Biomicroscopic examination of the ocular fundus with a +150 dioptre lens

This article describes the design of a +150 dioptre compound lens for biomicroscopic examination of the fundus. To compare the lens with other fundal examination techniques a method is described for measuring the magnification and vertical angle of view of the various examination lenses. By this method the +150 dioptre lens is shown to have an angle of view of 60 degrees. This is similar to that of the indirect ophthalmoscope when used with a 20 dioptre lens which has an angle of view of 57 degrees. However, the magnification of the +150 dioptre lens is greater at X5.2 compared with X3.0 for the indirect ophthalmoscope. The practical applications of the lens are discussed. In comparison the field of view of the +78 and +90 dioptre lenses are 37 degrees and 29 degrees respectively. The +150 dioptre lens has proved a useful adjunct enabling a rapid global screening of the ocular fundus on the slit-lamp before examining any particular area of interest in more detail.