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Ophthalmoscope
An ophthalmoscope enables a physician to examine the interior of the eye
to detect abnormalities or signs of disease on the retina and lens of the
eye. It does this by directing a tiny beam of light through the pupil. The
pupil is the black "window" of the eye.
Babbage and Helmholtz
The first ophthalmoscope was invented in 1847 by Charles Babbage
(1792-1871), an English mathematician. Babbage gave the device to a
physician for testing, but it was laid aside and forgotten. Four years
later, German physician and physiologist Hermann von Helmholtz (1821-1894)
developed his own version of the ophthalmoscope. Helmholtz was unaware of
Babbage's instrument. Because he had better luck making his device
known, Helmholtz is often credited as the sole inventor.
Helmholtz's instrument operated by using a mirror to shine a beam
of light into the eye. The observer would look through a tiny aperture
(opening) in the mirror. Helmholtz found that looking through the lens
into the back of the eye only produced a red reflection. By attaching a
condenser lens he obtained a clearer inverted image, which was then
magnified five times. He called this combination of a mirror and condenser
lens an indirect ophthalmoscope. It was used regularly for eye
examinations until 1920.
Helmholtz also invented the ophthalmometer, which was used to measure the
curvature of the eye. The eye's curvature determines whether the
focal point of an object's image will be on the lens of the eye, or
in front or behind the lens. If the focal point isn't on the lens,
the person will be near-or far-sighted. In addition, Helmholtz studied
color blindness and the speed of nervous impulses. He also wrote the
classic
Handbook of Physiological Optics.
Swedish ophthalmologist Allvar Gull-strand (1862-1930), who also studied
physiological optics, developed another version of the ophthalmoscope. He
also invented a slit lamp, used with a microscope, that enabled a
physician to locate foreign bodies in the eye.
The Modern Opthalmoscope
The modern ophthalmoscope is a hand-held instrument. It contains a small
battery-powered lamp that directs the beam of light by way of a mirrored
prism. The observer looks through a tiny hole in the prism. The instrument
magnifies the image and can be focused by a series of revolving lenses.
The lens needed to focus the image gives the doctor an approximation of
the glasses lens prescription needed to correct the patient's
vision.
A modern ophthalmoscope in use.
A new type of ophthalmoscope that can project a laser beam is used in eye
surgery to correct a detached retina. Another, larger type of
ophthalmoscope, called the binocular ophthalmoscope, is used in clinical
research. It provides an image of the eye that is magnified fifteen times.
User Contributions:
Martin B. Zieman OD
⚠
The picture which shows "a modern ophthalmoscope in use" is actually a retinoscope!
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