To achieve optimal vision correction, what should be added to the HVID measurement?

To achieve optimal vision correction, it is typically recommended to add 2 mm to the Horizontal Visible Iris Diameter (HVID) measurement. The reason for this addition is rooted in the fitting of contact lenses.

When selecting contact lenses, especially soft lenses, the diameter of the lens is crucial for an appropriate fit. The HVID gives an indication of the width of the visible part of the iris, but in order to ensure that the contact lens covers the cornea adequately and provides comfort, stability, and proper vision, the added measurement helps tailor the lens selection to each individual’s eye anatomy.

Adding 2 mm accounts for the necessary overlap of the lens beyond the iris to enhance the fit and ensure there are no areas of exposure on the eye, which could lead to discomfort or other vision-related issues. This adjustment is commonly used in practice to ensure optimal lens coverage and patient satisfaction.

The other choices would not offer the same level of comfort or fit; they either under- or over-estimate the necessary diameter for effective lens wear, which could compromise vision or comfort during use.