classification of squint
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Classification of Squint7/10/2013
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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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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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•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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•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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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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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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•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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•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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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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•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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•If the alteration in the extent of the deviation is large this may be described as the V – phenomenon
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•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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A - ESO A - EXO
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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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•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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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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•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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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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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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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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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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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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