ABO Binocular Vision & Strabismus 2 — Questions and Answers
Question 1: In a patient with exotropia, the deviating eye turns in which direction?
- Inward (nasal)
- Upward (superior)
- Outward (temporal) (Correct answer)
- Downward (inferior)
Correct answer: Outward (temporal)
Exotropia is an outward (temporal/lateral) deviation of the eye, often called 'wall-eye.'
Question 2: The Maddox rod test is primarily used to assess:
- Binocular visual acuity under normal conditions
- The magnitude and direction of a phoria (Correct answer)
- Stereoacuity in arc seconds
- Corneal topography
Correct answer: The magnitude and direction of a phoria
The Maddox rod converts a point light source into a streak, completely dissociating the eyes so that any phoria can be measured with neutralizing prisms.
Question 3: Anisometropic amblyopia develops primarily because:
- A significant refractive difference between the two eyes causes chronic blur in one eye (Correct answer)
- A constant unilateral strabismus suppresses one eye
- Congenital media opacity prevents form vision
- Ptosis occludes the visual axis
Correct answer: A significant refractive difference between the two eyes causes chronic blur in one eye
A large interocular refractive difference results in one eye receiving a chronically defocused image, leading to cortical suppression and amblyopia despite proper alignment.
Question 4: Clinically normal stereoacuity is typically defined as a threshold of:
- 100–200 arc seconds
- 40 arc seconds or better (Correct answer)
- 500 arc seconds
- 1,000 arc seconds
Correct answer: 40 arc seconds or better
A stereoacuity of 40 arc seconds or better (on tests such as the Randot or Titmus) is considered within normal limits for bifoveal stereopsis.
Question 5: The Worth 4-Dot test uses red and green filters to evaluate:
- Stereoacuity in arc seconds
- Suppression and the quality of binocular fusion (Correct answer)
- The full refractive error of each eye
- Accommodation amplitude
Correct answer: Suppression and the quality of binocular fusion
By presenting red dots only to one eye and green dots only to the other, the Worth 4-Dot test reveals whether the patient is fusing, suppressing one eye, or experiencing diplopia.
Question 6: Strabismic amblyopia results from which specific cause?
- A large interocular refractive difference
- Constant unilateral strabismus causing chronic suppression of the deviating eye (Correct answer)
- Congenital cataract obstructing the visual axis
- Uncorrected bilateral high myopia
Correct answer: Constant unilateral strabismus causing chronic suppression of the deviating eye
Constant unilateral strabismus leads to persistent cortical suppression of the deviating eye's fovea, causing amblyopia due to lack of normal visual stimulation.
Question 7: Convergence insufficiency is most characteristically defined by:
- A high AC/A ratio with esophoria at near
- Exophoria or exotropia that is greater at near than at distance (Correct answer)
- Esophoria at distance with orthophoria at near
- Hyperphoria at near fixation
Correct answer: Exophoria or exotropia that is greater at near than at distance
Convergence insufficiency is characterized by an exodeviation (often exophoria) that is significantly larger at near than at distance, reflecting reduced fusional convergence.
ABO Binocular Vision & Strabismus 2
In a patient with exotropia, the deviating eye turns in which direction?