1. Field of the Invention
This invention relates to the ophthalmoscope art and more particularly to an improved coaxial ophthalmoscope having both an improved light trap for preventing reflection of unused light into the eye of the viewer and filtering means for filtering out the light reflected from the cornea of the eye under examination.
2. Description of the Prior Art
Ophthalmoscopes utilized for examining the interior structure of an eye such as the retina, have long been known. One class of such ophthalmoscopes is termed coaxial ophthalmoscopes and in such coaxial ophthalmoscopes the axis of viewing of the eye under examination coincides with the axis of the light directed into the eye under examination. The advantages of such a coaxial arrangement are, of course, well known in the art. However, in order to provide such a coaxial viewing of the eye under examination it is necessary that the portion of the generated light not directed to the eye under examination be substantially absorbed in order to provent reflection of this light back onto the eye of the viewer. Such devices for absorbing light are generally termed light traps.
The patents to Tillyer, U.S. Pat. No. 1,664,953 and 1,859,756 both show essentially coaxial ophthalmoscope arrangements incorporating a light trap. However, the light trap shown therein has not proven to be sufficiently effective in preventing transmission of the unused portion of the light back into the eye of the viewer.
Similarly, in Tillyer, U.S. Pat. No. 1,889,456 there is a light trap similar to that shown in 1,859,756.
Other ophthalmoscope arrangements are shown in U.S. Pat. Nos. 3,524,702; 3,543,746; 3,572,910; 3,586,424; 3,600,067 and 3,602,581. However, in none of these patents is there a recognition of the problem inherent in allowing unused light to reflect back into the eye of the viewer nor the necessity for absorbing substantially all of such unused light.
Additionally, in examination of the retina utilizing such an ophthalmoscope, it has been found that light reflected from the cornea tends to obscure the light reflected from the retina thereby preventing or inhibiting detailed examination thereof.
Accordingly, a filter to remove the light reflected from the cornea but allowing the light reflected from the retina to pass therethrough is desired. The patent to Jasgur U.S. Pat. No. 3,567,409 discloses a filtering technique for a viewing device employing a pair of polarizing elements. However, Jasqur does not disclose the positional arrangement for polarizing elements in an ophthalmoscope.