The following arises from a discussion in the DOC-L mail list sponsored by SCO. The topic was the use of binasal occluders (varying opacity sectoral occlusion applied to spectacle lenses to encourage lateral muscle function and spatial awareness). Typically, such occlusion is implemented as either nail polish or adhesive tape (Scotch Tape) along the nasal aspect of the external face of the lenses.
One poster commented that a local ophthalmologist was livid that he, an optometrist, would recommend such a treatment and that he should essentially back off and let the OMD and his orthoptist take care of things. Part of the rationale is that, according to the OMD, ‘sectoral patching will lead to sectoral amblyopia’ – perhaps forgetting that BCVA on the periphery will never surpass 6/60.
There are many clinical, scientific, moral, and financial problems with this attitude toward vision rehab. Let’s take the clinical first. From our friend and colleague Curt Baxstrom, a re-known clinical lecturer on vision rehab, the following comments (presented here paraphrased, annotated by SysOp, and with permission from Dr. Baxstrom):
Eyes with sectoral occlusion (especially semi-translucent) will still be fully exposed to unoccluded visual stimulus from simple lateral and vertical movement. The idea that any amblyopia would develop is nil. We should keep in mind that a full patch is much more amblyogenic. There is no evidence-based research that shows this effect. It is true that in chick studies, _attached_ astigmatic lenses that move with the eye do cause sectoral amblyopia, but this is to be expected as we find with meridional amblyopia. What we are talking about with binasal occlusion is something very different. It’s also worth noting that other OMD’s also use binasal occlusion for years.
As for the benefits of binasal occlusion, there are many benefits: (These are all benefits of binasal occlusion, and all are likely visual challenges secondary to the timing of the esotropia.)
- Decrease or eliminate cross fixation pattern
- Improve lateral tracking and decrease abduction deficit
- Eliminates active suppression in lateral gaze(looking laterally, the contra eye doesn’t have to suppress as the sector decreases input)
- Promotes peripheral fusion
- Effectively penailzes fixation pattern to allow lateral eye to lead fixation(R eye should lead into R gaze, vice versa)
- Promotes proprioceptive activation of lateral recti to lead localization
- Promotes motion processing nasal to temporal(thus improved pursuits, saccades and OKN)
- Helps establish nasal retina to lead localization over temporal retina(which is more related to stereopsis)
- Promote alternation of input from R and L visual fields with each eye
The point is that binasals have a lot more to offer than simply ‘straightening’ an eye.
Scientifically, it simply cannot be shown that binasal occlusion will induce sectoral amblyopia. It’s that simple, and with a medical profession preaching evidence-based medicine, perhaps a little science would help in this case.
Morally, the OD in this case is on the right side of science and clinical practice, so it become morally questionable for the OMD to prescribe his brand of tx, and proscribe the visual rehab approach. This is where professional hubris becomes more than an obstacle to care, but a burden to taxpayers.