This invention pertains to binocular indirect ophthalmoscopes and, more particularly, to such an ophthalmoscope having small pupil capability but without the several adjustments required in prior art ophthalmoscopes of this nature.
For optimum binocular ophthalmoscopy, three inverted images should be formed in the patient's pupil. These are the observer's two pupils and the light source. This is pointed out in an article entitled "Clinical Evaluation of the Small Pupil Binocular Indirect Ophthalmoscope," by Horland, Elzeneiny, and Schepens appearing in Vol. 82, Archives of Ophthalmology, Oct. 1969, at pages 466-474. It is also important that the three images be separated as much as possible. The images of the observer's pupils should be separated in order to provide maximum stereopsis. The light source image must be separated from the pupil images in order to minimize reflections from the cornea and the crystalline lens. A number of prior art ophthalmoscopes are capable of such results when viewing the fundus through a normally dilated pupil. However, approximately one per cent (1%) of patients have pupils which do not dilate or have other conditions resulting in partial obscuration of the pupil. In order to properly examine these patients, small pupil ophthalmoscopes have been employed.
The previously cited article in the Archives of Ophthalmology discloses a small pupil ophthalmoscope which may be employed in pupils as small as 1.5 millimeters while retaining stereopsis and reducing reflection. However, a number of adjustments are required of the user in making examinations through a small pupil. First, of course, there is the usual adjustment for the interpupillary distance (PD) of the observer. In addition, three adjustable mirrors are provided -- one for the light source and one for each of the observer's pupils. As a result of the several additional adjustments required for use as a small pupil instrument, the ophthalmoscope is more complex and expensive than is desirable. Accordingly, it is the primary object of the present invention to provide a binocular indirect ophthalmoscope which is capable of examination through small pupils but does not require the additional adjustments of prior art instruments. Another object is to provide such an instrument which retains optimum stereopsis and minimum reflection. Other objects, features, and advantages will be apparent from the following description and appended claims.