REFRACTIVE DISORDERS

Posted by e-Medical PPT Monday, July 9, 2012
Types of refractive errors
MYOPIA ( nearsightedness )
Converging power of the cornea and lens is too great. Collimated light is light whose rays are nearly parallel,
For near vision, light rays are focused on the retina with little or no accommodation depending on the degree of
myopia and the distance at which the object is held.
This is the reason why shortsighted people can often read without glasses even late in life.

Complications of Myopia
People with high myopia are more likely to have retinal detachments and primary open angle glaucoma.They are also more likely to experience floaters, shadow-like shapes which appear singly or in clusters in the field of vision.Roughly 30% of myopes have high myopia

forms of myopia ( clinical classification)
Simple myopia is more common than other types of myopia and is characterized by an eye that is too long for its optical power           or optically too powerful for its axial length.   
Degenerative myopia, also known as malignant, pathological, or progressive Myopia .( Associated with staphyloma)
Pseudomyoipia is the blurring of distant vision brought about by spasm of the ciliary muscle.
Nocturnal myopia  also known as night myopia or twilight myopia.
Induced myopia, also known as acquired myopia.

Hypermetropia (generally )
Extremely good distant vision (6/4) or near vision they need to accommodate more than the normal people.
Typically, hypermetropic people need reading glasses at about 30 years of age.
They are more susceptible to closed angle glaucoma because there smaller eyes are more likely to have shallow                                                          
Astigmatism
Astigmatism present when the cornea curvature is irregular (Refractive power of the cornea in different planes is not equal).
Normally the cornea is a perfect sphere, but it is elliptically shaped in the astigmatic eye.
In short, astigmatism occurs whenever the vertical curvature of the cornea is different from the horizontal.
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