A refractive error is a very common eye disorder. It occurs when the eye cannot clearly focus the images from the outside world. The result of refractive errors is blurred vision, which is sometimes so severe that it causes visual impairment.

The four most common refractive errors are:

• Myopia (nearsightedness): difficulty in seeing distant objects clearly;
• Hyperopia (farsightedness): difficulty in seeing close objects clearly;
• Astigmatism: distorted vision resulting from an irregularly curved cornea, the clear covering of the eyeball.
• Presbyopia: which leads to difficulty in reading or seeing at arm's length, it is linked to ageing and occurs almost universally.

Refractive errors cannot be prevented, but they can be diagnosed by an eye examination and treated with corrective glasses, contact lenses or refractive surgery. If corrected in time and by eye-care professionals, they do not impede the full development of good visual function. Correction is provided in different forms according to the defect, the age of the person, the requirements in terms of work of activity performed.