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AC/A Ratio
Mahendra Singh
Assistant Professor and consultant
Optometrist.
CL Gupta Eye Institute. UP India
AC/A Ratio
 Definition:
The AC/A Ratio is the ratio of the amount
of accommodative –convergence measured
in prism diopters to the number of diopter
of accommodation which causes this
convergence.
Different methods of measuring
Surgical method
 The Heterophoria method
 The gradient method
 The major amblyoscope method
 The graphic method
 The fixation disparity method
Normal range of AC/A Ratio
 The Normal range of AC/A Ratio is 3:1 to
5:1
 It is expressed as 3 to 5
 As the convergence measured is related to
one diopter of accommodation
The assessment of the AC/A
Ratio
 The heterophoria method:
 This method compare the measurements of the
latent deviation of the eyes, using the prism
&alternate cover method at point distant fixation
(6 meters)
 The point of near fixation at 1/3rd meter with care
to ensure the steady accommodation at both
distance of fixation by the use of target which
contains detail like a snellen chart
 The use of an appropriate spectacle
corrections when there is any significant
refractive error
 It may be concluded that when the
measurement for distance and near is equal
the Normal range of AC/A Ratio is normal
 When it is greater for distance than near the
AC/A Ratio is low
 When it is greater for near than the distance
the AC/A Ratio is high
 It must be conceded that some degree of
difference (possibly as much as 10 D)is
within normal limits
Formula for Heterophoria method
 AC/A =I.P.D+△2-△1
F1
Where
AC=accommodative convergence in prism
diopters (△)
A=Accommodation in diopters (D)
I.P.D.=interpupillary distance in prism
diopters
△1=latent deviation for distance (6 M)
△2= latent deviation for NEAR(1/3M)
F1=Distance of near fixation in diopters
 F2= Distance of near fixation in meters
Example
 I.P.D =6cms
△1=4prism exo
△2=10prismexo
F1=3D
AC/A=6+(-10-(-4)_ )
3
=6+(-10+4)
3
=6+(-2)
=4
The gradient method
 The AC/A Ratio is measured by an estimation of
the difference between the deviation for the eyes
for a given distance
 The Maddox rod is use in front of one eye and
correcting prism in front of the other eye
 It is done before placing convex or concave
spherical lenses in front of the eye
The gradient method
 The lenses are place so that there is change in
their accommodation and therefore in their
convergence
 The convex lenses by decreasing the amount of
accommodation necessary for the given distance
decreases the amount of convergence
 The concave lenses by increasing the amount of
accommodation necessary for the given distance
increase the amount of convergence
The gradient method
 It is important to achieve this deviation of the eye
by ensuring that patient exerts the the full amount
of accommodation for the particular distance
 This is achieved by the use of an object which
contain much fine detail in conjunction with the
alternate prism and cover test in preference to use
simply of a fixation light as in the maddox rod
test
The gradient method
 It is of course necessary in measuring the
difference of the deviation to regard it as the
subtraction of the first deviation from the second
deviation
 It is important to note down the sign properly
before calculation
 Plus measurement when it is esodeviation
 Minus measurement when it is exodeviation
The gradient method
 In arriving for the final figure of the ratio it
is necessary to divide the difference in the
deviation by the power of the lenses used
in order to reduce it to single unit of
accommodation for ease of comparison
AC/A Ratio by gradient method
 As a general rule the values of AC/A Ratio by the
gradient method is slightly lower than those
obtained by the heterophoria method
 This is because the fixed distance used in the
gradient method (unlike the heterophoria method
which adopts two different distances of fixation)
 This is due to the factor of proximal convergence
and this method has advantage that it induces
convergence mainly due to the patients subjective
accommodative effort
Formula of gradient method
 AC/A=2-1
D
WHEREAC=accommodative convergence in prism
diopters ()
A=accommodation in diopters(D)
1=original deviation in prism diopters
2=deviation in prism diopters with the spherical
lenses
D1=power of lenses used in diopters
Examples
 If 1=3 eso.
