Residual stromal bed (RSB) calculator

This calculator returns the residual stromal bed (RSB) and percent tissue altered (PTA) for laser vision correction planning, for LASIK, SMILE and surface ablation.

What it calculates

RSB is the stromal thickness remaining beneath the flap or cap after ablation: central pachymetry minus flap (or cap) thickness minus ablation depth. PTA expresses the total tissue affected as a proportion of preoperative pachymetry.

Inputs

Central corneal thickness, planned sphere and cylinder, optical zone, and the flap or cap thickness for the platform being used. Sphere and cylinder entries are snapped to the 0.25 D grid.

Frequently asked questions

What is residual stromal bed?

The residual stromal bed is the thickness of corneal stroma left untouched below the LASIK flap or SMILE cap after the ablation or lenticule removal is complete.

How is percent tissue altered calculated?

PTA is the flap or cap thickness plus the ablation depth, divided by the preoperative central corneal thickness, expressed as a percentage.

See also the cylinder transposition calculator.