Once you have a suitably fast shutter speed, you needn't adjust ISO. It is my belief that ISO only needs to be adjusted if and only if the image cannot be made sharply by adjusting shutter speed and aperture. Adjusting ISO will allow more sensitivity, which will permit smaller apertures and shorter shutter speeds. Always use the lowest practical ISO, bearing in mind that the camera will perform at it's best at it's native ISO - which is sometimes not the lowest ISO setting possible.
Light and position of artificial light will be the largest impact to how the eyes render. If light is retroreflected back to the camera's film plane, meaning that a high amount of the light is reflected at an angle perpendicular to the sensor, you will have red eye, this is mostly a concern with flash photography since the flash is typically very intense and narrowly focused - but I would imagine that any light retroreflected off the cornea will have a dulling effect. As for more practical applications, I'll let someone with more experience answer...