What instrument is best used to observe contact lens rotation?

The slit lamp is the most suitable instrument for observing contact lens rotation because it provides high magnification and illumination, allowing for detailed examination of the eyelids, cornea, and the interaction of contact lenses with the ocular surface. When assessing lens rotation, the slit lamp's slit beam can be adjusted to visualize the lens' position on the cornea and track any movement the lens makes with eye blinks or head movements. This capability is crucial for evaluating lens fit, ensuring proper alignment, and determining whether the lens is stable on the eye.

In contrast, a keratometer is primarily used to measure the curvature of the cornea, which is important for fitting lenses but does not provide the necessary view of lens rotation. An autorefractor measures refractive error but does not offer any assessment of contact lens positioning. A phoropter is utilized mainly for refraction testing and cannot adequately assess lens dynamics on the eye. Therefore, the slit lamp stands out as the most effective choice for observing contact lens rotation.