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.

  • Alfred Smee
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. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    47/66 page 47
    (138.) In short-sightedness the image is formed anterior to the re- tina, and a focal lengthener is required to cause it to fall into its proper place. I must now refer you to my former lecture on the different cases of short-sightedness; and when you think it advisable to use glasses, begin with those which barely suffice to effect the desired object, and in all cases leave the eye some work to do, otherwise the eye will gradually accommo- date itself to the glass, and require a continual increase of its power. Very great mischief is inflicted on patients by allowing them to employ glasses too deep, and on that account glasses should always be used of such a power that some range of adjustment is left for the eye. (139.) Short-sighted persons should have two pair of spectacles, one to be used for near, the other for distant objects, and the glasses should be so arranged that the light from the object shall pass perpendicularly through I the lens to the eye. Short-sighted glasses for reading should be directed I towards a point about fifteen inches distant; for distant objects, they should I he on the same plane, or, to divide the error over every possible distance, I a slight convergence may be allowed. (140.) These convergent spectacles I have before introduced to your I notice under the term of caloscopic spectacles, and I believe that their ex- I tensive application will save the vision of hundreds. From my own expe- I rience, I should say that nearly two-thirds of all who use focal lengtheners, lor concave glasses, practically employ but one eye, because their specta- Icles have been so made that they could only adjust one glass to the axis of I vision. In the manufacture of these spectacles care should be taken that I each glass converges equally to the part viewed; and for this purpose I have I pointed out one or two contrivances, which I do not think it necessary to I describe here. The necessity of this mode of arranging glasses must be I immediately apparent if you look through the lens obliquely at a book; I for in one position you will increase the length of the letters, and in the ■ other you will separate them. (141.) Where focal lengtheners are employed, it is of very great conse- I quence that the centre of each glass should be exactly central to the pupil I of the eye. From neglect of this point alone I have been consulted, on I numerous occasions, by gentlemen of sedentary habits, who neglect the use I of one eye and employ but one organ for vision. You will now, gentlemen, I perceive that the laborious and tedious minuteness with which I have I dwelt upon the functions of the two eyes has not been thrown away; for, in I this case, you find, that, from the careless application of glasses alone, ex- I tensive damage has been effected, and thousands of persons now exist who I have been cut off from the full enjoyment of the beauty of external objects I by the ignorance or carelessness of spectacle-sellers. (142.) By using spectacles, the glasses of which are either too wide I apart or too narrow, double vision is produced, to prevent the embarrass-
    digitised image 1
    digitised image 2
    digitised image 3