Assessment of Binocular Vision

Question 1

What symptoms does BV anomalies commonly cause? Why is cover test useful?

Answer 1

BV anomalies frequently cause sxs such as asthenopia, HAs, difficulty reading & diplopia
Also 3-4% of the population develop a childhood strabismus in either the loss or degradation of BV
Cover test is absolute gold standard for detecting BV:
* Some pxs have BV but it looks as if they are squinting due to anatomical factors (pseudostrabismus)
* Use a torch with cover test – no looking in distance – get them to look at light first, then accommodative target at near then picture on chart in distance
* Look for reflections to be central & symmetrical

Question 2

Features to look for when thinking pseudostrabismus?

Answer 2

• Epicanthus
• Lid anomalies
• Globe positon
• Orbit & facial asymmetry
• Pupillary anomalies
• Iris anomalies

Question 3

Describe corneal reflections and the predicted amounts of displacement in prism dioptres?

Answer 3

• Ask px to fixate a pen torch at near & distance
• If reflected images from cornea appear central & symmetrical
  o Assume eyes (visual axes) are aligned
   If corneal reflection sitting lower down that eye is higher, if corneal reflection is nasal then eye is exo – always looking for manifest deviation first – can get idea of how much vision the eye has in how it takes up fixation
• 1mm of displacement of corneal reflection corresponds to 7°of deviation of visual axis (Hirschberg)
  o Displaced temporally = eso deviation
  o Displaced nasally = exo deviation
   1° = 0.50D
   20° = ~10-12D
   45° = ~25-30D

Question 4

Describe cover test and alternate cover test in the diagnosis of BV?

Answer 4

• Cover test (CT) an objective 3 part dissociation test
  o Cover-uncover test to detect heterotropia (manifest strabismus)
   Slowly remove cover – tells you about BV & how much vision in that eye
   If have a manifest movement then no latent movement but if not manifest then they have a latent – look for latent when remove cover from eye that’s been covered
   No manifest to start with but it is there under cover then may have phoria
  o Cover-uncover test to detect heterophoria (latent strabismus)
   Need to break dissociation for long enough
  o Alternate cover test to detect maximum deviation
   Only need to do a few times to find out what maximum angle is
   If don’t do it slowly enough then wont see a movement that is there – slow it done & trust yourself
  Glasses on begin with then glasses off & repeat
  Torch first
  Then accommodative target – something interesting
  Then look at 6m to an interesting target
  Sometimes get to look at 20m too

Question 5

Describe esotropia, exotropia, hypertropia and hypotropia?

Answer 5

Esotropia (convergent squint):
* Eye deviated inwards (convergent)
* Uncovered eye will move outwards (temporally) to take up fixation
* On removal of cover eye will move inward again

Exotropia (divergent squint):
* Eye is deviated outwards i.e. divergent
* Uncovered eye will move inwards (nasally) to take up fixation
* On removal of cover eye will move outward again

Hypertropia (vertical squint):
* Eye is deviated upwards i.e elevated
* Uncovered eye will move downwards to take up fixation
* On removal of cover eye will move upward again

Hypotropia (vertical squint):
* Eye is deviated downwards i.e. depressed
* Uncovered eye will move upwards to take up fixation
* On removal of cover eye will move downward again

Question 6

How do you record a manifest deviation?

Answer 6

• Squinting eye & direction of deviation
• The fixation if the vision is good in the affected eye it will take up fixation & may continue to fixate i.e. stay straight when cover is removed from other eye; if vison is equal in both eyes then a squint may freely alternate between the 2 eyes; if amblyopia is present fixation may be poor
• Size of deviation (slight, moderate or marked)
• Changes in deviation at different distances
• Changes in deviation if accommodation is exerted
• Changes in deviation with & without glasses

Question 7

How do you record a latent deviation?

Answer 7

• Direction of deviation
• Size of deviation (slight, moderate or marked)
• Movement of eye to take up fixation is known as reecovery movement - indicates how well compensated heterophoria is
• Recovery is usually referred to as rapid or good, moderate, slow or delayed
• Changes in the deviation at different differences
• Changes in the deviation with & without glasses

Question 8

Why is cover test useful?

Answer 8

• Detects all manifest & latent strabismus
• Indicates size & variation in deviation with distance & effect of any refractive error
• Gives an indication of level of VA in either eye - fixation
• Indicates if a latent deviation is controlled (well compensated) - rate of recovery