Heterotropias & Heterophorias

• What is the overview of projection in normal binocular single vision (BSV)?

  • Subjective interpretation of the direction of an object
  • Each retinal element projects to a specific point in space
  • Fovea projects straight ahead
• What does the temporal retina project to?

  Nasal retina
• What does the nasal retina project to?

  Temporal retina
• What does the superior retina project to?

  Inferior retina
• What does the inferior retina project to?

  Superior retina
• What is normal retinal correspondence (NRC)?

  • A binocular condition
  • Fovea and areas on the nasal & temporal side of one retina correspond to the fovea and temporal & nasal retina of the other eye
  • Example: Left fovea corresponds to right fovea
• What is heterotropia?

  Manifest strabismus where one visual axis is not directed towards the fixation point
• What happens when both eyes are open in heterotropia?

  One eye will fixate the target while the other deviates
• What are the types of heterotropia?

  • Esotropia: One eye deviates nasally
  • Exotropia: One eye deviates temporally
  • Hypertropia: One eye deviates upwards
  • Hypotropia: One eye deviates downwards
• What is pathological binocular diplopia?

  Double vision from simultaneous perception of two separate images caused by non-corresponding points
• What is binocular confusion?

  Dissimilar images formed on corresponding retinal points leading to incorrect perception of different objects
• What is the difference between homonymous and heteronymous diplopia?

  • Homonymous (uncrossed): Image from esotropic eye stimulates nasal retina and projects temporally
  • Heteronymous (crossed): Image from exotropic eye stimulates temporal retina and projects nasally
• What is the result of hypertropia?

  Diplopic image from the deviating eye is seen below the real target
• What is the result of hypotropia?

  Diplopic image from the deviating eye is seen above the real target
• What are the adaptations to avoid diplopia and confusion?

  • Suppression
  • Abnormal retinal correspondence
• What is suppression in the context of strabismus?

  Mental inhibition of visual sensations to eliminate confusion and diplopia
• What is abnormal retinal correspondence?

  Sensory adaptation allowing strabismic patients to use both eyes without diplopia or confusion
• What is heterophoria?

  • Latent strabismus
  • Fusion maintains correct alignment of the two eyes
  • Deviation visible when fusion is prevented
• What are the types of heterophoria?

  • Esophoria: Eyes deviate inwards
  • Exophoria: Eyes deviate outwards
  • Hyperphoria/Hypophoria: One eye deviates upwards and the other downwards
• How is manifest and latent strabismus detected?

  • Manifest: Heterotropia
  • Latent: Heterophoria
• What is the cover test?

  • An objective dissociation test
  • Elicits presence of manifest or latent deviation
  • Observes eye movements while covering and uncovering each eye
• What equipment is used in the cover test?

  • Occluder (black opaque / Spielmann translucent)
  • Pen torch
  • Accommodative target
  • Distance fixation target
• What is the first step in the cover test procedure?

  Use light at 1/3m to look at corneal reflections and note position
• What indicates manifest strabismus in the cover/uncover test?

  Movement of the uncovered eye when the other eye is covered
• What is observed in right exotropia during the cover/uncover test?

  The uncovered eye moves inwards
• What does the procedure reveal in latent strabismus?


  It reveals latent strabismus
• What is the characteristic of esophoria in corneal reflections?

  The corneal reflections are symmetrical
• What is the significance of the recovery time in the alternate cover test for exophoria?

  It indicates the recovery from phoria