Errors associated with IOLMaster biometry as a function of internal ocular dimensions.
OBJECTIVE
To evaluate the error in the estimation of axial length (AL) with the IOLMaster partial coherence interferometry (PCI) biometer and obtain a correction factor that varies as a function of AL and crystalline lens thickness (LT).


METHODS
Optical simulations were produced for theoretical eyes using Zemax-EE software. Thirty-three combinations including eleven different AL (from 20mm to 30mm in 1mm steps) and three different LT (3.6mm, 4.2mm and 4.8mm) were used. Errors were obtained comparing the AL measured for a constant equivalent refractive index of 1.3549 and for the actual combinations of indices and intra-ocular dimensions of LT and AL in each model eye.


RESULTS
In the range from 20mm to 30mm AL and 3.6-4.8mm LT, the instrument measurements yielded an error between -0.043mm and +0.089mm. Regression analyses for the three LT condition were combined in order to derive a correction factor as a function of the instrument measured AL for each combination of AL and LT in the theoretical eye.


CONCLUSIONS
The assumption of a single "average" refractive index in the estimation of AL by the IOLMaster PCI biometer only induces very small errors in a wide range of combinations of ocular dimensions. Even so, the accurate estimation of those errors may help to improve accuracy of intra-ocular lens calculations through exact ray tracing, particularly in longer eyes and eyes with thicker or thinner crystalline lenses.
Clinical & Experimental Optometry Research Lab, School of Sciences (Optometry), University of Minho, Braga, Portugal. Electronic address: mig.afr@gmail.com.
Miguel
M
Faria-Ribeiro
Clinical & Experimental Optometry Research Lab, School of Sciences (Optometry), University of Minho, Braga, Portugal.
Daniela
D
Lopes-Ferreira
Ciencias de la Visión, Facultad de Óptica y Optometría, Universidad de Murcia, Murcia, Spain.
Norberto
N
López-Gil
Clinical & Experimental Optometry Research Lab, School of Sciences (Optometry), University of Minho, Braga, Portugal.
Jorge
J
Jorge
Clinical & Experimental Optometry Research Lab, School of Sciences (Optometry), University of Minho, Braga, Portugal.
José Manuel
JM
González-Méijome
D058452:Axial Length, Eye / Q000033:anatomy & histology; D001699:Biometry / Q000295:instrumentation*; D019781:Corneal Topography; D006801:Humans; D007368:Interferometry / Q000295:instrumentation; D019654:Lens Implantation, Intraocular; D007908:Lens, Crystalline / Q000473:pathology*; D007910:Lenses, Intraocular; D008954:Models, Biological; D012044:Regression Analysis
Axial length measurement; Cálculo de LIO; Cálculo de lentes intra-oculares; IOL calculation; Intra-ocular lens calculation; Medición de la longitud axial