C constant: new concept for ray tracing-assisted intraocular lens power calculation.
OBJECTIVE
To evaluate the accuracy of the C constant for ray tracing-assisted intraocular lens (IOL) power calculation.


METHODS
Case series.


METHODS
Public university hospital and private clinic.


METHODS
Preoperatively, all intraocular distances were measured using laser biometry. Various IOL designs were studied; powers ranged from -5.0 diopters (D) to +38.0 D. The IOL power calculation was performed with the Olsen formula using the C constant and compared with the Haigis, Hoffer Q, Holladay 1, and the SRK/T formulas on optimized datasets. Outcome measures were the error of the prediction, expressed as the arithmetic error, and the absolute error between the observed refraction and the predicted refraction.


RESULTS
Two thousand forty-three cases from the 2 centers were studied. No significant differences were found between the Haigis, Hoffer Q, Holladay 1, and SRK/T formulas with the exception of the SRK/T formula, which performed better than the other thin-lens formulas in eyes with an axial length (AL) greater than 27.0 mm (P<.01). Compared with the SRK/T formula, the Olsen formula showed an improvement of 15% and 14% in the mean absolute error and a 39% and 85% reduction in the number of large errors (>1.0 D) for the 2 series, respectively (P<.0001). Contrary to the Olsen formula, all thin-lens formulas showed a significant bias in terms of the AL, keratometry reading, and anterior segment length (P<.0001).


CONCLUSIONS
The C constant is a promising concept for ray tracing-assisted IOL power calculation.
From the University Eye Clinic (Olsen), Aarhus Hospital NBG, Aarhus C, Denmark, and the Augen- und Laserklinik (Hoffmann), Castrop-Rauxel, Germany. Electronic address: tkolsen@dadlnet.dk.
Thomas
T
Olsen
From the University Eye Clinic (Olsen), Aarhus Hospital NBG, Aarhus C, Denmark, and the Augen- und Laserklinik (Hoffmann), Castrop-Rauxel, Germany.
Peter
P
Hoffmann
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D058452:Axial Length, Eye; D001699:Biometry / Q000379:methods*; D005260:Female; D006801:Humans; D007368:Interferometry; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008027:Light; D008297:Male; D008875:Middle Aged; D055095:Optics and Photonics; D018918:Phacoemulsification; D011474:Prosthesis Design; D012029:Refraction, Ocular / Q000502:physiology; D015203:Reproducibility of Results; D041623:Tomography, Optical Coherence; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult