Refractive techniques in amblyopia

Question 1

Define amblyopia

Answer 1

Reduced visual acuity (6/9) in one or both eyes. with no pathological cause for the reduced VA.

Question 2

What visual acuity is usually taken to be amblyopia?

Answer 2

6/9 or Logmar 0.2 approx, or worse

Question 3

What is amblyopia caused by?

Answer 3

Abnormal visual development during the ‘critical period’ for visual development
(children 7-8 years old, when their VA is supposed to improve and thus they grow to be deprived of a clear retinal image)

Question 4

What % of the population does amblyopia affect?

Answer 4

Between 1 and 4% of the population

Question 5

List 3 different types of amblyopia

Answer 5

• refractive
• stimulus deprivation
• strabismic

Question 6

Describe how refractive amblyopia occurs

Answer 6

Results from uncorrected refractive error in one or both eyes (during the critical period of first 7-8 years of life)
e.g. anisometropia RE: +4.00 LE :emmetropic
if the left eye is covered and the right eye wants to see clearly in the distance, it will have to accommodate by +4D. if the right eye is covered, the emmetropic eye (LE) doesn’t need to accommodate to see clearly.
when both eyes are open, the right eye won’t accommodate by +4D and the left eye won’t accommodate at all, as both eyes always accommodate by the same amount and in this case the eyes won’t accommodate at all, so right eye will have +4D of blur and if this happens during the critical period, the px’s va’s cannot develop properly = amblyopic for both DV and NV

Question 7

Describe how stimulus deprivation amblyopia occurs

Answer 7

Occlusion e.g. monocular ptosis (affected eye has no clear retinal image during critical period)

Question 8

List 7 refractive techniques required to be carried out properly in a amblyopic px

Answer 8

• choice of dioptric interval
• crossed cyl target
• crossed cyl power
• fan and block
• pinhole disc
• binocular balancing
• retinoscopy in strabismic amblyopia

Question 9

What is the problem with a dioptric interval that is too small on an amblyope

Answer 9

Invites the wrong results and wastes time e.g. for a +4D with 6/12 VA, using a +0.25D for bsv will always look the same to px, as they can’t see a significant enough difference, for a long time thus your subjective will be very off.

Question 10

What is the best choice of powers to use whilst doing BVS in a bracketing approach on a amblyopic patient

Answer 10

• using higher dioptric powers as it gives a clearer response e.g. for a 6/12 px, use ±1.00D or ±0.50D lens, and don’t give -ve lenses if the patient reports that the letters look the same
• use higher power spheres to begin with
• choice of power depends on patients acuity and ability to discriminate change
• may use +1.00DS or +2.00DS initially, especially those with a visual impairment

Question 11

When will you know which choice of power for BVS on an amblyope is best to use?

Answer 11

Choice of power depends on patients acuity and ability to discriminate change

Question 12

Which powers may you initially use on a px that is visually impaired when doing BVS?

Answer 12

+1.00DS or +2.00DS initially

Question 13

When may you refine your BVS with smaller dioptric intervals

Answer 13

If noticed by the px e.g. +1.00D or +0.50D, use +0.25D spheres last or if at all, it is up to us to decide, but not really needed for an amblyope. (With Amblyopia px can’t always appreciate the change in vision bought about by a low powered lens).

Question 14

What is the inner ring of the concentric rings of a cross cyl target equivalent to?

Answer 14

approx 6/6 snellen letter

Question 15

What is the outer ring of the concentric rings of a cross cyl target equivalent to?

Answer 15

approx 6/15 snellen letter

Question 16

Which level of vision is best for use of the the cross cyl ring targets in subjective?

Answer 16

Vision of 6/12 or better

if worse than 6/12, concentric rings is not a good target

Question 17

Describe the 4 steps of cross cyl bracketing approach

Answer 17

• use a higher powered cross cyl (±0.50DC is usually the only one available) to begin with
• use ±0.25DC crossed cyl, but only if changes produced by this cross cyl are appreciated by the patient
• may use ±0.75DC or even ±1.00DC initially with visually impaired patients
• refine results with smaller powers, but only if changes produced by these cross cyl are appreciated by the patient

Question 18

Which powers of cross cyl would you initially use on a visually impaired px?

