Near point and far point of accommodation

near point of accommodation,

1. NEAR POINT AND FAR POINT OF ACCOMMODATION PRESENTED BY, SUBHAM KUMAR AND MINDAR RONGPI B.OPTOM 2 ND YEAR 2017 BATCH RIDLEY COLLEGE OF OPTOMETRY JORHAT

2. ACCOMMODATION Definition:- Accommodation is the mechanism by which the eye changes refractive power by altering the shape of lens in order to focus objects at variable distances.

3. Mechanism of accommodation According to Von Helmholtz’s capsular theory

4. Types of accommodation Tonic accommodation It is also known as dark accommodation. It is due to tone of ciliary muscle and is active in absence of a stimulus. Proximal accommodation Is induced by the awareness of the nearness of a target. This is independent of the actual dioptric stimulus

5. Reflex accommodation Is an automatic adjustment response to blur which is made to maintain a clear and sharp retinal image Convergence accommodation Amount of accommodation stimulated or relaxed associated with convergence. The link between accommodation and convergence is known as accommodative convergence and is expressed clinically as AC/A ratio

6. Near point and far point Near point:- T he point nearest the eye at which an object is accurately focused on the retina at full accommodation is called near point and punctum proximum The minimum distance ,at which objects can be seen most distinctly without strain is called the near point of the eye For a young adult with normal vision,the near point is about 25 cm.

7. Far point :- The point farthest from the eye at which an object is accurately focused on the retina when the accommodation is completely relaxed is called far point or punctum remotum The farthest point up to which the eye can see objects clearly is called the far point of the eye It is infinity for a normal eye A normal eye can see objects clearly that are between 25 cm and infinity

8. Far point and near point of the eye vary with the static refraction of the eye. In emmetropic eye Far point is at infinity and near point varies with age In hyperopic eye Far point is virtual and lies behind the eye In myopic eye It is real and lies in front of the eye

9. Rough estimated of amplitude of accommodation and near point at different ages Age(in years) Amplitude of accommodation Near point in cms 10 14D 7 20 10D 10 30 07D 14 40 04D 25 50 02D 50 60 01D 100

10. Range and amplitude of accommodation Range of accommodation The distance between the near point and the far point is called the range of accommodation Amplitude of accommodation The difference between the dioptric power needed to focus at near point(P) and far point (R) is called amplitude of accommodation(A) thus A=P-R

11. References Anatomy and physiology of the eye by A K Khurana Primary care optometry I C E E giying SIGHT

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