Diffuse optics and interferometry

Diffuse optics offers a noninvasive portable approach for examining biological tissues, including the human brain, in vivo [1]. Near-infrared spectroscopy (NIRS) [2] and diffuse correlation spectroscopy (DCS) are the primary diffuse optical modalities [3, 4]. In both approaches, the light illuminates the tissue, and diffusively scattered photons are collected at some distance from the emitter (typically 2-3 cm). NIRS uses the detected signal to estimate optical properties (absorption and scattering), while DCS quantifies the blood flow from temporal changes of the remitted light intensity. Although these methods have been applied to monitor brain oxygenation and blood flow, their most widely adopted versions rely on continuous wavelength (CW) lasers, precluding absolute measures of the optical and dynamical tissue properties [5].

Time-domain NIRS (TD-NIRS) enables quantification of the optical properties through the sample’s photon time-of-flight distribution (TOF distribution) [9-12]. This capability can also be combined with correlation spectroscopy to achieve TOF- (or photon path-length-) resolved blood flow information. So, we could better distinguish photons traversing superficial layers (short TOFs) from photons traveling deep into the brain (long TOFs). Also, given the TOF distribution, we could estimate the optical properties to achieve the absolute blood flow index (BFI), effectively combining the capabilities of TD-NIRS with DCS into a single modality. Such an approach is called time-domain diffuse correlation spectroscopy (TD-DCS) [6, 7].

Though TD-DCS is a powerful technique even applied in clinics, it relies only on light intensity. Therefore, TD-DCS does not enable the detection of the optical phase [8]. The optical phase is accessible in interferometric near-infrared spectroscopy (iNIRS) [9].

Interferometry in brain monitoring

Image: Interferometry in brain monitoring.

The optical phase is accessible in interferometric near-infrared spectroscopy (iNIRS). The iNIRS approach uses interferometry based on a temporally coherent tunable laser to achieve TOF resolution. Specifically, iNIRS supplements the conventional NIRS configuration with the tunable light source and the reference arm. The field remitted from the sample is recombined with the reference field. The beat frequency of the signal encodes photon path lengths (or times-of-flight). Short paths produce lower beat frequencies than long paths. Consequently, the photon time-of-flight distribution can be achieved by inverse-Fourier transforming the recorded signal. However, iNIRS provides much more information through the two-dimensional autocorrelation function (ACF) of the reemitted optical field. In iNIRS, the ACF is measured as a function of time lag with TOF resolution. This two-dimensional measurement (figure below) encodes information about the sample’s absorption, scattering, and blood flow index (BFI).

iNIRS was validated in in liquid phantoms [9], mouse brain [10], and human brain in vivo [11]. However, the original iNIRS (as DCS and TD-DCS) uses single-mode fibers for light collection, requiring integration times of 0.5-1 second. This time frame is too long, precluding the ability to detect rapid blood flow changes in the human brain that could be linked to neural signals.

To overcome those limitations, we recently proposed parallel interferometric near-infrared spectroscopy (πNIRS). In πNIRS we use multi-mode fibers for light collection and a high-speed, two-dimensional camera for light detection. Each camera pixel acts effectively as a single iNIRS channel. So, the processed signals from each pixel are spatially averaged to reduce the overall integration time. Moreover, interferometric detection provides us with the unique capability of accessing complex information (amplitude and phase) about the light remitted from the sample, which with more than 8000 parallel channels, enabled us to sense the cerebral blood flow with only a 10 msec integration time (∼100x faster than conventional iNIRS). We used such an approach to monitor the pulsatile blood flow in a human forearm in vivo. Also, we demonstrated that this approach could monitor the activation of the prefrontal cortex by recording the change in blood flow in the forehead of the subject while he was reading an unknown text [12].

Text: Dawid Borycki, PhD habil.


Dawid Borycki, PhD habil.