2=6 eso.
D1=1Dsph(concave)
AC/A=6-3
1
=3
The major Amblyoscope method
The major amblyoscope methods
 There are two ways of assessing the AC/A Ratio
with the major amblyoscope
 The instrument is adjusted to the patients
interpupillary distance in the usual manner
 The correcting spectacle arte worn
 Targets are used which ensure foveal fixation
 The subjective angle is determined ,and the
reading taken from the prism
Diopter scale .minus lenses usually –3.00
D.S., are inserted in the lens holder of the
instument and the measurement is repeated
 This method is comparable to yhe gradient
method when using the snellen’s test types
 It has the advantage that small deviation can
be measured more accurately than when
done by prism and cover tet
Formula for the amblyoscope
method
 AC/A = 2- 1
D
 WHERE 1is the subjective angle
measured with patient’s own spectacles.
 2is the subjective angle measured with the
adddition of the –3.00D.S.
 Dis the strength in dioters of the concave
spherical lens used
Example of the major
amblyoscope method
 E.g. if 2=19 eso
1=7 eso
D= -3.00Dsph
AC/A =+19-(+7)
3
=4
The Graphic Method
 The instrument is adjusted to suit the I.P.D. of
the patient
 The object is to determine the patient’s subjective
angle but instead of using the usual S.F.P. slides
and recording the deviation on the degree scale , a
reduced test-type slide is placed before one eye
and a black vertical line before the other,such test
type ensures accurate fixation
 Correct accommodation is achieved by the patient
being told to read the test-type from largest to the
smallest row of letters
 Then by moving the slide carrier containing the
vertical line to cause the line to bisect the
smallest row of letters which he can see clearly
 The angle at which he achieves is recorded on the
prism diopter scale and is noted as the patients
subjective angle
 The measurement is repeated with the
introduction of –1.0.-2.0,-3.0,-4.0 dioptre
spheres successively before the patient’s
correcting spectacles
 The measurement represent the
accommodative –convergence.
 Diopters of
accommodation
1
2
3
4
 Prism diopter of convergence
(both eyes )
6(2metre angles3)
12(4metre angles3)
18(6 2metre angles3)
24(8 2metre angles3)
The fixation disparity method
 In the fixation disparity method the AC/A Ratio is
measured by an assessment of the The fixation
disparity which is found in the heterophoria
,when targets mainly identical features but also
certain dissimilar features are presented to the
eyes by means of haploscopioc device
 Fusion occurs readily and is mainted for the
identical features of the targets but a displacement
occurs for the dissimilar features according to the
direction of the hetrophoria
The fixation disparity method
 The displacement is measured in two
different circumstances
 First-it is measured in various positions of
positive convergence and negative
convergence ,as induced by the
superimposition of varying prisms (base-
out and base-in respectively )
The fixation disparity method
 The production of positive convergence by the
base out prism causes an exo-disparity and the
production of negative convergence by the use of
base-in prism causes an eso-disparity
 These results are recorded graphically with the
strength of the prisms along the abscissa (base-
out to the right and base-in to the left) and the
degree of disparity along the ordinate (eso
disparity upwards,exo-disparity downwards )
 These findings are termed as disparity –prism
data
The fixation disparity method
 Secondly it is measured during the various
changes in the stimulus to positive and negative
accommodation as induced by the
superimposition of varying spherical lenses
(concave or convex)
 This are place in front of one or both eyes during
the maintenance of binocular fixation on a target
at constant distance usually 40 cms
The fixation disparity method
 The stimulus to the positive
accommodation by the use of concave
spherical lenses causes an eso-disparity
 The stimulus to the negative
accommodation by the use of convex
spherical lenses causes an exo-disparity
 This is recorded on the graph
The significance of the AC/A
Ratio
 An appreciation of the AC/A Ratio gives an
indication that there are two types of
accommodative esotropia
 There is accommodative esotropia in which the
determining fact is the uncorrected hypermetropia
