Presbyopia is an age related effect which affects every human at the age of about 40 years. So far reading glasses
are the conventional treatment. According to Helmholtz' theory of accommodation one of the mayor reasons for
the development of presbyopia is the increasing sclerosis of the lens. In contrast to that the ciliary muscle and
the lens capsule remain mostly active and elastic the whole life. So a possible treatment could be the increase of
the flexibility of the lens by creating gliding planes with fs-laser pulses inside the lens tissue.
In former studies it was shown that fs-laser pulses were able to increase the flexibility of ex vivo porcine lenses
as well as ex vivo human donor lenses. Our current aim was to evaluate the effect of the fs-laser pulses on the
crystalline lens of living rabbit eyes due to the fs-lentotomy treatment. The main focus of the evaluation was
the exclusion of possible side effects of the treatment like cataract formation or retina damage. The treated eyes
were monitored using optical coherence tomography (OCT) and Scheimpflug imaging for localizing and studying
the tissue effects of the incisions. Furthermore histological sections of the lens and retina were prepared. The
rabbits were investigated pre operatively and up to six months post operatively.
The fs-laser induced micro incisions were successfully applied to the left lens of each rabbit. The micro
incisions within the crystalline lens were detectable with OCT and Scheimpflug imaging up to six month. The
imaging within the lens showed a progressive fading of the incisional opacities generated by the femtosecond
laser during the six months and no indication of cataract formation was found. OCT and Scheimpflug images
emphasize themselves as necessary tools to monitor the micro incisions over time. Histopathological sections of
the lens tissue support the findings of the non invasive imaging techniques. Also the histopathological sections
of the retina show no thermal induced change due to the irradiation of the fs-pulses.
Up to now reading glasses are the conventional treatment of presbyopia, an age related effect for every human.
According to the Helmholtz theory the reason for the development of accommodative loss is a decreasing elasticity
of the lens due to the increasing sclerosis. Since the ciliary muscle and the lens capsule remain active and elastic
the whole life, a possible treatment could be the increase of the flexibility by creating gliding planes with fs-laser
flexibility of ex vivo porcine as well
as human donor lenses with a laboratory laser system. We will present new results with a compact 100 kHz
repetition rate turn key laser system which speeds up the treatment time by a factor of 10. This will offer the
opportunity for future clinical trials. Furthermore first in-vivo results on rabbits are presented.
According to Helmholtz' theory of accommodation one of the mayor reasons for the development of presbyopia is
the increasing sclerosis of the lens. One concept to overcome this hardening of the lens is to regain its flexibility
by inducing gliding planes inside the lens. Femtosecond laser pulses are a suitable tool for this treatment.
Showing in former work that we could increase the flexibility of enucleated porcine (ex vivo) lenses up to 25%,
we focused our recent work on human autopsy lenses. The age of the human donors ranged between 20 and
70 years. For an evaluation of the gain in flexibility the lens' thickness was measured undertaking the Fisher's
spinning test before and after laser treatment. Depending on the age and the quality of applied cutting pattern
the lens thickness increased after treatment up to 0.4 mm leading to an theoretical increase of several dioptres
of optical power. The flexibility could be increased up to 70 % compared to the measurements before treatment.
Since the age of the human donors had a broad range, leading to different degrees of lens hardening, the variance
of the measured flexibility changes was up to 30%. An addition the influence of the laser treatment onto the lens
on the accommodation amplitude will be shown in a three dimensional finite-element simulation.
Presbyopia is one age related effect every human is suffering beginning at the age of about 45 years. Reading
glasses are the conventional treatment so far. According to the Helmholtz theory the loss of accommodation in
age is due to the hardening and the resulting loss of elasticity of the crystalline lens. However the ciliary muscle
and the lens capsule stay active, respectively. Therefore a possible treatment concept is to regain the flexibility
by inducing gliding planes in form of microcuts inside the lens. The increase of flexibility in young porcine lenses
by different cutting patterns was shown by Ripken et al.1, 2 who verified the increase in flexibility by the spinning
test introduced by Fisher.3
We will present our first measurements of flexibility increase of human donor lenses. Furthermore the influence
of the laser cuts into the lens on the accommodation amplitude will be shown in a three dimensional finite-element simulation.
