Posters

Development of a nomogram for FS-laser arcuate keratotomy

Poster Details

First Author: P.Hoffmann GERMANY

Co Author(s):    M. Abraham   C. Lindemann           

Abstract Details

Purpose:

Corneal astigmatism can be reduced by fs-Laser arcuate keratotomies. No dedicated nomogram existed so we had to develop a new one with a steady dose - effect relationship. This is an ongoing study.

Setting:

Private eye clinic in Germany

Methods:

Arcuate incisions were performed with the B&L Technolas Victus Femtosecond Laser platform. All incisions were executed in an epithelium penetrating fashion down to 80% of local corneal depth. Optical zone was 8.5 mm and 2 symmetrical incisions were performed. As target astigmatism we chose the vector mean of autokeratometry (Lenstar, Haag-Streit) and 'real astigmatism' (TMS-5, Tomey) like we do in toric IOL surgery. As a starting point, we modified Oshika's nomogram and introduced an age dependency. After evaluation of 70 procedures, we developed a new nomogram with the refractive effect as dependent variable and arc length and age as independent variables. Refractive results and corneal measurements were evaluated at 1 month, 3 months and 1 year timepoints. Cylindrical prediction error (CPE, vector difference between achieved and predicted cylindrical refraction) was also evaluated as this represents the precision of the whole treatment path including diagnostics, calculation, surgery and refraction.

Results:

Mean arc length was 44 ± 7 degrees. Mean preoperative corneal cylinder was 1.42 ± 0.70 D, subjective postoperative cylinder was 0.57 ± 0.34 D at 1 month and 0.56 ± 0.34 D at 3 months. One year results will be given in the final presentation. Based on the modified Oshika nomogram, intended correction (TIA) was 1.38 ± 0.37 D and achieved cylinder change (SIA) was 1.25 ± 0.51 D at 1 month and 1.24 ± 0.55 D at 3 months, equivalent to a correction index (CI) of 0.90. A new dose-effect relationship was calculated with 48 3-months data sets and found the following regression equation: effect [D] = - 2,6295 + 0,0635 * arclength [°] + 0,0148 * age [years] CPE using the new nomogram is 0.57 ± 0.39 dpt.

Conclusions:

Penetrating fs-Laser arcuate incisions with arc lengths of 30° to 60° (equivalent to 0.5 to 2.25 D in a 70 year old patient) can deliver predictable astigmatic correction during cataract surgery. CPE is only slightly worse than with toric IOL and applying the same diagnostics (0.50 ± 0.37) in the same clinic. The newly developed steady and easy to use nomogram will help surgeons achieve better astigmatic corrections. FINANCIAL INTEREST: NONE