Nandhini Elango, M. Optom
Student, SRM Medical College Hospital & Research Centre, Tamil Nadu, India
Atmospheric turbulence, which refers to small-scale, irregular air motions characterised by winds that vary in speed and direction. It significantly reduces the angular resolution of the telescope (figure:1). (1) Adaptive optics (AO) is a method of compensating for image degradation in real time. Babcock was the first to propose the technique (1953) to improve the astronomical images. (2) The human eye has differences in refractive index, lower and higher order aberrations (HOAs), chromatic aberrations and fluctuations in tear, thus it reduces image contrast and resolution by limiting the optical quality of the human eye. (3)
Figure 1: Image of the star; (A) Without Adaptive optics; (B) with Adaptive Optics
Image courtesy: https://www.eso.org/public/images/elt-res-comp-slide3_4/.
Components of Adaptive Optics(2)
- A wavefront sensor measures the shape distortions of light waves.
- A deformable mirror that continuously modifies its reflecting surface to account for the deformation of the light wave.
- Command and control system, processes the sensor’s data and operates the deformable mirror.
Applications in Ophthalmology
Wavefront aberrations in keratoconic eyes,(4) were addressed by AO visual simulators.
Compared to normal eyes, amblyopic eyes exhibit more severe HOAs. In anisometropic amblyopia the modulation transfer function and contrast sensitivity functions were enhanced by the AO system.(5)
AO has been utilised to alter the eye’s aberrations in order to investigate visual performance. (6)
When compared to fellow control eyes, an AO picture revealed altered lamina cribrosa morphology in glaucomatous eyes. Utilizing an AO-Optical Coherence Tomography, AO-Scanning Laser Ophthalmoscopy, retinal nerve fibre layer bundles can also be evaluated. (7)
Retinal vascular imaging is used for direct anatomical measurement of the artery wall and lumen diameter. This is possible using an AO retinal camera. (8) In retinal photoreceptor imaging cone packing density and cone spacing has also been analysed. (9)
Thus, AO has extensive clinical applications. Nevertheless, the price makes it unaffordable in a clinical office setting. Despite this, statistics on the numerous applications of AO have proliferated in recent years. The various applications of the AO retinal image aided in the early identification, progression, and follow-ups of macular hole, age-related macular degeneration, retinal vasculitis, diabetic retinopathy and improved the outcome of refractive surgeries.
- Roddier, F. (1981). V the effects of atmospheric turbulence in optical astronomy. In Progress in optics (Vol. 19, pp. 281-376). Elsevier.
- Roddier, F. (Ed.). (1999). Adaptive optics in astronomy.
- Vera-Díaz, F. A., & Doble, N. (2012). The human eye and adaptive optics (pp. 119-150). Riejeka, Croatia: InTech.
- Rocha, K. M., Vabre, L., Chateau, N., & Krueger, R. R. (2010). Enhanced visual acuity and image perception following correction of highly aberrated eyes using an adaptive optics visual simulator. Journal of Refractive Surgery, 26(1), 52-56.
- Liao, M., Zhao, H., Liu, L., Li, Q., Dai, Y., Zhang, Y., & Zhou, Y. (2016). Training to improve contrast sensitivity in amblyopia: correction of high-order aberrations. Scientific reports, 6(1), 1-8.
- Piers, P. A., Fernandez, E. J., Manzanera, S., Norrby, S., & Artal, P. (2004). Adaptive optics simulation of intraocular lenses with modified spherical aberration. Investigative ophthalmology & visual science, 45(12), 4601-4610.
- Nork, T. M., Ver Hoeve, J. N., Poulsen, G. L., Nickells, R. W., Davis, M. D., Weber, A. J., … & Millecchia, L. L. (2000). Swelling and loss of photoreceptors in chronic human and experimental glaucomas. Archives of ophthalmology, 118(2), 235-245.
- Baleanu, D., Ritt, M., Harazny, J., Heckmann, J., Schmieder, R. E., & Michelson, G. (2009). Wall-to-lumen ratio of retinal arterioles and arteriole-to-venule ratio of retinal vessels in patients with cerebrovascular damage. Investigative ophthalmology & visual science, 50(9), 4351-4359.
- Supriya, D., Shwetha, M., Kiran Anupama, K., Kummelil Mathew, K., Berendschot, T. T., Schouten, J. S., … & Hegde, B. (2015). Structural and function correlation of cone packing utilizing adaptive optics and microperimetry. BioMed Research International, 2015.