The two great inventions of Hermann von Helmholtz are the ophthalmoscope for seeing into the internal structure of the eye and the ophthalmometer for measuring the curvature of the cornea. Together these have become primary tools of ophthalmologists and optometrists.

In 1850, Helmholtz built the first ophthalmoscope to illustrate the physiology of the eye for his students. It was a crude device consisting of a light source and microscope glass slides mounted on a handle at 45œ to the eye and observer. The idea was to shine the light into the eye, where it would be reflected by the retina. Helmholtz knew that the light would follow the same path out as going in, so he reflected the outgoing light by 90œ to his eye. Present-day ophthalmoscopes are more complex and often consist of a battery-operated light source and a concave mirror that focuses the light into the eye. The physician views the interior of the eye with lenses of different powers through a small aperture in the mirror.

Helmholtz invented the ophthalmometer in 1855 to measure the accommodation of the living eye to different focal distances. The ophthalmometer measures the reflection of objects in the convex surface of the cornea. These measurements determine, among other things, whether the cornea focuses on the lens or in front or behind it. If the focal point is not on the lens, the person is either nearsighted or farsighted. The amount and direction of astigmatism can also be measured by the degree to which the reflected image is displaced from the center of the front surface of the eye.

In his research, Helmholtz invented many other devices for the quantitative measure of the physiology of the eye and ear and the ability to perceive light and sound. As in all of his studies, his primary objective was to understand the fundamental mechanisms by which the eye and ear work.

The tools that Helmholtz invented helped to establish the field of ophthalmology and are the main measuring devices for determining problems of vision. In addition, there are other diseases that have consequences for the eyes and that can be recognized by studying the eye. For example, the ophthalmoscope is used to examine retinal blood vessels, from which information can be obtained about high blood pressure and diabetes. The ophthalmometer can measure the ability of the eye to accommodate to situations such as different focal distances and can also measure astigmatism. Before the invention of the ophthalmoscope and the ophthalmometer, there were only limited means to determine the state of health of the eyes and what could be done to improve vision. Simple eyeglasses were available and could be fitted by trial and error, but many other vision problems could not even be recognized. With these two instruments, optometrists could design glasses to correct for defective vision.

From his studies in physiological optics, Helmholtz came up with a theory of three-color vision similar to that of the earlier scheme of Robert Young. This theory is now called the Helmholtz-Young theory of color vision and is important in understanding color blindness.

Helmholtz was also interested in how the human ear perceived sounds. As an expert pianist, he wanted to know how pitch and tone were distinguished. He suggested that the inner ear could resonate at certain frequencies, enabling it to differentiate tones, overtones, and timbres--thus enabling the ear to distinguish different instruments playing the same note.

Free term papers are not written to satisfy your specific instructions. You can use our professional writing services to buy a custom written research paper, term paper, or essay on Health at affordable price. CustomTermPapers is the best solution for those who seek help in writing term papers, essays, and research papers related to Health and other relevant topics.