Femtosecond astigmatic calculator

This calculator is used for planning astigmatic correction using the Catalys™ femtosecond laser system. It is based on intrastromal keratotomy femtosecond laser cylinder incisions. The OCT scanner automatically determines local corneal pachymmetry.

Guidance for using this calculator

Parameters to program into Catalys™

Start depth 20%
End depth 80%
Diameter 8.0mm
Limbal centred

The current nomogram is at v3 and is based on regression analysis of 50 eyes based on v2. Parameters which the nomogram takes into account are:

Corneal cylinder to be corrected
Angle of the steep meridian of the cylinder

The cylinder to be corrected is 0.82 to 3.0 dc
The angle is 0 to 180 degrees
Age is 30 to 90 years

In order to determine the cylinder to be corrected corneal topography or automated keratometry can be used. This nomogram is based on pre-op IOL Master, though for nomogram development corneal cylinder was determined by multiple corneal topography scans:

IOL Master


The effect of the primary incision and side-ports
The effect of the primary incision and any side ports has to be taken into account, so the calculator requires entry of the mean effect of the primary incision and angle. For my own 2.75mm clear corneal temporal manual incision and 2 2.0mm width side ports the mean astigmatic vector change is 0.3 dc steepening at 90 degrees. An against the wound shift. The effect of your incision(s) is programmed first and then the intended cylinder change you wish to achieve.

When intended cylinder change, angle and age are entered the online calculator will return the intrastromal cylinder arc angle and meridian. This is commonly NOT the meridian of the cylinder based on the corneal topography or keratometry as the vector calculator adds the effect of the primary incision(s) and the intended corneal cylinder effect.