Karsten Plamann

• PhD
• Professor (Full) at École Nationale Supérieure de Techniques Avancées

La cornée est la première des deux lentilles de l’oeil. La transparence de la cornée saine est due à sa structure très régulière qui peut être perturbée en présence de pathologies. Pour diagnostiquer la transparence cornéenne, nous avons développé des méthodes basées sur l’analyse d’images obtenues par tomographie par cohérence optique (OCT) qui pe...

While some optical properties of cornea like its stromal birefringence had been known since the early nineteenth century, theories explaining its transparency remained inconclusive until the publication of David Maurice' emblematic paper in 1957 Maurice made a model calculation of light scattering by a single collagen fibril as a “dielectric needle...

Corneal transparency is essential to provide a clear view into and out of the eye, yet clinical means to assess such transparency are extremely limited and usually involve a subjective grading of visible opacities by means of slit-lamp biomicroscopy. Here, we describe an automated algorithm allowing extraction of quantitative corneal transparency p...

PURPOSE: To develop an automated algorithm allowing extraction of quantitative corneal transparency parameters from clinical spectral-domain OCT images. To establish a representative dataset of normative transparency values from healthy corneas. METHODS: SD-OCT images of 83 normal corneas (ages 22-50 years) from a standard clinical device (RTVue-XR...

We present an automated data analysis procedure for clinical spectral-domain OCT, capable of correcting instrument-related hyperreflective artifacts, and its application to normal corneas. Quantitative parameters related to corneal transparency are extracted from 85 eyes.

To develop an automated algorithm for clinical spectral domain OCT (SD-OCT) images, capable of correcting hyperreflective artifacts associated with the instrumental configuration and the patient’s eye position. The automated pre-processing algorithm (Python Software Foundation, v2.7.4) developed standardizes raw images (flattening, segmentation, no...

We present an automated data analysis procedure for clinical SD-OCT images, capable of correcting hyperreflective artifacts due to the instrument. Quantitative parameters related to corneal transparency are extracted from n=85 normal corneas. ECBO 2021, paper EW1C.5.

Loss of corneal transparency, as occurs with various pathologies, infections, immune reactions, trauma, aging, and surgery, is a major cause of visual handicap worldwide. However, current means to assess corneal transparency are extremely limited and clinical and eye-bank practice usually involve a subjective and qualitative observation of opacitie...

We demonstrate the feasibility of deriving quantitative measures of corneal transparency from objective analysis of stromal light backscattering with full-field optical coherence tomography (FF-OCT), addressing an unmet need in ophthalmology.

We uncover the significance of a previously unappreciated structural feature in corneal stroma, important to its biomechanics. Vogt striae are a known clinical indicator of keratoconus, and consist of dark, vertical lines crossing the corneal depth. However we detected stromal striae in most corneas, not only keratoconus. We observed striae with mu...

PurposeSome forms of keratoplasty assisted by ultrashort-pulse lasers require performing laser cuts close to the endothelium, which requires the knowledge of “safe” values concerning incision depth and pulse energy preserving endothelial cell viability. Our study aims to determine the thresholds for cell death in porcine corneas exposed to ultrasho...

Assessment of stromal light backscattering with full-field optical coherence tomographic microscopy shows promise as objective means to quantify corneal transparency, addressing an unmet yet critical need in anterior segment ophthalmology.

Background: A study on the role of laser wavelength in keratoplasty assisted by ultrashort pulse lasers is presented. Material and methods: This article gives a summary of the principal physical mechanisms contributing to the transparency of healthy corneas and presents transparency measurements as well as laboratory experiments on tissue with l...

Hyperglycemia-induced fibrillar collagen formation in the Descemet’s membrane is highlighted in diabetic rat corneas by in vivo confocal microscopy, in vivo SHG microscopy and electron microscopy. Abnormalities are also observed in ex vivo human corneas.

We have determined the threshold radiant exposure for cell death in the endothelium of porcine cornea exposed to ultrashort laser pulses in the context of keratoplasty and the preparation of endothelial grafts. In this study, by progressively increasing the radiant threshold towards the higher values we have observed a decrease of living corneal en...