Michał Dąbrowski, PhD

Klaudia Nowacka, MEng


  1. S. Samaei, P. Sawosz, M. Kacprzak, Z. Pastuszak, D. Borycki, and A. Liebert, “Time-domain diffuse correlation spectroscopy (TD-DCS) for noninvasive, depth-dependent blood flow quantification in human tissue in vivo,” Sci Rep 11, 1817 (2021).
  2. D. Borycki, O. Kholiqov, and V. J. Srinivasan, “Interferometric near-infrared spectroscopy directly quantifies optical field dynamics in turbid media,” Optica 3, 1471-1476 (2016).
  3. D. Borycki, O. Kholiqov, S. P. Chong, and V. J. Srinivasan, “Interferometric Near-Infrared Spectroscopy (iNIRS) for determination of optical and dynamical properties of turbid media,” Opt Express 24, 329-354 (2016).
  4. D. Borycki, O. Kholiqov, and V. J. Srinivasan, “Reflectance-mode interferometric near-infrared spectroscopy quantifies brain absorption, scattering, and blood flow index in vivo,” Opt Lett 42, 591-594 (2017).
  5. S. Samaei, K. Nowacka, A. Gerega, Z. Pastuszak, and D. Borycki, “Continuous-wave parallel interferometric near-infrared spectroscopy (CW piNIRS) with a fast two-dimensional camera,” Biomed Opt Express 13, 5753-5774 (2022).

Flicker Optoretinography (f-ORG)

For many years visual inspection of fundus photography [1] and examination of images acquired with optical coherence tomography (OCT) [2] have been used by ophthalmologists for eye disease diagnosis and monitoring therapy progress thanks to their ability to detect morphological changes in the retina. However, imaging the morphological manifestation of retinal diseases alone does not provide sufficient information on the loss of functionality of retinal neurons.

Over a decade ago, it was shown that optical coherence tomography (OCT) can detect small changes in the intensity of infrared light reflected from animal retinas in vitro [3,4] and in vivo [5] occurring after simultaneous stimulation with visible light. These findings laid the foundations for the development of optoretinography (ORG) [6], a method that measures photoreceptors’ response to light, thus giving a possibility for obtaining information about the functionality of retinal neurons.

At ICTER, we work on both ORG with a single pulse and flicker stimulation of the retina [7]. To acquire the ORG data, we use a Spatio-Temporal Optical Coherence-Tomography (STOC-T) [8] that records 3-D volumetric retina images within a few milliseconds each. After data processing, we extract the ORG signals by tracking subtle changes in the retina occurring between inner and outer photoreceptor junction (IS/OS) and the cone outer segment tips (COST). Fig. (a). presents the source of the ORG signal on an exemplary tomographic image of a human retina.

Exemplary results showing dark-adapted retinas’ responses to single pulse light stimulus are shown in Fig. (b) and (c). The (b) presents a spatially averaged ORG signal in function of time for uniformly distributed stimulus. The (c) shows the maximum amplitude of the ORG signal across imaged part of the retina surface in response to a projected pattern (letter E).

In the f-ORG experiments, which are the main subject of our works, a flickering light is used to stimulate the retina. First, such a study was performed by Schmoll et al. and measured photoreceptors’ response to a 5 Hz flicker [9], while, more recently, the group from Lübeck measured the response to different flicker frequencies (between 1 Hz and 6.6 Hz) [10].

Our f-ORG methodology allows for measuring retinas’ responses in a broader range of frequencies and mapping the photoreceptors’ response to a flickering light across the retinas’ surfaces. Exemplary results of measured frequency characteristics of the responses in four healthy human subjects are presented in Fig. (d). While an example of a spatially detected retina’s response to a DMD patterned stimulus with strips of light flickering at different frequencies is presented in Fig. (e).

Text: Sławomir Tomczewski, PhD, e-mail: stomczewski@ichf.edu.pl.


Sławomir Tomczewski, PhD

Piotr Węgrzyn, MSc

Dawid Borycki, PhD habil.

Egidijus Auksorius, PhD

Maciej Wielgo, MSc

Prof. Maciej Wojtkowski

Andrea Curatolo, PhD

Keywords: Optical Coherence Tomography, STOC-T, OCT, Optoretinography, Flicker ORG.


