Axial eye length measurement using coherence revival and ... · 2019-04-18 13 Use of eye length...
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Axial eye length measurement using coherence revival and extended imaging depth
Carl Zeiss Meditec, Inc., Dublin, CA
IITE 2019 , April 27th, 2019 Abstract # 3195611
Muzammil A Arain, Simon A. Bello, Sophie Kubach, and Jochen Straub
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Axial eye length measurement using coherence revival and extended imaging depth
DisclosuresMuzammil A Arain, Ph.D, (E), Carl Zeiss Meditec, Inc., Dublin, CA Simon A. Bello, Ph.D, (E), Carl Zeiss Meditec, Inc., Dublin, CA Sophie Kubach, M.S., (E), Carl Zeiss Meditec, Inc., Dublin, CAJochen Straub, Ph.D, (E), Carl Zeiss Meditec, Inc., Dublin, CA
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Motivation of this study
Myopia (also called nearsightedness) is the most common cause of impaired vision in young people
Myopia is related to elongated eye lengths
Measuring and tracking eye length is important for:
Early detection of myopia
Understanding the progression of myopia
Obtaining the true retinal curvature from widefield optical coherence tomography (OCT) scans
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Myopia is turning into an epidemic
https://www.capitaleyes.co.nz/news/2018/7/18/myopia-epidemic
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Axial length (AL) measurements techniques
Biometry Techniques
Ultrasound
Applanation Immersion
Optical
PCI OCT
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Study Aims
Explore measurement of axial eye length using Coherence Revival (CR) property of Swept Source Optical Coherence Tomography (SS-OCT) system using External Cavity Tunable Laser (ECTL)
Evaluate axial eye length measurement accuracy and range
Use eye length to obtain true retinal curvature
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Lc
What is Coherence Revival in ECTLs?
BART JOHNSON, * WALID ATIA, MARK KUZNETSOV, BRIAN D. GOLDBERG, PETER WHITNEY, AND DALE C. FLANDERS
Axsun Technologies, Billerica, Massachusetts, USA Real OCT image
Multiple virtual OCT images due to CRat multiples of Lc
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Principle of eye length (Le) using CR property of ECTL
A. H. Dhalla, D. Nankivil, T. Bustamante, A. Kuo, J. A. Izatt, “Simultaneous swept source optical coherence tomography of the anterior segment and retina using coherence revival,” Opt. Lett. 37, 1883–1885 (2012).
LeLc < n.Le
Lc = n.Le
Lc > n.Le
Lc = Laser cavity lengthn = Assumed index of the eye=1.36Le=Eye axial length
Simultaneous imaging of cornea and retina
Separate paths for retinal and corneal imaging
Single optical path Single shot image No need to adjust focus or delay line position
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Method
Align subject Adjust vertical offset and delay line position until the retina scan and the
corneal signal are visible in the scan window Acquire data and calculate eye length during post processing
Six human subjects
Align test eye Save raw data Offline processing to produce extended 32 mm axial depth image
and calculate axial length
Test eye
Device / equipment Prototype SS-OCT system with 200 kHz A-scan rate Axial depth range from 6-16 mm Offline access to mirror image enabling 32 mm axial depth 16 mm lateral FOV line scan ECTL laser from Axsun Technologies, MA, USA
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Results on human subjects
Le=(Lc-(corneal offset + retinal offset))/nRetinal offset
Corneal offset
OSLe= 23.24 mm
OSLe= 23.44 mm
ODLe= 25.01 mm
6 m
m
16 mm
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Results
Human Subjects Summary
Limitations Suitable for 21-26 mm eye lengths only There is an error that could be due to:
Error in cavity length measurements Error in aligning cornea perpendicular to retina Error in locating fovea Error in fixation
Eye length of all six human subjects was measured successfully
The difference between our measurement and IOL Master 700 measurement is within ± 0.25 mm
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Extending range of eye length measurements using extended depth imaging
Covers 21-26 mm eye length range
6 mm Markus Kohlhaas and et al., “Effect of Central Corneal Thickness, Corneal Curvature, and Axial Length on Applanation Tonometry,” ARCH OPHTHALMOL / VOL 124, APR 2006
Youn
g ch
ildre
n
High myopic eyes
21-26 mm
16 mm extended depth
Covers 21-31 mm eye length range*
Test eye imageNote: Cavity length of the laser can be tuned to cover eye lengths > 31mm
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Use of eye length measurements to correct retinal curvature*
*Manuel A. J. Steidle; Jochen Straub , “Estimating the shape of the human eye using widefield optical coherence tomography (OCT),”, Proceedings Volume 10685, Biophotonics: Photonic Solutions for Better Health Care VI; 106851V (2018) https://doi.org/10.1117/12.2306604
Uncorrected retinal curvature
Corrected true retinal curvature
Use measured eye length to correct for retinal curvature
IITEJon Bumstead et al, Poster # PB034Jochen Straub et al, Poster # PB0143
ARVOJochen Straub et al, Poster #1599 - A0359
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Conclusions
We have demonstrated a new method of measuring eye length using a prototype SS-OCT instrument using ECTL in a single acquisition without refocusing, delay line adjustment, or multiple optical paths
The demonstrated method can be incorporated in regular work flow during routine eye exams for tracking eye length
Extended depth feature will enable measurement of eye length for a larger population range
Measured eye length can be used to obtain the true curvature of the eye from widefield OCT scans
This method is not a replacement of high precision eye length measurements using biometry instruments, but rather is a tool to obtain true retinal curvature and allow for monitoring changes in eye length
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Acknowledgements
Carl Zeiss Meditec, Inc., Dublin, CA
Allison Ferro
Tilman Schmoll
Rick Williams
Conor Leahy
Jon Bumstead
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