Visual defects: Myopia, Hyperopia, Astigmatism, Presbyopia
myopia is a vision disorder where the person sees objects blurry from a distance, because the lens is too curved, therefore too convergent, and the light rays meet in front of the retina. In other words, the myopic person sees less well from a distance than from near. This can be corrected by glasses, contact lenses or refractive surgery. 26% of the world's population is myopic.
In astigmatism, the curvature of the cornea is not the same in all axes: instead of being round like a football, the cornea is flattened like a rugby ball.
This leads to a distortion of images both from a distance and from near. Often myopia and hyperopia are associated with a certain degree of astigmatism.
In hyperopia, the eye is too short and the light rays are focused behind the retina: we see blurry up close or even far away and this causes fatigue.
The young patient does not notice it immediately because the accommodation efforts of his lens – still flexible – allow him to compensate for this hyperopia.
The presbyopia: Around the age of 45, we all become presbyopic.
This presbyopia is linked to the loss of elasticity of the crystalline lens, it leads to a progressive loss of accommodation and involves wearing a reading correction.
Myopes with presbyopia are often able to read without glasses, because to some extent the presbyopia compensates for the near myopia, but in distance vision, the person will always keep the same degree of myopia, despite the presbyopia.
Visual defects can be corrected by laser surgery:
