I received a message requesting to know what I prescribed for the illustrative case of anisometropic hyperopic amblyopia that I gave in Part One, something I definitely could have made clearer!
To review, here were the objective refractive findings:
OD: 1) 0.00 – 0.50 x 107 2) +1.25 – 0.50 x 113 3) +0.50 – 0.50 x 105
OS: 1) +1.50 – 0.75 x 85 2) +2.00 – 0.50 x 80 3) +2.00 – 0.50 x 88
OD: 1) +1.50 sphere 2) +1.50 – 0.25 x 100 3) +1.25 sphere
OS: 1) +3.25 -0.50 x 85 2) +3.25 sphere 3) +3.25 sphere
Unaided VA was 20/20-1 right eye, but it was a shaky 20/20. Through the left eye we obtained 20/30, but that was with alot of encouraged guessing. There was no clinically significant difference between whole line and isolated letters. Subjective refraction was conducted to provide the best binocular profile at distance and near, through which I derived an Rx of OD: +0.25 sph and OS: +0.75 sph.
In this instance the +0.75 OS made no difference in monocular acuity. Even though we obtained a monocular BVA of 20/25 OS through +1.25 sphere OS, the patient experienced better performance on stereoscopic acuity and binocular balance through +0.75 sphere. So the big paradigm shift here is to resist the temptation to prescribe the lens that provides the best monocular visual acuity if that isn’t also the lens that provides the best binocular profile.
The de-emphasis on Rxing the lens that provides the best monocular VA is consistent with a de-emphasis on monocular treatment. We do no occlusion therapy, with the exception of cases in which the amblyopia is so dense that there isn’t any meaningful change in binocular interaction with the Rx. Bob Sanet, Pilar Vergara and I published our perspective on this in VDR, and we’ll be stating our case that monocular treatment may delay or retard the optimal outcome, certainly in most cases of refractive amblyopia and to some extent in strabismic amblyopia, during our upcoming presentation in Toronto. Recall that PEDIG studies have shown that the Rx alone provides a significant aid in rehabilitating refractive amblyopia, and can have a salient effect even in strabismic amblyopia. They found that adding therapy activities to the Rx had relatively little impact. However, PEDIG philosophy follows conventional wisdom in Rxing primarily for monocular BVA in each eye independently, and in implementing occlusion or penalization therapy at the outset. As monumental as the work of PEDIG has been, we believe that the potential exists to obtain even greater endpoint results in terms of visual acuity, stereo acuity, and overall improvement in binocular performance.
One more thought regarding re-directing the spotlight toward binocular performance in amblyopia. In the prototypical case of reverse-engineering of hyperopic anisometropic refractive amblyopia that Dr. Daniel Press and I co-authored in 2012, we cut the plus a bit in both eyes and progressively reduced it further while nudging the patient toward isometropia. At that time we felt that the VEP was an effective tool in demonstrating this process objectively, and we used it to illustrate that changes in binocular summation were occurring at the level of V1 (and gratified that others picked up on this, thank you Dr. Mozlin!). While this remains a useful clinical tool, there are many other guides available to you in assessing binocular performance ranging from stereopsis to binocular accommodative balance to VO Star/Cheiro Trace and oodles more.