with its excessive accommodative requirement
leading to an excessive convergence the AC/A
Ratio is normal
The significance of the AC/A
Ratio
 Secondly, there is an accommodative esotropia in
which the determining factor is the excessively
high response of the convergence mechanism to
any accommodative effort because the AC/A
Ratio is high
 This distinction between these two different
forms of accommodative esotopia is importyant
in determining the method of treatment of such
cases
The significance of the AC/A
Ratio
 When the AC/A Ratio is relatively normal –
correction of refractive error alone may be
sufficient to correct the ocular deviation but not
when the AC/A Ratio is high
 When AC/A Ratio is high –occlusion(although
the value in eliminating suppression or
amblyopia) causes an esotropia to increase in
amount o that it ceases to have any latent
component
 This is because an over convergence inevitably
follows the loss of the fusional control which
occurs during occlusion
The influence of method of
treatment on the AC/A Ratio
 Correcting spherical lenses
 Miotic therapy
 Surgical method
Correcting spherical lenses
 This alters the AC/A Ratio
 For example a case in which there is
orthophoria on distant fixation and
esotropia on near fixation without any
spectacle correction may show orthophoria
on both distant and near fixation after the
use of spectacle correction
Miotic therapy
 Miotics such as pilocarpine, DFP, causes the
change in the AC/A Ratio
 This is because the lesser innervations which is
require to produce a diopter of accommodation is
associated with the decrement in the innervations
of the ciliary muscles and a proportionate
decrement in the innervations to the medial recti
so that there is decrease in the AC/A Ratio
Surgical method
 There is evidence that a decrease in the
effectiveness of the medial rectus muscle or
muscles by a recession in accommodative
esotropia results in a reduction of
abnormally high Surgical method
Medical care of Esotropia, with High
AC/A Ratio
 Treatment of nonrefractive accommodative
esotropia consists of full correction for the
distance refractive error and bifocals for near
vision to suspend the accommodative drive and to
lessen accommodative convergence.
 Bifocal power should be +2.50 to +3.00 diopters,
and bifocals should be placed such that the upper
boarder of the bifocal segment bisects the pupil.
 Miotics, which lower the AC/A ratio, are
successful in some patients.
 In cases of amblyopia, early treatment
of patching the normal (unaffected) eye
is the mainstay of treatment.
Surgical care Esotropia,
with High AC/A Ratio
 Surgery may be required if the esodeviation
becomes refractory to optical treatment. Surgery
often is needed when optical treatment is delayed.
 Surgical treatment typically entails recession or
weakening of the inward-pulling medial rectus
muscle in each eye.
 Surgery is performed for the nonaccommodative
component only. The operation is not intended to
discontinue use of glasses.
FOLLOW-UP Section 6 of 8
Esophoria With Myopic
Correction have high AC/A Ratio
 When myopes are esophoric this may mean a
several things.
 Two of which are they have a high ac/a or are
overminused
 There is some suggestions that this may be one
type of myope that can lead to myopic
progression if overminused (there was a study)
 With myopic esophores that were fit with bfl
contacts
Treatment for Esophoria With Myopic
Correction and high AC/A Ratio
1. Make sure they are not overminused
2. Can consider a PAL or BFL (add is clinically
figured out by finding the the add that makes
them ortho at near)or a SV near rx.
3. For those you mentioned they can just take off
their Rx to read.
4. Or rx the least amount of minus that gets them
20/happy...dont over minus them!
Diagnosis and treatment of exotropia
with high AC/A Ratio
 Patients with exotropia often have a fusional
mechanism at near, which masks the true near
deviation.
 Consequently, determination of the
accommodation convergence–accommodation
(AC/A) ratio in patients with exotropia must be
based on near measurements obtained after
prolonged monocular occlusion (typically 1
hour).
 When determined in that manner, the
presence of a highAC/A ratio before
surgery in an exotropic patient has been
reported to be predictive of an esotropia at
near after surgery.
