Classification of Heterophoria & Heterotropia

Question 1

Describe a heterophoria - latent squint?

Answer 1

• Most binocular anomalies result in misalignment of visual axes
• Fusion reflex maintains correct alignment of the 2 eyes
• If this fusion reflex is suspended eyes will adopt ‘fusion free position & a measurable deviation of visual axes will occur
• Error of alignment that takes place when fusion is suspended is heterophoria
• Not manifest if have enough fusion to control it
  If eyes remain exactly parallel on dissociation for either near or distance fixation this is termed orthophoria ‘straight’
  In normal there is nearly always a slight tendency for the eyes to deviate slightly on dissociation
  The cover test will reveal this dissociation

Question 2

Describe cover test in heterophoria?

Answer 2

• Performed to diagnose the presence of a heterophoria & heterotropia
• In heterophoria one eye is covered and that eye will deviate (i.e. under the cover)
• When cover is removed the movement to regain fixation with that eye is seen
• Other eye will also make these movements on dissociation
• Cover test removes fusion

Question 3

What are all the types of esophoria?

Answer 3

• Convergence Excess (Type Esophoria):
  o Deviation 10^ greater at near fixation
• Divergence Weakness:
  o Deviation 10^ greater at distance fixation
• Non-specific:
  o Deviation similar at near and distance fixation
  o Even if difference 6^ between near & distance

Question 4

What are all the types of exophoria?

Answer 4

• Convergence weakness
  o Deviation 10^ greater at near fixation
  o DO NOT CONFUSE THIS WITH CONVERGENCE INSUFFICIENCY
• Divergence excess
  o Deviation 10^ greater at distance fixation
• Non-specific
  o Deviation similar at near & distance fixation

Question 5

Describe vertical heterophoria?

Answer 5

• Eye moves upwards under the cover & will then be seen to come down once cover removed – HYPERphoria
• Eye moves downwards under cover & will then be seen to come up once cover is removed – HYPOphoria
• Nomenclature of deviation is determined by high eye  right HYPERphoria = left HYPOphoria = R/L
• If vertical phoria it will be highly unlikely they have full motility – usually slight under action/over action to compensate

Question 6

Describe cyclophoria?

Answer 6

• Excyclophoria:
  o Upper poles of corneas deviate outwards when fusion prevented
  o Superior oblique & superior recurs are intorters – if under action eye will be extorted
• Incyclophoria:
  o Upper poles of corneas deviate inwards when fusion prevented
  o Inferior oblique and inferior recurs are extorters – if undersction eye will be intorted
• Highly unlikely they will have full motility – usually slight under action/over action to compensate
• This deviation is hard to see on cover test – look at point on iris to see if it is rotating

Question 7

Describe concomitant and incomitant heterophoria?

Answer 7

Concomitant Heterophoria: dissociated deviation remains same whichever eye is made to fixate. No significant change in 9 positions of gaze
Incomitant Heterophoria: dissociated deviation increases when one eye is made to fixate and decreases when other eye fixated OR it increases and decreases when eyes are dissociated in different positions of gaze

Question 8

What is the aetiology of incomitant heterophoria?

Answer 8

• Most are seen in presence of para lyrical or mechanical strabismus
• Diagnosed according to underlying cause e.g. esophoria in 6th nerve palsy or hypophoria in Thyroid Eye Disease or hyperphoria in 4th nerve palsy
• Hyperphoria, hypophoria, cyclophoria are almost always incomitant

Question 9

What can incomitancy be due to?

Answer 9

• Undersection of one or more of EOMs as result of cranial nerve palsy or mechanical or myogenic factors
• Uncorrected or undercorrected spherical anisometropia
  o This requires more accommodation and therefore more convergence when one eye fixated than when other fixates
  o Accurate correction should result in concomitance being restored
  o Therefore test pxs with and without glasses – if px has been incorrectly dispensed can appear as a problem – if optical centres have moved for px then can induce prism

Question 10

With an incomitant heterophoria, what does the dissociated deviation do?

Answer 10

• Increases when paralytic eye made to fixate (secondary deviation)
• Decreases when fellow eye fixated (primary deviation)
• Varies when dissociated in different positions of gaze

Question 11

What is the important thing to note in heterophoria unless problem with refractive error?

