Refractive techniques in amblyopia Flashcards
(35 cards)
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.
