8.1.1 Assessing BV Status

Question 1

For the below tests, consider:

• Target required
• Working distance to perform test
• Do you require spectacle correction?
• Technique to perform
• Instructions to give the patient.
• Consider how a particular technique will help with diagnosis

Answer 1

For the below tests, consider:

• Target required
• Working distance to perform test
• Do you require spectacle correction?
• Technique to perform
• Instructions to give the patient.
• Consider how a particular technique will help with diagnosis

Question 2

Cover Test

Answer 2

• Target required - Patient fixates on a letter one line above the VA of the worst eye.
  Use a spotlight if VA worse than 6/18 in one eye.
• Working distance - either distance or near (distance where patient reads most comfortably)
• With & Without Spectacle correction for distance & near
• Technique to perform:
  
  • Cover & Uncover —> do this once for each eye for 3-4 seconds (literally count in your head!). You can distinguish between tropia & phoria. Allows binocular fusion when eyes uncovered
  • Alternating Cover —> Prevents binocular fusion as eyes are only briefly uncovered.
    Cannot distinguish between a tropia and phoria.
    Reveals the total tropia and phoria - usually when the px is tired or stressed.
    Reveals intermittent tropias (phorias that break down into a tropia)
  • Rule of thumb for estimation of size of squint: Movement small, but seen on careful cover test = 5-10Δ. Easy to see on cover test, but cosmetically acceptable = 10-20Δ. Large movement on cover test, cosmetically obvious = 20-30Δ.
• Instructions - ‘this test allows me to determine how well your eye muscles are
  working together’ …. ‘all I want you to do is look at this target - if it appears to move, please follow it with your eyes’.
• Prism cover test - this is again, objective and can gather the size of the deviation
• Must know the differences between different phorias & tropias e.g. how does a hypo/hyperphoria look like?

Question 3

Cover test on motility

Answer 3

• Target required - pen torch to note corneal reflexes as you do the test
• Working distance - 55-60cm best to prevent accommodation being induced. Can lead to pseudotropias!
• Spectacle correction - none
• Technique to perform - head kept still, track out the eyes until they stop moving & just where the reflex goes away. Always ask if the patient reports double vision, whether it is horizontal or vertical
• Instructions - “I am going to check how well the muscles of your eyes are working. Follow this light with your eyes, keeping your head nice & still and tell me if you get any pain or double vision.” You may need to double check if the patient gets double vision in certain positions by asking them

Question 4

Subjective tests for assessing BV

Answer 4

• stereopsis
• fusional reserves
• fixation disparity
• NPC
• Accommodation
• Maddox Rod
• Maddox Wing

Question 5

How to assess stereo

Answer 5

Remember the 3 stages of binocularity. This is the last step! However, if patient is struggling even to do step number 2 i.e. fuse the images together & maintain it, then getting accurate stereopsis will not be as easy. This may be the case in a near decompensating phoria or convergence insufficiency

• Target required - depends on test used
• Working distance - 40cm
• Spectacle correction - near correction preferrable
• Technique to perform - depends on test. Titmus is quite basic for adults to understand
• Instructions - “I’ll just be checking how good your depth perception is and this will give me an idea of how well your eyes are working together.” Titmus - “On number 1, there are 4 circles. Tell me which one is coming out towards you or is sticking out compared to the rest, top, bottom, left or right?”

Answer 6

vertical - 2- dioptres

Horizontal
- Positive = 20
- negative = 6-8

Question 7

Fixation Disparity

Answer 7

• Target required - OXO
• Working distance - depends on if doing near or distance
• Spectacle correction - required depending on working distance`

Question 8

Management of Hetrophoria (6 lines of action)

Answer 8

1. Removing the cause of decompensation e.g. illness
2. Refractive management - We need a balance between the two eyes and a clear image in case of refractive management. The goal is to reduce modification over time, reviewing 3-4months (if needed)
3. Giving eye exercises - look into convergence & divergence excersises. In the BV lectures!
4. Prescribing prism (not the best to use for CI as convergence not used when prism in place!)
5. Referral to another practitioner.
6. Monitoring if nothing to manage.