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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 11, Iss. 7 — Apr. 7, 2003
  • pp: 810–817
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On the possibility of intraocular adaptive optics

Gleb Vdovin, Mikhail Loktev, and Alexander Naumov  »View Author Affiliations


Optics Express, Vol. 11, Issue 7, pp. 810-817 (2003)
http://dx.doi.org/10.1364/OE.11.000810


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Abstract

We consider the technical possibility of an adaptive contact lens and an adaptive eye lens implant based on the modal liquid-crystal wavefront corrector, aimed to correct the accommodation loss and higher-order aberrations of the human eye. Our first demonstrator with 5 mm optical aperture is capable of changing the focusing power in the range of 0 to +3 diopters and can be controlled via a wireless capacitive link. These properties make the corrector potentially suitable for implantation into the human eye or for use as an adaptive contact lens. We also discuss possible feedback strategies, aimed to improve visual acuity and to achieve supernormal vision with implantable adaptive optics.

© 2003 Optical Society of America

1. Introduction

It was shown recently that the aberrations of the human eye can significantly contribute to the loss of the visual acuity [1

1. J. Liang, B. Grimm, S. Goelz, and J. F. Bille, “Objective measurement of wave aberrations of the human eye with the use of a hartmann-shack wave-front sensor,” J. Opt. Soc. Am. 11, 1949–1957 (1994). [CrossRef]

]. The resolution of the retina is higher than the optical resolving power of the human eye [2

2. K. N. Ogle, “On the resolving power of the human eye,” J. Opt. Soc. Am. 41, 517–520 (1951). [CrossRef] [PubMed]

]. Traditional correction with spectacles is useful for only two aberrations – defocus and astigmatism [3

3. R. Navarro, E. Moreno-Barriuso, S. Bara, and Teresa Mancebo, “Phase plates for wave-aberration compensation in the human eye,” Opt. Lett. 25, 236–238 (2000). [CrossRef]

, 4

4. M. P. Cagigal, V. F. Canales, J. F. Castejon-Mochon, P. M. Prieto, N. Lopez-Gil, and P. Artal, “Statistical description of wave-front aberration in the human eye,” Opt. Lett. 27, 37–39 (2002). [CrossRef]

]. To facilitate the correction of higher-order aberrations, the corrector should be optically conjugated to the eye pupil. To achieve such a conjugation, an imaging optical system is used to make the image of the corrector co-incident with the eye. Breadboard adaptive optical setups, based on this principle, were successfully built to demonstrate the feasibility of high-order correction [5

5. N. Doble, G. Yoon, L. Chen, P. Bierden, S. Oliver, and D. R. Williams, “Use of a microelectromechanical mirror for adaptive optics in the human eye,” Opt. Lett. 27, 1537–1539 (2002). [CrossRef]

, 6

6. F. Vargas-Martin, P. M. Prieto, and P. Artal, “Correction of the aberrations in the human eye with a liquid-crystal spatial light modulator: limits to performance,” J. Opt. Soc. Am. A 15, 2552–2562 (1998). [CrossRef]

, 7

7. E. J. Fernandez, I. Iglesias, and P. Artal, “Closed-loop adaptive optics in the human eye,” Opt. Lett. 26, 746–748 (2001). [CrossRef]

] and the conclusions were that the resolution of the eye can be improved over the natural limit, leading to “supernormal” vision.

The breadboard setups realized so far are applicable only for clinical and laboratory use and cannot be converted into wearable devices due to their bulkiness and complexity.

Another ophthalmic problem that can be corrected with adaptive optics is the age-related or post-surgery loss of accommodation. Attempts were made to develop a corrector for presbyopia [8

8. C.W. Fowler and E.S. Pateras, “Liquid crystal lens review,” Ophthal. Physiol. Opt. 10, 186–194 (1990). [CrossRef]

] with little practical success.

Here we present the first results of our experiments with wireless control of liquid-crystal wavefront corrector, proving the technical feasibility of dynamic correction of human-eye aberrations by placing the wavefront corrector directly into the pupil of the human eye. We consider two possibilities:

  • A non-invasive way, which suggests integration of the wavefront corrector into a contact lens;
  • the invasive approach, which suggests implantation of the wavefront corrector directly into the human eye (see Fig. 1).
Fig. 1. Implantable adaptive eye lens

2. Liquid-crystal wavefront correctors

Fig. 2. Defocus (V=3.64 V, F=2.44 kHz) and spherical aberration (V=2.0 V, F=3 kHz) formed with a 10 mm LC lens.