Answer 18

±0.75DC or even ±1.00DC initially

Question 19

What are the lines on the fan and block chart approx equivalent to?

Answer 19

6/15 snellen

Question 20

When should you not consider using fan and block?

Answer 20

when a px’s va’s are worse than 6/12

Question 21

How is a pinhole disc useful in amblyopes?

Answer 21

to distinguish between poor acuity/vision due to a bad refraction or poor acuity/vision due to amblyopia (or eye disease)
if acuity/vision does not improve with a pinhole, then you are unlikely to improve acuity during your refraction

Question 22

Which patients are suitable for binocular balancing?

Answer 22

All patients with binocular vision and good acuity in each eye

Question 23

List 6 types of patients that you should not binocular balance

Answer 23

• px with a squint
• px with amblyopia
• px who are monocular
• px with VA differences of 3 or more lines
• pxs who are presbyopes (60 years or over)

Question 24

Explain why there is no point bincouarly balancing on a px who is 6/5 in one eye and 6/18 in the other

Answer 24

because by using a +0.75 or +1.00DS lens to blur the good eye, it is still not going to make the acuity as bad as the amblyopic eye.

Question 25

What is a possible theoretical method of binocular balancing on an amblyope?

Answer 25

Using the septum method - Turville’s infinity balance test or TIB test

Question 26

Explain how you would carry out binocular balancing using TIB on an amblyopic px

Answer 26

• to push the septum (stick) across the mirror right in-between the left and right circles on the duo chrome
• so when correctly positioned, the patient sees the black ring on the red and green by the left eye on the left side, & on the right hand side black rings against the red & green by the right eye ONLY
• if you equalise the rings on the left side & clarify them & do the same on the right side whilst each eye is covered, then you have balanced them
• if left eye = 6/9 (amblyopic) you can still equalise the circles on the red & green and won’t be as clear as seen by right side of right eye
• but your only trying to equalise the left side circles as seen by the left eye

Question 27

When is it worth binocular balancing in monocular amblyopia?

Answer 27

when the non-amblyopic eye va = 6/5 and amblyopic eye va = 6/9 then MAYBE try it

Question 28

When is there no point in binocular balancing in monocular amblyopia?

Answer 28

when the non-amblyopic eye va = 6/5 and amblyopic eye va = 6/12, 6/18, 6/24 or worse

Question 29

When is it worth maybe binocular balancing in binocular amblyopia

Answer 29

when binocular VA = 6/9

Question 30

When is there no point in binocular balancing in binocular amblyopia

Answer 30

When VA = 6/12 or worse binocularly

Question 31

When can you get binocular amblyopia?

Answer 31

if a patient has had uncorrected astigmatism in both eyes, making them amblyopic in both eyes

Question 32

How do you carry out ret on a strabismic patient?

Answer 32

When doing ret on a px with a squint - you must do ret on the patient’s visual axis, if not this can produce astigmatic errors.

Question 33

What can be a possible solution for carrying out ret on a strabismic px if you are struggling to do it on their axis?
And what is a possible drawback of this solution?

Answer 33

Occlude the fixing eye (brings squinting eye back into fixation) - but optometrist’s head now gets in the way of the target AND px will also accommodate

Question 34

When is it worth doing retinoscopy (distance fixation) on a px with a strabismus via occluding the non-deviated eye and what is a possible drawback to this method?

Answer 34

• if the eye is not off axis that much
• but patient is more likely to accommodate monocularly (because with the two eyes open, convergence helps to keep accommodation steady)
• probably worth doing if squint is greater than 10 prism dioptres (to cover the good eye, but px more likely to accommodate & will slightly be off-axis)

Question 35

Explain how you would carry out retinoscopy with someone who has a strabismus with near fixation and the drawbacks to this method.

Answer 35

• occlude fixing eye - but not recommended as accommodation is very unstable - thus you may want to use a cycloplegic drug
• position ret where two axes meet - but location may change during retinoscopy