What are tropias?
Visual axes misalignment in binocular viewing
Tropias can manifest where the deviation occurs at different positions of gaze.
What is the difference between stimulus and response in oculomotor function?
- Stimulus: Changes in distance or prisms
- Response: Accomodation, vergence, and eye movements
Prisms move the image toward the apex and bend light toward the base.
Define comitancy.
Symmetry of eye movements
Eyes must move together in different gazes and vergence movements to achieve BSV.
What is incomitancy?
Eyes move at different rates, causing diplopia and strabismus
Can be due to vergence accommodation disorders, neurogenic, mechanical, and anisometropia.
State Hering’s Law.
Impulse to ocular muscle has equal impulse to its contralateral synergist to also contract
This law relates to the coordination of eye movements.
What does Sherrington’s Law state?
Impulse to EOM gives equal and opposite impulse to the antagonist to relax
This law ensures balanced muscle action during eye movements.
What does Donders’ Law pertain to?
Eye orientation is the same when looking at a specific direction
This law relates to the positioning of the eyes in different gazes.
Differentiate between primary deviation and secondary deviation.
- Primary deviation: Deviation when fixing with the unaffected eye
- Secondary deviation: Deviation when fixing with the affected eye
This distinction is important in diagnosing strabismus.
What does RADSIN stand for?
Rec7 Adduct and Superior Intort
This mnemonic helps remember extraocular muscle innervation.
What do exo and eso indicate in terms of diplopia?
- Exo: Crossed diplopia
- Eso: Uncrossed diplopia
These terms describe the direction of misalignment in strabismus.
How is the alternating cover test used?
Assesses positions of gaze at each position of gaze
Ensures no corneal reflex is seen in the covered eye.
What is anisophoria?
Asymmetrical accommodation causing one eye to converge more
If eye movements are not equal, RE and LE are assessed for anisophoria.
How is cyclotorsion assessed?
Using the double Maddox rod
If one line is more tilted than the other, there is torsion.
What is the purpose of the Hess screen?
Assesses extraocular muscle (EOM) underaction and overaction over time
Used in strabismus, palsies, amblyopia; requires good fixation and motility.
What does the Hess screen help identify clinically?
- Weak (underacting) muscle
- Secondary overaction of contralateral muscles
Helps differentiate paretic vs restrictive conditions.
What is the purpose of the Parks 3-Step test?
To isolate a single paretic vertical muscle causing hypertropia
Especially useful for superior oblique palsy.
What do you assess in Step 1 of Parks 3-Step?
Measure deviation in primary position to determine which eye is hypertropic
Helps identify possible muscles involved.
What do you assess in Step 2 of Parks 3-Step?
Check deviation in left vs right gaze
If hypertropia is worse in left gaze, left eye muscle is involved.
What do you assess in Step 3 of Parks 3-Step?
Check deviation with head tilt (Bielschowsky test)
If hypertropia is worse on right tilt, right eye muscle is involved.
What is the key advantage of the Parks 3-Step test?
Narrows diagnosis to one specific muscle
Highly sensitive for superior oblique palsy.
What is Sheard’s Criterion used for?
Used for exophoria
Compensating fusional vergence (PFV/BO) ≥ 2 × phoria.
How do you apply Sheard’s Criterion clinically?
Example: Exophoria = 6Δ, PFV = 10Δ, Required PFV = 12Δ → fails (10 < 12)
Likely symptoms: eye strain, diplopia.
What does failing Sheard’s Criterion indicate?
Insufficient positive fusional vergence → poor compensation of exophoria → symptoms
Indicates a need for further assessment or intervention.
What is Percival’s Criterion used for?
Used for esophoria
Larger vergence reserve ≤ 2 × smaller reserve.
