Invisibility/Analysis

Required Secondary Powers
Applies not just to you, but to things you are carrying, or wearing. Any dirt on you becomes invisible, and either you get clothes made of some suitable material, or provide some Fan Service. Also, your light distortion fits that of your surroundings, and food remains invisible through the digestive process.

Also, to work properly an eye normally must at least have a lens bending the light (thus being visible at least as glass-like objects), pigments in sensitive cells absorbing the light (as opposed to passing right through just like, say, x-rays) and something preventing the retina from blanket exposure by light not focused with the lens, that is, blocking all the rays not coming in via the pupil, including those from behind the retina. Oh, wait, doesn't that add up to almost a complete eyeball?

All of which really raises the question, what counts as an invisible person's body? Just his own cells with his own DNA? Then what about the bacterial colonies in the intestinal tract? What about the mitochondria in each cell, which have their own DNA? What about the lifeless liquids such as stomach acid and fluid in the eyes? What about dead cells, like hair and fingernails? Or the entire outer layers of skin, for that matter?

Some Invisible characters can extend the light-warping field over whatever they touch, eliminating some problems but adding others—conscious selectivity is required, otherwise if they bump into something, that item might blink in and out of sight, making them fairly easy to track, especially crossing a crowded room. The issue of how large an object their field can cover also comes up in many continuities. Invisible Streaker is usually the result of lacking these Required Secondary Powers. A standard aversion of these required secondary powers is psychic invisibility, which is a mental or hypnotic effect that causes everybody to ignore you. The upside is that this automatically also foils hearing and smell; the downside is that it tends not to work on cameras.
 * You could be filmed, sure, but if it's a mere mortal manning the security cameras (or watching them later for whatever reason), your power may extend through the camera to the viewer as well. So again, you're there, but no one sees you. Depends on the inner mechanics of the power.
 * Some story exacerbates this power to the point of forcing people to retcon their perception to ignore the psychically invisible character. For example, if he takes your sandwich, you change your memory so that you never had it, and possibly wonder why you bought a Coke but not a sandwich, considering you are hungry.
 * Of course, that does not keep you from triggering the laser tripwire that fills the room with toxic gas or anything else that is automated, unless the automation takes the form of a sentient AI.

Michio Kaku of Scifi Science proposed the best practical path to invisibility is a form-fitting suit that bends surrounding light. This suit has small eyeholes which doesn't have this light-bending attribute, allowing the user to see. His eyes would still be somewhat visible, though they may not be that noticeable, depending on the environment.