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Updated: June 1, 2025
When any one passes from the bright daylight into a darkened room, the irises of his eyes expand themselves to their utmost extent in a few seconds of time; but it is very long before the optic nerve, after having been stimulated by the greater light of the day, becomes sensible of the less degree of it in the room; and, if the room is not too obscure, the irises will again contract themselves in some degree, as the sensibility of the retina returns.
"That rays from points outside the optic axis may be united exactly in the same way as those in the optic axis, so that the apertures of glasses may be made of any size desired without impairing distinctness of vision!"
It was evident that when the eye was completely turned in the swordfish could not see at all. Probably this was for close battle. The muscles were very heavy and strong, one attached at the rim of the eye and the other farther back. The optic nerve was as large as the median nerve of a man's arm that is to say, half the size of a lead-pencil.
In the curves we call flowing and graceful, we have, on the contrary, a more natural and rhythmical set of movements in the optic muscles; and certain points in the various gyrations make rhymes and assonances, as it were, to the eye that reaches them. We find ourselves at every turn reawakening, with a variation, the sense of the previous position.
This being so, it will be readily understood that though any given organ of the physical body must always have as its counterpart a certain amount of astral matter, it does not retain the same particles for more than a few seconds at a time, and consequently there is nothing corresponding to the specialization of physical nerve-matter into optic or auditory nerves, and so on.
Thus it came about that, as the little optic tube of Galilei slowly developed into the giant telescope of Herschel, and then into the powerful refracting telescopes of the United States of our time; as the new science of photography provided observers with a new eye a sensitive plate that will register messages, which the human eye cannot detect, from far-off regions; and as a new instrument, the spectroscope, endowed astronomers with a power of perceiving fresh aspects of the inhabitants of space, the horizon rolled backward, and the mind contemplated a universe of colossal extent and power.
The optic disc becomes deeply cupped and the tissues of the optic disc and optic nerve extremely atrophied. The crystalline lens may become cataractous and shrunken. Spontaneous rupture of the suspensory ligament with consequent subluxation of the lens may follow. Secondary Glaucoma. The pathological conditions that precede secondary glaucoma are many and differ widely.
Atrophy and cystic degeneration of the nerve trunk follows destruction of retinal neurons and cupping of the disc. Neuroglia remains in part. Connective tissue elements increase in the optic nerve as the nerve fibers disappear. Glaucomatous Ring.
That merely minute, indefinite variations in all directions should unaided have independently built up the shoulder structure of the pterodactyles and carinate birds, and have laterally depressed their optic lobes, at a time so far back as the deposition of the Oolite strata, is a coincidence of the highest improbability; but that an innate power and evolutionary law, aided by the corrective action of "Natural Selection," should have furnished like needs with like aids, is not at all improbable.
"'There was no big dog, said Hetheridge, shaking his head, as the fact for the first time dawned upon me that, although I had seen the old lady clearly enough to make a sketch of her, even to the features of her care-worn, eager old face, I had not been able to recognise the well-known countenance of James Hetheridge. "'That's what comes of reading till the optic nerve is weakened," he went on.
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