  1. V. J. Srinivasan, M. Wojtkowski, J. G. Fujimoto, and J. S. Duker, “In vivo measurement of retinal physiology with high-speed ultrahigh-resolution optical coherence tomography,” Opt. Lett. 31, 2308 (2006).
  2. S. Tomczewski, P. Węgrzyn, D. Borycki, E. Auksorius, M. Wojtkowski, and A. Curatolo, “Light-adapted flicker optoretinograms captured with a spatio-temporal optical coherence-tomography (STOC-T) system,” Biomed. Opt. Express 13, 2186 (2022).
  3. E. Auksorius, D. Borycki, P. Wegrzyn, B. L. Sikorski, K. Lizewski, I. Zickiene, M. Rapolu, K. Adomavicius, S. Tomczewski, and M. Wojtkowski, “Spatio-Temporal Optical Coherence Tomography provides full thickness imaging of the chorioretinal complex,” iScience 25, 105513 (2022).

Two-Photon Excited-Fluorescence Scanning Laser Ophthalmoscope (TPEF-SLO)

The ability to noninvasively access metabolic processes during the visual cycle is crucial for developing therapies against retinal degenerative diseases. We have developed a protocol for obtaining in vivo two-photon excited fluorescence images of the fundus in the human eye.

The visual cycle is a series of chemical transformations during which various fluorescent intermediates are formed. Blue-induced fundus autofluorescence allows visualization of retinal fluorophores. However, due to fundamental limitations, this method is limited to imaging lipofuscin, which contains byproducts of the visual cycle but does not directly reflect changes in photoreceptor function. The absorption spectra of fluorophores participating in the visual cycle, such as retinyl esters, lie in the UV spectral range. However, absorption and scattering in the front of the eye, as well as safety concerns, exclude UV from applications in ophthalmic imaging.

Two-photon excitation allows us to bypass this limitation and excite previously unavailable fluorophores, creating novel diagnostic capabilities. Retinal fluorophores can be excited with minimal absorption and much lower scattering and phototoxicity using femtosecond pulses at near-infrared wavelengths. Previously, we have shown imaging with a two-photon excited fluorescence scanning laser ophthalmoscope (TPEF-SLO) proved to be very useful in mice. Recently, in 2022 we report for the first time in vivo imaging of the human eye using a two-photon excited fluorescence (TPEF) with near-infrared light. We have built a compact instrument based on scanning laser ophthalmoscope (SLO) with a custom femtosecond fiber-based laser and efficient photon detection, and designed advanced data post-processing that enabled measurement of TPEF signals on the sub-single photon level. As a result, we can visualize the distribution of retinal fluorophores with exposure far below the safety limits for the human eye.

We heave measured dozens of volunteers to confirm the robustness of the technique and extend the experimental setup to work with mice models to investigate different eye diseases, like age-related or Stargardt macular degeneration. Imaging was performed in a dark room with no prior dark adaptation or pupil dilation. We were able to record the fluorescence signal and reconstruct the image in the majority of cases.  This technique allays safety concerns by allowing for the acquisition of informative images at low laser exposure. We confirmed the applicability of the system for future clinical use of this imaging modality. These results constitute an essential step towards functional imaging of the human eye that directly reflects local changes in the retina’s function.

Author: Michał Dąbrowski, PhD

Figure 1: a Example TPEF images of the human retina with different spectra filter on PMT detector.      b The same but for mice retina. c Comparison of fluorescence signal intensity for different spectra filter both for humans and several mice models. d FLIM images along with phasor plot representations.
Figure 1: a Example TPEF images of the human retina with different spectra filter on PMT detector. b The same but for mice retina. c Comparison of fluorescence signal intensity for different spectra filter both for humans and several mice models. d FLIM images along with phasor plot representations


