Side Illumination

Side ILLUMINATION (or focal illumination), one of the basic methods of clinical eye examination. The examination itself using this method is conducted in a dark room. The light source (an ordinary lamp) is placed to the side and slightly in front of the patient so that his eye is brightly illuminated. The doctor takes a strong converging lens (13-20 diopters) in hand and positions it in such a way that the focus of the rays collected by the lens falls exactly on the area of the patient's eye being examined. Such side illumination, or focal illumination, is used in examining the cornea and iris of the eye. The slightest clouding of the cornea or the most insignificant structural abnormalities of the iris become clearly visible with the side illumination method. It is especially convenient to perform the examination using two lenses, one of which serves specifically for illumination, and through the other the doctor observes the illuminated area of the eye in magnified form. Instead of this second lens, one can use a complex achromatic Hartnack magnifying glass, which gives magnification of six and ten times.