Anterior fundus examination with a gonioscope through a flat surface on a contact lens is of comparatively recent date.1 It has been used for viewing the fundus as far forward as the ora serrata and pars plana, using either simple scleral depression or a transillumination technique.2 It provides greater magnification of the extreme fundus periphery than can be obtained with ordinary indirect ophthalmoscopy. Experience with this method aided the designing of diagnostic contact lens and a completely mobile slit lamp-gonioscope.
An oblique plano surface on a contact lens for anterior fundus examination can be obtained by oblique section of a cylindrical plexiglass lens.1 The same is achieved by cutting an oblique slice from the mushroom head of the Troncoso type lens (plano facet) (Fig la, b). Another way of achieving the same effect is to fit the convex surface of the Troncoso lens with
SCHIRMER KE. Faceted Contact Lens With a Modified Viewing Device for Fundus Examination. Arch Ophthalmol. 1965;74(4):465-469. doi:10.1001/archopht.1965.00970040467006