Importance of measurement of
AC/A Ratio
 Near measurements used to calculate the
AC/Aratio in exotropic patients must be
made after prolonged monocular occlusion.
 Otherwise, many patients with a pseudo–
highAC/A ratio will be thought to have a
true high AC/A ratio.
 The presence of a high AC/A ratio is
infrequent in patients with esotropia, but it
is highly predictive of a postoperative
esotropia at near fixation.
Accommodative esotropia with
normal AC/A Ratio
 Total esotropia eliminated
 a. refractive - high hyperopia
 bilateral not unilateral
 normal range of AC/A ratio
Accommodative esotropia with
normal AC/A Ratio
Low AC/A Ratio
 Convergence Insufficiency - (clinical
condition) the inability of the eyes to turn
inward and/or sustain an inward turn.
 Symptoms include eye strain with reading
and using a computer, headaches, loss of
comprehension, difficulty concentrating,
blurred or double vision, and eye fatigue.
Low AC/A Ratio
 Clinical signs include: near point of
convergence of greater than 4 inches
(10 cm), greater exophoria at near than
at distance, and low AC/A ratio.
Vision therapy is an effective
treatment option.
High AC/A Ratio
 Convergence Excess - a clinical
condition in which the eyes have a
tendency to turn excessively inward
when viewing an object at a near
distance.
 Symptoms may include visual fatigue
while reading or using a computer,
occasional blurred or double vision,
and inability to comprehend or
concentrate while reading.
High AC/A Ratio
 Clinical signs include: greater
esophoria at near than distance,
high AC/A ratio, and a high lag of
accommodation. Can be improved
with vision therapy and/or glasses.
(See "Esophoria")
The Exotropias
CHARACTERISTICS OF COMITANT
EXOTROPIA
 AC/A ratio; normal or low
 symptoms; photophobia, squinting
 prognosis; usually good
INTERMITTENT EXOTROPIA OF THE
DIVERGENCE EXCESS TYPE
 distance angle > near angle
 deviation is intermittent
 angle of deviation increases
with fixation distance
 weak accommodative skills
 high AC/A ratio?
 near-far AC/A calculation -
gradient AC/A determination
AC/A ratio

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AC/A ratio

  • 1. AC/A Ratio Mahendra Singh Assistant Professor and consultant Optometrist. CL Gupta Eye Institute. UP India
  • 2. AC/A Ratio  Definition: The AC/A Ratio is the ratio of the amount of accommodative –convergence measured in prism diopters to the number of diopter of accommodation which causes this convergence.
  • 3. Different methods of measuring Surgical method  The Heterophoria method  The gradient method  The major amblyoscope method  The graphic method  The fixation disparity method
  • 4. Normal range of AC/A Ratio  The Normal range of AC/A Ratio is 3:1 to 5:1  It is expressed as 3 to 5  As the convergence measured is related to one diopter of accommodation
  • 5. The assessment of the AC/A Ratio  The heterophoria method:  This method compare the measurements of the latent deviation of the eyes, using the prism &alternate cover method at point distant fixation (6 meters)  The point of near fixation at 1/3rd meter with care to ensure the steady accommodation at both distance of fixation by the use of target which contains detail like a snellen chart
  • 6.  The use of an appropriate spectacle corrections when there is any significant refractive error  It may be concluded that when the measurement for distance and near is equal the Normal range of AC/A Ratio is normal  When it is greater for distance than near the AC/A Ratio is low
  • 7.  When it is greater for near than the distance the AC/A Ratio is high  It must be conceded that some degree of difference (possibly as much as 10 D)is within normal limits
  • 8. Formula for Heterophoria method  AC/A =I.P.D+△2-△1 F1 Where AC=accommodative convergence in prism diopters (△) A=Accommodation in diopters (D)
  • 9. I.P.D.=interpupillary distance in prism diopters △1=latent deviation for distance (6 M) △2= latent deviation for NEAR(1/3M) F1=Distance of near fixation in diopters  F2= Distance of near fixation in meters
  • 10. Example  I.P.D =6cms △1=4prism exo △2=10prismexo F1=3D AC/A=6+(-10-(-4)_ ) 3 =6+(-10+4) 3 =6+(-2) =4
  • 11. The gradient method  The AC/A Ratio is measured by an estimation of the difference between the deviation for the eyes for a given distance  The Maddox rod is use in front of one eye and correcting prism in front of the other eye  It is done before placing convex or concave spherical lenses in front of the eye
