What is the horizontal visible iris diameter (HVID) for the patient in the example?

• A. 11.8 mm
• B. 12.5 mm
• C. 11.0 mm
• D. 12.0 mm

Answer: (A)

Horizontal visible iris diameter is the width of the iris seen across the horizontal axis, measured from the nasal iris edge to the temporal iris edge as viewed through the cornea. To measure it, align a slit-lamp or pupillometer along the 9 to 3 o'clock axis and read the distance between the iris boundaries on the millimeter scale, keeping the eye looking straight ahead and ensuring eyelids and lashes don’t obscure the edges.

In the example, the horizontal span across the iris is measured at 11.8 mm, so the HVID is 11.8 mm. This value helps guide the selection of a gas-permeable lens diameter to ensure proper corneal coverage and comfortable edge alignment. Accurate measurement depends on proper alignment, minimal parallax, and fully exposing the iris edges at 3 and 9 o'clock.