Purpose: To evaluate the influence of wavelength on penetration depth and quality of femtosecond laser corneal incisions in view of optimizing procedures in corneal surgery assisted by ultrashort pulse lasers. Methods: We performed penetrating and lamellar incisions on eye bank corneas using several ultrashort pulse laser sources. Several wavele...

An optical device for measuring the transmission and diffusion of a tissue of the front segment of an eye, includes: a light source; an optical collimation system for directing the collimated light beam towards a tissue of the front segment of an eye to be characterized; an optical mire placed on the optical path between the optical collimation sys...

This study aimed to highlight structural corneal changes in a model of type 2 diabetes, using in vivo corneal confocal microscopy (CCM). The abnormalities were also characterized by transmission electron microscopy (TEM) and second harmonic generation (SHG) microscopy in rat and human corneas. Goto-Kakizaki (GK) rats were observed at age 12 weeks (...

Background: Second Harmonic Generation (SHG) microscopy recently appeared as an efficient optical imaging technique to probe unstained collagen-rich tissues like cornea. Moreover, corneal remodeling occurs in many diseases and precise characterization requires overcoming the limitations of conventional techniques. In this work, we focus on diabete...

Ex vivo SHG microscopy from the posterior cornea of a diabetic rat. Frontal optical sections are recorded at increasing depth from the posterior stroma (striations all over the field of view) to the Descemet’s membrane (micrometer-sized deposits). Scale bar: 30 µm, field of view: 108×108 µm2, z-step: 0.5 µm. (AVI)

Ex vivo SHG microscopy from the posterior cornea of a diabetic rat: transverse numerical reconstructions. Scale bar: 30 µm, field of view: 108×30 µm2, y-step: 0.25 µm. (AVI)

Ex vivo SHG microscopy from the Descemet’s membrane of a diabetic human donor, 3D views: 90×90×13 µm3. (AVI)

Ex vivo SHG microscopy from the Descemet’s membrane of a diabetic rat, 3D views: 108×108×7 µm3. (AVI)

Ex vivo SHG microscopy from the posterior cornea of a diabetic human donor. Frontal optical sections are recorded at increasing depth from the posterior stroma (striations all over the field of view) to the Descemet’s membrane (micrometer-sized deposits). Scale bar: 30 µm, field of view: 90×90 µm2, z-step: 0.5 µm. (AVI)

We present an ultrahigh resolution spectral-domain optical coherence tomography imaging system using a broadband superluminescent diode light source emitting at a center wavelength of 1.3 μm. The light source consists of two spectrally shifted superluminescent diodes that are coupled together into a single mode fiber. The effective emission power s...

Glaucoma is a disease of the optic nerve that is usually associated with an increased internal pressure of the eye and can lead to a decreased vision and eventually blindness. It is the second leading cause of blindness worldwide with more than 80 million people affected and approximately 6 million blind. The standard clinical treatment for glaucom...

We present a first evaluation of the results of the NOUGAT project which has been funded by the French National Research Agency through the 2008 edition of its TecSan program. The objective of the project is to conceive and realise an innovative device for ocular surgery by ultrafast pulse laser for glaucoma surgery assisted by an in situ imaging s...

Femtosecond laser surgery in the volume of corneal tissue is typically performed wavelengths of about 1 mum, which gives excellent results on transparent corneas. However, the outcome is much worse in the case of oedematous or pathological corneas as the laser beam propagation is disturbed by optical scattering. Our studies suggest that this phenom...

p>The optical properties of the cornea have been a research subject of great interest for many years. Several early theories have been put forward to explain with more or less success the optical transparency of this tissue, but it was not until Maurice demonstrated in a very elegant way during the 50s that this optical transparency could be explai...

p>Femtosecond laser surgery in the volume of corneal tissue is typically performed wavelengths of about 1 µm, which gives excellent results on transparent corneas. However, the outcome is much worse in the case of oedematous or pathological corneas as the laser beam propagation is disturbed by optical scattering. Our studies suggest that this pheno...

In the last decade, femtosecond laser applications in the biology and medicine have largely developed. The ultrashort laser has proved to be a strongly accurate and selective cutting tool, by depositing energy in a very confined volume with minimum collateral effects.

