Definition of Refractive Conditions: These are a group of eye conditions in which the most optimally focused light rays fall short or pass the macula because the shape of the eye is too short or too long, or the shape of the cornea is asymmetrical.
Farsightedness is also called called hyperopia. This is a condition in which the length of the eye is too short, causing light rays to focus behind the retina rather than on it, resulting in blurred near vision. In some patients additional symptoms may be present, these include eyestrain, squinting and headaches.
Figure 1. The light rays pass the retina of the eye resulting in Farsightedness (hyperopia).
This condition is easily corrected with refrective lenses. More common in older individuals. The causes are unknown.
Nearsightedness: Also called myopia. This is a condition in which the length of the eye is too long, causing light rays to focus in front of the retina rather than on it, resulting in blurred distance vision. Patients may often complain of additional symptoms which include eyestrain, headaches, poor night vision and squinting. Note that there is blurred vision in both far and near sightedness.
Figure 2. The light rays do not reach the retina of the eye resulting in the condition known as shortsightedness (myopia).
This condition is easily corrected with refrective lenses. More common in school children.
Astigmatism: A very common condition in which the curvature of the cornea is asymmetrical (the eye is shaped like a football or egg instead of a baseball); light rays are focused at two points on the retina instead of just one. This results in blurred vision. In addition to blurred vision, patients may complain of distorted vision, eyestrain, and shadows on letters, squinting and double vision. Headaches are sometimes present.
Figure 3. The light rays do not focus on the retina of the eye resulting in astigmatism or blurred vision.
Presbyopia: Another common condition in which the aging eye is unable to focus on near objects. This condition is due to the natural hardening of the lens of the eye. It results in the lens not being able to focus the light on the macula. It typically begins around age 40.
All diagrams are from the illinoiseyecenter whose address is illinoiseyecenter.com
These notes are for educational and informational purposes. Only appropriately trained professionals can make a diagnosis.
