When will the optical center and MRP be located at the same point on the lens?

The optical center and the major reference point (MRP) of a lens are aligned at the same point primarily in the presence of prescribed prism. This alignment is crucial when correcting for prism to ensure that the optical axis of the lens and the direction of the desired visual image align properly for effective vision correction.

When prism is incorporated into a prescription, the optical center should ideally match the MRP to ensure that the prismatic effect is delivered accurately to the patient's line of sight. If they were not located at the same point, the patient would not experience the intended visual correction, potentially leading to discomfort or an ineffective lens.

In scenarios without prism or when face form is adjusted, the optical center and MRP may not coincide, as those elements impact how the lens is positioned and how light enters the eye. The addition of "add" for multifocal lenses can also affect where the MRP is placed relative to the optical center, further complicating the alignment without necessarily ensuring they are at the same point. Therefore, the condition where both the optical center and MRP are located at the same point is specifically relevant to the presence of prism.