A treatise on diseases of the nervous system / by William A. Hammond.

Date:
1873
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on diseases of the nervous system / by William A. Hammond. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    quarter inches in diameter, concave, and perforated in the centre by a hole about the one-twelfth of an inch in diameter. The edges of this aperture are bevelled so as to afford as lit- tle obstacle as possible to the passage of the rays of light to the eye of the observer. The mirror is set into a bronze ring with a handle, and there is attached also to this ring a clip for holding a concave ocular lens, which.in some conditions of refraction, either in the eye of the patient or that of the observer, is necessary in order to produce the necessary divergence of the parallel rays emanating from the patient's eye, and thus render the imao-e of. the fundus distinct. A direct image is thus ob- tained The lamp, which should furnish a steady flame, is placed on the side of the patient's head corresponding to the eye to be examined, and the eye of the observer very dose to that of the patient. This process gives a very satisfac- tory view of the fundus with the optic disk and.retmal ves- sels, but requires care, and is more difficult than that by which the inverted image is obtained. _ In this case the observer illuminates the fundus with the ophthalmoscopic mirror, and then interposes between the mirror and the eye a double-convex lens which he holds lio-htly between the thumb and finger, resting the ring im- £er on the forehead of the patient, so as to make the hand steady, and the little-finger being disengaged so as to be employed in raising the eyelid if necessary. The obiect-lens should have a focal distance of about two inches, and it should be held so as to bring the focus on the pupil. The lamp is placed behind and a little to one side o he eye to be examined. In order to see the optic disk the patient is told to look at the ear of the observer on h side opposite to the eye being examined. In tins way the axis of vision is directed inward, and the optic disk readily ^Ttetamin^tions are made in a room lighted only by the lamp used in the processes. It is sometimes necessary