myopia

The myopia rate is expressed by the professional in diopters.
This rate does not have any link with visual acuity which is expressed in tenth.
Myopes have difficulties with distance vision : however, they have a clear near vision and as a matter of fact, for myopes, the higher the myopia rate is, the closer to the eye the distance has to be to see well without glasses







hyperopia


The hyperopia rate is also measured in diopters, but is expressed in "positive"; plus 3 diopters shows a level of hyperopia, which is, in this case, average.

The hyperopic eye is too short and the image appears behind the cornea.
SCHEMA

The myopes' glasses are thick on the sides and shrink the size of the eye. The higher the myopia is, the more unaesthetic the glasses are, despite the important progress made by the professional to thin down the glasses.

The myopic eye is too long and the image appears in front of the retina.
SCHEMA

This rate is expressed in "negative" ; minus 3 diopters (- 3.00 diopters), for instance, shows the level of myopia which is, in this case, rather low. The myope have difficulties with distance vision as soon as the myopia rate reaches 1 diopter.

This means that even for a "low" myopia, the myope experiences troubles in his daily activities such as driving or watching television.
This handicap increases when the myopia rate is high.
Most of myopes have a rate between 2 and 6 diopters.

The hyperopes' glasses are thick and produce a magnifying glass effect: the size of the eye, seen through the glasses, is increased.
The hyperope has a near vision problem without glasses: but over a certain rate and a certain age, the hyperope also has distance vision difficulties.

astigmatism

The astigmatism rate is also measured in diopters.
An axis (for example, 90 degrees) is added, which indicates the direction of the image distortion.
Indeed, the astigmatic patient sees blurred and distorted; high astigmatic patients see elongated and flattened forms which depends on the axis. Some great astigmatic painters (Le Greco) painted or sculpted very elongated forms !

The astigmatic cornea has an irregular shape and is better analyzed during the pre-operative exam by corneal topography.

presbyopia

Presbyopia is the disorder that affects everybody without any exception over 45 years old. It's a disorder that creates difficulties to read.
The Presbyopic patient wears glasses for near vision, and if he has a disorder described above, he wears glasses which combine distance and near vision correction (progressive or bifocals glasses).

The astigmatic patient sees blurred and distorted...