Two sides of the ocular metaphor:
1. Tinted lenses: 'If only we could see things unimpeded! Our lenses shamefully limit us.'
2. Spectacles: 'Without our lenses there is only blurry continuum! Our lenses are all we have.'
(Aren't we told so often to 'be reasonable' and see through one type of lens with one eye and the another with the other? No wonder we get sea-sick on dry land!)
Both sides of the metaphor rely on a beginning a middle and an end: An 'outside' which somehow gets 'inside' via a liminal point that transforms and protects the outside and inside, respectively. Both versions of the metaphor require the tripartite schema. Thereby, a more elongated, complicated schema is rendered unthinkable; for example, a schema of trajectories, trains or chains with many points of transformation rather than just one.
It is not that there is no transformation (everything being essentially of the same underlying substance), it is that there is no one point of transformation where one substance is trans-substantiated into another (nature into mind, things into thought, world into words). We need to be able to understand transformations where they actually happen without being prejudiced a priori as to where they supposedly must happen (at the liminal point between 'inside and outside' -- always). The location of transformation is a question of fact rather than principle, as is the quality and quantity of transformations (we must assume that there are many).
We can't be the realists of the tinted lenses cursing our luck at the stubborn obduracy of these lenses, nor can we be the anti-realists dismissing all the outside as so much unseeable nebulous hazyness. We must be realists of transformation, wheresoever it occurs.
Therefore, the ocular metaphor is useless for us (unless we can perhaps come up an example of a delicately arrayed series of lenses that are all necessary but independently insufficient to their collective refraction -- but even then we might be reducing each lens to the whole, which would take us back to square one).