On defects of vision which are remediable by Optical appliances : A course of lectures delivered at the Royal College of Surgeons of England.

  • Carter, Robert Brudenell, 1828-1918.
Date:
1877
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Licence: Public Domain Mark

Credit: On defects of vision which are remediable by Optical appliances : A course of lectures delivered at the Royal College of Surgeons of England. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    return on a future occasion, my object in this preliminary lecture being to define the general principles by which the varieties and degrees of ametropia are recognised and expressed. In the foregoing method of examination with lenses and test- types we have to deal only with subjective phenomena; and, except for the check afforded by repeating the examination at a different distance, we are almost entirely dependent upon the statements made to us by the patient. It follows, of course, that we are also dependent upon his good faith and accuracy of observation ; and there are many conditions in which these cannot command our implicit trust. In young children, or in persons of defective intelligence, we may be deceived by the patient without intention; and in other cases, as by soldiers seeking to be dis- charged, or perhaps sometimes by railway plaintiffs, we may be deceived with full intention. It is therefore important to be able to test ametropia objectively, and independently of the statements which are made to us; and this can to some extent be accom- plished by the aid of the ophthalmoscope. The course of the rays which enter an eye, to form or not to form a picture upon the retina, and the course of the rays which leave it, are strictly correlated phenomena; and, when a glass is required to afford the patient a clear view of outward objects, a similar glass is also needed in order to afford a clear view of the retina of such a patient to the surgeon. The glass used with the ophthalmoscope may therefore be a measure of ametropia. But a more complete account of this method of examination, and of the hmitations of its usefulness, will be most suitably entered upon in a future lecture, after the influence of accommodation and the varieties of ametropia have been more fully described. Another contrivance which promises to be useful in the measure- ment of refraction, and which at the same time affords a certain amount of control over the statements of the patient, is an optometer which has recently been suggested by Dr. Hirschberg, of Berlin. This instrument, which is now being made at my request by Mr. Browning, superficially resembles a binocular opera- glass. The distance apart of its two tubes can be regulated to