Answer 11

Unless problem with refractive error – deviation should be same in both eyes

Question 12

What is a manifest squint? What happens when someone with a manifest squint relaxes accomm?

Answer 12

Manifest squint – when both eyes are open one eye will fixate the target and the other will deviate
In some pxs when they relax the accommodation (make the image blurry) the eyes go straight
Normal retinal correspondence

Question 13

Describe cover test in a patient with heterotropia?

Answer 13

• In heterophoria one eye is covered and other eye is observed
• If uncovered eye moves to take up fixation, a heterotropia or manifest deviation of that eye is present
• Horizontal and vertical squints can Co-exist
• Hererotropia can be in one eye or both (alternating) although not at same time

Question 14

Describer vertical heterotropia?

Answer 14

• If uncovered eye moves downwards to take up fixation a hypertropia is present
• If uncovered eye moves upwards to take up fixation a hypertropia is present
• Nomenclature of deviation is determined by which eye shows manifest deviation
• If px shows a manifest R Elevation on cover test we would refer to this as right hypertropia as they are not fixing with RE

Question 15

Describe cyclotropia?

Answer 15

• Excyclotropia: upper poles of corneas deviate outwards
• Incyclotropia: upper poles of corneas deviate inwards
• Highly unusual in px who didn’t have cranial nerve weakness

Question 16

What is concomitant heterotropia?

Answer 16

• Ocular movement is within normal limits at time of onset of strabismus
• Angle of deviation is virtually same whichever eye is used for fixation in primary position

Question 17

What is incomitant heterotropia?

Answer 17

• Synonym – paralytic strabismus
• Occurs when there is limitation of ocular movement
• Angle of deviation increases as eyes are turned in direction of limitation and decreases when turned in opposite direction, with exception of mechanical palsies where movement may be limited in opposing direction.
• The secondary deviation exceeds the primary deviation – the development of secondary comitance in long-standing cases can result in equality

Question 18

What are the 3 overarching types of esotropia?

Answer 18

o Primary
o Secondary - primary cause was loss of vision
o Consecutive - previously XOT – something has made it go from exo to eso

Question 19

What is a primary esotropia?

Answer 19

• The convergent deviation constitutes the initial defect
• Present in all positions of gaze and at all viewing distance (near and distance)

Question 20

Describe a constant primary esotropia with and without accomm?

Answer 20

o Esotropia is present under all conditions
 With an accommodative element: the deviation increases when accommodation is exerted i.e. when hypermetropic correction is removed
* Hyperopia correction – not full accommodative as become straight – hyperopia just decreases the size of it. They are still constant, they have no binocularity, they are not wired up to have normal retinal correspondence
 Without an accommodative element: the deviation is unaffected by state of accommodation i.e. no hypermetropia
* Without accommodative element – they have no hyperopia but have an SOT
* Accom doesn’t change size of their squint
* May be slightly bigger at near since we all accommodate at near (but not much)

Question 21

Describe intermittent esotropia?

Answer 21

o SOT is only present under certain conditions
o These pxs have normal retinal correspondence (NRC)
o Accommodative Esotropia:
 State of convergent deviation is affected by state of accomm, & this is the primary factor in the aetiology of the squint i.e. hypermetropia or high AC/A
* Is it uncorrected hypermetropia that is making them squint?

Question 22

Describe infantile esotropia? (constant esotropia)

Answer 22

• Constant primary esotropia
• Onset <6/12
  o 50-year-old px could be seen and can identify as infantile SOT – due to unique features of it
• Large up to 45^
• Constant angle of deviation
• Cross fixates
  o So much squinting that when look to left use RE as pointing in that direction – don’t even attempt to abduct as angles so large they just use the other eye
• Usually alternating – they can swap between eyes – can be quite free sometimes
  o So NO AMBLYOPIA
• Not accommodative
• Associated with Dissociated Vertical Divergence (DVD) and latent nystagmus that develops 12-18mths (seen when cover one eye)

Question 23

Describe fully accommodative esotropia? (intermittent esotropia)

Answer 23

• Normal binocular vision present for all distances when hypermetropia is corrected
• Will always be at least 3-5D hypermetropia – which is why they squint at near and distance

Question 24

What is the AC/A ratio?

