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Reducing errors in measuring refractive errors: De Zeng refractometer
  1. Richard Keeler,
  2. Arun D Singh,
  3. Harminder S Dua

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Thomas Young's optometer, invented in 1800, was the first in a long line of instruments designed to measure the refractive errors of the eye. In 1895, Henry L De Zeng Jnr patented his refractometer (figure 1). This was to be the first of 40 other inventions he patented between 1895 and 1925.

Figure 1

Drawings of the refractometer for the patent.

His refractometer was an advance on the others that prevailed at the time, in both ease of use and accuracy in measuring the refractive state of the eye. Another advantage was that the instrument …

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