Michał Dąbrowski, PhD

Sławomir Tomczewski, PhD

Agata Kotulska, PhD

Marcin J. Marzejon, PhD

Jakub Bogusławski, PhD

Prof. Maciej Wojtkowski


  1. G. Palczewska, J. Boguslawski, P. Stremplewski, Ł. Kornaszewski, J. Zhang, Z. Dong, X.-X. Liang, E. Gratton, A. Vogel, M. Wojtkowski, and K. Palczewski, Noninvasive two-photon optical biopsy of retinal fluorophores, Proc. Natl. Acad. Sci. U. S. A 117, 22532 (2020)
  2. D. Stachowiak, J. Bogusławski, A. Głuszek, Z. Łaszczych, M. Wojtkowski, and G. Soboń, “Frequency-doubled femtosecond Er-doped fiber laser for two-photon excited fluorescence imaging, Biomed. Opt. Express 11, 4431 (2020)
  3. J. Boguslawski, G. Palczewska, S. Tomczewski, J. Milkiewicz, P.Kasprzycki, D. Stachowiak, K. Komar, M. J. Marzejon, B. L. Sikorski, A. Hudzikowski, A. Głuszek, Z. Łaszczych, K. Karnowski, G. Soboń, K. Palczewski, and M. Wojtkowski, In vivo imaginh of the human eye using a 2-photon-excited fluorescence scanning laser ophthalmoscope, JCI 132, 154218 (2022)
  4. J. Bogusławski, S. Tomczewski, M. Dąbrowski, K. Komar, J. Milkiewicz, G. Palczewska, K. Palczewski, and M. Wojtkowski, In vivo imaging of the muna retina using a two-photon excited fluorescence ophthalmoscope, STAR Protocols 4, 102225 (2023)
  5. G. Palczewska, M. Wojtkowski, and K. Palczewski, From mouse to human: Accessing the biochemistry of vision in vivo by two-photon excitation, Prog. Retin. Eye Res. 93, 101170 (2023)

Two-photon vision

Vision allows for receiving stimuli from the surrounding world through electromagnetic waves from 400 to 780 nm, called visible light. It begins when a photon of such light is absorbed by the visual pigment of the photoreceptor in the light-sensitive part of the eye – the retina. Absorption of a photon initiates a series of biochemical reactions, as a result of which light is converted into an electrical signal, which is later processed in the brain.

Two-photon vision relies on the two-photon absorption occurring in visual pigments upon irradiation by ultrashort near-infrared lasers. The visual system reacts as if one photon of light is absorbed in the photoreceptors, while two photons of infrared radiation of twice the lower energy are absorbed. The observer perceives the stimulus as if it had a color corresponding to about half the excitation wavelength of the infrared laser beam.

Two-photon vision has several interesting properties different from “normal” one-photon vision. First, it occurs for a different spectral range: from about 800 nm to 1300 nm – for these wavelengths; the color impression changes from blue, green, yellow, and finally, red. Second, the brightness of a two-photon stimulus varies quadratically with the power of optical radiation, so light scattered in the eye will not be perceived. Brightness also depends on the beam’s focus on the observer’s retina. Observed stimuli have better contrast and sharpness than “normal” one-photon vision.

At the International Centre for Translational Eye Research, we study the phenomenon of two-photon vision – we discover its properties and describe them for the first time. We are also looking for applications of this phenomenon in medical diagnostics (e.g., two-photon microperimetry) and visualization systems (virtual retinal displays).

Two-photon microperimetry

The conventional approach to visual field testing is based on displaying visible stimuli at various locations on the patient’s retina and recording their response. Unfortunately, the accuracy and reproducibility of classical visual field testing methods are limited. Moreover, we cannot use it in cases of patients with opacities of the eye media (e.g., cataracts).

Two-photon microperimetry, a new diagnostic technique that uses pulsed infrared beams to stimulate the retina of the subject, may be the answer to these challenges. Such stimuli are perceived through the process of two-photon vision. The use of two-photon perception for visual field testing has several advantages. Unlike visible light, infrared radiation is less scattered on the opacities of the eye’s optical medium. In addition, two-photon vision is a nonlinear optical process, resulting in smaller spread of visual threshold values compared to classical microperimetry. This translates into better reproducibility of the visual field examination.

At the International Centre for Translational Eye Research, we are developing the technique of two-photon microperimetry, including studying the effects of different parameters of pulsed laser sources – wavelength, pulse length and repetition rate – on the efficiency of retinal stimulation.

