The appearance of certain ocular structure changes due to changes in absorption, reflection, and optical transmission depends on the wavelength of light. By means of this physical quality of the light, it is possible to demonstrate certain parts of the fundus better than others. Several examples described in this article demonstrate how degenerative vascular alterations can be judged much better and more safely by use of monochromatic light and light of varying wavelengths. Alterations of blood vessel caliber show the most contrast in yellow-green light where there is maximum absorption by the blood. Alterations in blood vessel wall reflection that are invisible in white light can be demonstrated in short-wave light and also partially in red light. Ophthalmoscopy in connection with the xenon arc lamp as a method of examination is suprior to photography alone.