The calculation made by Recalculator Toric is based on differential vectorial analysis between the preoperative refractive or corneal defect (i.e., that used to calculate the power of the implanted IOL) and the postoperative refractive defect.
Because of this, it is important to precisely determine the patient's refraction when the eye shows no corneal edema or any other transient alteration that could affect this measurement.
It is also important to check that the surgical procedure has not modified the corneal astigmatism (axis or power) from its preoperative state. If this occurs it will not be possible to resolve the postoperative refractive defect by rotating the lens and another form of treatment will have to be decided upon.
To perform the calculation, all the data requested by the system should be introduced considering that the cylinder should appear positive in the refractive script.
Residual astigmatism will depend on the cylinder power of the implanted IOL and the angle correction (rotation) indicated by Recalculator Toric, such that small differences in the angle rotation calculated will have a greater effect as the cylinder of the implanted lens increases. For example, a 5º rotation of a toric lens of 2D of astigmatism, will mean a much reduced refractive change than a similar rotation of 5º for a lens of 4D of cylinder power.
Calculating the rotation to be undertaken is applicable to refractive procedures involving placement of an IOL with an adjustable axis, whether phakic or pseudophakic.
The Recalculator Toric will provide a figure that refers to the number of degrees the IOL should be rotated preceded by a plus or minus sign. This plus or minus sign indicates the direction of rotation of the IOL: plus means clockwise and minus anticlockwise.
It is left to the surgeon to carefully evaluate the indicated change or rotation since errors could exist in the calculation of sphere and/or cylinder power that obviously cannot be judged by the system.