Final answer:
The maximum depth of penetration for iontophoresis is typically 4 mm, which is suitable for superficial tissues but not deep structures like the entire eye.
Step-by-step explanation:
The depth of penetration for iontophoresis is typically less than a few centimeters. The provided data suggests that an effective penetration depth of 3.85 cm is sufficient to examine the eye, which is more than needed based on a requirement of about 3.00 cm. However, considering the context of iontophoresis, which is often used for localized drug delivery through the skin, the typical maximal depth of penetration is much less than that required for examining the entire eye. Based on the typical application of iontophoresis, the depth of penetration is more likely to be in the millimeter range rather than the centimeter range listed in the question.
Therefore, the final answer for the maximum depth of penetration for iontophoresis, which is often used for transdermal drug delivery, is d. 4 mm.
The penetration depth generally doesn't exceed this depth, making it suitable for targeting superficial tissues but not for deeper structures, such as the entire eye. Thus, none of the provided depths in the question match the maximum depth for iontophoresis, which can be confirmed from reliable medical sources and studies on iontophoresis.