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Updated: May 11, 2025
The accurate control of normal intra-ocular pressure, by mutual adjustment of inflow and outflow of fluid, is scarcely conceivable without some highly specialized, extremely sensitive nerve mechanism to preside over it. This is suggested by analogy with the regulation of secretion in the lacrimal, salivary, or peptic glands, or the maintenance of blood pressure in the heart and arteries.
We are all familiar with the attention which was directed some years ago to the statements coming from French clinics that the treatment of glaucoma should include the administration of osmotic substances as adjuvants in the reduction of increased intra-ocular tension.
Darier has reported that a single subconjunctival injection of a milligram of iodate of sodium has cleared the cornea and lessened the intra-ocular pain in glaucoma. What shall be said in regard to certain medicinal agents which stimulate the lymphagogue activity of the eyeball in their relation to the reduction of intra-ocular tension, notably of dionin?
The venous blood pressure permits the eyeball to become perfectly soft. We have all seen tension of 5 mm., or even less; and general venous pressure does not rise to the normal intra-ocular tension. Increased intra-ocular pressure requires that there must be some obstacle that keeps the intra-ocular fluid from reaching the general venous system.
The third group are cases associated with glaucoma only as causes. In eyes with low nutritive power, or subject to exacerbations of increased intra-ocular pressure, uveal inflammations may prove disastrous.
In cases of chronic increase of intra-ocular tension associated with a quiet uveitis or an iridokeratitis, when the patient exhibits traces of old synechiae, or where there is danger of their re-formation, I do not hesitate to use atropia as long as the wound of operation has not healed.
It is well known, this observer points out, that after the period of excitation and muscular rigidity disappears, there is a lowering of blood pressure in chloroform narcosis and coincidently a sinking of the intra-ocular pressure. Not only this, the intra-ocular tension of normal eyes during this narcosis drops several millimeters.
There is reason that we should give careful attention to the views of Heerfordt and Zirm, that obstruction to the venous outflow may be the effective cause of the disease. Zirm believes the venous plexus of the choroid is an essential part of the mechanism for the regulation of intra-ocular tension, the necessary vaso-motor control depending on nerve centers situated in the iris. Nerve Control
This brings us at once to the consideration of that theory which probably has held our attention for the longest period of time, i. e., the volumetric theory. According to it, the normal intra-ocular tension depends on the volume of fluids within the eyeball.
But complete experimental proof of such action is wanting, and it is probable that myosis follows a direct stimulation of the sphincter muscle fibers, aided, perhaps, by contraction of the iris vessels, although the last named effect is denied by so competent an authority as Hobart Hare. Exactly how the myotics reduce intra-ocular tension is not definitely proven.
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