Landolt Ophthalmodynamometer
The Landolt ophthalmodynamometer is a rare and fascinating antique instrument with a distinguished history in vision science. It was invented by Edmund Landolt to determine the amplitude of convergence — the range over which the eyes can converge to maintain single binocular vision. This example is presented in its original fitted case with rich orange velvet lining.
Two Different Instruments
It is important to note that two instruments carry the ophthalmodynamometer name. The more recent ophthalmodynamometer measures systolic and diastolic ophthalmic artery pressures within the eye. The Landolt instrument described here is entirely different — it was designed specifically for the determination of accommodation and convergence.
The Landolt Design
In 1885 Landolt commissioned Roulet in Paris to manufacture this instrument. Landolt chose the name “dynamometer” deliberately. He felt there was a meaningful difference between “static” and “dynamic” refraction — one in which accommodation played an active role.
The instrument is essentially a black chimney with a slit in it and frosted glass behind the slit. This was placed over a candle to supply the light source. A tape measure was then stretched from the patient’s face to the instrument. The patient was brought closer while focusing on the slit of light until it became double. The distance at which this occurred was considered the amplitude of convergence.
Electric Version
Once electricity became widely available, a version with an electric light bulb replaced the candle-lit original. This example appears to be the earlier candle version.
Condition
This particular example does not have the tape measure in the box — it is shown separately. The instrument itself and the fitted orange velvet case are in good condition. The frosted glass slit element and black chimney body are intact.
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