Definition: Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.
Input: Abstract: The four methods of illumination in the use of slit-lamp biomicroscopy of the anterior segment, described first by Vogt, are equally useful in the posterior part of the eye. Examination of the ocular fundus is more difficult. In particular, photography of the central and peripheral parts of the fundus demands additional technical arrangements if all the appearances of biomicroscopy are to be recorded.

Retinal Vessels