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The Research of Alfonso Jimenez Villar

Alfonso Jimenez Villar

Ophthalmic diagnostics integrating optics and biomechanics

The eye is a complex dynamic system of optical elements exhibiting different optical properties, which ensures vision. However, biomechanics of the ocular structures also influences physiology of the eye, playing role in the development of the diseases like glaucoma, myopia, presbyopia, keratoconus or vitreo-retinal diseases [1]. Biomechanics of ocular tissues can also impact the outcome of refractive surgery, and it has to be taken into account during measurement of intraocular pressure (IOP). Therefore, an accurate description of eye functionality should take into account both optical and biomechanical aspects of the as well as mutual relations between them.

Biomechanical properties are routinely assessed by application of the external force to the measured sample and monitoring its reaction. A novel concept is based on applying the force in a non-contact way. An example of such stimulus is a puff of the air applied in a brief period of time to deform ocular tissues (e.g. cornea). Both inward and outward movement of the cornea is used to determine the corneal deformation, and indirectly, the elastic and the possible viscoelastic properties of this tissue [2]. Currently, there are two commercial systems for IOP measurement, which are able to show parameters associated with corneal biomechanics: Optical Response Analyser (ORA) and the Corvis-ST [3].

A prototype optical system to image the deformation of the ocular structures

My PhD project aims at comprehensive in vivo investigation of deformation of the eye after applying mechanical stimulus such as air puff. A critical step in the project was to develop a long depth range Optical Coherence Tomography (OCT) instrument integrated with a non-contact stimulation subsystem to be able to determine the reaction of all ocular structures to mechanical stimulation.

OCT is a non-contact imaging technique based on low-coherence interferometry that detect light back-scattered from the internal structures inside the eye. OCT represents one of the main breakthroughs in ophthalmic diagnostics since it provides cross-sectional and volumetric images with extremely high resolution. In comparison with others OCT generations, OCT utilizing wavelength-tunable light source (swept source) demonstrates the advantages in terms of resolution, sensitivity and imaging range due to several improvements in photonic technologies. In addition, ability to image the eye through its entire axial length made SS-OCT a precise and accurate ocular biometry tool.

The scheme of the developed system is shown in Fig. 1. The prototype SS-OCT was based on a Michelson interferometer with a short external cavity laser operating at central wavelength of 1.05 µm and the imaging speed of 30 kA-scans/second. The system was characterized by an imaging depth range of 29 mm. The sample arm of the interferometer was integrated with an air-puff chamber from a commercial non-contact tonometer, where the optical beam is collinear with the direction of the air puff. The proposed configuration enabled high-speed monitoring of the dynamics of intraocular distances during and after air puff along with simultaneous acquisition of the air-puff force [4]. The system was optimized and deployed to the ophthalmic clinic.

Fig. 1. Scheme of the prototype SS-OCT ocular biometer merged with an air-puff chamber.

Eye reaction to the air puff is defined by the eye biomechanics

The next step in my research was to determine biomechanical behaviour of the eye when the air puff is applied to the subject eye. Currently, the developed technology enables measurement of the eye reaction only along visual axis. However, we were able to extract information on the movement of the whole eye (retraction) during eye stimulation apart from the access to the reaction of each separate ocular component (Fig. 2). Comparing the position of cornea, crystalline lens and retina at different moments, we observed and quantified the effects like corneal deflection, corneal hysteresis (due to the viscoelasticity), crystalline lens wobbling and eye retraction. Moreover, compression of the ocular tissues could be also determined.

Fig. 2. Eye reaction to the air puff and mechanical properties under the influence of the eye retraction (a) SS-OCT image. (b) Corneal deformation before and after eye retraction correction (deflection). (c) Lens deformation before and after eye retraction correction (wobbling). (d) Impact of the eye retraction in the corneal hysteresis.

Ability to test new technology in a clinical setting allowed to identify the parameters that may become future biomarkers of the ocular diseases that are related to biomechanics. Since IOP measurements are not precise with the current technology, I was interested to find possible correlations between extracted parameters and different IOP levels [5]. The experimental results shown in Fig. 3 indicated that the response of the cornea to the air puff is strongly correlated with the IOP.

Fig. 3. Correlation of selected parameters with the IOP. (a) Cornea deflection. (b) Corneal Hysteresis. (c) Anterior Chamber Depth compression. (d) Lens Deformation. (e) Crystalline lens compression. (f) Corneal velocity time interval. R, Pearson correlation coefficient. p, P-value.

Predicting biomechanical behaviour of the eye: A rheological model.

