Myopia occurs when light entering the eye focuses in front of the retina instead of directly on it. Myopia is caused by a cornea that is steeper, or an eye that is longer, than a normal eye. Nearsighted people typically see well up close, but have difficulty seeing far away.
Hyperopia occurs when light entering the eye focuses behind the retina, instead of directly on it. Hyperopia is caused by a cornea that is flatter, or an eye that is shorter, than a normal eye. Farsighted people usually have trouble seeing up close, but may also have difficulty seeing far away as well.
Astigmatism occurs when the cornea is oval like a football instead of spherical like a basketball. Most astigmatic corneas have two curves – a steeper curve and a flatter curve. This causes light to focus on more than one point in the eye, resulting in blurred vision at distance or near. Astigmatism often occurs along with nearsightedness or farsightedness.
Presbyopia occurs when the natural lens can no longer focus on near objects. Accommodation is the eye’s way of changing its focusing distance: the lens thickens, increasing its ability to focus close-up. At about the age of 40, the lens becomes less flexible and accommodation is gradually lost. It’s a normal process that everyone eventually experiences. Unfortunately, to date, a laser vision correction procedure that can completely manage this condition effectively does not exist.
Monovision describes a situation where one of the eyes, typically the dominant eye, is corrected for distance and the other eye is left slightly nearsighted to help with reading. There is typically a period of adaptation required, with the most successful patients being those who have experienced monovision with their contact lenses. It is not recommended, however, for patients who require optimal distance or near correction, and/or astute depth perception, as these will be slightly compromised.