Amongst the most utilised instruments for eye observation are the ophthalmoscope and the tonometer.
The ophthalmoscope observes changes to the eye through magnification. The tonometer measures eye health through pressure measurement.
The ophthalmoscope (‘eye looker’) looks at the inside of the eye. Inside the eye is the only place in the body where the nerves and blood vessels can be seen without cutting the skin. There is some debate about who actually invented the instrument but priority is generally given to Hermann von Helmholtz who created his device in 1851 using a mirror with a lens and a candle as a source of illumination. The term ophthalmoscope came into use in 1854. Many different clinicians developed different forms of ophthalmoscope. A medical instrument catalogue from 1885 lists ten different types. The next advance came when incandescent globes and dry cell batteries facilitated the reduction of its size to that of a pen-like instrument such as it appears, today.
In contrast to the ophthalmoscope the tonometer evaluates eye-health through direct pressure measurements obtained from contact with the cornea. This technique was pioneered in France during the nineteenth century. In recent decades a method of non-contact tonometry has been developed which uses a rapid air pulse to infer pressure measurements from the cornea.