Frequency of Visual Disorders Refractive errors, that is, optical errors of the lens system of the eye, are very common. A distribution of refractive errors is shown in Figure 29.
Refractive errors are fairly obvious to a person.
There is also a reduced near point of convergence with this condition. People with convergence insufficiency have no difficulty in aligning their eyes to view distance objects. They must, however, exert extra effort to make their eyes converge for viewing near objects. That extra effort may immediately, or over time, produce some visual discomfort. This condition may be relieved by a prism correction in their eyeglasses.