Editing Slit lamp (section)

=== Indirect illumination ===
[[File:Indirect lateral illumination.jpg|thumb|100px|Indirect lateral illumination of corneal ulcer]]
With this method, light enters the eye through a narrow to medium slit (2 to 4&nbsp;mm) to one side of the area to be examined. The axes of illuminating and viewing path do not intersect at the point of image focus, to achieve this; the illuminating [[Prism (optics)|prism]] is decentered by rotating it about its vertical axis off the normal position. In this way, reflected, indirect light illuminates the area of the anterior chamber or cornea to be examined. The observed corneal area then lies between the incident light section through the cornea and the irradiated area of the iris. Observation is thus against a comparatively dark background.<ref name="Zeiss p. 17">"Eye Examination with the Slit Lamp", Zeiss, p. 17</ref>