  • 12. The gradient method  The lenses are place so that there is change in their accommodation and therefore in their convergence  The convex lenses by decreasing the amount of accommodation necessary for the given distance decreases the amount of convergence  The concave lenses by increasing the amount of accommodation necessary for the given distance increase the amount of convergence
  • 13. The gradient method  It is important to achieve this deviation of the eye by ensuring that patient exerts the the full amount of accommodation for the particular distance  This is achieved by the use of an object which contain much fine detail in conjunction with the alternate prism and cover test in preference to use simply of a fixation light as in the maddox rod test
  • 14. The gradient method  It is of course necessary in measuring the difference of the deviation to regard it as the subtraction of the first deviation from the second deviation  It is important to note down the sign properly before calculation  Plus measurement when it is esodeviation  Minus measurement when it is exodeviation
  • 15. The gradient method  In arriving for the final figure of the ratio it is necessary to divide the difference in the deviation by the power of the lenses used in order to reduce it to single unit of accommodation for ease of comparison
  • 16. AC/A Ratio by gradient method  As a general rule the values of AC/A Ratio by the gradient method is slightly lower than those obtained by the heterophoria method  This is because the fixed distance used in the gradient method (unlike the heterophoria method which adopts two different distances of fixation)  This is due to the factor of proximal convergence and this method has advantage that it induces convergence mainly due to the patients subjective accommodative effort
  • 17. Formula of gradient method  AC/A=2-1 D WHEREAC=accommodative convergence in prism diopters () A=accommodation in diopters(D) 1=original deviation in prism diopters 2=deviation in prism diopters with the spherical lenses D1=power of lenses used in diopters
  • 18. Examples  If 1=3 eso. 2=6 eso. D1=1Dsph(concave) AC/A=6-3 1 =3
  • 20. The major amblyoscope methods  There are two ways of assessing the AC/A Ratio with the major amblyoscope  The instrument is adjusted to the patients interpupillary distance in the usual manner  The correcting spectacle arte worn  Targets are used which ensure foveal fixation  The subjective angle is determined ,and the reading taken from the prism
  • 21. Diopter scale .minus lenses usually –3.00 D.S., are inserted in the lens holder of the instument and the measurement is repeated  This method is comparable to yhe gradient method when using the snellen’s test types  It has the advantage that small deviation can be measured more accurately than when done by prism and cover tet
  • 22. Formula for the amblyoscope method  AC/A = 2- 1 D  WHERE 1is the subjective angle measured with patient’s own spectacles.  2is the subjective angle measured with the adddition of the –3.00D.S.  Dis the strength in dioters of the concave spherical lens used
  • 23. Example of the major amblyoscope method  E.g. if 2=19 eso 1=7 eso D= -3.00Dsph AC/A =+19-(+7) 3 =4
  • 24. The Graphic Method  The instrument is adjusted to suit the I.P.D. of the patient  The object is to determine the patient’s subjective angle but instead of using the usual S.F.P. slides and recording the deviation on the degree scale , a reduced test-type slide is placed before one eye and a black vertical line before the other,such test type ensures accurate fixation
  • 25.  Correct accommodation is achieved by the patient being told to read the test-type from largest to the smallest row of letters  Then by moving the slide carrier containing the vertical line to cause the line to bisect the smallest row of letters which he can see clearly  The angle at which he achieves is recorded on the prism diopter scale and is noted as the patients subjective angle
  • 26.  The measurement is repeated with the introduction of –1.0.-2.0,-3.0,-4.0 dioptre spheres successively before the patient’s correcting spectacles  The measurement represent the accommodative –convergence.
