Astigmatism
An imperfection in the cornea preventing light rays from an object from focusing on a single point. The cornea is shaped more like the side of a football rather than a basketball. Depending on the amount of astigmatism, a person may or may not experience vision difficulties. Usually, astigmatisms are easily corrected with minor spectacles or contact lenses.
Cataract
An opacity in the crystalline lens of the eye. There may be small or large regions of cloudiness that may cause some vision impairment.
Glaucoma
An ocular disease where normal fluid drainage is blocked or the eye produces more fluid than usual. As a result the added pressure causes damage to the optic nerve head, leading to loss of vision.
Hyperopia
Commonly referred to as farsightedness, this is a refractive error where light rays are focused behind the retina when the eye is relaxed. As a result, images are out of focus and most hyperopic patients see better at far distances than near. Fatigue and discomfort are common complaints because of the effort required to bring images into focus. This problem can be rectified with corrective lenses.
Myopia
Known as nearsightedness, it also occurs because of a refractive anomaly, but light rays are focused in front of the retina not behind as in farsightedness. Images are again out of focus, but objects closer to the patient may be in focus and clear. Corrective lenses will properly focus unclear images.
Phoria
A binocular vision problem. This is a tendency for one eye to move horizontally or vertically away from the point of focus. Phoria can cause discomfort and headaches associated with the use of the eyes at distances, close up, or both. Some patients with phorias will see double when they get tired. Phoria can be detected with a cover test.
Presbyopia
Vision condition that is related to aging. The crystalline lens of the eye loses its flexibility and as a consequence the ability to focus on images at a normal reading distance. The tendency to hold reading materials farther away, blurred near objects, and discomfort with reading are indicators. Corrective lenses are usually prescribed to compensate for the difficulty with near vision (bifocals, trifocals, or progressive addition lenses).
O.D.
Oculus dexter, this is the medical term for the right eye.
O.S.
Oculus sinister, this is the medical term for the left eye.
Strabismus or tropia
This is when only one eye fixates on an object and the other eye does not. Typical examples are “cross-eyed” or “wall-eyed” individuals. Usually with a strabismus, the image from the other eye is suppressed. If the turning of the eye is due to a recent cause, the patient may see double. A strabismic patient loses stereopsis and thus some depth perception.