Amblyopia can be prevented if detected at an early age - screening, identifying the risk factors (family history), correction of refractive errors esp. if px has full accommodative strabismus, anisometropia, high astigmatism. If px is less than 10 years old with VA of 6/24 or better the spec correction may improve the VA on its own. You would get the px to wear the new rx and reassess in 6-8 weeks.
Occlusion
- Total occlusion - excluding all light and form (patch, spec occluder, opaque contact lens)
- Total occlusion excluding form only - frosted glass
- Partial occlusion - allows form appreciation but diminishes acuity (clear nail varnish, ND filters, also near occlusion only)
- Bagerter and Cuppers thought indirect was best for amblyopia associated with eccentric fixation in an attempy to weaken the EF through disuse.
- Von Noorden found no evidence that direct occlusion reinforces eccentric fixation and found it superior to direct occlusion in children under 4.
- Schapero found that direct occlusion does not intensify EF. It's a simpler approach and should be the initial approach for all age groups
- Indirect occlusion could be of value to the px who doesn't respond well to direct occlusion or has steady EF prior to direct patching
- The most common method of occlusion is direct & total excluding light but when binocularity is present as in small angle SOT, intermittent strab & anisometropia w/out strab partial patching is preferable
- For px under 4 part time occlusion for several hours a day is better and prevents deprivation amblyopia. It should be assessed every week at first
- For strabismic amblyopes over 4 years full time occlusion is best. It gets quicker results, is less disturbing to the Px and prevents ARC. Anisometropic Px can be patched full or part time.
- It's important to obtain maximum VA before the child goes to school.
- If there's no improvement after two weeks discontinue & check fields and VA with a view to determining an organic cause.
- When VA has stabilised remove occlusion gradually to prevent the amblyopia returning
- When doing direct occlusion it's best to give the Px a visual task like crossing out letter Es in newsprint or something like that.
This involves fogging the non-amblyopic eye for distance by sticking an additional +3.00 in front of it, sorta like a reading add. The amblyopic eye is then used for distance and the good eye for near. It can be worn either full time or in the evenings for tv. It's more acceptable cosmetically but not as effective as occlusion.
Drug Penalisation/Cycloplegia
This is achieved by using 1% atropine ointment on the non-amblyopic eye. This is the reverse of optical penalisation in that the Px uses the amblyopic eye for near and the non-amblyopic eye for distance. This treatment is good for supplementing or replacing occlusion but is rarely the first thing tried. It's good when co-operation is poor. Unfortunately it's only useful in mild/moderate amblyopia - if the amblyopia is too deep then the non-amblyopic eye will still be used. The lack of involvement of patching or glasses means it's good when cosmesis is a problem (ie in older kids).
If the patient has nystagmus with a latent component this method is also very good. If you patch the good eye and the other eye starts doing a nystagmus movement then it's obvious that you aren't going to get good 6/5 vision in that eye.
CAM Visual Stimulator
Px exposed to intense visual stimulation for short periods of time w/good eye occluded. Rotating grating of different contrast & spatial frequencies to stimulate large number of cells at one time. Method is better in anisometropic amblyopia rather than strabismic but the results are dubious.
Pleoptic Treatment
After-images - useful when EF is present. A large bright after image is produced in the amblyopic eye - a ring centred on and also sparing the fovea. It desensitises the EF point - Px then looks at a near fixation target with true foveal fixation. It requires a mydriatic and daily treatment is required. Very time consuming, not easy or popular.
After Image Transfer Method
This was first used for eccentric fixation but has been shown useful in amblyopia too. A central AI is created in the dominant eye and then transferred to the amblyopic eye. Px is then asked to locate AI at the point of fixation and to see the smaller fixation letters. This must be repeated as the AI fades. Best if VA is 6/24 or better esp when VA has deteriorated again following success with other orthoptic procedures.
Anti-Suppression
Useful in older Px w/good chance of binocularity
Mallett Intermittent Photic Stimulator Unit
Red light stimulation at 4Hz with an interesting detailed visual task for 20-30 minutes. One or two times a week. Results dubious again.
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