What is the purpose of a trial frame in fitting?

The purpose of a trial frame in fitting is primarily to test lens types for the best fit. This tool allows an optician to assess the patient's vision with different lens options while ensuring comfort and proper alignment with the eyes. By using a trial frame, the optician can easily swap out lenses to determine which ones provide the clearest vision and the most comfort for the patient. This process is crucial in personalizing the eyewear to meet the specific visual needs and preferences of the wearer, leading to a more satisfactory final product.

The other options, while relating to different aspects of eyewear fitting, do not capture the primary reason for utilizing a trial frame. For instance, limiting adjustments to one lens does not reflect the function of the trial frame, which is designed to evaluate multiple lenses for optimal vision. Demonstrating lens thickness options may be part of the fitting process, but it does not encompass the broader capability of the trial frame. Similarly, displaying frame styles is another aspect of eyewear fitting, but it's not directly related to the function of testing vision through variable lenses in a trial frame.