2. Squint
• Squint is a condition not disease in which two
visual axes are not directed towards the fixatory
object or fixation target
• Squint may be further divided into two
categories
• 1. Heterophoria
• 2. Heterotropia
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3. Heterophoria
• Heterophoria is a condition of latent squint in
which the deviation of the visual axes is present
on dissociation of the two eye, but is absent on
removal of dissociating factor
• Heterophoria is classified according to the
direction of deviation
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5. -
• Esophoria or latent convergent squint
• A tendency of one eye to turn in relative to other
• Exophoria or latent divergent squint
• A tendency of one eye to turn out relative to
other
• Hyperphoria or latent sursumvergent
strabismus
• A tendency for one eye to turn up relative to the
other
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6. • Cyclophoria or latent torsional squint
• A tendency of one eye to wheel rotate relative to
other
• Incyclophoria
• When the 12’o clock meridian of the cornea of
the affected eye tends to lean toward the nasal
side or medial side
• Excyclophoria
• When the 12’o clock meridian of the cornea of
the affected eye tends to lean toward the
temporal side or lateral side
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7. Heterotropia
• Heterotropia is a condition of manifest squint,
which may not be present in all direction of gaze
in certain cases
• Heterotropia may be classified in several
different ways
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8. 1. Classification according to direction
of the deviation
• Esotropia or manifest convergent
strabismus
• A turning in of one eye relative to the other eye
• Exotropia or manifest divergent
strabismus
• A turning out of one eye relative to the other
• Hypertropia or manifest sursumvergent
strabismus
• A turning up of one eye relative to other
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9. • Hypotropia or manifest deorsumvergent
strabismus
• A turning down of one eye relative to other eye
• Cyclotropia or manifest torsional
strabismus
• A wheel rotation of one eye relative to other
• Incyclotropia
• When the 12’o clock meridian of the cornea of
the affected eye leans to the nasal or medial side
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10. • Excyclotropia
• When the 12’o clock meridian of the cornea leans
to the temporal side or lateral side
• It should be noted that vertical and torsional
deviation rarely occur as isolated phenomena
• A vertical deviation is usually associated with
horizontal deviation
• A torsional deviation is usually associated with
vertical deviation
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11. Classification based on comitancy
• Comitant or Concomitant squint
• A comitant squint is one in which the eye moves
in completely co-ordinated manner
• Angle of deviation which is present in primary
gaze is maintained to an equal extent in all
direction of gaze
• Angle of deviation is equal in all distances of
fixation
• Angle of deviation is equal on fixation with
either eye
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12. • Complete comitancy is rare
• It is common for the angle of a squint to vary
according to the direction of gaze, particularly
on vertical movements
• A convergent deviation usually decrease on
looking up and increases on looking down
• A divergent deviation usually increases on
looking up and decreases on looking down
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13. • If the alteration in the extent of the deviation is
large this may be described as the V –
phenomenon
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14. • If the convergent deviation found to increase on
looking up and decrease on looking down
• If the divergent deviation found to increase on
looking down and increase on looking up then
the alteration of deviation is termed as A -
phenomenon
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15. A - ESO A - EXO
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16. Incomitant or Noncomitant squint
• A non comitant or incomitant squint is one in
which the eyes move in an in-coordinated
manner so that
• 1. The angle of deviation varies in different
direction of gaze
• 2. Angle of deviation varies on changing fixation
from one eye to another
• 3. Angle of deviation varies in either eye
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17. • Incomitant squint is due to presence of a paresis
(partial failure of action) or of a paralysis (total
failure of action) of one or more extra ocular
muscles
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18. Classification based on duration
• This classification is based on whether
heterotropia is constant or only occurs in certain
circumstances or at certain times
• 1. Constant strabismus
• A constant strabismus is one in which there is a
constant deviation of the visual axes in all
directions of gaze in all distances of fixation and
irrespective of which eye is used for fixation
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19. • 2. Intermittent strabismus
• An intermittent strabismus is sometimes present
and sometimes absent in the same condition of
vision e.g. accommodative convergent squint
• 3. Periodic strabismus
• A periodic strabismus is one in which the
deviation occurs only in certain circumstances or
after regular interval
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20. Classification based on laterality
• Unilateral/ Uniocular
• A uniocular strabismus is one in which the
squinting eye is always the same except under
conditions of testing which force the squinting
eye to take up fixation
• Bilateral/ Alternating
• An alternating strabismus is one in which the
deviation may occur in either eye and in which
there is no obvious preference for one eye to
remain fixing eye
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21. Classification based on
Accommodation
• Accommodative Squint
• Deviation induced by influence of
accommodation. E.g. Accommodative
convergent squint
• Non – Accommodative Squint
• Deviation present in the absence of
accommodation effort
• The deviation increases on the exercise of
accommodation
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22. Fleeting Squint
• This occurs in babies during the first few months
of life before the establishment of normal
binocular reflexes
• Such a squint is usually momentary occurring
usually when the baby is upset
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23. Purposive Squint
• This is the term applied to a convergent squint
which may be produced voluntarily in persons
with normal binocular function
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24. Pseudo strabismus
• This the term applied to a false appearance of
squint in the absence of any deviation and it may
occur under different condition
• Visual axes are aligned toward fixation object
• Any abnormality to lids, canthii or orbit may
lead to pseudo strabismus
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