It is the ability of the crystalline lens to change its chape to
focus objects of any distance up on the retina.
• Far point: Position of an object when its image clearly falls on retina with
• Near point: Nearest point clearly seen with maximum accommodation.
• Range of accommodation: Distance between far point and near point.
• 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
• RAF rule
• RAF ruler:-
• Royal Air Force rule
• Long rule with a slider holding a rotating four-sided cube each side has a
• Near point of accommodation NPA.
• Near point of convergence NPC.
• Monocular & binocularly measured.
• 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.
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 .
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.
• 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 .
• 1-GRADIENT METHOD
• For agiven distance of fixation,minus lenses placed in front of the
eye increase accommodation and plus lenses decrease
• 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.
• 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.
USES OF AC/A RATIO
• Diagnosis of convergence excess type of esodeviation.
• Divergence excess exoodeviation.
• Convergence insufficiency.
• Divergence insufficiency