The document discusses accommodation, convergence, and the AC/A ratio. It defines accommodation as the ability of the crystalline lens to change shape to focus on objects at different distances. Convergence is the inward movement of the eyes to focus on near objects. The AC/A ratio measures the relationship between accommodation and convergence induced. There are several methods to measure accommodation, convergence, and the AC/A ratio clinically including using a RAF ruler, push-up test, lenses, and recording near and far points of focus and convergence.

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