Over ten million people in the United States have some form of vision problem, from simple nearsightedness to legal blindness. The majority of people will have vision problems in their lifetime, whether they were born with poor sight or it was a gradual progression with age. It’s not surprising; for such a small organ, the eye has many parts and a large responsibility, allowing for many areas in which something could go wrong. Consider how often cameras break or need to be replaced; eye health is critical in this regard as the possibility for error is so high and even the smallest problems can have a huge impact on eyesight.Most people don’t have critical vision impairment, although there are roughly 1.3 million Americans who are considered legally blind. Some of the most common vision problems are caused by refractive errors within the eye and include amblyopia, myopia, hyperopia, presbyopia, and astigmatism.
20/20 vision is considered normal human vision. In essence, this means that our eyes can see an object twenty feet away as if the object truly is twenty feet away. If someone has 20/30 vision, they can see objects twenty feet away as though they are thirty feet away, meaning their vision is weaker than the average human. 20/10 vision, on the other hand, indicates that an individual can see something twenty feet away as though it is only ten feet away, designating above average vision. Most people who have vision significantly worse than 20/20 wear glasses or corrective lenses.
20/20 vision does not indicate perfect vision, however. Things like depth perception, peripheral vision, and the ability to differentiate colors all are included in what is considered perfect vision.
Myopia is better known as nearsightedness and affects over twenty-five percent of the population. People with myopia are able to see near objects clearly but struggle to see distant objects. Myopia is generally caused when the eyeball is slightly too long, causing the retina to incorrectly perceive light from distant objects. Light still reaches the cones and rods but does so improperly, causing objects in the distance to become blurred and out of focus.
Myopia can also be caused when the cornea is curved or bulged, causing light waves to become distorted. The refraction that results mimics the effects of an elongated eyeball, causing the same symptoms.
People who experience myopia are generally diagnosed in late childhood or early adolescence and in most cases continue to worsen until early adulthood. Myopia is a hereditary disease and, despite urban legend, isn’t caused by reading in dim light or any other form of eye strain. Most people who suffer from myopia can temporarily correct the problem with glasses or corrective contact lenses.
While myopia is nearsightedness, hyperopia is farsightedness. In this refractive error, items in the distance appear clear but near objects are blurry or out of focus. Its cause is the opposite of myopia: hyperopia is caused when the eyeball is too short, allowing light waves to hit the retina before fully coming into focus. Like myopia, an improperly curved cornea can also be at fault.
Hyperopia is also hereditary and is generally diagnosed in children or adolescents. Most young children have hyperopia to a small degree that goes away naturally in the teenage years.
As our bodies age, the crystalline lens, the part of the eye that allows us to focus, becomes more rigid and less flexible. When this happens, we lose our ability to focus on small, near details like words and images close by, such as in books or on menus.
Most people first notice presbyopia around the age of 40. Presbyopia occurs in all people, regardless of other vision problems. Presbyopia is unavoidable. Most people treat it by wearing bifocals or reading glasses.
Unlike myopia and hyperopia, which only affect a certain range of vision, astigmatism is the overall inability to focus clearly in general. Astigmatism is generally caused by an irregular curvature of the cornea, allowing light waves to refract in a way that causes blurry or distorted vision at all ranges. Corrective lenses are generally employed to correct astigmatism.
Updated May 5th, 2015