What is the most consistent reference point for traditional bifocal height measurement?

The lower limbus is the most consistent reference point for traditional bifocal height measurement because it provides a reliable anatomical landmark for positioning the bifocal segment on the lens. The lower limbus, which is the border between the cornea and the sclera, is relatively stable across individuals and can be easily identified during an eye examination. When fitting bifocals, the height at which the bifocal segment is placed is crucial for ensuring that it aligns properly with the wearer’s line of sight for reading tasks.

Using the lower limbus for measurement helps to accommodate variations in facial features and makes it easier to achieve consistent results across different patients. Other reference points such as the top of the lower lid or the center of the pupil may vary significantly between individuals due to factors like eye shape or position, making them less reliable for standardized measurements. The lower edge of the pupil can also be influenced by pupil size in different lighting conditions, thereby compromising consistency. Thus, the lower limbus stands out as the optimal choice for achieving accurate bifocal fit.