What is a Refractive Error?
The ability to focus comes from the cornea and the lens of the eye. Refractive errors are vision problems that occur when the shape of the eye prevents you from focusing well. Causes of Refractive Errors could be due ot the length of the eye being too short or too long, aging of the natural lens, or the changing in the shape or condition of the cornea.
Four common refractive errors are:
Myopia, also known as nearsightedness, is when light rays entering the eye come to their focus point in front of the retina. The anatomy of the eye is usually responsible with either the cornea being very steep or the eye being much longer than average. Myopia tends to be hereditary and eyes may continue to lengthen with age. However, most myopia will stabilize before 30 years of age. Also, if the lens thickens with aging, older patients can notice their vision changing with distances becoming more blurred and natural near vision improving. This condition also known as “second sight” is a precursor to cataract development.
Hyperopia, also known as farsightedness, is when light rays entering the eye come to their focus point behind the retina. The anatomy of the eye is usually responsible with either the cornea being very flat or the eye being much shorter than average. Objects in close proximity will appear blurred as well as those at a distance. Hyperopia is also hereditary and is common in babies and children. As the eye grows, the degree of hyperopia lessens.
Presbyopia is the natural loss of accommodation with aging. Accommodation is the ability of a perfectly focused young eye to have range with vision from distance to near. For example, if you can read a road sign you can also read the road map. As the lens of the eye ages it also hardens and is no longer able to flex and bend. When the lens becomes sufficiently hard, near focus is lost and reading glasses are required. The average age presbyopia begins to occur is 40 years.
Astigmatism is a visual distortion created by an oval shaped cornea or lens. Light rays entering the eye are split and come to focus at two different distinct points creating visual distortion for both distance and near vision. Like myopia and hyperopia, astigmatism is also hereditary.