In case the LC lens is implanted into the human eye or used as a contact lens, it should satisfy the following requirements:

  • Both the LC material and the lens optics should be biologically compatible. Not all LC materials satisfy these requirements [14

    14. B. Simon-Hettich and W. Becker, “Toxicological investigations of liquid crystals,” In 28th Freiburg Workshop on Liquid Crystals, Freiburg; Germany, (1999).

    ]. Merck’s data sheets declare liquid-crystal materials “not acutely toxic”, moreover according to tests conducted on 224 liquid-crystal substances [15

    15. W. Becker, B. Simon-Hettich, and P. Hnicke, “Toxicological and ecotoxicological investigations of liquid crystals and disposal of lcds,” Merck brochure, Merck KGaA, Liquid Crystals Division and Institute of Toxicology 64271 Darmstadt, September 25 (2001).

    ], 215 compounds did not have any acute toxic potential. Eye irritation tests performed with 14 LC compounds proved all 14 compounds to be non-irritant.
  • The corrector should combine adaptive optics with the receiving of external control signals. In addition, some kind of feedback – either psychophysical or objective – should be present to generate the control signals. In the simplest case, manual control of the focusing power and spherical aberration of the corrector can be implemented.
  • While the implantable lens dimensions should not exceed 4 mm in thickness and 9 mm in diameter – about the size of the eye lens [16

    16. E. Hecht. “Optics,” chapter 5, pages 203–205, Addison Wesley Longman Inc., 3rd edition (1998).

    ], the adaptive contact lens thickness should be limited to several tens of micrometers – the typical thickness of an ordinary soft contact lens.
  • A simple LC lens acts only on one polarization state of light. There are two ways to use the lens with randomly polarized light: to combine it with a linear polarizer – resulting in a light loss of 50%, or to combine two lenses acting on orthogonal polarization states.

3. Wireless control

The adaptive lenses, described above can easily be fabricated to match the size of the human eye lens. However, it is much more difficult to organize the wireless control, as, we believe, no wires can be used in the human eye and no battery can be embedded into the lens.

The typical power required to drive the lens is in the range of 50 µW to 1 mW (see Fig. 3), depending on the control frequency and the parameters of the coating and the liquid-crystal. This power should be transferred to the lens through the wireless link.

Fig. 3. Experimentally measured reactive power required to drive the LC lens as a function of the driving voltage and the focusing power. Since the lens is a reactive load, the active power dissipated in the lens is considerably smaller than shown in this graph.
Fig. 4. Schematic of inductive (left), capacitive (middle) and optical (right) control of an implantable LC lens.

  • An inductive link using linked coils – see Fig. 4 left. The transmitter coil is integrated into the frame of the spectacles, while the receiver coil is integrated in the adaptive LC lens, around the optically active area – see 3D model in Fig. 5.
  • Electrostatic link via linked capacitors – see Fig. 4 middle. The field inside the external capacitor (formed for instance between the conductive coating on the spectacles and the active plate of the LC lens) is driving the LC lens.
  • Optical IR link to the photovoltaic receiver integrated into the LC lens – see Fig. 4 right.
  • Finally, feasibility research should be done to control the lens using the bioelectrical signals that normally control the natural accommodation of the eye.

4. Experimental proof of concept

We have fabricated a number of adaptive LC lenses with a diameter of 15 mm and thickness of 4 mm, with a clear light aperture of 5mm and the LC layer thickness of 25 and 50 µm (see Fig. 5). These dimensions were dictated by the ease of manufacture. Nevertheless, the optical parameters of the lens are close to those required for intra-ocular application; the main difference is the overall size and the lack of integrated control electronics and a wireless link.

Fig. 5. Adaptive LC lens fabricated for experiment with wireless control (top) and 3D model of a wireless implantable LC corrector with integrated receiver coil for remote control (bottom).

Fig. 6. Interferometric patterns obtained experimentally for green (543 nm), yellow (594 nm) and red (632 nm) colors (left to right) using wireless capacitive control of the adaptive LC lens.

Fig. 7. Voltage-frequency calibration curves for three different LC lenses.

As for the photo-voltaic control, the main problem is the biological compatibility of such a control with the human eye. In fact, we need to have an optical source with a power of the order of 50µW to 1 mW, permanently shining into the area around the eye pupil. Though the wavelength can be in the invisible range, the long-term effect of such an exposure can be negative, though the situation can be improved by optimization of the configuration of the optical link.

