What is considered a prescription lens?

The definition of a prescription lens is best captured by the idea that it is any device that alters the visual powers of the human eye. This encompasses a broad range of lenses that are designed to correct refractive errors or enhance vision in some way. Prescription lenses can take many forms, including glasses and contact lenses, and they are specifically prescribed to address an individual's unique visual needs based on a comprehensive eye examination.

Options that refer to lenses for cosmetic purposes or enhancement without correction do not fit under the classification of prescription lenses because they do not serve the primary function of correcting vision impairments. Similarly, a plano contact lens, which does not correct vision but instead may be used for cosmetic enhancement or comfort, does not qualify as a prescription lens since it does not alter the visual powers of the eye. Thus, option C accurately captures the essence of what constitutes a prescription lens in optometric practice.