Under what condition are the OC and MRP at the same point on the lens?

The correct answer indicates that the Optical Center (OC) and the Major Reference Point (MRP) coincide when prism is prescribed. This is because, in the presence of a prism, the appropriate positioning of the lenses becomes critical to ensure proper vision alignment.

When prism is incorporated into a lens, it creates a deviation of light that the eye must compensate for. To achieve the desired optical effect, the OC must be aligned with the MRP. This alignment ensures that the optics of the lens function effectively, allowing the prescribed prism to direct the light properly for optimal vision. If the OC and MRP were not coincident under these circumstances, the patient would experience visual discomfort or improper alignment of images.

Other scenarios do not lead to the OC and MRP being in the same point. For example, measuring MRP height involves determining the height at which the MRP is positioned but does not inherently relate the two points in the presence of optical corrections. The presence of a cylinder, which is used for astigmatism correction, also does not necessitate that the OC and MRP be at the same point since cylindrical lenses are designed to correct astigmatism without requiring a specific alignment of the OC and MRP. Similarly, when dealing