The most probable reason for presbyopia is an age related loss of elasticity of the lens. It progresses typically during the whole life and at the age of about 45 it leads to a considerable loss of the ability to accommodate within the next decade. However, both, the ciliary muscle and the lens capsule stay active and elastic, respectively. With respect to this, one concept is to regain the deformability of the lens without changing the capsule or zonular apparatus. Since the investigations of Ripken et al. proofed that the flexibility of the presbyopic lens tissue can be increased through the creation of fs-laser induced microcuts inside the lens, this is one possible approach to treat presbyopia. On this account a finite-element-method model with ANSYS of the human lens during accommodation will be presented. The analysis premises all lens materials to be linear elastic and allow large displacements. A first analysis of this method for the treatment of presbyopia is accomplished. Therefore the mechanical analysis of untreated and treated lens are compared. In addition ex-vivo elasticity measurements of untreated and treated lenses will be presented. As a result an improvement of the flexibility of the lens tissue is found and as its consequence a change of the lens radii of curvature is established. After suitable processing of the output data the change in optical power between untreated and treated lenses are calculated. The finite element simulation shows similar behaviour compared to the treated porcine lenses.
According to Helmholtz' theory of accommodation one of the mayor reasons for the development of presbyopia is the increasing sclerosis of the lens. One concept to delay the process of sclerosis or even regain the deformation ability of the lens might be the treatment of the lens by femtosecond laser pulses. Our aim was to evaluate appropriate laser parameters for this possible treatment and to analyse potential changes in deformation ability of the treated lenses. We performed different cutting patterns in enucleated pig lenses (ex vivo) using the disruptive effect of an ultrafast near-infrared laser induced optical breakdown. Pulse energies and spot separation of the laser pulses were varied to investigate the effect on the generated cut. For an evaluation of the gain in deformation ability the lenses were rotated before and after treatment and the changes in lens thickness due to centrifugal forces were measured. In result, a smooth cutting was possible with appropriate parameters. The experiments showed an increase of elasticity in 70% of the eyes. When the lenses were treated more statistically, an average deformation ability increase of nearly 20%, determined by the change of thickness between untreated and treated lens, was measured.
The most probable reason for presbyopia is an age-related loss of
the elasticity of the lens. It develops through the whole life,
but is first noticeable typically at the age of about 45. From that on it leads within 15 years to a total loss of the accommodation ability. However, both, the ciliary muscle and the lens capsule
stay active and elastic, respectively. With respect to this, a
possible treatment conception is to increase or regain the elasticity. The possibility to increase elasticity with ps-laser induced cuts inside the lens was already shown by Krueger. We made an improvement in cutting quality while using a fs laser with 5~kHz repetition rate emitting in the near infrared. Different fs-laser-induced μm smooth cuts inside fresh enucleated ex-vivo pig lenses will be presented.
Ultrafast lasers are suitable for different surgical procedures in the eye: As a main goal in our group, the application of fs-lasers in refractive surgery is studied. Therefore,experiments in living rabbits were conducted, with wound healing studies up to 120 ays after surgery. Moreover,highly precise cuts inside the cornea were used to do keratoplasty an lamellar keratoplasty. Further applications like a new technique to overcome presbyopia are shown.
The most probable reason for presbyopia, the age-related loss of the
accomodation-ability of the eye, is an age-related loss of the elasticity of the lens. To increase the elasticity, resp. regain elasticity we performed different fs-laser-induced cuts with an near-infrared 5 kHz femtosecond laser inside ex-vivo and in-vivo rabbit lenses. Sagittal and annulus cutting patterns in the lens were produced by focusing the laser beam through the cornea inside the lens and creating a laser induced optical breakdown. The cutting results were recorded with light microscopy and finally, after euthanization, changes in the optical fibers of the lens tissue were described.
Laser induced ultrasound provides a powerful tool for solving a major problem of laser cyclophotocoagulation, which is caused by difficulties in localization and determination of optical properties. Furthermore it adds the possibility of an online control mechanism for the process of coagulation of the ciliary body. We have developed a transducer system which is based on a fiber with 600 micrometers core diameter surrounded by a ring shaped piezoelectric PVDF detector. With this detector it is possible to localize the lateral position of the ciliary body on enucleated pigs and rabbit eyes as well as its depth. Our findings correspond well with histological sections of the measured area. Additionally, the changes in the tissue's optical properties induced by coagulation with a diode laser have been detected in real time.
