De praecipius visus symptomatis eorumque causis Physica & Medica contemplatio

LXXVIII.
For just as the spirit acts upon the aisthētēria sensory organs with the powers received from above, so it is affected by the impression of the sensible objects from them. For this purpose, indeed, such a systasis constitution/composition was required: since it had to be subtle in order to produce action, and pure from all impurities of matter, yet also somewhat solid for receiving and preserving the forms of external things, or, to use the words of the philosophers, it must be syphylaktoteron more apt to preserve together and dypolēptoteron more apt to comprehend.

LXXIX.
From this it is clear that excessive thinness, both in every animal spirit and also in the optic [spirit], is to be condemned dia tēn anastatheian (hē de aisthēsis paschei) on account of the instability (for the sense suffers) and also because of the weakness of light. It becomes too subtle when that heat boiling over from the heart has not been precisely altered due to excessive heat of the brain. Hence, the bilious, the phrenetic, the manic, the unstable wanderers, the headstrong, and not rarely also the amblōpes dim-sighted, since they do not tolerate the gazing upon luminous bodies on account of the easy dissipation of the spirit.

LXXX.
Truly, little spirit flows to the eyes, and yet it is akratos unmixed/pure, [a condition caused] more by the narrowness and thinness of the nerves than by any defect of the brain. For then not only a little, but also a vicious and impure [spirit] would flow forth, as is often to be observed in the sick. For the corrupted effect follows the depraved cause.

LXXXI.
But it does not perceive remote things, because it is dispersed by the light of the intervening air while it strains its vision. Hence such people look about with a hand held out, like a veil, so that they may ward off the brightness rushing in from everywhere.

A catchword "fulgorem" brightness appears at the bottom of the page to link to the next.