Calculation of Optical Power of Toric IOL at Pathological Cornea
Narrative Responses:
Purpose
To assess the effectiveness of the method of calculating the optical power of the toric IOL at the changed cornea.
Methods
Toric IOLs were implanted in 63 patients aged from 15 to 72 years who have different initial corneal changes – keratoconus of I-II degrees (14 patients), corneal scarring after keratoplasty, keratotomy (24 patients) and posttraumatic scars (25 patients). Refractive corneal properties were investigated on the complex topographical scanner Pentacam. For calculating the IOL power we assessed a frontal corneal scan in the central area with a diameter of 3.0 and 5.0 mm, irregular astigmatism along the main meridians and the profile of the optical power of the cornea. The optical characteristics were putting into the On-line calculator.
Results
With using Pentacam data, obtained in the zone with 3.0 mm diameter, the incidence of refractive errors within 0, 75 D ± 0, 25 D was 19.6%, more than 1.5 D ± 0, 25 D - 8.9%. In the case of search area enlargement of main meridians the incidence of errors in the calculation increased by 1.75 times. If the difference of refraction between strong and weak meridians of cornea was more than 6.0 D, and in the presence of insignificant irregular astigmatism in central zone, the refractive effect was less predictable.
Conclusion
For the calculation of the toric IOL optical power the keratotopographic Pentacam data should be used in 3.0 mm zone. To avoid the refractive surprises the irregularity of astigmatism and profile of optical corneal curvature should be considered.