What is the maximum recommended tolerance for segment heights in the ANSI standard?

The ANSI standard specifies that the maximum recommended tolerance for segment heights in multifocal lenses is 1mm. This tolerance is critical because it ensures that the segment of the lens, which provides the added magnification for near vision, is positioned correctly in relation to the pupil of the eye when the patient is wearing the glasses.

If the segment height deviates beyond this 1mm tolerance, it can lead to visual discomfort or inadequate performance of the lens, as the wearer may find it difficult to transition between different focal points. Maintaining this standard helps achieve optimal visual acuity and comfort for the patient, which is essential in lens fitting and overall optical health. This focus on precision underscores the importance of adhering to the prescribed measurements during the fitting process.