Final answer:
Retroillumination is the technique used to examine the anterior structures of the eye and is based on total internal reflection.
Step-by-step explanation:
The illumination technique where the illumination beam is focused on the limbus to create internal reflection through the cornea is known as retroillumination. This technique is used in ophthalmology for examining the anterior structures of the eye, like the cornea, iris, and lens. It is based on the principle of total internal reflection, similar to the way light is reflected in optical fibers and binoculars, allowing clinicians to detect irregularities that may not be visible with direct illumination methods.