Ametropias: myopia, hyperopia, astigmatism, presbyopia

Ametropias: myopia, hyperopia, astigmatism, presbyopia

The ‘defects’ of the eye
An eye suffering from optical anomalies is a healthy eye, but vision is disturbed because the image is not focused on the retina but in front (myopia), behind (hyperopia) or because the image is distorted (astigmatism). There are 3 types of optical anomalies:

 

Myopia

This is the most common optical anomaly. A myopic eye is one in which the eyeball is too long. The image of an object seen by a myopic eye is formed in front of the retina. Near vision is sharp, far vision is blurred.

 

 

Hyperopia

This is the opposite of myopia. The eyeball is not long enough. The image of an object seen by a hyperopic eye is formed behind the retina. Near and far vision is blurred.

 

 

Astigmatism

The cornea is curved more in one axis than in another instead of being round. It is impossible to focus images, because some lines (e.g. vertical) are sharp and others (e.g. horizontal) are blurred. The astigmatic eye therefore sees more clearly in one direction than in the other. Can be combined with myopia or hyperopia.

Presbyopia.

From the age of 40 onwards in all human beings, a decrease in near vision for reading. It can be combined with myopia, hyperopia or astigmatism from this age.
It is a loss of elasticity of the lens due to old age. The eye is no longer able to accommodate, i.e. to make an effort to focus for close-up vision. Short-sighted people have an advantage in presbyopia because some can remove their glasses to see close up. In other cases, progressive lenses are indicated. Hypermetropes are at a disadvantage when they also become presbyopic, and will need to wear progressives.