The outcome of ultrashort pulse laser surgery of the cornea is strongly influenced by the light scattering properties of the tissue, for which little data are available. The purpose of the present study is to provide quantitative values for light scattering and its relation to the degree of edema. An experimental optical measuring setup based on co...

Purpose We realized an innovative device for ocular surgery by ultrafast pulse laser optimised for corneal grafting. Methods We constructed a demonstrator device that reproduces surgical conditions of corneal transplant. It is thus possible to realize with the help of an easy handling automatised interface all the kinds of already existing corneal...

The strongly localized interaction process of ultrashort laser pulses with tissue makes femtosecond lasers a powerful tool for eye surgery. These lasers are now routinely used in refractive surgery and other forms of surgery of the anterior segment of the eye. Several clinical laser systems also offer options for corneal grafting and the potential...

The use of ultrashort pulse lasers is current in refractive surgery and has recently been extended to corneal grafting (keratoplasty). When performing keratoplasty, however, permanent degradation of the optical properties of the patient's cornea compromises the penetration depth of the laser and the quality of the incisions, therefore causing unwan...

To evaluate the potential of third-harmonic generation (THG) microscopy combined with second-harmonic generation (SHG) and two-photon excited fluorescence (2PEF) microscopies for visualizing the microstructure of the human cornea and trabecular meshwork based on their intrinsic nonlinear properties. Fresh human corneal buttons and corneoscleral dis...

We present a first evaluation of the results of the GRECO project which aims to conceive and realise an innovative device for ocular surgery by ultrafast pulse laser optimised for corneal grafting.

In this study we present combined third-harmonic generation (THG) and second-harmonic generation (SHG) microscopy images of intact human corneas, and we analyze experimentally and theoretically the origin of the THG signal. Multiharmonic microscopy provides detailed images of the cornea microstructure over its entire thickness. A component of the T...

The purpose of this study was to evaluate the quality of femtosecond laser corneal trephination in eye bank eyes by histologic and ultrastructural investigation. We performed Z-shaped, tophat-shaped, and mushroom-shaped trephinations of swelled corneas from eye bank eyes using an Intralase FS60 system. The corneoscleral discs were fixed immediately...

Femtosecond laser surgery in the volume of corneal tissue is difficult in the case of oedematous or pathological corneas: in those corneas, the propagation of the laser beam is perturbed by the optical scattering. This phenomenon can be greatly reduced by using a better suited laser wavelength. A series of ex vivo surgical experiments has been cond...

The specular transmittance spectrum of human corneas is studied using a confocal geometry set-up. The comparison of the obtained spectrum with the total transmittance spectrum permits the determination of the stromal scattering spectrum of pathological corneas. The dependence of the scattering cross section on wavelength dependence is analyzed.

We present a femtosecond Optical Parametric Amplificator (OPA) which was conceived to perform surgical interventions on eyes using eye-safe wavelengths. It is pumped by a Ti: sapphire laser. An OPA scheme using consecutively beta-BaB2O4 (BBO) crystal and BiB3O6 (BiBO) provides the required behaviour. For the first stage, a type I BBO is used becaus...

Purpose:Femtosecond lasers are nowadays routinely used in corneal surgery, mainly in the context of refractive surgery. Some of the clinical systems also have options for corneal grafting. However, interventions in the depth of the tissue are difficult in the case of oedematous or otherwise pathological corneas. This difficulty principally arises f...

New, compact, and wavelength-optimized ultrashort-pulse laser systems may facilitate corneal grafting and enable new forms of glaucoma surgery.

To evaluate femtosecond laser interaction with the applanation lens during pre-programmed penetrating keratoplasty corneal cuts. Three different-shaped penetrating keratoplasty dissections were performed on edematous corneas from bank eyes using a clinical femtosecond laser system (Intralase FS60) with energies higher than 2 microJ, and the "depth...

Nowadays, femtosecond lasers are routinely used in refractive eye surgery. Until recently, commercialised clinical systems were exclusively based on ytterbium or neodymium-doped solid state lasers emitting sub-picosecond pulses at a wavelength of about 1 µm and repetition rates of a few 10 kHz. These systems use pulse energies in the µJ range and f...

Total arterial stiffness plays a contributory role throughout aging and in numerous cardiovascular diseases, including hypertension. Aortic stiffening is responsible for an increased characteristic impedance (ie, the impedance to the left ventricular pulsatile flow), thus increasing the forward pressure-wave amplitude that contributes to pulse pres...

