The Ophthalmoscope: Its Theory and Practical Uses

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Duncan Brothers, 1882 - Ophthalmoscope and ophthalmoscopy - 150 pages
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Page 24 - ... the angle of reflection is always equal to the angle of incidence, the image for any point can be seen only in the reflected ray prolonged.
Page 22 - Dense bodies and particularly those with smooth or light-colored surfaces, reflect light most perfectly, and any surface which reflects light well is called a mirror. There are three general classes of mirrors known as plane, concave, and convex. It is more particularly with the concave mirror that we shall have to do. When light falls upon a plane reflecting surface, it is a well-known law that the angle of reflection is equal to the angle of incidence. If the reflecting surface be concave or convex,...
Page 142 - Determination of the Optical Condition of the Eye by the Ophthalmoscope, with a new modification of the Instrument for that purpose, Am. Journ. of the Medical /Sciences. 1870, p. 323, etc. . The method is, indeed, nothing but the ophthalmoscopic application of the determination of the length of the ocular axis from known degrees of ametropia.
Page 24 - ... more complicated, for the present we treat only, of the case of a small pencil incident directly. Principal FOcus. If a small pencil of parallel rays, parallel to the axis of the mirror, is incident directly on a concave mirror, these rays after reflexion are found to converge to a point on the axis of the mirror. This point is called the principal focus of the mirror. If the mirror be convex the rays after reflexion appear to diverge from a point on the axis behind the mirror, this point is...
Page 54 - D, which can be brought round and applied over the .glass of the disc behind the hole in the mirror. Thus, with the superposition of a single glass (plus 16 or minus 16) and with an uninterrupted rotation, a series is obtained of successive dioptrics from 1 to 23 plus, and from 1 to 24 minus, and a half series with the addition of the 0.5 D from 0.5 to 8 plus, and from 0.5 to 9 minus, or sixty-five glasses in all. The value of the glasses and the combinations is read off on the disc by a method peculiar...
Page 61 - ... table which also carries a lamp, and on which they may be moved freely. My first trials with this arrangement satisfied me that it would work better than, any other; and also showed that it could be made to afford an image of greater enlargement than any other, as well as a brighter illumination. It has already been pointed out that the greater the focal length of the object lens the greater will be the size of the image; but the limits of enlargement thus attainable by hand instruments are soon...
Page 62 - I place my mirror forty inches from the eye of the patient, which gives a visual distance of twenty-two inches for the observer. In order to obtain sufficient illumination, the lamp is brought up from its usual position, and is placed nearly in the focus of the mirror, while the face of the patient is guarded from direct lamplight by the interposition of a metal screen, for use without atropine, and in order to avoid contraction of the pupil, a plate of glass, slightly tinted with cobalt blue, is...
Page 157 - Evidently much investigation, thought and carefulness have entered into the production of this work, and we believe it to be worthy a place in every household." — The Magnet. * * * »we have carefully examined the work and shall cheerfully recommend it for family use. The directions as to what food and drinks, and modes of preparation are very judicious.
Page 156 - Useful Hints Connected with the Selection and Use of the Instrument; also Some Discussion of the Claims and Capacity of the Modern High-Angled Objectives, as Compared with those of Medium Aperture; with Instructions as to the Selection and Use of American Object - Glasses of Wide Apertures. BV J. EDWARDS SMITH, MD, PROFESS'.
Page 61 - ... part of it should be absolutely independent of every other part, and capable by itself of quick and easy adjustment. For this purpose the mirror and lens are placed upon separate pedestals; a similar pedestal supports the chin of the patient, and they all stand upon a table which also carries a lamp, and on which they may be moved freely. My first trials with this arrangement satisfied me that it would work better than any other; and also showed that it could be made to afford an image of greater...

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