Abstract

Adaptive optics (AO) ophthalmoscopes have garnered increased clinical and scientific use for imaging the microscopic retina. Unlike conventional ophthalmoscopes, however, AO systems are commonly designed with spherical mirrors that must be used off-axis. This arrangement causes astigmatism to accumulate at the retina and pupil conjugate planes, degrading AO performance. To mitigate this effect and more fully tap the benefit of AO, we investigated a novel solution based on toroidal mirrors. Derived 2nd order analytic solutions along with commercial ray tracing predict performance benefit of toroidal mirrors for ophthalmoscopic use. For the Indiana AO ophthalmoscope, a minimum of three toroids is required to achieve performance criteria for retinal image quality, beam displacement, and beam ellipticity. Measurements with fabricated toroids and retinal imaging on subjects substantiate the theoretical predictions. Comparison to off-the-plane method is also presented.

© 2013 Optical Society of America

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References

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2012

2011

2009

2008

2007

2006

2005

2004

2002

1997

1987

1981

R. H. Webb and G. W. Hughes, “Scanning laser ophthalmoscope,” IEEE Trans. Biomed. Eng.28(7), 488–492 (1981).
[CrossRef] [PubMed]

Ahnelt, P. K.

Artal, P.

Atchison, D. A.

Bigelow, C. E.

Bower, B. A.

Bradu, A.

Brown, J. M.

Burns, S. A.

Campbell, M.

Carroll, J.

Cense, B.

Choi, S.

Choi, S. S.

Cooper, R. F.

Dainty, C.

Delori, F. C.

Derby, J. C.

Donnelly III, W.

Drexler, W.

Dubis, A. M.

Dubra, A.

Duncan, J. L.

Elsner, A. E.

Evans, J. W.

Felberer, F.

Fercher, A. F.

Ferguson, D.

Ferguson, R. D.

Fernández, E. J.

Gao, W.

Gómez-Vieyra, A.

Hammer, D. X.

Hebert, T.

Herde, A. E.

Hermann, B.

Hitzenberger, C. K.

Hofer, B.

Hughes, G. W.

R. H. Webb, G. W. Hughes, and F. C. Delori, “Confocal scanning laser ophthalmoscope,” Appl. Opt.26(8), 1492–1499 (1987).
[CrossRef] [PubMed]

R. H. Webb and G. W. Hughes, “Scanning laser ophthalmoscope,” IEEE Trans. Biomed. Eng.28(7), 488–492 (1981).
[CrossRef] [PubMed]

Iftimia, N. V.

Izatt, J. A.

Jones, S.

Jones, S. M.

Jonnal, R. S.

Kocaoglu, O. P.

Koperda, E.

Kroisamer, J. S.

Laut, S.

Lee, S.

Liang, J.

Malacara-Hernández, D.

Merino, D.

Miller, D. T.

Norris, J. L.

Oliver, S. S.

Olivier, S.

Olivier, S. S.

Pircher, M.

Podoleanu, A. G.

Poonja, S.

Povazay, B.

Prieto, P. M.

Queener, H.

Rha, J.

Romero-Borja, F.

Roorda, A.

Sattmann, H.

Smith, G.

Sulai, Y.

Tiruveedhula, P.

Torti, C.

Tumbar, R.

Unterhuber, A.

Ustun, T. E.

Wang, Q.

Webb, R. H.

R. H. Webb, G. W. Hughes, and F. C. Delori, “Confocal scanning laser ophthalmoscope,” Appl. Opt.26(8), 1492–1499 (1987).
[CrossRef] [PubMed]

R. H. Webb and G. W. Hughes, “Scanning laser ophthalmoscope,” IEEE Trans. Biomed. Eng.28(7), 488–492 (1981).
[CrossRef] [PubMed]

Werner, J. S.

Williams, D. R.

Zawadzki, R. J.

Zhang, Y.

Zhao, M.

Appl. Opt.

Biomed. Opt. Express

IEEE Trans. Biomed. Eng.

R. H. Webb and G. W. Hughes, “Scanning laser ophthalmoscope,” IEEE Trans. Biomed. Eng.28(7), 488–492 (1981).
[CrossRef] [PubMed]

J. Opt. Soc. Am. A

Opt. Express

D. Merino, C. Dainty, A. Bradu, and A. G. Podoleanu, “Adaptive optics enhanced simultaneous en-face optical coherence tomography and scanning laser ophthalmoscopy,” Opt. Express14(8), 3345–3353 (2006).
[CrossRef] [PubMed]

D. X. Hammer, R. D. Ferguson, C. E. Bigelow, N. V. Iftimia, T. E. Ustun, and S. A. Burns, “Adaptive optics scanning laser ophthalmoscope for stabilized retinal imaging,” Opt. Express14(8), 3354–3367 (2006).
[CrossRef] [PubMed]

Y. Zhang, B. Cense, J. Rha, R. S. Jonnal, W. Gao, R. J. Zawadzki, J. S. Werner, S. Jones, S. Olivier, and D. T. Miller, “High-speed volumetric imaging of cone photoreceptors with adaptive optics spectral-domain optical coherence tomography,” Opt. Express14(10), 4380–4394 (2006).
[CrossRef] [PubMed]

