Which statement is true regarding the routine maintenance of a phoropter?

The statement regarding covering a phoropter with a protective dust cover when not in use is true because dust and debris can accumulate on the instrument, potentially affecting its performance and the accuracy of patient exams. Utilizing a dust cover helps preserve the cleanliness and integrity of the lenses and mechanics, minimizing the need for frequent cleaning and maintenance. This practice contributes to the longevity of the equipment and ensures that it remains in optimal working condition.

While other maintenance practices may be essential, such as checking lens placement and performing regular cleaning, they do not specifically relate to the preservation of the phoropter when it is not being actively used. Regular preventative maintenance routines may vary in frequency based on specific guidelines, and using alcohol on lenses can potentially harm coatings, which is why other answers do not convey the best practice.