A practical treatise on diseases of the eye / by Robert Brudenell Carter.
- Robert Brudenell Carter
- Date:
- 1875
Licence: Public Domain Mark
Credit: A practical treatise on diseases of the eye / by Robert Brudenell Carter. Source: Wellcome Collection.
28/618 page 6
![perforated for tlie passage of the optic nerve and retinal vessels, and the perforation is very slightly smaller than that of the sclerotic, over which it is superimposed, and is bounded and strengthened by a circle of connective tissue fibres, some of which send out processes that pass between the nerve bundles and are lost in the lamina cribrosa. The choroid consists almost entirely of blood-vessels, supported by a delicate web of connective tissue, but is abundantly supplied with nerves, and contains also bundles of unstriped muscular fibre. The interstices of the stroma are filled by cells containing dark brown pigment, which, together with the blood in the vessels, gives to the membrane a reddish-brown or chocolate colour. The quantity of pigment varies much in different individuals. It is most abundant in dark people and in the dark races, is found only in small quantity in very fair persons, and is altogether vvanting in albinos. For convenience of descrip- tion, the choroid is divided into layers ; but this division is arbitrary, and has been carried to an unnecessary degree of refinement by many writers. Two layers may, however, be recognized in practice; the external, containing large vessels and abundant pigment, and the internal, containing small vessels or capillaries, and comparatively little pigment. The most conspicuous vessels of the external layer are the stellate clusters of veins known as the vena3 vorticosae. These clusters are usually four, sometimes five or six, in number ; and each one is composed of ten or twelve veins which converge to a common central trunk. The convergent veins are so placed that, when seen only in a small part of their course, they appear nearly ]Darallel to those contiguous to them; and the interspaces are usually filled up by loose cells loaded with pigment. Hence, when seen from within by the ophthalmoscope, the choroid presents a striped appearance—the stripes being due to the alternation of nearly parallel veins, through which the colour of the blood is visible, with linear interspaces rendered dark by pigment. The choroidal veins are not visible with the ophthal- moscope under ordinary conditions, but when they become visible they can be immediately recognized by their approach to a parallel arrangement. The central trunks of the vence vorticosfe pass out through the sclera by very oblique channels](https://iiif.wellcomecollection.org/image/b20401590_0028.jp2/full/800%2C/0/default.jpg)