F. Felberer, J. S. Kroisamer, C. K. Hitzenberger, and M. Pircher, “Lens based adaptive optics scanning laser ophthalmoscope,” Opt. Express20(16), 17297–17310 (2012).
[CrossRef] [PubMed]

R. J. Zawadzki, S. M. Jones, S. S. Olivier, M. Zhao, B. A. Bower, J. A. Izatt, S. Choi, S. Laut, and J. S. Werner, “Adaptive-optics optical coherence tomography for high-resolution and high-speed 3D retinal in vivo imaging,” Opt. Express13(21), 8532–8546 (2005).
[CrossRef] [PubMed]

A. Roorda, F. Romero-Borja, W. Donnelly III, H. Queener, T. Hebert, and M. Campbell, “Adaptive optics scanning laser ophthalmoscopy,” Opt. Express10(9), 405–412 (2002).
[CrossRef] [PubMed]

B. Cense, E. Koperda, J. M. Brown, O. P. Kocaoglu, W. Gao, R. S. Jonnal, and D. T. Miller, “Volumetric retinal imaging with ultrahigh-resolution spectral-domain optical coherence tomography and adaptive optics using two broadband light sources,” Opt. Express17(5), 4095–4111 (2009).
[CrossRef] [PubMed]

A. Gómez-Vieyra, A. Dubra, D. Malacara-Hernández, and D. R. Williams, “First-order design of off-axis reflective ophthalmic adaptive optics systems using afocal telescopes,” Opt. Express17(21), 18906–18919 (2009).
[CrossRef] [PubMed]

C. Torti, B. Povazay, B. Hofer, A. Unterhuber, J. Carroll, P. K. Ahnelt, and W. Drexler, “Adaptive optics optical coherence tomography at 120,000 depth scans/s for non-invasive cellular phenotyping of the living human retina,” Opt. Express17(22), 19382–19400 (2009).
[CrossRef] [PubMed]

Opt. Lett.

Other

J. Porter, H. M. Queener, J. E. Lin, K. Thorn, and A. Awwal, eds., Adaptive Optics for Vision Science Principles, Practices, Design, and Applications (John Wiley & Sons, Hoboken, NJ, 2006).

J. M. Geary, ed., Introduction to Lens Design: With Practical ZEMAX Examples (Willmann-Bell, Inc., 2002).

A.N.S.I. Z136, 1, Safe Use of Lasers (Laser Institute of America, 2007).

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Figures (14)

Fig. 1
Fig. 1

Schematic of the Indiana AO-OCT system for retinal imaging. The sample arm contains a woofer-tweeter AO system for correction of ocular aberrations, two galvanometer scanners, and five relay afocal telescopes, each consisting of two spherical mirrors. The AO cascades a 97-actuator (1500 µm pitch) voice-coil actuated membrane mirror from ALPAO and a 140-discrete-actuator deformable mirror (400 µm pitch) from BMC. Wavefront measurements are obtained with a SHWS (20 × 20 lenslet array; 500 µm pitch). Pitch of the lenslet array at the BMC, ALPAO, and eye pupil planes is 200 µm, 667 µm and 334 µm, respectively. A Femtolaser Integral (λc ~800 nm, Δλ = 160 nm, bandpassed at λc ~809 nm, Δλ = 81 nm) provides the SHWS beacon as well as OCT imaging.

Fig. 2
Fig. 2

Off axis performance of a toroidal mirror, T1. Variables are defined in the text.

Fig. 3
Fig. 3

Finite conjugate case ( s= r 1 /2 ) for an in-the-plane afocal telescope formed by a pair of off-axis toroidal mirrors.

Fig. 4
Fig. 4

Infinite conjugate case (s =) for an in-the-plane afocal telescope formed by a pair of off-axis toroidal mirrors.

Fig. 5
Fig. 5

Predicted astigmatism at (top row) retina and (bottom row) pupil conjugate planes for each of the five afocal telescopes in the Indiana AO-OCT system. Two constraints are applied, zeroing astigmatism at (left column) retina conjugate planes and (right column) pupil conjugate planes. Filled triangles (▲) denote telescopes with all spherical mirrors. Unfilled triangles (Δ) denote telescopes with the second mirror toroidal. Solid curves generalize the five telescopes (with second mirror as toroid) to arbitrary incident angle, I1.

Fig. 6
Fig. 6

Predicted image quality of the Indiana AO-OCT sample arm as function of scan angle with perfect eye (aberration free). PSF spot diagrams at the retina were generated by ray trace modeling with (left) all spherical mirrors and (right) spherical mirror #8 (see Fig. 1 and Table 1) replaced with a toroidal one. Wavefront correctors were flat for both configurations. Shape of the toroid (rt and rs) was determined by ray trace optimization. Solid red circles denote diffraction-limited blur size. Note the left and right spot diagrams are on different spatial scales.

