The soft lens diameter should be HVID plus how many millimeters?

The soft lens diameter should be HVID plus how many millimeters?

• A. 1 mm
• B. 2 mm
• C. 3 mm
• D. 4 mm

Answer: (C)

Soft lens diameter is chosen to provide full corneal coverage while allowing stable centration and smooth lid movement. The standard approach is to take the horizontal visible iris diameter (HVID) and add about 3 millimeters. This creates a diameter that typically covers the cornea and sits comfortably on the sclera, promoting good tear exchange and lens stability during blinking. Adding only 1–2 mm often yields insufficient corneal coverage and poorer centration, while adding 4 mm can make the edge too wide, increasing the chance of lid interaction problems and discomfort. Therefore, HVID plus 3 millimeters is the typical guideline.

Soft lens diameter is chosen to provide full corneal coverage while allowing stable centration and smooth lid movement. The standard approach is to take the horizontal visible iris diameter (HVID) and add about 3 millimeters. This creates a diameter that typically covers the cornea and sits comfortably on the sclera, promoting good tear exchange and lens stability during blinking. Adding only 1–2 mm often yields insufficient corneal coverage and poorer centration, while adding 4 mm can make the edge too wide, increasing the chance of lid interaction problems and discomfort. Therefore, HVID plus 3 millimeters is the typical guideline.