Monovision is a method of correcting presbyopia. In monovision, the right eye (or dominant eye) is corrected for distance and the other eye is corrected for near vision.
The concept generally is that the dominant eye is made slightly myopic while the other eye is given a correction for near. There are 2 images, one clear and one blur for a given distance and the brain ignores the blurrer image. Thus vision with both eyes open is equal to the vision of the better seeing eye for the given distance. However, this may not be so for all people.
Each eye has a depth of focus which extends the range of clear vision. This depth of focus is affected in part by the pupil size. Monovision for intermediate vision would thus be better with a small pupil. This occurs in bright lighting conditions. Conversely, the intermediate range of vision may be worse in poor lighting conditions.
Tolerance of monovision correction can first be tested by use of the trial frames for spectacle correction or contact lenses if refractive surgery or intraocular lenses are contemplated.