binocular vision Flashcards
duane’s retraction syndrome cause
caused by inner action of the lateral rectus by extra branches of CN3 due to an absent/ atrophic CN6
3 types of duane’s
type 1 - limitation of abduction
type 2 - limitation of adduction
type 3 - limitation of abduction + adduction
duane’s adduction
narrowing of palpebral aperture, upshoots and globe retraction
duane’s abduction
limitation of abduction and widening of palpebral aperture
Brown’s syndrome cause
mechanical restriction of superior oblique caused by inflammation or trauma to trochlear region
Brown’s syndrome
- usually unilateral
- mechanical restriction of SO (inflammation or trauma)
- little deviation in primary position
- overaction of contralateral SR
- clicking if nodule gets through tendon and becomes stuck
incomitant
angle of deviation changes in different positions of gaze
neurogenic
relates to problem with nerve supply to a muscle
myogenic vs mechanical
myogenic = weakness of muscle itself
mechanical = physical limitation/ restriction
contralateral synergist
muscles in different eyes which move eyes in the same direction
e.g., R lateral rectus + L medial rectus
ipsilateral antagonist
muscles in same eyes which move in different directions
e.g., R lateral rectus + R medial rectus
ipsilateral synergist
muscles in same eyes which move in same direction
e.g., superior oblique + inferior rectus both depress eyes
herrings law of equal innervation
when increased innervation is sent to a muscle to contract it, a simultaneous and equal impulse is sent to the contralateral synergist
sherringtons law of reciprocal innervation
when increased innervation is sent to a muscle to contract it, decreased innervation goes to the direct antagonist (same eye) which is therefore relaxed
RADSIN
recti adduct (obliques abduct)
superior intort (inferior extort)
muscle sequelae steps
- underaction of primary muscle
- overaction of contralateral synergist
- overaction of ipsilateral antagonist
- secondary inhibition palsy of contralateral antagonist
deviation in primary positions
mechanical vs neurogenic
mechanical - little or no deviation in PP
neurogenic - depending on extent of palsy, deviation can be marked
diplopia in mechanical vs neurogenic
mechanical - reversal of diplopia (e.g., between upgaze + downgaze)
neurogenic - except in 3rd, nature of diplopia remains the same in all POG
pain on movement mechanical vs neurogenic
pain on movement in mechanical whereas no pain in neurogenic
muscle sequelae mechanical vs neurogenic palsy
mechanical = steps 1+2 only
neurogenic = if complete, full sequelae
CN3 signs
dilated pupil, ptosis, headache, pain around eye
PP - eye down + out (XOT + hypotropia) - larger at near
cannot adduct, elevate or depress
CN3 management
emergency referral - phone ARC
CN3 causes
pupil involvement = suspect aneurysm of posterior communicating artery
pupil spared = suspect underlying vascular cause (diabetes)
trauma, compression
CN4
trochlear nerve affected which supplies superior oblique muscle
CN4 causes
- trauma (longest nerve so more susceptible)
- decompensating congenital palsy
- microvascular causes
CN4 signs
- vertical diplopia (worse at near + looking down)
- hypertropia in PP
- size of deviation worsens when head tilted to affected side
CN6 palsy
abducens nerve affected which supplies the lateral rectus
CN6 causes
usually microvascular - diabetes, trauma, intracranial hypertension
CN6 signs
- px presents with horizontal diplopia (worse at distance)
- deviation in PP (SOT)
amblyopia
developmental condition characterised by reduced vision in one eye
VA worse than 6/9 not due to uncorrected refractive error/ pathology
due to presence of sensory impediment to visual development
different types of amblyopia
- stimulus deprivation - due to ptosis or congenital cataract
- strabismic
- anisometropic
- ametropia
- meridonial
critical period
when visual development is most vulnerable and plastic
vision - birth to 3yrs
BSV - birth to 5yrs
sensitive period
visual development is vulnerable to damage but may still respond to correction + treatment
vision 3-8yrs old
BSV 5-8yrs old
px presents with unequal VAs but no strabismus
prescribe full rx FT then 3/12 review
then referral if no improvement in amblyopic eye
ESOPHORIA REFRACTIVE MANAGEMENT
needs hyperopic/ max plus correction
max plus relaxes accommodates -> relaxes convergence -> reduces SOP
SOP at near only may need bifs so DVA still clear
EXOPHORIA REFRACTIVE MANAGEMENT
needs full myopic correction / over minus
more minus = px accommodates over that to correct XOP i.e., more accommodate more convergence to reduce XOP
BIX BOS
EXO = neutralised by base in prism
ESO = neutralised by base out prism
sheards criterion
if more than half the fusional reserves need to be used to control the phoria then the visual system will be under stress and phoria decompensates
maddox rod vs fixation disparity
maddox rod measures full size of deviation
fixation disparity measures degree of prism relief required to neutralise any FD present i.e., amount of phoria not being controlled by fusional reserves
fusional reserves
amount of divergence or convergence that can be induced before fusion compromised / blurred or double vision occurs
jump exercises
used for convergence insufficiency
move pen to nose until goes double - look at distance object until goes clear then look back at pen
when is prisms used?
when eye exercises inappropriate due to age/ ill health/ lack of time/ lack of incentive
power prescribed is minimum that just allows phoria to become compensated
when may referral be considered for diplopia?
factor contributing to decompensation that requires attention of another practitioner
cause of anomaly suspected to be pathological/ recent head injury
anomaly not responded to refractive correction, exercises or prisms
fusion amplitude
phoria becomes decompensated when fusion amplitude insufficient
poor positive fusion amplitude on XOP, poor negative in SOP
recession vs resection
recession weakens the muscles whereas resections strengthens muscles
risk of squint
no strabismic relative = 1% chance
1 parent or sibling = 15% risk
2 or more parents/siblings = >20%
BHHT
allows differentiate of SO palsy from one affecting contralateral SR
head tilt to affected side - if hypertropia increases = SO palsy
