), and astigmatism?
This is a common question asked at Eye Specialists of Santa Barbara. All three conditions are influenced by the eye’s cornea which passively bends (or refracts) light. The cornea is the eye’s transparent outer covering that also shields inner layers from germs, foreign objects, and UV light.
When light enters the eye, it is refracted by the cornea and the lens in order to converge on a single focal point: the fovea. This is a small area on the back of the eye that has a high concentration of photoreceptors. When all light lands directly on the fovea, our vision is clear. When a patient has near-sightedness, far-sightedness, or an astigmatism, light is incorrectly refracted and therefore will not perfectly converge onto the fovea. These three conditions are known as refractive errors.
Near-sightedness, or myopia, is a condition where light refracts through the cornea and lens, but converges in front of the fovea. This generally occurs because the eye is too long or the cornea is more curved. This causes distance vision to seem blurred. Myopia can be corrected by divergent lenses which cause the light to converge deeper within the eye. Alternately, refractive surgery can be used to reshape the cornea or implant a lens within the eye’s posterior capsule to correct myopia.
Far-sightedness, or hyperopia, is the opposite of myopia. Light that refracts through the cornea and lens converges at a point behind the fovea. This often occurs because the eye is too short or the cornea is flatter. This leads to blurred near and sometimes intermediate vision. Hyperopia is corrected by convergent lenses or refractive surgery which allow light to land specifically on the fovea.
Astigmatism is a condition where the cornea is not oval-shaped. Often it is more shaped like a football. This irregular shape causes different light rays to land on different parts of the eye. Some rays may land on the fovea, but others may land in front, behind, or around the fovea. This often leads to blurred vision in near, intermediate, and distance vision. Astigmatism is corrected by custom lenses or refractive surgery.
At Eye Specialists of Santa Barbara, during consultations and follow-up appointments, Dr. Jacobson assesses each patient’s vision. When a patient has a refractive error and is dissatisfied with their vision, Dr. Jacobson can prescribe lenses or perform refractive surgeries including Visian ICL and Clear Lens Exchange to correct these errors. If you are dissatisfied with your vision and have not had a recent comprehensive ophthalmic examination, we will be glad to evaluate you and discuss your vision correction options.