5. Compensation of chromatic aberrations

The chromatic aberration of the human eye can reach ~0.75 D in the wavelength range 400 to 650 nm with longer focus corresponding to a shorter wavelength [17

17. R.E. Bedford and G. Wyszecki,“Axial chromatic aberration of the human eye,” J.Opt. Soc. Am. 47, 564–565 (1947).

, 18

18. L. Llorente, L. Diaz-Santana, D. Lara-Saucedo, and Sl. L. Marcos, “Aberrations of the human eye in visible and near infrared illumination,” Optometry and Vision Science 80, 26–35 (2003). [CrossRef] [PubMed]

]. Liquid-crystal lenses feature chromatic aberration of the opposite sign [19

19. T. L. Kelly, A.F. Naumov, M.Yu. Loktev, M.A. Rakhmatulin, and O.A. Zayakin, “Focusing of astigmatic laser diode beam by combination of adaptive liquid crystal lenses,” Opt. Commun. 181, 295 (2000). [CrossRef]

], with shorter focal length corresponding to the shorter wavelength. This is illustrated in Fig. 8 by computer reconstruction of the interferograms in Fig. 6.

Fig. 8. Interferograms in Fig. 6, reconstructed for three color components. Chromatic focal lengths of the LC lens evaluated from these data are ~26 cm for green, ~30 cm for yellow and ~32 cm for red light.

An adaptive LC lens will naturally compensate for the chromatic aberration of the human eye.

6. Control algorithms

To our knowledge there is no experience with control of intra-ocular adaptive optics. Authors suggest that low-order aberrations, such as defocus and astigmatism, can be corrected dynamically by a psycho-physical feedback or even manual adjustment of the focusing power, spherical aberration and astigmatism. Higher-order aberrations should be compensated dynamically by the means of automatic feedback with the wavefront sensor embedded, for instance, in a wireless controller or by using the neural bioelectric signals that are generated by the human brain.

7. Conclusions

As published recently [2

2. K. N. Ogle, “On the resolving power of the human eye,” J. Opt. Soc. Am. 41, 517–520 (1951). [CrossRef] [PubMed]

, 5

5. N. Doble, G. Yoon, L. Chen, P. Bierden, S. Oliver, and D. R. Williams, “Use of a microelectromechanical mirror for adaptive optics in the human eye,” Opt. Lett. 27, 1537–1539 (2002). [CrossRef]

, 6

6. F. Vargas-Martin, P. M. Prieto, and P. Artal, “Correction of the aberrations in the human eye with a liquid-crystal spatial light modulator: limits to performance,” J. Opt. Soc. Am. A 15, 2552–2562 (1998). [CrossRef]

] the resolution of the human eye can be improved by correcting the eye lens aberrations. Compensation of high-order aberrations is possible only if the corrector is optically conjugated with the eye lens.

Based on the results of our preliminary experiments, it seems possible to develop a wireless-controlled adaptive contact lens or eye lens implant for correction of accommodation loss and also, in the future, multichannel correctors for dynamic correction of high-order aberrations of the human eye.

Acknowledgements

Authors acknowledge the contribution provided by Svetlana Kotova to the fabrication of the LC lens demonstrators.

References and links

1.

J. Liang, B. Grimm, S. Goelz, and J. F. Bille, “Objective measurement of wave aberrations of the human eye with the use of a hartmann-shack wave-front sensor,” J. Opt. Soc. Am. 11, 1949–1957 (1994). [CrossRef]

2.

K. N. Ogle, “On the resolving power of the human eye,” J. Opt. Soc. Am. 41, 517–520 (1951). [CrossRef] [PubMed]

3.

R. Navarro, E. Moreno-Barriuso, S. Bara, and Teresa Mancebo, “Phase plates for wave-aberration compensation in the human eye,” Opt. Lett. 25, 236–238 (2000). [CrossRef]

4.

M. P. Cagigal, V. F. Canales, J. F. Castejon-Mochon, P. M. Prieto, N. Lopez-Gil, and P. Artal, “Statistical description of wave-front aberration in the human eye,” Opt. Lett. 27, 37–39 (2002). [CrossRef]

5.

N. Doble, G. Yoon, L. Chen, P. Bierden, S. Oliver, and D. R. Williams, “Use of a microelectromechanical mirror for adaptive optics in the human eye,” Opt. Lett. 27, 1537–1539 (2002). [CrossRef]

6.

F. Vargas-Martin, P. M. Prieto, and P. Artal, “Correction of the aberrations in the human eye with a liquid-crystal spatial light modulator: limits to performance,” J. Opt. Soc. Am. A 15, 2552–2562 (1998). [CrossRef]

7.

E. J. Fernandez, I. Iglesias, and P. Artal, “Closed-loop adaptive optics in the human eye,” Opt. Lett. 26, 746–748 (2001). [CrossRef]

8.

C.W. Fowler and E.S. Pateras, “Liquid crystal lens review,” Ophthal. Physiol. Opt. 10, 186–194 (1990). [CrossRef]

9.

A. F. Naumov, M. Yu. Loktev, I. R. Guralnik, and G. Vdovin, “Liquid-crystal adaptive lenses with modal control,” Opt. Lett. 23, 992–994 (1998). [CrossRef]

10.

A. F. Naumov and G. Vdovin, “Multichannel liquid-crystal-based wave-front corrector with modal influence functions,” Opt. Lett. 23, 1550–1552 (1998). [CrossRef]

11.

S. P. Kotova, M. Yu. Kvashnin, M. A. Rakhmatulin, O. A. Zayakin, I. R. Guralnik, N. A. Klimov, P. Clark, Gordon D. Love, A. F. Naumov, C. D. Saunter, M. Yu. Loktev, G. V. Vdovin, and L. V. Toporkova, “Modal liquid crystal wavefront corrector,” Opt. Express 22, 1258 (2002) http://www.opticsexpress.org/abstract.cfm?URI=OPEX-10-22-1258. [CrossRef]

12.

A. F. Naumov, Gordon Love, M. Yu. Loktev, and F. L. Vladimirov,“Control optimization of spherical modal liquid crystal lenses,” Opt. Express 4, 344–352 (1999), http://www.opticsexpress.org/abstract.cfm?URI=OPEX-4-9-344 [CrossRef] [PubMed]

13.

J. Bruines, “Process outlook for analog and rf applications,” Microelectronic Engineering 54, 35–48 (2000). [CrossRef]

14.

B. Simon-Hettich and W. Becker, “Toxicological investigations of liquid crystals,” In 28th Freiburg Workshop on Liquid Crystals, Freiburg; Germany, (1999).

15.

W. Becker, B. Simon-Hettich, and P. Hnicke, “Toxicological and ecotoxicological investigations of liquid crystals and disposal of lcds,” Merck brochure, Merck KGaA, Liquid Crystals Division and Institute of Toxicology 64271 Darmstadt, September 25 (2001).

16.

E. Hecht. “Optics,” chapter 5, pages 203–205, Addison Wesley Longman Inc., 3rd edition (1998).

17.

R.E. Bedford and G. Wyszecki,“Axial chromatic aberration of the human eye,” J.Opt. Soc. Am. 47, 564–565 (1947).

18.

L. Llorente, L. Diaz-Santana, D. Lara-Saucedo, and Sl. L. Marcos, “Aberrations of the human eye in visible and near infrared illumination,” Optometry and Vision Science 80, 26–35 (2003). [CrossRef] [PubMed]

19.

T. L. Kelly, A.F. Naumov, M.Yu. Loktev, M.A. Rakhmatulin, and O.A. Zayakin, “Focusing of astigmatic laser diode beam by combination of adaptive liquid crystal lenses,” Opt. Commun. 181, 295 (2000). [CrossRef]

OCIS Codes
(010.1080) Atmospheric and oceanic optics : Active or adaptive optics
(170.4460) Medical optics and biotechnology : Ophthalmic optics and devices
(330.1070) Vision, color, and visual optics : Vision - acuity

ToC Category:
Research Papers

History
Original Manuscript: February 12, 2003
Revised Manuscript: March 28, 2003
Published: April 7, 2003

Citation
Gleb Vdovin, Mikhail Loktev, and Alexander Naumov, "On the possibility of intraocular adaptive optics," Opt. Express 11, 810-817 (2003)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-11-7-810


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References

  1. J. Liang, B. Grimm, S. Goelz, and J. F. Bille, �??Objective measurement of wave aberrations of the human eye with the use of a hartmann-shack wave-front sensor,�?? J. Opt. Soc. Am. 11, 1949-1957 (1994). [CrossRef]
  2. K. N. Ogle, �??On the resolving power of the human eye,�?? J. Opt. Soc. Am. 41, 517-520 (1951). [CrossRef] [PubMed]
  3. R. Navarro, E. Moreno-Barriuso, S. Bara, Teresa Mancebo, �??Phase plates for wave-aberration compensation in the human eye,�?? Opt. Lett. 25, 236-238 (2000). [CrossRef]
  4. M. P. Cagigal, V. F. Canales, J. F. Castejon-Mochon, P. M. Prieto, N. Lopez-Gil, P. Artal, �??Statistical description of wave-front aberration in the human eye,�?? Opt. Lett. 27, 37�??39 (2002). [CrossRef]
  5. N. Doble, G. Yoon, L. Chen, P. Bierden, S. Oliver, D. R. Williams, �??Use of a microelectromechanical mirror for adaptive optics in the human eye,�?? Opt. Lett. 27, 1537-1539 (2002). [CrossRef]
  6. F. Vargas-Martin, P. M. Prieto, P. Artal, �??Correction of the aberrations in the human eye with a liquid-crystal spatial light modulator: limits to performance,�?? J. Opt. Soc. Am. A 15, 2552-2562 (1998). [CrossRef]
  7. E. J. Fernandez, I. Iglesias, P. Artal, �??Closed-loop adaptive optics in the human eye,�?? Opt. Lett. 26, 746-748 (2001). [CrossRef]
  8. C.W. Fowler and E.S. Pateras, �??Liquid crystal lens review,�?? Ophthal. Physiol. Opt. 10, 186-194 (1990). [CrossRef]
  9. A. F. Naumov, M. Yu. Loktev, I. R. Guralnik, G. Vdovin, �??Liquid-crystal adaptive lenses with modal control,�?? Opt. Lett. 23, 992-994 (1998). [CrossRef]
  10. A. F. Naumov, G. Vdovin, �??Multichannel liquid-crystal-based wave-front corrector with modal in.uence functions,�?? Opt. Lett. 23, 1550-1552 (1998). [CrossRef]
  11. S. P. Kotova, M. Yu. Kvashnin, M. A. Rakhmatulin, O. A. Zayakin, I. R. Guralnik, N. A. Klimov, P. Clark, Gordon D. Love, A. F. Naumov, C. D. Saunter, M. Yu. Loktev, G. V. Vdovin, L. V. Toporkova, �??Modal liquid crystal wavefront corrector,�?? Opt. Express 22, 1258 (2002), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-10-22-1258">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-10-22-1258</a>. [CrossRef]
  12. A. F. Naumov, Gordon Love, M. Yu. Loktev, F. L. Vladimirov, �??Control optimization of spherical modal liquid crystal lenses,�?? Opt. Express 4, 344-352 (1999), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-4-9-344">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-4-9-344</a> [CrossRef] [PubMed]
  13. J. Bruines, �??Process outlook for analog and rf applications,�?? Microelectronic Engineering 54, 35-48 (2000). [CrossRef]
  14. B. Simon-Hettich, W. Becker, �??Toxicological investigations of liquid crystals,�?? In 28th Freiburg Workshop on Liquid Crystals, Freiburg; Germany, (1999).
  15. W. Becker, B. Simon-Hettich, P. Hnicke, �??Toxicological and ecotoxicological investigations of liquid crystals and disposal of lcds,�?? Merck brochure, Merck KGaA, Liquid Crystals Division and Institute of Toxicology 64271 Darmstadt, September 25 (2001).
  16. E. Hecht, Optics, (Addison Wesley Longman Inc., 3rd edition, 1998) Chapter 5, pgs. 203�??205
  17. R.E. Bedford and G. Wyszecki, �??Axial chromatic aberration of the human eye,�?? J.Opt. Soc. Am. 47, 564-565 (1947).
  18. L. Llorente, L. Diaz-Santana, D. Lara-Saucedo, Sl. L. Marcos, �??Aberrations of the human eye in visible and near infrared illumination,�?? Optometry and Vision Science 80, 26-35 (2003). [CrossRef] [PubMed]
  19. T. L. Kelly, A.F. Naumov, M.Yu. Loktev, M.A. Rakhmatulin, O.A. Zayakin, �??Focusing of astigmatic laser diode beam by combination of adaptive liquid crystal lenses,�?? Opt. Commun. 181, 295 (2000). [CrossRef]

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