Enter the axial length, keratometry, and desired post-op refraction into the calculator to determine the intraocular lens (IOL) power using the Holladay 1 formula.

Holladay 1 Formula

The following formula is used to calculate the IOL power using the Holladay 1 formula:

IOL Power = Aconstant + (1.336 - (K / 1000) - (0.333 * AL)) - R


  • AL is the axial length of the eye (mm)
  • K is the average keratometry reading (D)
  • R is the desired post-operative refraction (D)
  • Aconstant is a lens-specific constant

To calculate the IOL power, you need to know the axial length of the eye, the keratometry reading, and the desired post-operative refraction. The Aconstant is specific to the lens being used and should be provided by the manufacturer.

What is the Holladay 1 Formula?

The Holladay 1 formula is a mathematical formula used by ophthalmologists to calculate the power of an intraocular lens (IOL) that is to be implanted in a patient’s eye during cataract surgery. The formula takes into account the axial length of the eye, the curvature of the cornea (keratometry), and the desired post-operative refraction to provide the most appropriate IOL power for the patient.

How to Calculate IOL Power Using Holladay 1 Formula?

The following steps outline how to calculate the IOL Power using the Holladay 1 Formula:

  1. First, determine the axial length of the eye (AL) in millimeters.
  2. Next, determine the average keratometry reading (K) in diopters (D).
  3. Next, determine the desired post-operative refraction (R) in diopters (D).
  4. Next, obtain the Aconstant for the specific lens being used.
  5. Finally, calculate the IOL Power using the Holladay 1 Formula.
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Axial Length (AL) = 23.5 mm

Keratometry (K) = 44.0 D

Desired Post-Op Refraction (R) = -0.50 D

Aconstant (specific to the lens) = 0.583