The application of femtosecond lasers in corneal transplant surgery requires high pulse energies to compensate for the strong optical scattering in pathological corneas. However, excessive energies deteriorate the quality of the incisions. The aim of this study is to demonstrate the dependence of side effects on local radiant exposure, numerical ap...

We present a new optical microscope in which the light transmitted by a sample-scanned transmission confocal microscope is frequency-tripled by SiOx nanocrystallites in lieu of being transmitted by a confocal pinhole. This imaging technique offers an increased contrast and a high scattered light rejection. It is demonstrated that the contrast close...

But Les auteurs présentent les résultats d’études histologiques et ultrastructurales des effets du laser femtoseconde sur des cornées humaines. Matériels et Méthodes Nous utilisons un laser femtoseconde Nd : verre équipé d’un système CPA. La longueur d’onde est de 1 065 nm. La fréquence de tir est ajustable de 1 à 10 kHz avec une énergie maximale...

Les auteurs présentent une nouvelle méthode d'utiliser l'émission optique non linéaire engendrée dans le tissu cornéen par laser femtoseconde chirurgical pour des fins d'imagerie et de contrôle de l'intervention in situ.

Femtosecond lasers start to be routinely used in refractive eye surgery. Current research focuses on their application to glaucoma and cataract surgery as well as cornea transplant procedures. To avoid unwanted tissue damage during the surgical intervention it is of utmost importance to maintain a working energy just above the ablation threshold an...

Hypertension is defined as either an elevation of systolic blood pressure (SBP) to ≥ 140 mmHg and/or elevation of diastolic blood pressure (DBP) to ≥ 90 mmHg for adults. Hypertension is a frequent, age-related disorder and a major risk factor for stroke, coronary heart disease, heart failure and renal failure. The relation between BP and cardiovasc...

We present a multiphoton imaging system mounted on a microsurgery experimental set-up using a Nd:glass femtosecond laser. The system permits to induce laser incisions in human cornea and sclera and to perform nonlinear imaging during the intervention. The laser is a chirped pulse amplification (CPA) system with a regenerative amplifier delivering p...

We present a beam-shaping technique for two-photon excitation (TPE) fluorescence microscopy. We show that by inserting a properly designed three-ring pupil filter in the illumination beam of the microscope, the effective optical sectioning capacity of such a system improves so that the point spread function gets a quasi-spherical shape. Such an imp...

Purpose: The authors present ultrastructural and histologic studies of femtosecond laser incisions in human cornea. Methods: We use a CPA femtosecond laser designed to match current instrumentation for femtosecond surgery, i.e. a Nd:Glass femtosecond laser at a 1065 nm wavelength. The repetition rate is adjustable from 1 to 10 KHz, with maximum pul...

Purpose: The authors present a multiphoton microscope set–up mounted on a microsurgery experimental system using a Nd:glass femtosecond laser. The system allows for non–linear optical imaging before, during, and after the surgical intervention. Methods: The femtosecond laser is a CPA system with a regenerative amplifier delivering pulses at a wavel...

We present a multiphoton microscope using a Cr4 + :forsterite femtosecond laser with an emission wavelength of 1260 nm for the excitation of the multiphoton processes. This wavelength is well adapted to the "optical window" in biological tissues and permits to reach higher imaging depths than systems using more conventional titanium:sapphire laser...

The concept of parallel confocal microscopy with aperture de-correlation has been developed in order to reduce acquisition time and to increase light efficiency over conventional scanning confocal microscopy. It consists in simultaneously observing numerous confocal volumes of a specimen, in lieu of scanning one confocal spot over the region of int...

Diode-pumped fiber lasers emit today more than 30W of fundamental mode power. Due to their compact realization at low costs, they are attractive for portable high power laser Doppler anemometers (LDA). We present the state-of-the-art of fiber lasers with emphasis on Nd:glass fiber lasers with high power emission in the infrared and up-conversion fi...

Diode pumped fiber lasers are compact reliable light sources and achieve today over 30 W fundamental mode power. Hence, they are attractive for the realization of portable laser Doppler anemometer (LDA) systems with high optical power. We present the application of fiber lasers together with diffraction optics for the realization of a miniaturized...

