Miopia
Refractive state in which rays of light from infinity focus before the retina, and the reason why there is difficulty in seeing objects at a distance.

Hipermetropia
Refractive state in which rays of light from infinity focus virtually after the retina, causing a blurred perception of images mainly in near vision.

Presbyopia
Refractive state caused by a progressive loss of lens accommodation capacity associated with age (patients over 40 years). The patient experiences a decrease in visual acuity for near vision.

Astigmatism
Refractive state in which rays from infinity do not focus on the same point as spherical defects, but at two different points due to an asymmetric curvature of the cornea. This presents difficulty seeing small details both near and far.

Cataract
A loss of transparency of any of the layers of the crystal lens.