Refractive techniques in amblyopia Flashcards
Define amblyopia
Reduced visual acuity (6/9) in one or both eyes. with no pathological cause for the reduced VA.
What visual acuity is usually taken to be amblyopia?
6/9 or Logmar 0.2 approx, or worse
What is amblyopia caused by?
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)
What % of the population does amblyopia affect?
Between 1 and 4% of the population
List 3 different types of amblyopia
- refractive
- stimulus deprivation
- strabismic
Describe how refractive amblyopia occurs
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
Describe how stimulus deprivation amblyopia occurs
Occlusion e.g. monocular ptosis (affected eye has no clear retinal image during critical period)
List 7 refractive techniques required to be carried out properly in a amblyopic px
- choice of dioptric interval
- crossed cyl target
- crossed cyl power
- fan and block
- pinhole disc
- binocular balancing
- retinoscopy in strabismic amblyopia
What is the problem with a dioptric interval that is too small on an amblyope
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.
What is the best choice of powers to use whilst doing BVS in a bracketing approach on a amblyopic patient
- 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
When will you know which choice of power for BVS on an amblyope is best to use?
Choice of power depends on patients acuity and ability to discriminate change
Which powers may you initially use on a px that is visually impaired when doing BVS?
+1.00DS or +2.00DS initially
When may you refine your BVS with smaller dioptric intervals
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).
What is the inner ring of the concentric rings of a cross cyl target equivalent to?
approx 6/6 snellen letter
What is the outer ring of the concentric rings of a cross cyl target equivalent to?
approx 6/15 snellen letter
Which level of vision is best for use of the the cross cyl ring targets in subjective?
Vision of 6/12 or better
if worse than 6/12, concentric rings is not a good target
Describe the 4 steps of cross cyl bracketing approach
- 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
Which powers of cross cyl would you initially use on a visually impaired px?
±0.75DC or even ±1.00DC initially
What are the lines on the fan and block chart approx equivalent to?
6/15 snellen
When should you not consider using fan and block?
when a px’s va’s are worse than 6/12
How is a pinhole disc useful in amblyopes?
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
Which patients are suitable for binocular balancing?
All patients with binocular vision and good acuity in each eye
List 6 types of patients that you should not binocular balance
- 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)
Explain why there is no point bincouarly balancing on a px who is 6/5 in one eye and 6/18 in the other
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.
What is a possible theoretical method of binocular balancing on an amblyope?
Using the septum method - Turville’s infinity balance test or TIB test
Explain how you would carry out binocular balancing using TIB on an amblyopic px
- 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
When is it worth binocular balancing in monocular amblyopia?
when the non-amblyopic eye va = 6/5 and amblyopic eye va = 6/9 then MAYBE try it
When is there no point in binocular balancing in monocular amblyopia?
when the non-amblyopic eye va = 6/5 and amblyopic eye va = 6/12, 6/18, 6/24 or worse
When is it worth maybe binocular balancing in binocular amblyopia
when binocular VA = 6/9
When is there no point in binocular balancing in binocular amblyopia
When VA = 6/12 or worse binocularly
When can you get binocular amblyopia?
if a patient has had uncorrected astigmatism in both eyes, making them amblyopic in both eyes
How do you carry out ret on a strabismic patient?
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.
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?
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
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?
- 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)
Explain how you would carry out retinoscopy with someone who has a strabismus with near fixation and the drawbacks to this method.
- 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
