Eye Conditions

20/20.
Normal visual acuity. 		 Upper number indicates standardized symbols on a chart 20 ft. away. The lower number indicates that the same symbols can be seen at 20 ft. by an eye with a normal optical system. The higher the bottom number correlates to worsened vision.
Astigmatism Visual deficiency in which refractive power is not uniform in all directions. Light rays entering the eye are bent unequally by different meridians. This prevents formation of a sharp image focus on the retina. Picture a football's shape. It is a lot longer from the tip of the ball to the center than from the side to the center,
Color blindness

The reduced ability to discriminate between colors, especially shades of red and green.

 
Binocular vision. The separate images seen by each eye are blending into one composite image.
Convergence Inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision as an object approaches.
Diplopia Double vision. Seeing two images from one object; images may be horizontal, vertical or diagonal.
Emmetropia Having no refractive error when accommodation is at rest. Images of distant objects are sharply focused on the retina without the need for corrective lenses.
Esotropia Eye misalignment (cross-eyes) in which one eye crosses inward (toward nose) while the other fixates normally.
Hyperopia (farsightedness) Blurring vision is due to the focusing of light rays of distant object past the point that they strike the retina . Farsighted people must expend a lot of focusing effort to see clearly in the distance. Close-up vision is blurred because it takes excess focusing effort (accommodation). Corrected by increased accommodation or by a plus lens (spectacle or contact) .
Lazy eye, or  Amblyopia The loss or lack of development of central vision in one eye that is unrelated to any eye health problem and is not correctable with lenses. It can result from a failure to use both eyes together. Lazy eye is often associated with crossed-eyes or a large difference in the degree of nearsightedness or farsightedness between the two eyes. It usually develops before age six and it does not affect side vision.

Symptoms may include noticeably favoring one eye or a tendency to bump into objects on one side. Symptoms are not always obvious.

Treatment for lazy eye may include a combination of prescription lenses, prisms and vision therapy. Vision therapy teaches the two eyes how to work together, which helps prevent lazy eye from reoccurring.

Early diagnosis increases the chance for a complete recovery. This is one reason why the American Optometric Association recommends that children have a comprehensive optometric examination by the age of six months and again at age three. Lazy eye will not go away on its own. If not diagnosed until the pre-teen, teen or adult years, treatment takes longer and is often less effective.
Myopia (nearsightedness) Focusing defect in which the eye is overpowered (long eye ball). Light rays coming from a distant object are brought to focus before reaching the retina. Requires a minus lens correction for clear distance vision.
Plus Lens. Lens that is thicker in the center than at the edges (convex), adding optical power to focus incoming light rays on the retina. It is used to corrects farsightedness.
Presbyopia Refractive condition in which there is a reduced power of accommodation arising from loss of elasticity of the crystalline lens, as occurs with aging. Usually affects persons age 40 and over.
Strabismus,
or Crossed−eyes		 One or both of the eyes turns in, out, up or down. Poor eye muscle control usually causes crossed-eyes. This misalignment often first appears before age 21 months but may develop as late as age six. This is one reason why the American Optometric Association recommends a comprehensive optometric examination before six months and again at age three.

There is a common misconception that a child will outgrow crossed-eyes. This is not true. In fact, the condition may get worse without treatment.

Treatment for crossed-eyes may include single vision or bifocal eyeglasses, prisms, vision therapy, and in some cases, surgery. Vision therapy helps align your eyes and solves the underlying cause of crossed-eyes by teaching
 your two eyes to work together. Surgery alone may straighten your eyes, but unless your eye muscle control is improved, your eyes may not remain straight.

If detected and treated early, crossed-eyes can often be corrected with excellent results.
Snellen chart. Test chart used to assess visual acuity. 
Contains rows of letters, numbers, or symbols in standardized sizes, with a designated test distance of 20 ft at which distance each row should be legible to a normal eye.