Accommodation and convenient

1. ACCOMMODATION.
It is the ability of the crystalline lens to change its chape to
focus objects of any distance up on the retina.

3. • Far point: Position of an object when its image clearly falls on retina with
no accommodation.
• Near point: Nearest point clearly seen with maximum accommodation.
• Range of accommodation: Distance between far point and near point.

6. Measurement
• the amplitude of accommodation is a measure of the
closest point at which the eye s can focus
• measured in diopter
• calculated in reciprocal of fixation distance
• F=1/f
• RAF rule

8. • RAF ruler:-
• Royal Air Force rule
• Long rule with a slider holding a rotating four-sided cube each side has a
different target.
• measurement:-
• Near point of accommodation NPA.
• Near point of convergence NPC.
• Monocular & binocularly measured.
• 100/NPA(cm)=AOA.

9. Push-up method :-
Done by (RAF ruler).
Near VA chart - ruler

10. • Trail lens method
• Minus and plus lenses
• With age

11. Convergence
•
• is the ability of the eye to simultaneously demonstrate inward movement of
both eyes toward each other.
• This is helpful in effort to make focus on near objects clearer.
• Three reactions occur simultaneously ;the eyes adduct, the ciliary muscles
contract, and the pupils become smaller.
• This action involves the contraction of the medial rectus muscles of the two
eyes and relaxation of the lateral rectus muscles.

12. TYPE'S OF CONVERGENCE
1-Tonic convergence: the stimulus to fusion is removed eye's are at
position of rest.
2 -Accommodative convergence is convergence stimulated by a near
target that requires a change in focus of the lens .

13. It is the convergence produced to ensure that similar retinal images are
projected on to corresponding retinal areas .
It is a response to disparate stimuli lying outside the pannum's area
for achievement of bifoveal single vision.
3-FUSIONAL CONVERGENCE

14. • This component of reflex convergence is induced by the proximity of
the object of regard or the awareness of the proximity of a near object .
It appears to be initiated by psychological factors , since it also occurs
when a subject just believes that he is looking at a near object
although he actually is not . For example , while using the haploscope
optically set at infinity , proximal convergence is often induced .
Proximal convergence

15. • Meter angle
• Unit of convergence
• The formula
• 1 / d X IPD

16. • Measurement of convergence
• Near point of convergence (NPC) is the closest point
at which an object can be seen point at singly.
• Subjective (NPC) patient report diplopia.

17. • Objective NPC clinician observe point when one eye turns out.
• Instrument - penlight, RAF ruler.
• Record in centimeters.
• Pupil dilation may occur indicating convergence break.

19. • Ac /A ratio
• The amount of accommodative convergence induced by each
amount of accommodation exerted
• Measured in prism diopter
• It depends on the IPD and the distance of the object from the
eyes

20. TYPES
• 1.Stimulus AC/A Ratio
• Ratio of accommodative convergence to stimulus to
accommodation.
• 2.Response AC/A-Ratio
• Ratio of accommodative convergence to response to
accommodation.

21. • Usually stimulus AC/A >Response AC/A
• It can be modified permanently by surgery to the extra ocular
muscles or temporarily by drugs and lenses that change the
accommodation.

22. •Method of measuring

23. • 1-GRADIENT METHOD
• For agiven distance of fixation,minus lenses placed in front of the
eye increase accommodation and plus lenses decrease
accommodation.
• 2-HETROPHORIA METHOD
• Full optical correction is given and deviation is masured at 6
distance and at 33cm distance in prism diopter and IPD is
measured in centimeters.

24. • 3-FIXATION DISPARITY METHOD
• 4-GRAPHICAl METHOD
• Convergence (in prism diopter)is plotted along the X-axis.
• Stimulus to accommodation is indicated along the y_ axis .
• Slope of graph represents AC/A ratio.

25. USES OF AC/A RATIO
• Diagnosis of convergence excess type of esodeviation.
• Divergence excess exoodeviation.
• Convergence insufficiency.
• Divergence insufficiency