Refractive indices used by the Haag-Streit Lenstar to calculate axial biometric dimensions

Suheimat, Marwan, Verkicharla, Pavan K., Mallen, Edward A.H., Rozema, Jos J., & Atchison, David A. (2015) Refractive indices used by the Haag-Streit Lenstar to calculate axial biometric dimensions. Ophthalmic and Physiological Optics, 35(1), pp. 90-96.

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Abstract

PURPOSE

To estimate refractive indices used by the Lenstar biometer to translate measured optical path lengths into geometrical path lengths within the eye.

METHODS

Axial lengths of model eyes were determined using the IOLMaster and Lenstar biometers; comparing those lengths gave an overall eye refractive index estimate for the Lenstar. Using the Lenstar Graphical User Interface, we noticed that boundaries between media could be manipulated and opposite changes in optical path lengths on either side of the boundary could be introduced. Those ratios were combined with the overall eye refractive index to estimate separate refractive indices. Furthermore, Haag-Streit provided us with a template to obtain 'air thicknesses' to compare with geometrical distances.

RESULTS

The axial length estimates obtained using the IOLMaster and the Lenstar agreed to within 0.01 mm. Estimates of group refractive indices used in the Lenstar were 1.340, 1.341, 1.415, and 1.354 for cornea, aqueous, lens, and overall eye, respectively. Those refractive indices did not match those of schematic eyes, but were close in the cases of aqueous and lens. Linear equations relating air thicknesses to geometrical thicknesses were consistent with our findings.

CONCLUSION

The Lenstar uses different refractive indices for different ocular media. Some of the refractive indices, such as that for the cornea, are not physiological; therefore, it is likely that the calibrations in the instrument correspond to instrument-specific corrections and are not the real optical path lengths.

Impact and interest:

5 citations in Scopus
5 citations in Web of Science®
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ID Code: 88612
Item Type: Journal Article
Refereed: Yes
Keywords: air thickness, axial length, Lenstar, partial coherence interferometry, refractive index
DOI: 10.1111/opo.12182
ISSN: 0275-5408
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Funding:
Deposited On: 05 Nov 2015 04:35
Last Modified: 25 Jun 2017 20:02

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