Klin Monbl Augenheilkd 2008; 225 - V51
DOI: 10.1055/s-2008-1057976

Intraocular lens power calculation after corneal refractive surgery: a comparison of ray-tracing method and thin-lens formulas

H Jin 1, 2, GU Auffarth 1, H Guo 2
  • 1Universitäts-Augenklinik Heidelberg
  • 2Guangdong Provincial Hospital (China)

Purpose: (1) to find out whether ray-tracing method has a higher accuracy than thin-lens formulas for IOL calculation after corneal refractive surgery; (2) to find out the relation between pseudophakic ACD used in ray-tracing method and effective lens position (ELP) used in thin-lens formulas. Methods: 25 eyes after corneal refractive surgery (LASIK or PRK) were retrospectively studied. 15 eyes were implanted with AMO AR40e IOL in department of Ophthalmology University of Heidelberg, Germany. 10 eyes were implanted with Alcon SA60AT IOL in Department of Ophthalmology Guangdong Provincial Hospital, China. Corneal refractive powers were calculated according to anterior radius obtained from topography (C-scan or Orbscan||z) with assumed posterior radius (6.4mm). Axial lengths were measured with IOL-master or ultrasound A-scan. IOL power and predictive pseudophakic refraction was calculated by an optical software Zemax, a modified double-K thin-lens formula, Holladay formula and HofferQ formula as well as SRK/T formula respectively. Back-calculation of ELP and pseudophakic ACD were calculated using double-K thin-lens formula and ray-tracing method respectively. Results: (1) Mean absolute predictive errors for ray-tracing method, double-K thin-lens, Holladay, HoferQ and SRK/T formulas were 0.59±0.43D, 0.59±0.43D, 1.04±0.87D, 0.59±0.48D and 1.51±0.93D respectively. There was no difference in absolute predictive error between ray-tracing method and double-K thin-lens formula. There was a perfect correlation between predictive errors (PE) of ray-tracing method and double-K thin-lens formula (PERay-tracing = 1.035 × PEThin-lens – 0.212, R2 = 0.975, P < 0.001); (2) There was a perfect correlation between back-calculation of Pseudophakic ACD and ELP (Pseudophakic ACD=1.0161 × ELP –0.3941, R2=0.986, P<0.001). Conclusion: With improved calculation of corneal power and double-K method for ELP prediction, thin-lens formula has a same accuracy as ray-tracing method in the calculation of IOL power after corneal refractive surgery.