Refractive Errors

 

1- Myopia:

A- Types:

– Axile myopia: the eye is too long in the anteroposterior direction; often proved at the age of 10 years; it does not exceed in general – 6.00 diopters.

– Index Myopia: decreasing the corneal radius of curvature (Keratometers cone) and / or the change of the refractive power of a medium (crystalline: nuclear cataract) can generate a myopic shift.

– Myopia disease (high) beyond – 6.00 diopters. Begins early, with time-family;

it combines eye alterations especially on the retina and choroid (stretching of tissue atrophy) and may be complicated by retinal detachment, macular hemorrhage and glaucoma ().

It evolves throughout life and may reach 30.00 diopters.

Myopia

Myopia

B- Complications:

* Chorioretinal atrophy Beaches posterior pole (staphyloma)

* Bleeding from macular choroidal rupture or choroidal neovascularization (Fuchs spot);

* Cataracts are common.

Correction glasses with divergent lenses

Hyperopic eye

Hyperopic eye

2- Hyperopia:

– Implementation permanent game of accommodation, for distance vision and near vision.

– Hyperopia axile is the most common

– At birth there is usually a type 2 or 3 diopters of hyperopia which gradually decreases until it disappears in adolescence

– Risk of premature onset of presbyopia if no correction

– Hyperopia in children is responsible for accommodative esotropia deviation (late start around the age of 3 years);his character is intermittent and progressive.

– Correction by glasses with converging lenses

astigmatic eye

Astigmatic Eye

3- Astigmatism:

– Its radius of curvature varies progressively between 2 values ​​corresponding to two planes of incidence, said principal planes that define astigmatism. These main planes are usually perpendicular to each other.

– In astigmatism give two linear images (focal) on these princi-pal plans. The most previous frame corresponds to the convergent plane.One of these two focal lengths at least not on the retinal plane.

– Simple Astigmatism -> if one of the two focal lengths is located on the retina; it will be simple myopic astigmatism if the second focus is in front of the retina …

– If the two focal lengths in forward and backward -> compound myopic astigmatism (in front of the retina) or hyperopic (behind the retina)

– Mixed Astigmatism: a back focal length of the retina and the other forward

– To know the value and the axis of astigmatism can use ophthalmometer Javal and retinoscopy or auto refractometer.

– Astigmatism can be responsible for a monocular diplopia.

– Correction by glasses with cylindrical lenses which deflects the rays located on a plane perpendicular to the axis.

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