Single vision glasses are the most common type of corrective prescription among people who have a refractive eye error. A refractive eye error is defined as a problem with the eye, which results in less than 20/20 vision. To help understand the most common types of refractive eye errors, and how common they are in the U.S., consider the information below:

Approximately half of all individuals aged 20 and older have refractive eye errors (according to a 2008 JAMA Ophthalmology article, which derived its results from a survey conducted between 1999 and 2004, involving a total of 12,010 participants).

The main refractive errors consisted of farsightedness (also called hyperopia, 3.6%); nearsightedness (also called myopia, 33.1%); and astigmatism (an eye condition characterized by irregularity in the shape of the cornea, resulting in visual blurriness or distortion; 36.2%).

In the 20 – 39 years age group, according to the original study, women were more likely to have nearsightedness than men. In the 60+ years age group, there was greater probability of individuals having farsightedness and astigmatism than in younger study participants. Also, in this older group, there was a greater chance of men having refractive error (66.8%) than women (59.2%). The older the individual, the more likely they are to have any refractive error (20 – 39 years, 46.3%; 40 – 59 years, 50.6%; 60+ years, 62.7%).

Single Versus Multi-Focal Vision Correction

Single vision glasses correct the vision of people who have one issue only affecting their visual acuity – farsightedness, nearsightedness or astigmatism. The focal correction is uniform over the entire area of the lens. Some people have a refractive eye error in just one of their eyes, so their glasses would only have a corrective lens corresponding to the affected eye (with the other consisting of plain glass). Other people have different degrees of refractive error in each eye, necessitating prescriptions tailored to correct each individually. These are all still examples of single vision prescriptions.

For individuals who have more than one refractive eye error in either or both of their eyes (e.g., having both nearsightedness and farsightedness together), visual correction requires a multi-focal lens, as discussed below.

Multi-Focal Corrective Lens Options

A bifocal lens treats two optical prescriptions (i.e., two refractive eye errors) in one lens. The lens has two focal points, usually one for up-close vision and the other for distance. Interestingly, Benjamin Franklin is credited with inventing the first bifocal lens.

Bifocal lenses have a distinct line or border separating the two focal points. The size and shape of the reading lens can vary. Bifocal glasses can also be incorporated in sunglasses.

Like bifocal lenses, progressive lenses offer correction of both nearsightedness and farsightedness in one lens. Unlike bifocals, however, they don’t have a visible line between the two focal points. In addition, they enable the wearer to view objects both close and far away, as well as at an intermediate distance.

In a progressive lens, also known as no-line bifocal lenses, the upper part of the lens corrects for nearsightedness, and the lens power smoothly graduates toward the lower part, which enables up-close viewing. There is no distinct line between the distance correction part of the lens and the reading correction portion. Also, the center section of the lens allows the wearer to clearly see objects at intermediate distance, such as the ground, a wall mirror or a computer screen. Progressive lenses have become popular because of their broader cosmetic appeal compared to the look of bifocal lenses.