Answer 24

• For every dioptre of accomm that we exert, eyes will turn in ~3-5^ - normal
• Normal AC/A ratio – should be normal convergence of about ~12-15^
• High AC/A ratio – 10:1 for every dioptre they accomm their eyes turn in 10^

Question 25

What is convergence excess esotropia? (intermittent esotropia)

Answer 25

• Normal binocular vision for distance fixation, esotropia on accommodation for near fixation
• Reading add – to reduce accommodative effort
  o They only squint at near, don’t squint in distance – when relax accommodation with reading add eyes straight
• Can be myopes too
• Generally low to no hyperopia
• High AC/A ratio and that’s why the squint at near

Question 26

Describe cover test findings of fully accommodative SOT vs convergence excess SOT?

Answer 26

• Fully accommodative SOT:
  o Hypermetropia
  o CT c gls N sl esophoria with gd rec
   D min esophoria with gd rec
   s gls N mod L Esotropia
• s gls D sm L Esotropia
• Convergence Excess SOT:
  o Low/no hypermetropia
  o CT N mod L esotropia
   D sl esophoria with gd rec
  o High AC/A ratio
  o Bifocal – N sm esophoria with gd rec
  o (tropia at near but phoria in distance)

Question 27

Describe fixation distance: near esotropia and distance exotropia? (intermittent esotropia)

Answer 27

• Near Esotropia:
  o Normal BV for distance fixation, esotropia on near fixation even if accommodative effort is relieved – normal AC/A ratio
  o Looks like convergence excess
   To differentiate – measure AC/A ratio – convergence excess will be higher than 5:1 (normal)
• In near esotropia, will have normal (or low) AC/A ratio
  o Only reason near esotropia is squinting is because of fixation distance
• Distance Esotropia:
  o Esotropia on distance fixation, binocular single vision on near fixation (ensure full abduction)
  o Esophoria at near – straight and controlled
  o Esotropia in distance – they are squinting
  o Worried about 6th nerve palsy – need to workout if this is concomitant esotropia or Incomitant

Question 28

Describe esotropias relating to time? (intermittent esotropia)

Answer 28

• Cyclic esotropia – every 24-48 hours
  o Deviation occurs at regular intervals – child may be hyperactive
  o Large angle esotropia that appears one day, goes away one day and comes back – on way to becoming a constant esotropia
• Non-specific:
  o Intermittent esotropia not conforming to any pattern – most squints start off intermittent & can control it but then becomes constant and cant control it

Question 29

Describe secondary esotropia?

Answer 29

• Esotropia which occurs after pathological loss or impairment of vision
• Esotropia due to cong cataract for e.g.
• If really reduced VA then may just diverge – nothing keeping it straight

Question 30

Describe consecutive esotropia?

Answer 30

• Esotropia in a px who has previously had exotropia or exophoria
• Either spontaneous, with passage of time or post-operative (they made them too straight)
  o Where are they suppressing – where have they got diplopia – which part of retina is being stimulated (temporal or nasal)

Question 31

What are the overarching types of exotropia?

Answer 31

• One or other eye deviates temporally
• 3 kinds:
  o Primary
  o Secondary
  o Consecutive
• More esotropes than exotropes in children
• Accommodation doesn’t really have influence here except from 1 type of exotropia squint

Question 32

Describe constant primary exotropia?

Answer 32

o Exotropia is present under all conditions
 Can gradually get bigger if no incentive for 2 eyes to work together – no BV – abnormal retinal correspondence
o Early onset: rare, suspect low VA
o Decompensated intermittent: often diagnosed from hx/photographs; BSV may be recoverable (NRC)
 Need to look for NRC and investigate it

Question 33

Describe intermittent exotropia?

