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22. Kongress der DGII 2008
Abstracts DGII 2008
V51
Intraocular lens power calculation after
corneal refractive surgery:
a comparison of
ray-tracing method and thin-lens formulas
Jin H1,2, Auffarth GU1, Guo H2
1 Universitäts-Augenklinik Heidelberg, 2 Guangdong
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 (6.4 mm). 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 € 0.43 D, 0.59 € 0.43 D, 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 (PERaytracing
= 1.035 x 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 x 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.
Erschienen in: Klin Monatsbl Augenheilkd 2008; 225: Suppl 1, S1–S24 |
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