Authors: Katarzyna Komar, PhD and Marcin Marzejon, PhD


Katarzyna Komar, PhD

Marcin Marzejon, PhD

Oliwia Kaczkoś, MSc

Agata Kotulska, PhD

Prof. Maciej Wojtkowski


  1. G. Palczewska, F. Vinberg, P. Stremplewski, M. P. Bircher, D. Salom, K. Komar, J. Zhang, M. Cascella, M. Wojtkowski, V. J. Kefalov, and K. Palczewski, “Human infrared vision is triggered by two-photon chromophore isomerization,” Proc. Natl. Acad. Sci. U. S. A. 111(50), E5445–E5454 (2014).
  2. D. Ruminski, G. Palczewska, M. Nowakowski, V. Kefalov, K. Komar, K. Palczewski, and M. Wojtkowski, “Two-photon microperimetry: sensitivity of human photoreceptors to infrared light,” Biomed. Opt. Express 10(9), 4551–4567 (2019).
  3. G. Łabuz, A. Rayamajhi, J. Usinger, K. Komar, P. Merz, R. Khoramnia, G. Palczewska, K. Palczewski, and G. U. Auffarth, “Clinical application of infrared-light microperimetry in the assessment of scotopic-eye sensitivity,” Transl. Vis. Sci. Technol. 9(8), 1–9 (2020).
  4. M. J. Marzejon, Ł. Kornaszewski, J. Bogusławski, P. Ciąćka, M. Martynow, G. Palczewska, S. Maćkowski, K. Palczewski, M. Wojtkowski, and K. Komar, “Two-photon microperimetry with picosecond pulses,” Biomed. Opt. Express 12(1), 462–479 (2021).
  5. M. Marzejon, Ł. Kornaszewski, M. Wojtkowski, and K. Komar, “Effects of laser pulse duration in two-photon vision threshold measurements,” in Ophthalmic Technologies XXXI, D. X. Hammer, K. M. Joos, and D. V Palanker, eds. (SPIE, 2021), 11623, pp. 74–79
  6. G. Łabuz, A. Rayamajhi, R. Khoramnia, G. Palczewska, K. Palczewski, A. Holschbach, and G. U. Auffarth, “The loss of infrared-light sensitivity of photoreceptor cells measured with two-photon excitation as an indicator of diabetic retinopathy: A pilot study,” Retina 41(6), 1302–1308 (2021).
  7. D. Stachowiak, M. Marzejon, J. Bogusławski, Z. Łaszczych, K. Komar, M. Wojtkowski, and G. Soboń, “Femtosecond Er-doped fiber laser source tunable from 872 to 1075 nm for two-photon vision studies in humans,” Biomed. Opt. Express 13(4), 1899–1911 (2022).
  8. A. Zielińska, P. Ciąćka, M. Szkulmowski, and K. Komar, “Pupillary Light Reflex Induced by Two-Photon Vision,” Investig. Opthalmology Vis. Sci. 62(15), 23 (2021).
  9. M. J. Marzejon, “Two-photon perimetry utilizing picosecond lasers,” Gdańsk University of Technology (2022).
  10. O. Kaczkoś, A. Zielińska, M. J. Marzejon, J. Solarz-Niesłuchowski, J. Pniewski, K. Komar, “Methods of determining the contrast sensitivity function for two-photon vision,” Proc. SPIE 12502, 1250215 (2022).
  11. G. Łabuz, A. Rayamajhi, K. Komar, R. Khoramnia, and G. U. Auffarth, “Infrared- and white-light retinal sensitivity in glaucomatous neuropathy,” Sci. Rep. 12(1), 1961 (2022).
  12. M. J. Marzejon, PhD thesis “Two-photon perimetry utilizing picosecond lasers”, Gdańsk University of Technology (2022).
  13. D. Stachowiak, M. Marzejon, J. Bogusławski, Z. Łaszczych, K. Komar, M. Wojtkowski, and G. Soboń, “Femtosecond Er-doped fiber laser source tunable from 872 to 1075 nm for two-photon vision studies in humans,” Biomed. Opt. Express 13(4), 1899–1911 (2022).
  14. M. J. Marzejon, Ł. Kornaszewski, M. Wojtkowski, and K. Komar, “Laser pulse train parameters determine the brightness of a two-photon stimulus”,  Biomed. Opt. Express 14(4), 2857-2872 (2023).


Multi-spot measurements of air-induced corneal deformations (IMCUSTOMEYE project)

The IMCUSTOMEYE project involves the cooperation of 10 partners, both academic and industrial, began in 2018. From day one, as a consortium, we have focused on developing new, non-invasive, imaging-based methods to change the paradigm in the diagnosis and treatment of various eye diseases.

