Munnerlyn's Formula Calculator

Treatment

PRK: enter epithelial thickness (~50 µm)

Patient (for printout)

Results:

Spherical Equivalent: --

Ablation Depth: --

Percent Tissue Altered (PTA): --

Residual Corneal Thickness: --

Maximum Correctable SE: --

Limits: residual thickness ≥ 300 µm and PTA < 40%. How is this calculated?

How it's calculated

Spherical equivalent (SE)
SE = Sphere + Cylinder ÷ 2
Ablation depth (Munnerlyn's formula)
Depth (µm) = |SE| (D) × Optical zone² (mm) ÷ 3
Percent tissue altered (PTA)
PTA = (Flap + Ablation depth) ÷ Pachymetry × 100
Residual corneal thickness
Residual = Pachymetry − Flap − Ablation depth
Maximum correctable SE
The largest myopic correction that keeps residual thickness ≥ 300 µm and PTA < 40%: Max SE = 3 × min(Pachymetry − Flap − 300, 0.4 × Pachymetry − Flap) ÷ Optical zone²

Your numbers appear in blue as you type. Valid for myopic treatments only. Results are rounded in the safer direction (ablation up, residual thickness down, PTA up).

Ablation depth: Munnerlyn CR, et al. J Cataract Refract Surg. 1988;14:46–52. PTA: Santhiago MR, et al. Am J Ophthalmol. 2014;158:87–95. For a full ectasia risk assessment, see the Randleman ectasia risk calculator. For clinical decision support only; verify results and use clinical judgment.