  • 27.  Diopters of accommodation 1 2 3 4  Prism diopter of convergence (both eyes ) 6(2metre angles3) 12(4metre angles3) 18(6 2metre angles3) 24(8 2metre angles3)
  • 28. The fixation disparity method  In the fixation disparity method the AC/A Ratio is measured by an assessment of the The fixation disparity which is found in the heterophoria ,when targets mainly identical features but also certain dissimilar features are presented to the eyes by means of haploscopioc device  Fusion occurs readily and is mainted for the identical features of the targets but a displacement occurs for the dissimilar features according to the direction of the hetrophoria
  • 29. The fixation disparity method  The displacement is measured in two different circumstances  First-it is measured in various positions of positive convergence and negative convergence ,as induced by the superimposition of varying prisms (base- out and base-in respectively )
  • 30. The fixation disparity method  The production of positive convergence by the base out prism causes an exo-disparity and the production of negative convergence by the use of base-in prism causes an eso-disparity  These results are recorded graphically with the strength of the prisms along the abscissa (base- out to the right and base-in to the left) and the degree of disparity along the ordinate (eso disparity upwards,exo-disparity downwards )  These findings are termed as disparity –prism data
  • 31. The fixation disparity method  Secondly it is measured during the various changes in the stimulus to positive and negative accommodation as induced by the superimposition of varying spherical lenses (concave or convex)  This are place in front of one or both eyes during the maintenance of binocular fixation on a target at constant distance usually 40 cms
  • 32. The fixation disparity method  The stimulus to the positive accommodation by the use of concave spherical lenses causes an eso-disparity  The stimulus to the negative accommodation by the use of convex spherical lenses causes an exo-disparity  This is recorded on the graph
  • 33. The significance of the AC/A Ratio  An appreciation of the AC/A Ratio gives an indication that there are two types of accommodative esotropia  There is accommodative esotropia in which the determining fact is the uncorrected hypermetropia with its excessive accommodative requirement leading to an excessive convergence the AC/A Ratio is normal
  • 34. The significance of the AC/A Ratio  Secondly, there is an accommodative esotropia in which the determining factor is the excessively high response of the convergence mechanism to any accommodative effort because the AC/A Ratio is high  This distinction between these two different forms of accommodative esotopia is importyant in determining the method of treatment of such cases
  • 35. The significance of the AC/A Ratio  When the AC/A Ratio is relatively normal – correction of refractive error alone may be sufficient to correct the ocular deviation but not when the AC/A Ratio is high  When AC/A Ratio is high –occlusion(although the value in eliminating suppression or amblyopia) causes an esotropia to increase in amount o that it ceases to have any latent component  This is because an over convergence inevitably follows the loss of the fusional control which occurs during occlusion
  • 36. The influence of method of treatment on the AC/A Ratio  Correcting spherical lenses  Miotic therapy  Surgical method
  • 37. Correcting spherical lenses  This alters the AC/A Ratio  For example a case in which there is orthophoria on distant fixation and esotropia on near fixation without any spectacle correction may show orthophoria on both distant and near fixation after the use of spectacle correction
  • 38. Miotic therapy  Miotics such as pilocarpine, DFP, causes the change in the AC/A Ratio  This is because the lesser innervations which is require to produce a diopter of accommodation is associated with the decrement in the innervations of the ciliary muscles and a proportionate decrement in the innervations to the medial recti so that there is decrease in the AC/A Ratio
  • 39. Surgical method  There is evidence that a decrease in the effectiveness of the medial rectus muscle or muscles by a recession in accommodative esotropia results in a reduction of abnormally high Surgical method
  • 40. Medical care of Esotropia, with High AC/A Ratio  Treatment of nonrefractive accommodative esotropia consists of full correction for the distance refractive error and bifocals for near vision to suspend the accommodative drive and to lessen accommodative convergence.  Bifocal power should be +2.50 to +3.00 diopters, and bifocals should be placed such that the upper boarder of the bifocal segment bisects the pupil.
