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Iomdina, E. N., Seliverstov, S., Sianosyan, A., Teplyakova, K., Rusova, A., & Goltsman, G. (2016). The prospects of using the radiation for the assessment of corneal and scleral hydration. In Acta Ophthalmol. (Vol. 94).
Abstract: Purpose
An adequate water balance (hydration extent) is one of the basic factors of normal eye function, including its external shells – the cornea and the sclera. THz systems creating images in reflected beams are likely to become ideal instruments of noninvasive testing of corneal and scleral hydration degree as THz radiation is highly sensitive to water content. The paper aims at studying the transmittance and reflectance spectra of the cornea and the sclera of rabbit and human eyes, as well as those of the whole rabbit eye, in the frequency range of 0.13–0.32 THz.
Methods
The experiments were carried out on 3 corneas and 3 rabbit scleras, 2 whole rabbit eyes, and 3 human healthy adult scleras using a specially developed THz system based on reliable and easy‐to‐use continuous wave sources: a backward‐wave oscillator and an avalanche transit‐time diode.
Results
The transmittance spectra of the cornea and the sclera and the dependence of the reflection coefficient of these tissues in THz range on water percentage content were determined. Comparison of the rabbit cornea hydrated from 73.2% to 76.3% concentration by mass demonstrated an approximately linear relationship between THz reflectivity and water concentration. The decrease of free water concentration by 1% leads to a drop of the reflectance coefficient by 13%. The parameters studied displayed noticeable differences between the sclera and the cornea of rabbits and between rabbit sclera and human sclera.
Conclusions
Preliminary results demonstrate that the proposed technique, based on continuous THz radiation, may be used to create a device for noninvasive testing of corneal and scleral hydration, which has good potential of wide‐scale practical application.
The work was supported by the Russian Foundation of Basic Research (grant No.15‐29‐03843)
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Tiulina, V., Iomdina, E., Goltsman, G., Seliverstov, S., Sianosyan, A., Teplyakova, K., et al. (2019). UVB promotes the initiation of uveitic inflammatory and changes in thehydration of the cornea in vivo (Vol. 9).
Abstract: Recently, active research has been conducted in the field of terahertz (THz) scanning of human tissues for noninvasive determination of their hydration level, which haves hown high diagnostic efficiency of this technology in various pathological conditions. Recently, we have developed a laboratory model of the facility for monitoring the state of the water balance of the cornea using THz scanning in vivo, which opens up the possibility of applying this approach in ophthalmology. The aim of the work wasto compare the results of the THz scan of the cornea with its clinical changes using the example of an experimental model of the UV induced keratouveitis. Anexperimental study, which included a comprehensive assessment of clinical changes in the cornea of rabbits during keratouveitis induction, revealed a decrease in the stability of the tear film, pathological changes in the corneal epithelium and stroma, as well as its anatomical and optical parameters. Comparison of data obtained in the THz scan of the cornea with tears production, optical coherence tomography and confocal microscopy showed their consistency in all observation periods, which allows us to conclude that the developed laboratory setup works and the feasibility of further research to promote the corneal hydration evaluation technology in clinical practice. Acknowledgements: Research was funded by the RSF, grant number 161500255.
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Seliverstov, S., Maslennikov, S., Ryabchun, S., Finkel, M., Klapwijk, T. M., Kaurova, N., et al. (2015). Fast and sensitive terahertz direct detector based on superconducting antenna-coupled hot electron bolometer. IEEE Trans. Appl. Supercond., 25(3), 2300304.
Abstract: We characterize superconducting antenna-coupled hot-electron bolometers for direct detection of terahertz radiation operating at a temperature of 9.0 K. The estimated value of responsivity obtained from lumped-element theory is strongly different from the measured one. A numerical calculation of the detector responsivity is developed, using the Euler method, applied to the system of heat balance equations written in recurrent form. This distributed element model takes into account the effect of nonuniform heating of the detector along its length and provides results that are in better agreement with the experiment. At a signal frequency of 2.5 THz, the measured value of the optical detector noise equivalent power is 2.0 × 10-13 W · Hz-0.5. The value of the bolometer time constant is 35 ps. The corresponding energy resolution is about 3 aJ. This detector has a sensitivity similar to that of the state-of-the-art sub-millimeter detectors operating at accessible cryogenic temperatures, but with a response time several orders of magnitude shorter.
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Shurakov, A., Seliverstov, S., Kaurova, N., Finkel, M., Voronov, B., & Goltsman, G. (2012). Input bandwidth of hot electron bolometer with spiral antenna. IEEE Trans. THz Sci. Technol., 2(4), 400–405.
Abstract: We report the results of our study of the input bandwidth of hot electron bolometers (HEB) embedded into the planar log-spiral antenna. The sensitive element is made of the ultrathin superconducting NbN film patterned as a bridge at the feed of the antenna. The contacts between the antenna and a sensitive element are made from in situ deposited gold (i.e., deposited over NbN film without breaking vacuum), which gives high quality contacts and makes the response of the HEB at higher frequencies less affected by the RF loss. An accurate experimental spectroscopic procedure is demonstrated that leads to the confirmation of the wide ( 8 THz) bandwidth in this antenna coupled device.
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Iomdina, E. N., Seliverstov, S. V., Teplyakova, K. O., Jani, E. V., Pozdniakova, V. V., Polyakova, O. N., et al. (2021). Terahertz scanning of the rabbit cornea with experimental UVB-induced damage: in vivo assessment of hydration and its verification. J. Biomed. Opt., 26(4).
Abstract: SIGNIFICANCE: Water content plays a vital role in the normally functioning visual system; even a minor disruption in the water balance may be harmful. Today, no direct method exists for corneal hydration assessment, while it could be instrumental in early diagnosis and control of a variety of eye diseases. The use of terahertz (THz) radiation, which is highly sensitive to water content, appears to be very promising. AIM: To find out how THz scanning parameters of corneal tissue measured by an experimental setup, specially developed for in vivo contactless estimations of corneal reflectivity coefficient (RC), are related to pathological changes in the cornea caused by B-band ultraviolet (UVB) exposure. APPROACH: The setup was tested on rabbit eyes in vivo. Prior to the course of UVB irradiation and 1, 5, and 30 days after it, a series of examinations of the corneal state was made. At the same time points, corneal hydration was assessed by measuring RC. RESULTS: The obtained data confirmed the negative impact of UVB irradiation course on the intensity of tear production and on the corneal thickness and optical parameters. A significant (1.8 times) increase in RC on the 5th day after the irradiation course, followed by a slight decrease on the 30th day after it was revealed. The RC increase measured 5 days after the UVB irradiation course generally corresponded to the increase (by a factor of 1.3) of tear production. RC increase occurred with the corneal edema, which was manifested by corneal thickening (by 18.2% in the middle area and 17.6% in corneal periphery) and an increased volume of corneal tissue (by 17.6%). CONCLUSIONS: Our results demonstrate that the proposed approach can be used for in vivo contactless estimation of the reflectivity of rabbit cornea in the THz range and, thereby, of cornea hydration.
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