POB group’s researchers, were tasked with constructing a compact, low-cost device to measure 3D dynamic corneal deformation of the human eye. As it is in life, and especially in physics, we had to make some compromises with respect to the prototype being constructed. Even if full three-dimensional imaging of a corneal deformation process lasting only 20 ms is possible, it would require considerable complication of the measurement system and generate unacceptable costs. We proposed an intermediate solution of simultaneous measurements at multiple points on the cornea, including the center of the cornea and 4 pairs of points placed opposite along 4 directions (horizontal, vertical and corresponding directions rotated by 45 degrees). This approach made it possible to prepare a prototype compact system to be placed in an eye clinic. In addition, we preliminarily verified the possibility of both further miniaturization of the system and the potential for a significant reduction in manufacturing costs.

Clinical prototype

Our clinical prototype has not only survived the 300+ kilometer trip to the clinic in Bydgoszcz, Poland, but has also measured more than 100 eyes to date. It is worth noting that the prototype has been prepared from the hardware and software side in such a way that it could be successfully operated by eye clinic staff.

To analyze the data, we extract temporal corneal deformation for each spot. The biomechanical asymmetry can be assessed by comparison of opposite spots. To provide more intuitive presentation of the results, we introduced “asymmetry vector” that can be plotted for any deformation parameter (e.g., displacements amplitudes, deformation area, deformation slopes). For each pair of opposite spots, we create a vector pointing towards spot with higher value of selected parameter with a magnitude given by the differences of values for both spots in pair.

Data analysis pipeline

Having vectors for all 4 pairs of spots we can calculate overall vector to show global effect. This approach was applied already to some of our early clinical data to show differences in biomechanical asymmetry between healthy and keratoconus corneas (presented here for displacement amplitude and area).

Early clinical results

Text: Dr. Karol Karnowski


Karol Karnowski, PhD

Jadwiga Milkiewicz, MSc

Angela Pachacz, Eng

Onur Cetinkaya, BEng

Rafał Pietruch, Eng

Andrea Curatolo, PhD

Prof. Maciej Wojtkowski


  1. D. Alonso-Caneiro, K. Karnowski, B. Kaluzny, A. Kowalczyk, and M. Wojtkowski, “Assessment of corneal dynamics with high-speed swept source Optical Coherence Tomography combined with an air puff system”, Optics Express, Vol. 19, Issue 15, pp. 14188-14199 (2011)
  2. S. Marcos, C. Dorronsoro, K. Karnowski, M. Wojtkowski, „Corneal biomechanics From Theory to Practice: OCT with air puff stimulus”, Kugler Publications 2016, edited by C.J. Roberts, J. Liu
  3. K. Karnowski, E. Maczynska, M. Nowakowski, B. Kaluzny, I. Grulkowski, M. Wojtkowski, “Impact of diurnal IOP variations on the dynamic corneal hysteresis measured with air-puff swept-source OCT”, Photonics Letters of Poland, (2018)
  4. 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”, J Biophotonics, 2019; 12:e201800154 (2019)
  5. A. Curatolo, J. S. Birkenfeld, E. Martinez-Enriquez, J. A. Germann, G. Muralidharan, J. Palací, D. Pascual, A. Eliasy, A. Abass, J. Solarski, K. Karnowski, Maciej Wojtkowski, Ahmed Elsheikh, and Susana Marcos, “Multi-meridian corneal imaging of air-puff induced deformation for improved detection of biomechanical abnormalities,” Biomed. Opt. Express 11, 6337-6355 (2020)

Spatio-Temporal Optical Coherence Tomography (STOC-T) imaging

Conventional scanning OCT combines time- with confocal gating enabling high-speed, high-resolution cross-sectional imaging of the human retina. Classic OCT, however, does not provide high-resolution en face images of the outer retinal layers due to eye aberrations and the fundamental tradeoff between imaging depth and transverse resolution.

This tradeoff is reduced by a full-field OCT (FF-OCT) method that uses a two-dimensional camera instead of a single-element photodiode. However, an attempt to boost the FF-OCT imaging speed by Fourier-domain (FD) detection resulted in another severe limitation – spatial coherence of the laser generates coherent artifacts, which reduces the spatial resolution and, as shown below, precludes visualization of deep retina layers.

