What is the appropriate soft lens diameter for a patient with a Horizontal Visible Iris Diameter (HVID) of 12mm?

The appropriate soft lens diameter for a patient with a Horizontal Visible Iris Diameter (HVID) of 12mm is typically larger than the HVID measurement itself to ensure proper coverage and stability of the contact lens on the eye. A diameter of 14mm is commonly recommended for a patient with an HVID of 12mm. This provides adequate coverage of the cornea and ensures that the lens remains centered, allowing for optimal vision and comfort.

A diameter that is significantly smaller than the HVID can lead to issues such as inadequate coverage of the iris and corneal surface, which may compromise both the fit and the performance of the lens. Therefore, selecting a lens with a larger diameter helps ensure that the lens sits properly on the eye and minimizes the risk of it shifting or moving during blinking or eye movement. The recommended size helps balance between comfort and effective vision correction while optimizing lens retention on the eye.