Currently, I work on the most challenging part of my project: to develop a rheological model to predict the elastic and viscoelastic properties of the whole eye for different IOP levels. A rheological or burger model is based on a linear combination of elastic and viscoelastic components which are represented by springs (Hooke) and dashpots (Newton) elements. The most common rheological models are Kelvin-Voigt model or Maxwell model. Generally, the response to the stimulus can be obtained by solving a set of differential equations, which is possible numerically.

Figure 4 presents the proposed burger model according to our experimental results. The elastic and viscoelastic components of the different ocular structures are well represented by a Kelvin-Voigt model. However, a mass component is required to include in the crystalline lens and the retina in order to simulate the lens wobbling and the eye retraction. The initial simulations have shown that our model fits quite well to the experimental results [6].

Fig. 4. Rheological eye model when the air puff works on the eye. E, elastic component. η viscoelastic component. M, mass component

Next step: towards understanding of accommodation and presbyopia development

Future steps to complete my PhD project include studies on the impact of accommodation on the response of the crystalline lens. We do believe that lens wobbling after the stimulus is associated with the action of the ciliary body and the zonules of Zinn. Since those two anatomical structures play a particular role in the accommodative processes and consequently, in the development of presbyopia, the wobbling characteristic parameters should vary between the eyes at different age and accommodative status.

Background of the researcher

After graduating my bachelor in Optics and Optometry in 2013 at University Complutense of Madrid, I started my master studies in “Optical technology and Imaging Systems”. At the same time, I had the opportunity to work in a consultancy firm related with design and manufacturing process of ophthalmic lenses.

In 2017, I started my PhD in the Bio-Optics & Optical Engineering Lab ( at the Nicolaus Copernicus University, in Torun, Poland, under supervision of Prof. I. Grulkowski. I was an Early Stage Researcher in the project ‘Advanced BiomEdical OPTICAL Imaging and Data Analysis’ (BE-OPTICAL) that was funded by the European Union's Horizon 2020 Programme under Marie Curie Sklodowska Action ( Currently, my research focuses on measurements of the biomechanical properties of the eye by an optical imaging system, and application of innovative acousto-optical system in high-resolution imaging.


  1. J. Liu and C. J. Roberts, “Influence of corneal biomechanics properties on intraocular pressure measurement: quantitative analysis”, J. Cataract Refract Surg., vol. 31, issue-1, pp. 146 – 155, Jan. 2005.
  2. E. Maczynska, K. Karnowski, K. Szulzycki, M. Malinowska, H. Dolezyczek, A. Cichanski, M. Wojtkowski, B. Kaluzny and I. Grulkowski, “Assessment of the influence of viscoelasticity of cornea in animal ex vivo model using air-puff optical coherence tomography and corneal hysteresis”, Journal of Biophotonics, vol. 12(2), pp. e201800154 (1 – 9), Feb. 2018.
  3. M. Jedzierowska, R. Koprowski and Z. Wrobel, “Overview of the ocular biomechanical properties measured by the Ocular Response Analyser and the Corvis ST”, Information Technologies in Biomedicine, Vol. 4, Springer Cham, pp. 377-386, Jan. 2014.
  4. A. Jiménez-Villar, E. Maczynska, A. Cichanski, M. Wojtkowski, B. Kaluzny and I. Grulkowski, “High-speed OCT-based ocular biometer combined with an air-puff system for determination of induced retraction-free eye dynamics”, Biomed. Opt. Express, Vol. 10, pp. 3663 – 3680, Jul. 2019.
  5. E. Maczynska, J. Rzeszewska-Zamiara, A. Jimenez-Villar, M. Wojtkowski, B. Kaluzny and I. Grulkowski, “Air-Puff-induced dynamics of ocular components measured with optical biometry”, Invest. Ophthalmol. Vis. Sci., Vol. 60(6), pp. 1979-1986, May 2019.
  6. A. Jiménez-Villar, M. Jannesari, M. Kadkhodaei, P. Mosaddegh, S. Grulkowski, B. Kaluzny, M. Wojtkowski, H. Kasprzak and I. Grulkowski, “SS-OCT based ocular biometry and rheological mechanical model for comprehensive analysis of the eye reaction to air-puff stimulus (Conference Presentation)”, Proc. SPIE, pp. 10880, 108800Y, Mar. 2019

Alfonso Jiménez-Villar, M. Sc.

Ph.D. Student

Nicolaus Copernicus University
Faculty of Physics, Astronomy and Informatics
Department of Biophysics

Ul. Grudziądzka 5
87-100, Toruń

Tel: +48 56 611 2414
E-mail: ajimenez[at]