Abstract

Optical coherence tomography (OCT) enables visualization of the living human retina with unprecedented high axial resolution. The transverse resolution of existing OCT approaches is relatively modest as compared to other retinal imaging techniques. In this context, the use of adaptive optics (AO) to correct for ocular aberrations in combination with OCT has recently been demonstrated to notably increase the transverse resolution of the retinal OCT tomograms. AO is required when imaging is performed through moderate and large pupil sizes. A fundamental difference of OCT as compared to other imaging techniques is the demand of polychromatic light to accomplish high axial resolution. In ophthalmic OCT applications, the performance is therefore also limited by ocular chromatic aberrations. In the current work, the effects of chromatic and monochromatic ocular aberrations on the quality of retinal OCT tomograms, especially concerning transverse resolution, sensitivity and contrast, are theoretically studied and characterized. The repercussion of the chosen spectral bandwidth and pupil size on the final transverse resolution of OCT tomograms is quantitatively examined. It is found that losses in the intensity of OCT images obtained with monochromatic aberration correction can be up to 80 %, using a pupil size of 8 mm diameter in combination with a spectral bandwidth of 120 nm full width at half maximum for AO ultrahigh resolution OCT. The limits to the performance of AO for correction of monochromatic aberrations in OCT are established. The reduction of the detected signal and the resulting transverse resolution caused by chromatic aberration of the human eye is found to be strongly dependent on the employed bandwidth and pupil size. Comparison of theoretical results with experimental findings obtained in living human eyes is also provided.

© 2005 Optical Society of America

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References

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App. Opt.

S. Kimura and T. Wilson, �??Confocal scanning optical microscope using single-mode fiber for signal detection,�?? App. Opt. 30, 2143-2150 (1991).
[CrossRef]

Appl. Opt.

J. Biomed. Opt.

W. Drexler, �??Ultrahigh resolution optical coherence tomography,�?? J. Biomed. Opt. 9, 47-74 (2004).
[CrossRef] [PubMed]

J. Opt. Soc. Am.

J. Opt. Soc. Am. A

Nature Medicine

W. Drexler, U. Morgner, R. K. Ghanta, F. X. Kärtner, J. S. Schuman, and J. G. Fujimoto, �??Ultrahighresolution ophthalmic optical coherence tomography,�?? Nature Medicine 7, 502-507 (2001).
[CrossRef] [PubMed]

Opt. Acta

A. van Meeteren, �??Calculations on the optical modulation function of the human eye for white light,�?? Opt. Acta 21, 395-412 (1972).
[CrossRef]

Opt. Express

E. J. Fernández, A. Unterhuber, P. M. Prieto, B. Hermann, W. Drexler, and P. Artal, �??Ocular aberrations as a function of wavelength in the near infrared measured with a femtosecond laser,�?? Opt. Express 13, 400- 409 (2005), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-2-400.">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-2-400.</a>
[CrossRef] [PubMed]

H. Hofer, L. Chen, G. Y. Yoon, B. Singer, Y. Yamauchi, and D. R. Williams, �??Performance of the Rochester 2nd generation adaptive optics system for the eye,�?? Opt. Express 8, 631�??643 (2001), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-8-11-631.">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-8-11-631.</a>
[CrossRef] [PubMed]

A. Roorda, F. Romero-Borja, W. J. Donnelly III, H. Queener, T. J. Hebert, and M. C. W. Campbell, �??Adaptive optics scanning laser ophthalmoscopy,�?? Opt. Express 10, 405-412 (2002), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-10-9-405">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-10-9-405</a>
[PubMed]

E. J. Fernández and P. Artal, �??Membrane deformable mirror for adaptive optics: performance limits in visual optics,�?? Opt. Express 11, 1056-1069 (2003), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-9-1056">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-9-1056</a>
[CrossRef] [PubMed]

Y. Zhang, J. Rha, R. S. Jonnal, and D. T. Miller, �??Adaptive optics spectral optical coherence tomography for imaging the living retina,�?? Opt. Express 13, 4792-4811 (2005), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-12-4792.">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-12-4792.</a>
[CrossRef] [PubMed]

Opt. Lett.

Proc. R. Soc. London, Ser. B

W. S. Stiles, �??The luminous efficiency of rays entering the eye pupil at different points,�?? Proc. R. Soc. London, Ser. B 112, 428-450 (1933).
[CrossRef]

Proc. SPIE

D. T. Miller, J. Qu, R. S. Jonnal, and K. Thorn, "Coherence gating and adaptive optics in the eye. In:" V. V. Tuchin, J. A. Izatt, and J. G. Fujimoto (Eds.), Coherence Domain Optical Methods and Optical Coherence Tomography in Biomedicine VII, Proc. SPIE 4956, 65-72 (2003).
[CrossRef]

Science

D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman,W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K. Gregory, C. A. Puliafito, and J. G. Fujimoto, �??Optical coherence tomography,�?? Science 254, 1178-1181 (1991).
[CrossRef] [PubMed]

Vis. Res.

