Which of the following factors is critical for assessing prismatic effects in lenses?

The critical factor for assessing prismatic effects in lenses is the power in both eyes. This is essential because the amount of prism correction needed in a lens is directly related to the differences in the refractive power between the lenses prescribed for the left and right eyes. When there is a significant disparity in power, it can lead to prismatic effects that need to be compensated for to ensure effective binocular vision.

Understanding the power in both eyes allows optometrists or dispensing opticians to determine how much prism is necessary to align images on the retina appropriately and to achieve a comfortable visual experience for the patient. This consideration is paramount in preventing symptoms like double vision or eye strain that can arise from improper alignment.

The other factors, such as tempered tip strength, base curve measurement, and lens material type, while important in their respective contexts, do not directly influence the assessment of prismatic effects as the powers of the lenses do.