  • 41.  Miotics, which lower the AC/A ratio, are successful in some patients.  In cases of amblyopia, early treatment of patching the normal (unaffected) eye is the mainstay of treatment.
  • 42. Surgical care Esotropia, with High AC/A Ratio  Surgery may be required if the esodeviation becomes refractory to optical treatment. Surgery often is needed when optical treatment is delayed.  Surgical treatment typically entails recession or weakening of the inward-pulling medial rectus muscle in each eye.  Surgery is performed for the nonaccommodative component only. The operation is not intended to discontinue use of glasses. FOLLOW-UP Section 6 of 8
  • 43. Esophoria With Myopic Correction have high AC/A Ratio  When myopes are esophoric this may mean a several things.  Two of which are they have a high ac/a or are overminused  There is some suggestions that this may be one type of myope that can lead to myopic progression if overminused (there was a study)  With myopic esophores that were fit with bfl contacts
  • 44. Treatment for Esophoria With Myopic Correction and high AC/A Ratio 1. Make sure they are not overminused 2. Can consider a PAL or BFL (add is clinically figured out by finding the the add that makes them ortho at near)or a SV near rx. 3. For those you mentioned they can just take off their Rx to read. 4. Or rx the least amount of minus that gets them 20/happy...dont over minus them!
  • 45. Diagnosis and treatment of exotropia with high AC/A Ratio  Patients with exotropia often have a fusional mechanism at near, which masks the true near deviation.  Consequently, determination of the accommodation convergence–accommodation (AC/A) ratio in patients with exotropia must be based on near measurements obtained after prolonged monocular occlusion (typically 1 hour).
  • 46.  When determined in that manner, the presence of a highAC/A ratio before surgery in an exotropic patient has been reported to be predictive of an esotropia at near after surgery.
  • 47. Importance of measurement of AC/A Ratio  Near measurements used to calculate the AC/Aratio in exotropic patients must be made after prolonged monocular occlusion.  Otherwise, many patients with a pseudo– highAC/A ratio will be thought to have a true high AC/A ratio.  The presence of a high AC/A ratio is infrequent in patients with esotropia, but it is highly predictive of a postoperative esotropia at near fixation.
  • 48. Accommodative esotropia with normal AC/A Ratio  Total esotropia eliminated  a. refractive - high hyperopia  bilateral not unilateral  normal range of AC/A ratio
  • 50. Low AC/A Ratio  Convergence Insufficiency - (clinical condition) the inability of the eyes to turn inward and/or sustain an inward turn.  Symptoms include eye strain with reading and using a computer, headaches, loss of comprehension, difficulty concentrating, blurred or double vision, and eye fatigue.
  • 51. Low AC/A Ratio  Clinical signs include: near point of convergence of greater than 4 inches (10 cm), greater exophoria at near than at distance, and low AC/A ratio. Vision therapy is an effective treatment option.
  • 52. High AC/A Ratio  Convergence Excess - a clinical condition in which the eyes have a tendency to turn excessively inward when viewing an object at a near distance.  Symptoms may include visual fatigue while reading or using a computer, occasional blurred or double vision, and inability to comprehend or concentrate while reading.
  • 53. High AC/A Ratio  Clinical signs include: greater esophoria at near than distance, high AC/A ratio, and a high lag of accommodation. Can be improved with vision therapy and/or glasses. (See "Esophoria")
  • 55. CHARACTERISTICS OF COMITANT EXOTROPIA  AC/A ratio; normal or low  symptoms; photophobia, squinting  prognosis; usually good
  • 56. INTERMITTENT EXOTROPIA OF THE DIVERGENCE EXCESS TYPE  distance angle > near angle  deviation is intermittent  angle of deviation increases with fixation distance  weak accommodative skills  high AC/A ratio?  near-far AC/A calculation - gradient AC/A determination