An ophthalmoscope is a medical instrument used to examine the eye. It is very important for a doctor to be able to view the interior of the eye, including the retina, located at the back of the eye. Although it is most often used to diagnose eye conditions, information gathered through an eye exam can be relevant to many other medical fields, including cardiology, neurology, and pediatrics. It has become one of the most commonly seen and recognized medical screening devices.
The most common type of ophthalmoscope consists of a concave mirror that reflects a small light within the instrument. A doctor examines the eye by looking through a monocular eyepiece into the eye of the patient. It is possible to view different depths of the eye at different magnifications by rotating a disc of varying lenses within the instrument itself. A routine examination of the eyes can be done quickly in a doctor's office. If the need exists for a more thorough examination, the doctor will sometimes dilate the patient's pupils beforehand, to provide a clearer and wider view of the inside of the eye.
The type of ophthalmoscope described above is also known as a direct ophthalmoscope. Less commonly used is the indirect ophthalmoscope, although these operate on basically the same principle. They usually consist of a light attached to a headband which is worn by the doctor. The doctor uses a hand-held lens to examine the eye. This type of instrument can provide a wider view of the eye, and is still quite useful, even if there are cataracts in the lens of the eye that would otherwise obscure the view.
As is the case with many inventions, more than one person can be said to have invented the ophthalmoscope. The first doctor ever to fashion a device for viewing the retina was Johannes Purkinje in 1823. In 1847, Charles Babbage developed a very functional early version of the device, but did not widely publicize the invention. The man who did was the German physician Hermann von Helmholtz, in 1850. He modified the earlier design slightly and made a model of it for demonstration.
For these reasons, Helmholtz is often credited with the invention. The first people to develop an ophthalmoscope that resembles the modern ones we know were Josh Zele and Jon Palumbo. In 1915, they came up with a hand-held version that is similar to those used in doctors' offices today.