An essay on the physiology of the iris : with a different view of its relations and sympathies from the one usually received : and an attempt to establish a new theory of the action of light upon the eye / by John Walker.

John Walker

Date:: 1833

Credit: An essay on the physiology of the iris : with a different view of its relations and sympathies from the one usually received : and an attempt to establish a new theory of the action of light upon the eye / by John Walker. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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$If we refer to the state of cataract, in its perfect condition, we find the opaque lens blocking up the pupil much more effectually than any mechanical contrivance can ever doj whilst the Iris is left to the full influence of light, and yet every one knows that, with this ob- struction to the passage of light through the pupil, its motions are as perfect as ever. Here we are understood to speak of simple cataract, ' uncombined with any other morbid condition. Now surely, on the common theory, if we even admit that some few particles of light may insinuate themselves between the lens and Iris, still we ought to have a very feeble motion of the latter, and such motion as it had might be expected rather to dilate the pupil, to admit more light into the dark posterior chamber; but no, we find it still powerfully con- tracting on exposure to light, its sensibility unimpaired, its mobility \ undiminished. I have seen instances, where the pupil has been thus obstructed for years, by an opaque lens or capsule, where the latter has been partially adherent to the Iris, and where no perception of external objects existed, and yet the fibres of the Iris could be dis- tinctly observed to contract on exposure to light, and this quite , independently of any sympathy with the other eye. The same may ]i be said of closed pupil from injury or disease. In cases of central opacity of the cornea, where very little or no light could get into the pupil, the organ being in other respects healthy, I have frequently observed the distinct action of the Iris, and have sometimes been just able to discern the pupil open, but not more dilated than usual,—I might rather say contracted, from , the increased sensibility to light usually attending such cases. Instances, as before mentioned, have been observed where there has been complete amaurosis coexistent with regular contraction and dilatation of the pupil; and I have more than once noticed great into- lerance of light where there was not the least perception of objects, j That the sensibility and mobility of the Iris, in cases of cataract, are not always a proof of a sound condition of the Retina is well known to those whose attention has been much directed to that dis- ease. Operations for cataract have been frequently undertaken, where the Iris has been perfectly active, and the eye sensible to light, and yet after all the proceeding has been useless, from some morbid state of the Retina, optic nerve, or the brain itself. In a case, on which I operated, the patient was sensible to light$