Describe fully accommodative esotropia and how it’s managed
a strabismus secondary to refractive error onset between 2-5yrs (+2.00 to +7.00)
they manage visually sRx or they’d be bilateral refractive amblyopes
Give full Rx full-time wear and check post-cyclo, review in 1mth ensure no amblyopia/suppression
Describe partially accommodative esotropia
high AC:A with manifest deviation reduced by min.10D with specs
full rx doesn’t correct small strabismus; try exercises
if large consider surgery (be aware of divergence)
Describe convergence excess esotropia
ESOT@Near with corrected Rx due to >8:1 AC/A onset 2-5yrs
BSV for distance fixation
(+1.50 to +5.00)
noticeable when tired/ill
Describe infantile esotropia with its risk factors and management
onset <6mths with large 30∆ deviation
age-expected refraction, often crossed fixation
male, FOH, prematurity, systemic disorders/medication
refer for surgery, latent/manifest nystagmus or dissociated vertical deviation can persist post-surgery
Describe acquired non-accommodative esotropia
onset 6-24mths with 30-70∆ deviation, normal BV development until strabismus, normal AC/A
Explain intermittent exotropias at distance and near
Distance: likely asymptomatic, eye drift noticed by others (exercises for fusional reserves, over-minus)
Near: ≈myopic teenage with diplopia when reading (exercises/over-minus for small angles, surgery for large angles)
EXOT@D then EXOP@N vice versa
Describe microtropia, which is more common and its management
micro-strabismus less than
6∆/10∆ with mild amblyopia + anisometropia
Reduced stereo on Frisby with EF + HARC
Secodnary to larger treated deviation (surgery/exercises/specs)
Primary if no previous history (<3yrs old)
eso more common than exo
treat anisometropia/give exercises if <4/5yrs consider patching
Describe the significance of NMD on CT with nd without identity
With: HARC + absolute EF, Anomaly angle = Eccentricity angle (NMD)
Without: central/non-absolute EF, ARC can be ARC/NRC with central suppression/peripheral fusion or manifest deviation seen on CT
Define residual and consecutive tropias
Residual: from surgical under correction
Consecutive: from surgical over correction
Which 3 things will a strabismic px experience related to BV?
Diplopia/Visual confusion
Suppression
ARC
Describe the initial presentation of strabismus
if eyes are misaligned the sensory fusion can’t cope with the motor misalignment so there’s no longer a single percept
Perceived position from retinal location remains due to neural ‘wiring’ so percept is different from ‘real’ world
Explain how some diplopia is normal in terms of crossed + uncrossed
diplopic images on widespread NCP (outside Panum’s FA)
physiological diplopia
Crossed – focus @ distance near object will
have image on temporal retina each eye
Uncrossed – focus @ near, distance object
will have image on nasal retina of each eye
How is diplopia and visual confusion removed in young/older individuals?
Young: alter signalling/organisation of visual system
Binocular HARC or monocular suppression of strabismic eye’s binocular field
Older: occlude one eye, compensate for AHP, try to ignore image/confusion
Describe binocular suppression
a non-selective inhibitory process removing all stimuli n suppressed region from consciousness
occurs in plastic systems in response to strabismus/anisometropia/phorias
affected by fatigue/squint angles/fixation and can cause diplopia
When can normal suppression occur?
contradictory (non-fusable) supply each eye causing alternate suppression (binocular retinal rivalry)
physiological suppression against physiological diplopia
monovision CL wearers ignore non-required image
How does suppression relate to the fovea?
persists in binocular conditions, suppression areas localised to poor eye fovea + non-foveal area creating diplopic area
How is a Sbisa bar used to test for suppression?
filter bar of increasing density of sequential filters
medium density filter on good eye fixating a white spotlight
level of suppression measured with increasing filter density until 2 dots/white dot seen
Describe the classification of HARC and UnHARC
HARC: sensory realignment counteracts motor misalignment exactly
UnHARC: sensory realignment can’t fully counteract motor misalignment exactly - usually an artefact/px always diplopic
Describe the significance of HARC as a binocular adaptation
What are its advantages?
avoids diplopia/confusion, disappears on occluding 1 eye
natural viewing conditions with fixing eye’s fovea corresponding to retinal area at angle of squint in non-fixing eye
used alternatively to suppression
retains BSV while squinting and can achieve gross stereo depending on angle size/VA of non-fixing eye
How is HARC investigated and differentiated from suppression?
strabismic px with stereo must have HARC, detect via Bagolini for minimal visual disturbance
using monocular markers in a binocular environment (Mallett but near markers too small/require polarising filter so unnatural)
How can we grade depth of ARC?
Good ARC condition cause deep ARC otherwise shallow
ARC can break down into induced diplopia
assessed via ND filter bar in front of fixing eye, increase by 0.3 log steps, when streak/marker disappears suppression occurs
higher ND value ~ stable/deeper ARC
Explain why HARC doesn’t completely compromise binocularity
in a plastic system the visual system suppress the squinting eye fovea and appropriate non-foveal points to avoid diplopia/confusion
left with no (para)central binocularity but under favourable conditions a sufficient system further adapts to achieve a degree of binocularity via cortex reorganisation in response to motor misalignments
this sensory realignment is an ARC
Why don’t all strabismic have HARC?
ARC key requirement involve early onset squint (plastic system) and small, constant strabismus angle
