Most aberrations are considered off-axis viewing errors when?

The correct choice highlights that most aberrations are associated with off-axis viewing errors when the patient is not using the optical center of the lens for viewing. When light rays pass through the optical center, they typically follow the design parameters intended by the lens manufacturer. If a patient deviates from this center, especially in lenses with higher prescription powers or specific designs, the light entering the lens may experience distortion or aberration, resulting in a blurred or distorted image.

In scenarios where the lens surface is dirty, while it might obscure vision, it does not intrinsically change the optical properties of the lens regarding how it handles off-axis viewing. Similarly, if the lens is incorrectly prescribed, it may not optimize vision regardless of viewing position, but it does not specifically pertain to the off-axis viewing errors associated with lens design. Bifocals introduce multifocal components but do not directly correlate with aberrations from off-axis viewing; rather, they are designed to help users see at multiple distances while maintaining optical quality. Therefore, the phrase emphasizes the critical role of correctly using the optical center of lenses to minimize aberrations experienced during viewing.