Ophthalmoscope

The invention relates to a direct ophthalmoscope.

The state of the art and the invention are illustrated by means of the drawings.

FIG. 1a is a longitudinal section through a known direct opthalmoscope.

FIG. 1b is a representation of the fundus oculi as seen by an observer with the use of the opthalmoscope of FIG. 1a.

FIG. 2a is the longitudinal section of a second known opthalmoscope.

FIG. 2b is a representation of the fundus oculi as seen by an observer with the use of the opthalmoscope of FIG. 2a.

FIG. 3a is the longitudinal section of a direct opthalmoscope in accordance with the invention.

FIG. 3b is a representation of the fundus oculi as seen by an observer with the use of the opthalmoscope of FIG. 3a.

In the case of a widely dilated pupil on patient eye 13, a sufficiently large extent of the retina is illuminated by illumination beam 14. If the pupil of patient eye 13 is small, however, only a small part of the light reaches the retina of the patient, especially if the focal point of the lens system is located in the vicinity of deflection mirror 8, as shown in FIG 1a. If illumination beam 14 is focused in the vicinity of the pupil of patient eye 13, on the other hand, only a very narrow somewhat oval area 15 is visible as illuminated for eye 12 of the observer in case of a small patient pupil because of the thereby necessary larger parallax angle, which moreover is displaced upward, unlike the illuminated area 15 as per FIG. 1b into a range lying far outside the middle. If the opthalmoscope of FIG. 1a is used, on the other hand, not only is the illumination intensity low at the fundus oculi, but light falling on patient eye 13 is reflected backward by the iris and cornea in a broad beam to eye 12 of the observer, as indicated in the figures by the areas bounded by dashed lines. This makes the examination difficult if not impossible.

The object of the invention is that of designing an opthalmoscope in which as large an area 15 of the fundus oculi is illuminated with as good a utilization of the available light as possible, whereby reflections at patient eye 13 are avoided or suppressed as much as possible.

This task is achieved according to the invention when the condenser contains at least one lens element which presents at least one optically effective, preferably nonspherical, surface.

FIG. 3a shows an opthalmoscope designed in this way, in which condenser 4 presents lens 6 with a nonspherical surface in addition to one or more spherical lenses 5.

With the use of such a lens 6 in condenser 4, an approximately tubular course of illumination beam path 14 can be obtained between deflection mirror 8 and patient eye 13, which is very narrow in at least one direction over a relatively broad range. Consequently, the parallax angle between the illumination and observation beam paths can be kept very small, so that an almost circular illuminated area 15 is visible for eye 12 of the observer at the fundus oculi of patient 13. The light from the illumination beam path is thereby well utilized, so that area 15 is not only sufficiently large, but it is also illuminated with strong intensity. Light reflected at the cornea and iris of patient eye 13 is not reflected to eye 12 of the observer but instead to the side and below.