REFRATIVE ERROR BASICS FOR MEDICAL AND NURSING STUDENTS

Basics of refractive errors

1. Errors of refraction
Dr.Ishwarya.v

2. What is Refraction
•When rays of light travelling through air enter a denser transparent
medium,thespeed of light is reduced and the light rays proceed at a
different angle, i.e., they are refracted.
•Except when the rays are normal

3. EMMETROPIA
•It can be defined as a state of refraction
•Parallel light rays,froman object more than 6m away,arefocused at
the plane of the retina when accommodation is at rest.

4. REFRACTIVE ERRORS
•Anomalies of the optical state of eye
•MYOPIA
•HYPERMETROPIA
•PRESBYOPIA
•ASTIGMATISM

5. What is Myopia?
•Dioptericcondition of the eye where parallel incident rays from
optical infinity focus anterior to light sensitive layers of retina when
accommodation is at rest.
•The defect is due to elongation of eyeball or increased curvature of
the cornea.
•In this condition the person will not be able to see the distant objects
clearly.
•Common in younger induviduals,defectincreases as the age advances
due to increase in the size of eyeball.

6. CORRECTION
•Myopia is corrected by concave lens(diverging lens).
•Choice of power of lens for correction of refractive error is made by
the trial method.

7. HYPERMETROPIA
•Parallel rays of light come to a focus behind the retina when
accommodation is at rest.
•It is also called as farsightedness.
•SYMPTOMS:
•Blurred vision
•Headache
•Difficulty reading books
•Squinting
•Eye hand coordination can be decreased

8. DIAGNOSIS AND TREATMENT
•Golden standard –Snellen chart
•Subjective refraction –visual acuity chart at far and near distance.
•Objective refraction –auto refraction machine or retinoscopy.
•TREATMENT
•Glasses : convex lenses are prescribed particularly for children below 10yrs
•Contact lenses
•Keratophakia
•Epikeratophakia
•Keratomileusis
•Secondary IOL implantation in Aphakia

9. PRESBYOPIA
•It is an adult type hypermetropia.
•After the age of 40yrs the lens become larger,thickerand less elastic
due to denaturation of lens protein.
•A child has a power of accommodation of 14D. It decreases to 2D
during 5
th
decade of life.
•MANAGEMENT
•This condition is corrected by using a bifocal lens with upper segment
suitable for long distance and lower segment for near vision.

10. ASTIGMATISM
•The parallel beam of light rays incident on the cornea after refraction
are not focused to form a point image near or on the retina.
•SIGNS AND SYMPTOMS:
•Distoredvision at distance and near
•Letter confusion
•Squinting
•Headaches

11. TREATMENT
•EYEGLASSES
•CONTACT LENS
•LASIK SURGERY

12. THANK YOU