Vision in health and disease; the value of glasses for its restoration, and the mischief caused by their abuse. Being the substance of lectures delivered at the Central London Ophthalmic Hospital / by Alfred Smee ... ; illustrated by one plate and numerous woodcuts.

  • Smee, Alfred, 1818-1877.
Date:
1847
Catalogue details

Licence: Public Domain Mark

Credit: Vision in health and disease; the value of glasses for its restoration, and the mischief caused by their abuse. Being the substance of lectures delivered at the Central London Ophthalmic Hospital / by Alfred Smee ... ; illustrated by one plate and numerous woodcuts. Source: Wellcome Collection.

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    flection. As by practice we may bring the eye to see in the most feeble lights, SO should we only employ these contrivances to cut off the sun’s rays when the light is either too dazzling or distressing to the eye. When these glasses are worn, the spectacles should have two side parts of the same coloured glass, as, by this contrivance, the protection is ensured to the entire retina. (122.) Coloured glasses should on no account be worn on a dull day, in the dusk of the evening, nor, as a general rule, with artificial lights, or their pre- sei;vative power in strong lights would be impaired by accustoming the eye to the impressions of feeble illuminations. Some persons who have delicate or¬ gans commonly employ spectacles of lightly-tinted glass for reading or writing; though even here, as a general rule, they should be avoided. Coloured glasses are of great value to protect the eye from the brilliant reflection of the snow in mountain passes; they are also constantly employed by the chemist when he uses the oxy-hydrogen or voltaic light, for which purpose they can scarcely be too deeply coloured. They are employed by the mariner when taking his observations of the sun; and they are used when the eye has lately re¬ covered from inflammation, and is liable to be injured by excess of light. (123.) For some years I have employed coloured glasses for that singular malady known under the name of Hay Fever. This curious disease is greatly aggravated by intense brightness of the sun, when combined with heat, and assisted by dust. Light will not cause the malady alone, heat will not produce it alone; but light and heat appear to me to be the agents which operate most powerfully in producing it; and the presence of dust of every kind, such as the dust from the roads, the minute portions of chalk, or the pollen of flowers, much heightens the malady. You will find that a pair of dark-green spectacles will wonderfully alleviate the distressing symp¬ toms which are incidental to this complaint. They should be worn only in the middle of the day, when the rays of the sun are unpleasantly powerful; and they should be studiously put aside whenever the sun is clouded. (124.) In all cases where coloured glasses are employed, the two surfaces should be perfectly parallel, or more or less distortion will ensue. Glasses with parallel surfaces have no action on rays which strike the glass perpen¬ dicularly to the surface, though those which fall obliquely are reflected. In looking through them the object is neither increased nor diminished. (125.) To exclude light we do not invariably employ tinted glass; we sometimes use gauze made of wire or other materials. Ladies placed under circumstances requiring the aid of contrivances calculated to diminish light, instead of using spectacles, prefer to employ a very thick veil, which they sometimes even double. This contrivance is, perhaps.