Formula Comparison
SRK/T vs Barrett Universal II: When Does It Actually Matter?
For normal eyes, all formulas agree within 0.5D. For long eyes (AL>26mm) and short eyes (AL<22mm), the difference can exceed 2.0D. Here's how to decide which formula to trust.
Coming soon · Formula Comparison
Post-Refractive
Post-LASIK IOL Calculation: Why Flat K Misleads Standard Formulas
Standard formulas assume a prolate cornea. Post-LASIK corneas are oblate — every formula misestimates ELP as a result. The clinical consequences and how to correct them.
Coming soon · Post-Refractive Surgery
Toric Planning
Toric IOL Rotation: How 1° of Misalignment Affects Your Outcome
Every 1° of toric IOL rotation induces ~3.3% residual astigmatism. At 30° the toric effect is completely lost. Understanding the geometry helps you counsel patients and choose cylinder power.
Coming soon · Toric IOL
FDA Data
Defocus Curves Explained: What FDA SSED Data Actually Shows
The defocus curve from a PMA clinical trial is the most objective measure of IOL performance. This is what it measures, how to read it, and why it differs from manufacturer marketing materials.
Coming soon · Clinical Data
Formula Comparison
Holladay 1 vs Hoffer Q: The Short Eye Decision
For eyes shorter than 22mm, Hoffer Q is widely recommended — but the difference depends on corneal curvature and ACD. Here's the published data behind the recommendation.
Coming soon · Short Eyes
Surgeon Constants
Haigis a0, a1, a2: What the Three Constants Actually Do
Unlike the A-constant, Haigis uses three constants that independently control how ACD and AL affect ELP. Understanding this makes personalisation meaningfully more accurate.
Coming soon · Surgeon Constants