Answer 33

o Exotropia is only present under certain conditions
o Straight eyes are near – may be slight phoria – well controlled
o NRC – eyes wired normally
o As soon as look in distance one or other eye will diverge – manifest
 If have high AC/A ratio – that’s what is making them straight at near – that’s simulated type (can control at near because of high accommodative convergence ratio – changes management pattern)
 If put up +3 at near and makes no difference & they still phoria – then they are a true type XOT

Question 34

Describe distance exotropia (divergence excess)? (intermittent exotropia)

Answer 34

 Divergence excess exophoria – if they have remained latent in distance
* Manifest in distance – distance exotropia
 Exotropia on distance fixation & binocular vision on near fixation
 Angle of deviation for near may or may not increase on:
* Prolonged disruption of occlusion
* OR elimination of accommodation
 Cases which show increase for near are classified as ‘simulated’ and those who don’t as ‘true’
* If simulated – because of high AC/A ratio like convergence excess
 Features:
* NRC
* Exophoria at 33cms
* Exotropia at 6m and 20m
o Check far distance too – take them over to window and get them to look out
* True/simulated types
o Simulated – high AC/A ratio
o Simulated – high fusional control at near
o True – no change at near with accomm or fusion relieved
 Many of these come in later in childhood – as parent used to seeing baby up close – only notice when walk into a room at distance away from child
 Excessive fusional ability:
* Break fusion using cover test
* First do AC/A ratio – if still doesn’t change
* Then patch them for 1 hr - & take patch off & then bigger at near
* Then true if no difference

Question 35

Describe near exotropia? (intermittent exotropia)

Answer 35

• Normal BV for distance fixation
• Exotropia on near fixation
• Would also have reduced convergence near point
  o Differentiate primary convergence insufficiency or secondary CI because they have near exotropia
  o If can converge and still have near exotropia after treating CI then it is near exotropia type
• Straight in distance – slight exophoria
• As soon as look at near target get exotropia

Question 36

What is non-specific exotropia? (intermittent exotropia)

Answer 36

• Exotropia which shows intermittent BV not confirming to any pattern

Question 37

What is secondary exotropia?

Answer 37

• Exotropia which occurs after pathological loss or impairment of vision
• Visual loss as in hand movements or perception of light

Question 38

What is consecutive exotropia?

Answer 38

• Exotropia in a patient who has previously had esotropia or esophoria
• Either spontaneous with passage of time or post-operative

Question 39

Describe incomitant (paralytic) strabismus?

Answer 39

• Occurs when there is limitation of ocular movement
• May be congenital or acquired
• May be horizontal, vertical &/or cyclical
• Classified according to underlying cause of limitation of movement:
  o Neurogenic
  o Mechanical
  o Myogenic
• 6th nerve palsy – bigger in distance & when looking to right
  o This can look like esotropia but this is how to differentiate
• 3rd nerve palsy – could present as exotropia
  o Wont be able to adduct – may not be able to elevate or depress – may have ptosis

Question 40

Describe pathological binocular diplopia?

Answer 40

• Initially px appreciates diplopia
  o This is the first thing that happens for everyone regardless of age if start to develop squint
  o As soon as one eye is squinting will start to appreciate diplopia
• Results from simultaneous appreciation of 2 separate images caused by stimulation of non-corresponding points by same object
• The diplopia may be horizontal, vertical or torsional

Question 41

Describe homonymous (uncrossed) diplopia?

Answer 41

Binocular diplopia associated with esotropia, in which the image of fixating object is received on nasal retina of deviating eye and is therefore projected temporally it results when non-corresponding retinal points are stimulated by the same object

Question 42

Describe heteronymous (crossed) diplopia?

Answer 42

Binocular diplopia associated with exotropia, in which image of fixating object is received on temporal retina of deviating eye and is therefore projected nasally it results when non-corresponding retinal points are stimulated by the same object

Question 43

How does the visual system cope with pathological diplopia?

Answer 43

• At first when strabismus develops retinal correspondence is normal & suppression is absent, so diplopia & confusion occur
• In young children diplopia & confusion are rapidly ignored
  o This is termed suppression
• Suppression is a cortical mechanism
• This suppression mechanism only occurs in children under age of ~8 years
  o Suppression is cortical inhibition of images that are happening
  o At level of visual cortex (not at level of retina) that allows you to suppress
• When squint develop in older pxs diplopia is a very troublesome symptom
  o Everyone with a squint will have diplopia
  o May only last hours – brain so upset by complete mismatch that suppression comes in very quickly
• Abnormal retinal correspondence describes a condition in which normally non-corresponding retinal areas of the 2 eyes co-operate to produce a form of binocular single vision
  o ARC is NOT same as suppression

Question 44

What is confusion?

Answer 44

Confusion is the simultaneous appreciation of two superimposed images due to the stimulation of corresponding retinal points by two different images