Post-LASIK / PRK IOL Delta Calculator

Dr. Harald C. Gäckle · Refractive Planning Suite · Dr. med. Harald C. Gäckle · eagleyedrgaeckle@icloud.com

Estimates the correction needed for an IOL calculated with standard biometry after corneal laser ablation — using separate, established methods rather than a single rule-of-thumb model.

Not a validated medical device. This tool does not replace a primary post-refractive calculation (Barrett True-K „No History“, Haigis-L, Shammas-PL, EVO 2.0, the ASCRS Online Calculator or ray tracing). It provides a plausibility estimate of how much an IOL already calculated with a standard formula would need to change — for collegial cross-validation, not as a sole basis for the decision.
Always cross-check. If you have access to them, always compare this calculator’s results with the Haigis-L formula and other formulas, or with Barrett True-K „No History“ or EVO 2.0.

1Starting point — what the standard formula „saw“

The post-op measured K that fed the standard calculation. After myopic ablation it is too high (posterior-surface error).
Correctly measured post-op — does not enter the correction.

2Method for reconstructing the true corneal power

All available methods are shown side by side. The headline uses the selected method or the mean (ASCRS principle).

Rule of thumb ≈ 0.8–1.0. Does not replace a true vergence calculation.

CHMClinical History Method

Reconstructed from the pre-operative K and the refractive change effective at the corneal plane. Robust when valid pre-op data and a stable refraction before cataract onset are available.

Target usually plano → 0. Enter residual error if known.

IDXAdjusted keratometric index

Re-evaluates the post-op K with a corrected refractive index (Savini/Camellin) — no pre-op data needed, but tends to undercorrect.

Guide value myopic ≈ 1.3319 (Savini); hyperopic rather > 1.3375.

SHMShammas regression

Empirical no-history formula K_corr = 1.14 · K_post − 6.8. Validated for myopic ablation only; no further inputs.