refractive errors

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REFRACTIVE ERRORS:

REFRACTIVE ERRORS Dr.Abhijit Gogoi University of Fiji

Refractive Error:

Refractive Error The result of a mismatch between optics and the growth of the eye It is due to a combination of genetic and environmental influences It is NOT considered an eye disease Treatment includes spectacles, contact lenses, and refractive surgery

Types of Refractive Error:

Types of Refractive Error Emmetropia Myopia Hyperopia Astigmatism Presbyopia

Emmetropia:

Emmetropia The average emmetrope has a VA of 20/20 or better

Myopia:

Myopia When parallel rays of light enter the eye ( with accommodation relaxed ) and come to a single point focus in front of the retina

Myopia:

Myopia Blurry vision at distance Clear vision at near

Myopia:

Myopia It is corrected by divergent or minus lenses Power of corrective lens needed can be estimated by finding the far point where the patient can achieve clear vision Example Far point is at 20cm Focal length of corrective lens needed = 20cm Power of corrective lens needed = 1/f =1/0.2m = -5.00D Unit for Power = Diopter (D)

Hyperopia:

Hyperopia When parallel rays of light enter the eye ( with accommodation relaxed ) and come to a single point focus behind the retina

Hyperopia:

Hyperopia Blurry vision at distance and near Intermittent blurring of vision

Hyperopia:

Hyperopia It is corrected by convergent or plus lenses A young patient with low hyperopia can accommodate to focus the distant image on the retina Since accommodation decreases with age, a low hyperopic patient tends to wear corrective lenses for near work at an earlier age

Astigmatism:

Astigmatism When parallel rays of light enter the eye ( with accommodation relaxed ) and do not come to a single point focus on or near the retina

Astigmatism:

Astigmatism It is due to a distortion of the cornea and/or lens The refracting power is not uniform in all meridians The principal meridians are the meridians of greatest and least refracting powers The amount of astigmatism is equal to the difference in refracting power of the two principal meridians

Astigmatism:

Astigmatism Distorted vision Letter confusion P versus F A versus R H versus N

Astigmatism:

Astigmatism It is corrected by cylindrical or spherocylindrical lenses

Presbyopia:

Presbyopia Presbyopia = “old man’s eye” (Latin)

Presbyopia:

Presbyopia Decrease in the amplitude of accommodation or loss of accommodative ability with age

Presbyopia:

Presbyopia It is a natural part of the aging process The onset of presbyopia is at approximately 40 years of age and over though it may be earlier in low hyperopes

Presbyopia:

Presbyopia Blurry vision at near Difficult or impossible to accommodate sufficiently for near work

Presbyopia:

Presbyopia It is corrected by convergent or plus lenses for near work only (near Add)

Types of Lens:

Types of Lens Spherical lens Cylindrical lens Spherocylindrical lens

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