Percent Tissue Altered (LASIK Ectasia Risk)
Percent tissue altered (Santhiago 2014) = (flap thickness + ablation depth) / central corneal thickness x 100; PTA >= 40% is the strongest single predictor of post-LASIK ectasia.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Flap thickness
- 110 um
- Ablation depth
- 80 um
- Central corneal thickness
- 550 um
Result: Percent tissue altered 34.5% — below the 40% high-risk threshold.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- < 40%
- Below the high-risk threshold.
- >= 40%
- High risk of post-LASIK ectasia in a normal-topography eye (a lower threshold may apply if topography is abnormal). A risk metric, not a diagnosis.
What you enter
- Flap thickness
- Ablation depth
- Central corneal thickness
How this is calculated
Santhiago MR, Smadja D, Gomes BF, et al. Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography. Am J Ophthalmol. 2014;158(1):87-95. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.