To solve this problem, we developed a new way of controlling the optical phase called STOC (Spatio-Temporal Optical Coherence). Application of STOC to Fourier-domain full-field optical coherence tomography (FD-FF-OCT) is called STOC tomography (STOC-T) or STOC imaging and enabled obtaining in vivo high-resolution, volumetric images of human skin, retina, and cornea at unprecedented speeds.

In STOC imaging, we have extended FD-FF-OCT with a spatial phase modulator (SPM). The SPM dynamically modulates the phase of incident light by generating time-varying transverse mode (TEM) patterns. This is accomplished through the use of active modulators or long multimode optical fiber. The resulting signals are processed and averaged to produce noise-free volume images of the sample. Phase modulation acts here as an additional optical gating mechanism that isolates the signal used to create images. The result is improved images of the sample.

However, the en face images (XY projections) are distorted by eye or sample-induced aberrations. We overcome them in post-processing using the computational aberration correction (CAC). The CAC algorithm proceeds as sketched in the figure. Specifically, we iteratively (in the computer) correct the phase of the spatial spectrum until we optimize the image sharpness metric:

To achieve wide-field retina images, we perform measurements at different locations and then stitch resulting volumes together to render high-resolution, high-fidelity retinal images at different depths (indicated earlier). Specifically, we render the choroid, which was impossible with conventional Fourier-domain FF-OCT (without phase modulation).

Text: Dawid Borycki, PhD


Egidijus Auksorius

Dawid Borycki

Piotr Węgrzyn

Kamil Liżewski

Marta Mikuła – Zdańkowska

Sławomir Tomczewski

Maciej Wojtkowski


  1. M. Wojtkowski, P. Stremplewski, E. Auksorius, and D. Borycki, “Spatio-Temporal Optical Coherence Imaging – a new tool for in vivo microscopy,” Photonics Letters of Poland 11, 45-50 (2019). https://photonics.pl/PLP/index.php/letters/article/view/11-15
  2. Borycki, D. et al., Control of the optical field coherence by spatiotemporal light modulation, Opt. Lett., 2013 38(22): p. 4817-4820.
  3. Borycki, D., et al., Spatiotemporal optical coherence (STOC) manipulation suppresses coherent cross-talk in full-field swept-source optical coherence tomography. Biomed Opt Express, 2019. 10(4): p. 2032-2054.
  4. Stremplewski, P., et al., In vivo volumetric imaging by crosstalk-free full-field OCT. Optica, 2019. 6(5): p. 608-617.
  5. Auksorius, E., et al., Crosstalk-free volumetric in vivo imaging of a human retina with Fourier-domain full-field optical coherence tomography. Biomed Opt Express, 2019. 10(12): p. 6390-6407.
  6. Auksorius, E., et al., In vivo imaging of the human cornea with high-speed and high-resolution Fourier-domain full-field optical coherence tomography. Biomed Opt Express, 2020. 11(5): p. 2849-2865.
  7. Borycki, D., et al., Computational aberration correction in spatiotemporal optical coherence (STOC) imaging. Opt Lett, 2020. 45(6): p. 1293-1296.
  8. Egidijus Auksorius, Dawid Borycki, Maciej Wojtkowski, Multimode fiber enables control of spatial coherence in Fourier-domain full-field optical coherence tomography for in vivo corneal imaging, Opt Lett, 2021. 46(6): p. 1413-1416.
  9. Auksorius E., et al., Spatio-Temporal Optical Coherence Tomography provides advanced imaging of the human retina and choroid, arXiv preprint arXiv:2107.10672 (2021).
  10. Auksorius E., Fourier-domain full-field optical coherence tomography with real-time axial imaging, Opt Lett, 2021., Vol. 46(18): p. 4478-4481.
  11. Auksorius E., et al., Multimode fiber as a tool to reduce cross talk in Fourier-domain full-field optical coherence tomography. Opt Lett, 2022. 47(4): p. 838-841.
  12. Tomczewski S., et al., Light-adapted flicker optoretinograms captured with a spatio-temporal optical coherence-tomography (STOC-T) system. Biomed Opt Express, 2022 13(4): p. 2186-2201.
  13. Auksorius, E., et al., Spatio-temporal optical coherence tomography provides full thickness imaging of the chorioretinal complex. iScience, 2022 25(12) 105513.