The origin, nature, and properties of light : A sermon / [Henry Hunter].

  • Henry Hunter
Date:
1793
Catalogue details

Licence: Public Domain Mark

Credit: The origin, nature, and properties of light : A sermon / [Henry Hunter]. Source: Wellcome Collection.

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    the vessels not admitting many red globules; and it is chiefly in the more chronic stage that it occurs, the surface of the iris appearing of a pale yellow, or greenish yellow hue. In syphilitic iritis the ante¬ rior surface of the iris is often greatly inflamed, of a bright vermilion in the early stage, and orange or yellow coloured afterwards, when lymph is thrown out. When inflammation affects principally the membrane of the uvea, it is generally subacute or chronic, and often connected with some deep-seated ophthalmia, such as hyaloiditis or choroiditis. In such cases very little or no change of colour is ob¬ served. Inflammation affecting principally the true substance of the iris, and extending more or less to both its surfaces, is by far the most common form of the disease, and the one in which the morbid changes in colour are most remarkable and constant. When only the smaller circle of the iris is inflamed, and generally it is the part first affected, the change in colour will not extend much beyond it. The same may take place when the inflammation is confined to the greater circle of the iris—a comparatively very rare occurrence. II. Modification in the change of colour depending on the natural tint of the iris.—This is the main cause of the variety in the change of colour, in similar stages of iritis, in different persons. The morbid colour being always a compound of the natural colour of the iris with red, red and yellow, or yellow, according to the stage and severity of the inflammation. The following are the more common natural va¬ rieties in the colour of the iris:—Deep blue, or greyish blue; grey¬ ish blue with yellow markings, appearing greenish at a distance; basalt black ; clove brown ; hazel; citron, or wax-yellow. The first three varieties are most common in fair persons, the others in those of a dark complexion, though there are many exceptions. Besides these, there are several minor natural varieties; but most of them may be referred to one or other of the foregoing classes. The whole iris is not always of the same colour; the smaller ring being fre¬ quently of a lighter or darker, or even of a totally different hue from the rest of it. Attention to this is of some importance, in judging of the morbid changes in colour. When the chief part of the iris is deep blue, the inner circle is often blueish grey, or vice versa. In other cases, a generally blue, or blueish grey iris, has an inner ring of a citron or wax-yellow colour. A dark iris, with a yellowish or light olive inner circle, is also frequently met with ; but a blue iris with a hazel inner ring, or a dark iris with a light-blue one, are very rare varieties. The irides of the right and left eyes are for the most part alike; and when the colour of one has been changed by disease, it may, with very few exceptions, be correctly assumed to have been originally the same as that of the other. In some extremely rare cases the iris is of a different shade, or even of a totally different co¬ lour, at the opposite sides of the pupil. The following are the changes of colour usually observed in a na¬ turally full blue iris, in the successive stages of inflammation, affect-
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