The optical properties of human skin in the UV-range are not exactly known. Furthermore, the precise wavelength dependency of important photobiological processes (such as induction of skin cancer) could not be settled yet, either. A better knowledge of the optical properties is necessary in order to achieve a better understanding of UV-induced effects on human skin. Optoacoustics is a new approach to investigate the wavelength dependent optical properties of human skin in the UV-range. This technique allows non-invasive measurements on human skin in vivo, that are indispensable to gain meaningful results concerning the processes induced by UV-radiation in the living tissue. First attempts at measuring UV-induced optoacoustic transients of human skin in vivo and tissue phantoms with a new detector are shown. For analysis, fitting of simulated data onto the experimental data is applied in order to improve the determination of optical properties. First measurements of wavelength dependent optical properties in the UVB-(280-315 nm) and UVA-II-range (290-330 nm) comparing stained artificial layers to human skin in vivo are presented.
For enhanced optoacoustic imaging in biomedical applications more than one-dimensional detection is required. Tomographic images comparable to ultrasound B-scans can be generated with linear arrays. This work presents a detection scheme for such an array based on piezoelectric films. Each single detector consists of a ring shaped active area with a diameter of less than one millimeter, which leads to a high lateral resolution. Because of the small dimensions of the systems it is suitable for applications with limited accessibility like ophthalmic or endoscopic use. The sensitivity of a single detector is close to 0.5 mV/bar. First measurements on layered tissue phantoms made of gelatine and absorbing films show the potential of such an array for depth profiling as well as for two-dimensional imaging of simple structures.
The feasibility of optoacoustic imaging was investigated for ophthalmologic application in the treatment of glaucoma. Difficulties in the treatment with laser cyclophotocoagulation are mainly due to uncertainties in the localization of the ciliary body. With laser optoacoustics it is possible to localize the position of the ciliary body on enucleated porcine and rabbit eyes. Additionally, the changes in the optical properties of the tissue induced by coagulation with a diode laser were observed.
In this work, we show the capability of laser optoacoustics to localize the position of the ciliary body on enucleated porcine and rabbit eyes. Our findings correspond well with histological sections of the measured area. Different wavelengths for an optoacoustical detection system in combination with laser cyclophotocoagulation have been compared taking grayscale images of the region of interest of rabbit and porcine eyes for various wavelengths in the NIR spectral range. Additionally, the changes in the optical properties of the tissue induced by coagulation with a diode laser were observed. First online measurements of the changes due to coagulation show that the method of laser optoacoustics is suitable for an online therapy control system.
In this work, the localization of the ciliary body region of porcine eyes with laser optoacoustics was realized. The principle of laser optoacoustics combines the advantages of ultrasound and optical tomography. The absorption of short laser pulses in the near infrared generates thermoelastic stress waves in the ciliary muscle and the underlying pigmented epithelial layers. These stress transients were detected at the surface of the sclera with piezoelectric transducers in order to analyze the structure. The optoacoustical measurements of the ciliary body region at different positions from the corneoscleral limbus were composed to a grayscale image, which could be qualitatively compared to histological sections of this region. In these images the pigmented layers can be localized. The influence of the detectional wavelength on the optoacoustical signal in the NIR between 750 and 1052 nm was investigated. Furthermore, changes in the optoacoustic signal due to coagulation with a diode laser using typical therapeutical parameters could be observed.
In this work, the feasibility of optoacoustic tomography to act as diagnostic tool in laser cyclophotocoagulation was investigated. The experiments were performed with enucleated porcine and rabbit-eyes. The absorption of short laser pulses in the wavelength range between 750 and 1000 nm generated thermoelastic stress waves in the ciliary muscle and the underlying pigmented epithelial layers. These stress transients were detected at the surface of the sclera with piezoelectric transducers in order to analyze the structure. Depths of the ciliary body could be determined at different distances from the corneoscleral limbus. Furthermore, changes in the optoacoustic signal due to coagulation with a diode laser using typical therapeutical parameters could be observed.
Pulsed photothermal radiometry (PPTR) is a contact free nondestructive method of material inspection. It also is a promising tool for in vivo tissue spectroscopy and on-line dosimetry. For this approach, one has to consider light scattering and thus a complicated signal interpretation. Different models of light propagation in scattering media are compared, such as Monte Carlo simulation (MCS) and various approaches of diffusion theory. Simulated PPTR signals with these calculations are compared. The validity of the different models in order to describe PPTR measurements correctly is discussed.