The choroid membrane is a continuation of the iris, and is the colored membrane which lines the back part of the eyeball. It can be recognized only by means of the ophthalmoscope Figs. 448 and 449.

Fig. 448. Ophthalmoscope.

Fig. 448. Ophthalmoscope.

Fig. 449. Ophthalmoscope.

Fig. 449. Ophthalmoscope.

This instrument consists essentially of a concave mirror with an opening in its center, by means of which light is thrown into the eye of the patient, while the examiner looks into the eye through the small opening in the mirror. By means of this little instrument, the whole interior of the eye can be readily examined, its various structures being brought clearly into view. Fig. 449 illustrates the most improved form of the apparatus, which is furnished with a set of small lenses, arranged in such a manner as to be capable of being brought opposite the opening in the mirror, thus magnifying the view obtained by the mirror. Little was known respecting the diseases of the interior of the eye before the invention of the ophthalmoscope by Helmholtz, about thirty years ago. Disease of the choroid requires the attention of a skillful oculist.