Photothermal methods have turned out to be a very interesting way to carry out the study of complex materials such as functional ceramics (polycrystalline diamond - aluminium nitride -zirconia) whose thermal properties have to be determined at different spatial scales if one wants to optimize their thermal behaviour. Results at microscopic scales (...

We demonstrate a master-oscillator fiber power-amplifier system consisting of a diode-pumped monolithic nonplanar ring oscillator as the master oscillator and a Nd:glass double-clad fiber as the power amplifier. The system emits up to 5.5 W of single-frequency radiation at a wavelength of 1064 nm with an M 2 value of ∼ 1.1 . The optical emission sp...

Erosion and deposition at the vessel walls of the main chamber of JET were measured with long term samples during the whole operation period of the Mark I carbon divertor from April 1994 until March 1995. Assuming toroidal symmetry, about 70 g Ni+Cr+Fe was found to be eroded from the inner torus wall and about 55 g Be from the outer torus wall due...

We present a simple method for directional discrimination in laser Doppler anemometry (LDA) without using frequency shifting components. The measuring volume is imaged onto a twinned pair of receiving fibres, each of semi-circular cross section, which permit the separate detection of the leading and trailing part of the burst signal, thus revealing...

Summary form only given. We have realized a single frequency master oscillator fibre power amplifier system (MOFPA) with a diode pumped monolithic Nd:YAG nonplanar ring oscillator (NPRO) as master oscillator and a high power diode pumped 30 m long double clad Nd:glass fibre as power amplifier

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An ytterbium sensitised praseodymium-doped double-clad upconversion fibre laser pumped at 840 nm by a low brightness source is demonstrated. With a pump power of 3 W launched in the 25 μm pump core, a red output power of 440 mW at 635 nm is achieved

In recently published work our group has proposed a setup based on a diode-pumped double clad Nd:glass fiber laser for laser Doppler anemometry (LDA), which is very powerful as well as very compact. In the present contribution, we combine this system with a new simple method for directional discrimination that has several advantages in terms of sim...

Numerous applications in metrology, telecommunication, medicine and material processing require highly efficient and powerful yet reliable laser sources with excellent beam quality. In recent years, our group has focused on the development of rare earth doped glass fibre lasers pumped by commonly available near infrared laser diodes to provide lase...

Elastic Recoil Detection Analysis (ERDA) with primary ion beams having energies in the MeV/nucleon range allows the measurement of absolute concentrations and depth profiles especially of low Z elements in the surface layers of a solid. In the present work, we use simple mathematical relations for defining the optimal measurement geometry with resp...

We present a novel laser Doppler anemometer concept that combines a high portability and compactness with a high optical power. The LDA system is based on the application of a novel light source, a diode-pumped double-clad fiber laser. Besides the high fundamental mode power of currently up to 32 W, fiber lasers have several advantages, like the re...

It is of importance to characterize ceramics devoted to microelectronics applications such as polycristalline diamond, AIN and Al2O3 at various scales. Photothermal experiments will be shown as efficient experimental probes.

It is generally known that the microstructure of polycrystalline CVD diamond samples has a strong impact on their thermal properties. Despite the fact that nowadays layers can be deposited with macroscopic thermal conductivities or diffusivities rivalling those of type II natural diamonds, the samples are highly thermally inhomogeneous and sometime...

Following constant improvement in the synthesis methods of diamond in metastable conditions by chemical vapour deposition, it is nowadays possible to grow polycrystalline diamond with thermal conductivities of over 20 W K-1 cm-1. This gives rise to applications of this material in the thermal management of components in optronics and microelectroni...

A series of highly oriented and textured microwave CVD diamond films, where only the deposition time was varied, was deposited on silicon wafers in order to follow the evolution of the microstructure and defect content with film thickness. SEM, XRD, Raman spectroscopy, luminescence measurements, and ESR were applied to determine the microstructure...

The outstanding thermal conductivity of CVD diamond gives rise to many potential industrial applications, necessitating the availability of reliable, standardized, thermal measurement methods. Although, in general, these measurements are in agreement for traditional materials, for CVD diamond different measurement methods can yield significantly di...