What should be observed to determine the fit of a contact lens?

To determine the fit of a contact lens, observing the patient's comfort and lens adherence is essential. Patient comfort is an immediate indicator of how suitable the lens is for the individual. If the lens fits well, the patient should experience little to no discomfort, while any irritation or persistent discomfort may suggest that the lens is not fitting correctly.

Additionally, lens adherence refers to how well the lens stays in place on the eye without excessive movement or dislodgement. A properly fitting lens will move slightly with the eye's movement, allowing for even distribution of tears underneath the lens, which is crucial for proper hydration and health of the cornea.

The other options, while relevant to aspects of contact lens wear, do not directly assess fit as effectively. The color of the eyes does not influence the fit of the lens, duration of wear time is more related to comfort over time rather than immediate fit, and lens weight does not provide a reliable measurement for fit assessment. Thus, focusing on patient comfort and lens adherence is the best method for evaluating contact lens fit.