*3.1.2 Side effects of monovision technique*

Although monovision is the most common surgical management of presbyopia for cataract patients with millions of people having monovision corrections, some important drawbacks of this method should be described.

First, although monovision is related with significant satisfaction, the highest percentages of satisfied patients have been found in age older than 70 years, while patients younger than 60 years have the highest percentages of dissatisfaction caused mainly by asthenopia and spectacle dependence [52].

Secondly, it has been reported that anisometropia and blur differences cause a motion illusion that leads to a significant misperception of the distance and threedimensional direction of moving objects, since the blurred and sharp images are processed at different speeds. This phenomenon has a clinical impact on driving behavior, since these millisecond differences in processing speed could lead, for instance, to the misperception of the distance of cyclists by the width of a narrow street lane [54].

Finally, depth perception and distance stereopsis, especially for large disparities, may be compromised increasing the difficulty in navigation through the environment, obstacle avoidance, and stair walking. Reduction of distance stereopsis leads to a decrease in stability during locomotion, as well, increasing the risk factor for falls and hip fractures in aged population [55]. Near stereopsis is also reduced, although it remains within the normal range [52].