Fig. 7
Fig. 7

Illustration of beam displacement predicted by ray trace modeling for the Indiana AO-OCT system. Beam shape and location at the eye pupil and ALPAO planes are shown for two cases: (a) original system with all spherical mirrors and (b) system with three toroidal mirrors. Five beam locations at the retina are shown on top row: one centered on the system’s FOV (0°, 0°) and four at the corner edges (−1.8°, −1.8°), (−1.8°, 1.8°), (1.8°,-1.8°), and (1.8°, 1.8°). Locations in the FOV are color coded and depicted in the bottom left displacement plot. Note scaling of the eye pupil and ALPAO planes differ by a factor of two. False color maps in bottom row quantify beam displacement at ALPAO and eye pupil planes for arbitrary FOV (within ± 1.8°).

Fig. 8
Fig. 8

Predicted beam displacement and ellipticity at ALPAO and eye pupil planes for ± 1.8° vertical (Ver.) and horizontal (Hor.) scans. AO-OCT system performance is shown for various numbers of toroids: (a) zero and 10, (b) one, (c) two, and (d) three. Different combinations of toroids are specified by the numeric labels (1 through 10), which indicate mirror location (defined in Fig. 1). To the right of the numeric labels is the corresponding beam ellipticity, E. Infinite and finite labels refer to the conjugate constraint (finite or infinite) imposed on the first toroid of the two toroid system and the first two toroids of the three toroid system during optimization of toroid shapes. Dashed lines represent lenslet pitch at ALPAO and eye pupil planes.

Fig. 9
Fig. 9

Comparison of surface shape for the three toroidal mirrors (#1, #6, and #8) fabricated for the AO-OCT system. (a) Radii of curvature of the three toroids were determined from ray trace modeling and compared to that predicted by 2nd order theory. (b) Ray trace and measured surface maps are compared for the three fabricated toroidal mirrors. Surface elevation is coded on a color scale. PV is the peak-to-valley surface elevation; PVdifference is the difference in PV between design and measurement.

Fig. 10
Fig. 10

Comparison of image quality of AO-OCT system (a) predicted for all-spherical mirror design, (b) predicted for three-toroidal mirror design (#1, #6, #8) and (c) measured for three-toroidal mirror design using commercial HASO3 wavefront sensor. 6.67 mm wavefront error maps at the eye pupil plane are shown for five field locations: one centered on FOV (0°, 0°) and four at edge ( ± 1.8°, 0°), (0°, ± 1.8°). All cases are with a perfect eye (no ocular aberrations) and without AO correction (ALPAO and BMC flat). Numeric values denote wavefront RMS error in units of waves, defined as the center wavelength of the Indiana AO-OCT system.

Fig. 11
Fig. 11

Comparison of measured and predicted beam displacement of the three-toroid AO-OCT system for ± 1.8° vertical (Ver.) and horizontal (Hor.) scans. Predictions were determined from ray trace optimization and 2nd order theory. Displacement is at ALPAO and eye pupil planes. Dashed lines represent the lenslet pitch.

Fig. 12
Fig. 12

En face image of cone photoreceptor mosaic extracted from AO-OCT volume acquired at a retinal eccentricity of 4° nasal 3° superior. BMC and ALPAO were removed and replaced with high quality planar mirrors. Scale bar is 50 μm.

Fig. 13
Fig. 13

Photoreceptor mosaics extracted from AO-OCT volumes acquired on myopic subjects. (a) En face projections confined to the photoreceptor layer is shown for volumes acquired at 0.2°~0.3° and 4.5° retinal eccentricity in the left and right columns, respectively. Scale bars are 25μm (b) OCT B-scan is shown at the top with corresponding en face images of (left) IS/OS and (right) PTOS reflections below at 6° retinal eccentricity. Inset shows individual cones that exhibit an IS/OS reflection characteristic of a TEM10–like mode. Superimposed boxes are color coded and 7.8 μm in width. Scale bars are 10 μm.

Fig. 14
Fig. 14

Comparison of predicted image quality for three different designs of the same afocal telescope: (Δ) original, (o) off-the-plane, and ( + ) toroidal. The original has both mirrors spherical with beam confined to a single plane. Off-the-plane has both mirrors spherical with beam directed off the plane at 90° by the second mirror. Toroidal has the second mirror a toroid. Each plot shows the wavefront RMS error as a function of incident angle, I1, at the first mirror of the telescope. Left and right columns correspond to telescope #5 (1000:500) and #4 (300:1000), respectively, from the Indiana AO-OCT system (see legend of Fig. 5). Telescopes are optimized for (top row) pupil (finite) an (bottom row) retina (infinite) conjugate cases. Incident beam diameter was 6.67 mm. Wavelength was 809 nm, center of the AO-OCT system spectrum. Dashed lines represent diffraction-limited performance (RMS = λ/14).

Tables (1)

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Table 1 Indiana AO-OCT sample arm

Equations (3)

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M t = f t10 f t9 × f t8 f t7 ×...× f t2 f t1 ,
M s = f s10 f s9 × f s8 f s7 ×...× f s2 f s1 , and
E= min( M t , M s ) max( M t , M s ) .

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