Routine Screening

• What is heterophoria?

  Heterophoria is when the fusion-free position is different from the functional binocular position.
• What happens to the eyes when the stimulus to fusion is eliminated?

  The eyes adopt the fusion-free position and are said to be dissociated.
• What is orthophoria?

  Orthophoria is when the fusion-free position is identical to the functional binocular position.
• How is orthophoria clinically detected?

  No eye movement is detected clinically with or without occluding either eye.
• What is the clinical measurement for orthophoria in terms of deviation?

  Less than $1\Delta H$ and $0.25\Delta V$.
• What occurs in heterophoria when the cover is removed?

  Bifoveal fixation is regained.
• What test is used to assess heterophoria?

  The alternating cover test (CT).

  
• What is heterotropia?

  Heterotropia is when the visual axes do not intersect at the fixation point.
• What is another name for heterotropia?

  Strabismus.
• What can happen when heterotropia is congenital?

  Visual development might be poor, leading to amblyopia and/or strabismus.
• What are the various forms of heterotropia?

  Constant, intermittent, and alternating.
• How is heterotropia assessed?

  Using unilateral cover test.

  
• What are the types of eye movement under cover tests?

  • Exophoria (ExoP): Abduction (outwards)
  • Esophoria (EsoP): Adduction (inwards)
  • Hyperphoria (HyperP): Elevation (upwards)
  • Hypophoria (HypoP): Depression (downwards)

  
• What are the types of relative position of the deviating eye?

  • Exotropia (ExoT): Abduction (outwards)
  • Esotropia (EsoT): Adduction (inwards)
  • Hypertropia (HyperT): Elevation (upwards)
  • Hypotropia (HypoT): Depression (downwards)
• What is the critical test for oculo-motor imbalance?

  The cover test.

  
• What must be controlled during the cover test?

  Accommodation.
• What are the two types of cover tests?

  • Unilateral cover test
  • Alternating cover test
• What does the unilateral cover test differentiate?

  It differentiates phoria and tropia.
• What indicates a tropia during the unilateral cover test?

  If the uncovered eye moves to take up fixation.
• What indicates orthophoria during the unilateral cover test?

  If no movement is seen.
• What is the purpose of the alternating cover test?

  To assess phoria by alternating covering each eye.

  
• What does the presence of any movement in either eye during the alternating cover test indicate?

  It indicates phoria.

  
• What happens to the corrective fusion reflex during the alternating cover test?

  It is eliminated, disrupting fusion constantly.
• What are the steps involved in the unilateral cover test?

  1. Place cover over one eye.
  2. Observe if the uncovered eye moves.
  3. If it moves, it's tropia; if not, it's ortho/phoria.
  4. Cover the other eye for at least 3 seconds to dissociate fusion.

  
• What are the steps involved in the alternating cover test?

  1. Cover and uncover each eye alternately.
  2. Observe for any movement in either eye.
  3. If movement is detected, it indicates phoria; if not, it's ortho.
  4. Fusion is constantly disrupted during the test.

  
• What methods are used to quantify eye movement?

  Visual inspection, prism bar, Maddox rod, Von Graefe, Maddox wing, and Prentice card.

  
• How is movement quantified using visual inspection?

  By estimating the size of movement between $2\Delta$ to $8\Delta$.
• What is the procedure for using a prism bar?

  Start with the minimum amount of prism and combine with alternating CT to neutralize movement.
• What is the function of the Maddox rod?

  It distorts the retinal image of a point of light to a line perpendicular to the axis of the rod.

  
• How is the Maddox rod typically used in testing?

  It is placed over one eye while the other eye views a spot of light in a darkened room.

  
• What should be ensured when using the Maddox rod?

  The room should be completely dark and the chart flat to avoid light scatter.
• What is the purpose of the Von Graefe test?

  To measure deviations using dissociating and Risley prisms.
• What are the advantages of the Von Graefe test?

  It allows fine control of prism magnitude.
• What are the disadvantages of the Von Graefe test?

  It has the poorest repeatability compared to other tests and is limited to primary gaze.
• What is the purpose of the Prentice card?

  • Used for near phoria testing.
  • Indicates the direction of deviation (ExoP or EsoP).
  • Color coding helps identify the eye being tested.
• What is the Maddox Wing used for?

  • Achieves dissociation using a septum.
  • Measures cyclo deviations.
  • Cons: Scale figures may overestimate or underestimate deviations.

  
• What should be done before measuring phoria or tropia?

  Get the patient to blink a few times and check for stability of alignment.
• What are the normal values for distance and near phoria?

  Distance: $1XP \pm 1\Delta D$; Near: $3XP \pm 3\Delta D$.
• What are the five types of phoria and four types of tropia?

  Phoria types:

  • Exophoria
  • Esophoria
  • Hyperphoria
  • Hypophoria
  • Orthophoria

  
  

  Tropia types:

  • Exotropia
  • Esotropia
  • Hypertropia
  • Hypotropia
• What is the difference between phoria and tropia?

  Phoria is a latent deviation, while tropia is a manifest deviation.