Not to be confused with The Threepenny Opera, The Three Opias of hyperopia, anisometropia, and amblyopia can present a daunting clinical challenge when co-occurring. In the new paradigm for amblyopia therapy we address the binocular aspect of the problem while de-emphasizing punitive measures such as occlusion, penalization, and anti-suppression, something that Bob Sanet, Pilar Vergara and I will present in detail at COVD 2020 in Toronto. This places a premium on deriving the optimal lens Rx, for which opinions are many and varied.
Fundamental to deriving the Rx is the interrelationship between hyperopic refractive profiles, visual acuities, and indices of binocular function such as stereopsis. To some extent this is a chicken vs. egg question in considering whether the brain has orchestrated anisometropia at higher levels resulting in amblyopia, or if there is some fundamental difference in the refractive properties of the eyes that resulted in amblyopia.
It is interesting to note a basic difference between hyperopic anisometropic amblyopia in contrast to its myopic counterpart. In my experience, it is unheard of to find high unilateral hyperopia (I’ve personally never seen hyperopic aniso exceed four diopters other than in unilateral aphakia) whereas the same cannot be said for high unilateral myopia. This argues against axial length asymmetry as a precipitating factor for hyperopic aniso and associated amblyopia. If that assumption is correct, then guiding the patient functionally toward isometropia by re-balancing binocular vision is possible and desirable. On the other hand, high myopic aniso is likely caused by axial length being too long in the highly myopic eye, and efforts to attain binocular balance are often futile. Those cases, as well as unilateral aphakia, are exceptions to the new paradigm, and typically do require occlusion, penalization, or anti-suppression measures.
I’d like to share another clinical observation, one that I find very useful in prescribing for hyperopic aniso in the presence of amblyopia. While I realize that clinicians adept with a spot retinoscope can qualitatively observe what I’m about to relate, comparing a printout of the manifest autorefractor finding to the cycloplegic autorefractor finding can help considerably in prescribing for The Three Opias, as well as for demonstrating to parents what is happening.
Here is a representative set of findings, showing three consecutive readings for each eye, in a six year-old child with unaided VA of 20/20(-) OD and 20/30 OS:
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
When you see fluctuating plus sphere, latent hyperopia lurks. Even the eye with less plus, in this case the right eye, often lacks a clean 20/20 acuity due to hyperopic flux. The eye with higher plus on manifest is almost guaranteed to have amblyopia when the anisometropia exceeds +0.50. The more the aniso, the greater the amblyopia.
In Clinical Pearls, when I originally wrote the chapters addressing intelligent use of cycloplegia as well as autorefraction, I leaned toward pushing plus in these cases. In the ensuing years I’ve evolved toward Rxing just enough plus to jump start the system, with an eye toward minimizing the anisometropia even if adding extra plus to the (more) amblyopic eye initially results in better acuity. Seeing the amount of latent hyperopia on cycloplegia can still be a useful tool, particularly with helping parents understand how hard the child is working to maintain focus. (As an aside, it also helps clear up “but why did the other doctor say …”).
I blogged previously about the suite of subjective binocular vision tests that I rely on most heavily in conjunction with stereopsis. For binocular balance at near I use the Bernell slide #553. Its Duochrome Test is a sensitive gauge for the amount of plus that provides the best accommodative balance between the right and left eyes.
Keeping the Rx power and the aniso to a minimum while maximizing binocular balance is an effective way to counteract amblyopia. When the Rx is worn consistently by the patient, and the binocular balance is monitored by the doctor at regular intervals and the power adjusted accordingly, the lenses have a therapeutic effect. You’ll ultimately be able to achieve better endpoint acuity and higher levels of binocularity than the old-fashioned way of focusing on maximum Rx for best monocular acuities.
(Part Two follows here.)