An elementary treatise on the function of vision and its anomalies / by Dr. Giraud-Teulon ; translated from the second French edition by Lloyd Owen.

  • Owen Lloyd.
Date:
1880
Catalogue details

Licence: Public Domain Mark

Credit: An elementary treatise on the function of vision and its anomalies / by Dr. Giraud-Teulon ; translated from the second French edition by Lloyd Owen. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    cannot, in some cases, be held to be free from risks of a similar kind. Each act of convergence causes more or less notable increase of compression of the globe, and this excess is the more perceptible according to the degree of deviation of the plane of the optic axes from the plane of the horizon. Whence may be de- duced two important principles : i, to hold the object as far from the eyes as is compatible with distinct vision, say from 30 to 45 centimetres (11 to 17 inches) ; 2, to place it as far as possible in the neighbourhood of the horizontal plane of the eyes. Reading whilst lying on the back is particularly dan- gerous in this respect, and not less so in relation to the conditions of passive congestion of the upper parts of the body which this position induces. Now, no organ is more apt than the sponge-like choroid to feel the effects of this position. It is there- fore advisable in all occupations to maintain an upright and unembarrassed attitude. Which does not mean that the eyes should be kept elevated above the hori- zontal plane for a long period, for persistent direction of the vision upwards is by no means less unfavourable in relation to ocular pressure. Standing for a long time looking at objects in a museum will suffice to establish the truth of this proposition. § 142. Tl»e influence of liig-l** i«» vai-ious cleg-ree^i of illumination.—How shall we deter-