Amblyopia is a disorder of monocular as well as binocular vision. Monocular because the best-corrected visual acuity of the amblyopic eye is decreased, and binocular due to the fact, that also binocular vision and stereopsis are impacted, partly because of the decreased visual acuity of the amblyopic eye. The goal of amblyopia treatment is so not only to improve the visual acuity of the amblyopic eye (monocular function) but also to restore the binocularity and stereopsis (binocular function).
The positioning of the eyes defines the visual field and the ability for stereovision
The human visual field is approximately 180° wide, with the center 120° overlaying from both eyes. This overlay gives us a very good binocular function with an excellent perception of depth and objects in 3 dimensions. The main thing that enables us good binocular vision is the positioning of our two eyes. Obviously, they are both located in the front of our skulls and directed forward. This is in complete contrast to some other mammals, say ungulates, who have eyes positioned at the sides of their skulls. Thus, their visual field covers almost entire 360° with very limited or no overlay and hence no stereovision at all.
Why would then some animals benefit from a 360° wide visual field with no stereovision and some (like us) with only half of that but with excellent stereovision? It all has to do with the evolution and the predator-prey relationship. Evolutionarily, humans are hunters, as are most carnivores, which is why good stereovision with excellent depth perception is for us much more important than a wide visual field. On the other hand, the animals that are evolutionarily hunted do not require good stereovision but benefit immensely from a wide visual field for observing the surrounding for potential predators. Yup, mother nature really does everything for a reason.
The binocular and monocular visual function should be jointly addressed in amblyopia
Let us go back to binocular vision function and amblyopia now. As already mentioned, amblyopia impairs monocular as well as binocular visual function. Whilst amblyopia treatments such as penalization and occlusion markedly improve monocular visual function, binocular is somewhat harder to restore. Additional treatment options, such as near activities and vision training, particularly binocular dichoptic training, normally give better results in terms of binocularity as conventional treatment options such as occlusion.
Restoring binocularity is perhaps just as important, if not even more, as the improvement of monocular visual acuity of the amblyopic eye in amblyopia treatment. Even though most people most of the time will function just fine even without very well-developed stereovision, there are certain assignments (surgeons, pilots, etc.) that will require 20/20 vision and unimpaired stereovision. Thus, monocular as well as binocular function should be addressed during amblyopia management.