F. J. Castejón-Mochón, N. López-Gil, A. Benito, and P. Artal, �??Ocular wavefront aberration statistics in a normal young population,�?? Vis. Res. 42, 1611�??1617 (2002).
[CrossRef] [PubMed]

E. J. Fernández, B. Povazay, B. Hermann, A. Unterhuber, H. Sattmann, P. M. Prieto, R. Leitgeb, P. Ahnelt, P. Artal, and W. Drexler, �??Three Dimensional Adaptive Optics Ultrahigh-Resolution Optical Coherence Tomography using a liquid crystal spatial light modulator,�?? Vis. Res. In press (2005)

Other

T. Wilson, Ed., Confocal Microscopy (Academic, London, 1990).

M. Born and E. Wolf, Principles of Optics (7th ed., Pergamon, Oxford, 1999).

D. A. Atchinson and G. Smith, Optics of the Human Eye (Oxford: Butterworth-Heinemann, 2000).

A. G. Bennett and R. B. Rabbetts, Clinical Visual Optics (Butterworth-Heinemann, Oxford, 1998).

T. Wilson and C. J. R. Sheppard, Theory and Practice of Scanning Optical Microscopy (Academic press, London,1984).

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Figures (8)

Fig. 1.
Fig. 1.

Confocal polychromatic (Gaussian spectrum of 80 nm FWHM) point-spread functions obtained in the perfect case (columns 1 and 4), and for 2 subjects (S1 and S2) at different pupil sizes, ranging from 1 to 8 mm diameter. All the color-coded intensity images are normalized to their corresponding maxima. Blue color corresponds to 0 intensity while red indicates 1 (maximum intensity).

Fig. 2.
Fig. 2.

Modulation transfer functions calculated in the chromatic case, assuming perfect monochromatic aberration correction, at different pupil sizes for a Gaussian optical spectrum of 80 nm FWHM.

Fig. 3.
Fig. 3.

Modulation transfer functions in the chromatic case, in absence of monochromatic aberrations, for different Gaussian optical spectra (indicated with different colors) and different pupil sizes. The case of perfect aberration correction is also included in black color. Dashed line shows FWHM of the MTFs.

Fig. 4.
Fig. 4.

Contrast functions associated with different pupil diameters obtained for a Gaussian spectrum of 120 nm FWHM (chromatic case). Experimental resolution achieved in ophthalmic OCT is shown with a dashed line.

Fig. 5.
Fig. 5.

(a) Resolution for different Gaussian optical spectra (indicated with different colors, showing the FWHM) as a function of the pupil size, in the case of only monochromatic aberration correction. (b) Minimum transverse resolution for different Gaussian spectra (indicated with different colors, showing the FWHM) in the case of only monochromatic aberration correction. The required pupil diameter to achieve the optimal transverse resolution is also presented for each spectral bandwidth.

Fig. 6.
Fig. 6.

Confocal polychromatic Strehl ratio calculated for Subject 1 (S1) at different spectral bandwidths as a function of the pupil diameter.

Fig. 7.
Fig. 7.

Averaged confocal polychromatic Strehl ratios calculated for each subject as a function of pupil diameter.

Fig. 8.
Fig. 8.

Confocal polychromatic Strehl ratios at different spectral bandwidths as a function of the pupil diameter for perfect monochromatic aberration correction. The case of perfect aberration correction is presented with a dashed line. The average Strehl ratio calculated from four real eyes, including all the aberrations, is shown in black color.

Equations (8)

Equations on this page are rendered with MathJax. Learn more.

R = 2 π λ r sin ( α ) ,
Chromatic Defocus = 0,0021 ( λ 800 ) ,
I = PSF 1 2 { PSF 2 2 D } ,
PSF i ( λ , ρ ) ( 1 λ ) 2 Ai J 0 ( 2 πρr ) ξ ( λ , r ) exp [ i 2 π Φ ( λ , r ) ] rdr 2 .
Φ ( λ , r ) = i = 1 21 a i Z i ,
a 4 = ( r 2 4 3 ) 0.0021 ( λ 800 ) .
PSF Polychromatic = 1 K 1 M + PSF i ( λ , ρ ) G ( λ ) d λ .
ConfPSF Polychromatic = PSF Polychromatic 2 .

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