De praecipius visus symptomatis eorumque causis Physica & Medica contemplatio

a pragmateian treatise, which inquires into the causes of health as well as diseases and symptoms contrary to nature, and removes those that are found.

XLIX.
Since the eye is the proper instrument of seeing, its action is impeded in a twofold way: first, by a fault in the organ itself, whether from the failure of the faculty, or of the humors and especially the crystalline lens, or of the tunics; and this pertains to the care and observation of the physician. The other is a certain error and hallucination of sight, arising from the excessive distance of the object, or its diverse situation and position, or from an inequality of the medium, without the fault of the eyes, the reason for which opticians acutely demonstrate.

L0.
Nor is it the intention to treat of individual types of symptoms at present, as they concern excretions and the common affliction of the whole instrument, unless they hinder the primary function.

LI.
Furthermore, impaired action is in a triple difference: either it is entirely abolished and changed into a contrary state; or it is diminished in some measure from the just proportion of nature; or it is depraved against the prescribed law and order.

LII.
The deprivation of vision is blindness, the cause of which must be sought either in the faculty alone, or in the crystalline humor, or in the remaining parts serving it. The loss of the faculty depends on an affliction of either the brain or the optic nerves, whence either the spirit is not generated, or, if generated, it does not reach the eye.

LIII.
Among external causes, the glittering splendor of light is placed, which dissipates the visual spirit and disturbs the syschyas confusion/mixing of the humors. Whence Galen writes that the soldiers of Xenophon were severely injured in their eyes because of a march made through deep snow. Thus, the nefarious cruelty of Dionysius the Tyrant provided a new example of the same thing, when he suddenly blinded captives who had been led from a very dark prison into a most splendid house.

And