Final answer:
The technique using reflected light off deeper structures like the iris to study anterior structures is called retroillumination, which comes in two forms: coaxial and tangential.
Step-by-step explanation:
The illumination technique you are referring to employs light that is reflected off deeper structures like the iris, lens, or retina, illuminating more anterior structures in the process. This technique is known as retroillumination. There are two forms of retroillumination: coaxial retroillumination, where light is directed in the same path as the observer's line of sight, and tangential retroillumination, where the light is reflected at an angle to the line of sight. Coaxial retroillumination helps to highlight irregularities in a transparent medium, whereas tangential retroillumination is advantageous for observing the contour and elevation of lesions. The correct answer to the multiple-choice question is b. Retroillumination; coaxial and tangential.