WO2007073848A2

WO2007073848A2 - Device measuring eyes with the aid of dynamic light scattering

Info

Publication number: WO2007073848A2
Application number: PCT/EP2006/011836
Authority: WO
Inventors: Franz Fankhauser
Original assignee: Franz Fankhauser
Priority date: 2005-12-15
Filing date: 2006-12-08
Publication date: 2007-07-05
Also published as: WO2007073848A3

Abstract

Disclosed is a device (1) for measuring eyes with the aid of dynamic light scattering. Said device (1) comprises a radiation source (2) for producing scattered excitation light (3). A detection unit (29 to 32) is used for detecting scattered light (27) emitted by a scattering volume (12). An excitation beam path of the scattered excitation light (3) and a detection beam path of the scattered light (27) extend parallel to a common beam axis (28) in a beam path section (18, 20, 11, 12) adjoining the scattering volume (12). A detection extracting mirror (18) is provided for extracting the scattered light (27) from the excitation beam path. Said detection extracting mirror (18) is permeable to the scattered light (27) while being highly reflective to the scattered excitation light (3). The inventive eye measuring device allows scattered light to be more easily distinguished from the scattered excitation light.

Description

Eye measuring device with the help of dynamic light scattering

The invention relates to an eye measuring device with the aid of dynamic light scattering according to the preamble of claim 1.

Such an eye survey device is known from the habilitation thesis of F. Fankhauser "Dynamic Light Scattering in Ophthalmology", 2000.

In earlier work and historically, light scattering was used to determine the size and shape of dissolved macromolecules and properties of a large number of condensates, such As colloidal suspensions, gels and solid polymers to determine. Whenever light interacts with matter, the energy of the photons can change. Photon energy can be increased or decreased by translational, rotational, vibrational or electronic degrees of freedom of the molecules, whereby the resulting stray light experiences changes in frequency. These frequency changes, together with the angular distribution of the incident and scattered light, the polarization and the intensity of the scattered light correlate with the size, shape and intermolecular interactions of the scattering centers.

It is possible to make statements about the structure and dynamics of the scattering centers by measuring the scattering characteristics. In this section special attention is paid to the scattering resulting from translational and rotational molecular movements, the so-called Rayleigh scattering.

BESTÄTIGUNQSKOP1E The first scientific work on stray light probably goes back to Tyndall's 1869 work on aerosols. In 1871 Lord Rayleigh first came up with a theoretical explanation for observations of color and polarization of light scattered in the Earth's atmosphere. He showed that the blue color of the sky and the red sunsets alone are the result of preferential scattering of certain wavelengths by the gas molecules of the atmosphere. Rayleigh's law states that for non-interacting, non-absorbing, optically isotropic (uniformly distributed) particles - of a size substantially smaller than the wavelength of the light used - the intensity of the scattered light is reciprocal to the fourth power of the wavelength. Since then, the theory has been expanded and now covers the scattering properties of absorbing, optically anisotropic particles, which have a size comparable to the wavelength of the incident light (Mie scattering).

The progress of the light scattering theory mentioned so far mainly took into account the total intensity of the scattered light. The parallel development of dynamic light scattering was based on initial observations by Brillouin and Raman. The slow development in this field - despite the associated potential for quantifying the dynamic properties of condensates - is explained by the difficulty with the then existing technical means to detect the discrete wavelength changes at all. The first works of Raman go back to the late 40s. Only the introduction of lasers in the 1960s, which allowed investigations with almost monochromatic light, facilitated the detection of the expected small frequency changes. In 1964 Pecora showed in a theoretical work that scattered light from macroproteins in solution allowed conclusions to be drawn on the diffusion coefficients. The dynamic light scattering is based on the optical interference spectroscopy with the aim to detect small frequency changes in the scattered light. Similar techniques are used to receive radio signals in the frequency domain (heterodyne principle). The following points must be emphasized: The frequency of light results from the ratio of the speed of light and the wavelength (c = λ-v). Accordingly, light having the wavelength of 500 nm, a frequency of 6x10 ¹⁴ Hz. In the optical frequency domain, the bandwidth of the scattered light thus is approximately 500 Hz about 10 ^"12 the output frequency (-Wellenlänge). The measurement of frequency changes in this area would with optical filters, such as monochromators, not realizable and even using the best Fabry-Perot interferometers very difficult.

The first experimental studies of the DLS methodology were carried out independently of each other by two groups:

Cummins et al., Observation of diffusion broadening of Rayleigh scattered light. Phys Rev Lett, 1964. 12: p. 150-153, used heterodyne interference to analyze the scattered light resulting from the irradiation of a solution with polystyrene beads. Heterodyne optical interference means that both the scattered light and part of the non-scattered light interfere simultaneously on a sensor (photomultiplier).

The electrical output signal of the photomultiplier is then proportional to the interference frequency of the two beams. Heterodyne detection is now routinely used to improve properties such as Eg speed - A -

a steady flow, z. In a sample. Doppler velocity measurement is an example of heterodyne detection, whereby the frequency changes that result from the Doppler effect in the scattered light of moving particles are analyzed.

Ford and Benedek, Observation of the spectrum of light scattered from a pure fluid near its critical point. Phys Rev Lett, 1965. 15: p. 649-653, first used the principle of homodyne interference, also known as self-interference or optical mixing. Homodyne detection measures the diffusion motion of molecules caused by the randomized Brownian motion. In this case, the scattered light on the detector interferes with itself and the output of the photomultiplier contains information about the modulation of the optical field by the movement of the molecular scattering centers. The resulting variation of the time-dependent frequency of the output signal is in turn proportional to the frequency difference of closely adjacent optical frequencies.

These much smaller frequencies can be electronically filtered and measured in a relatively simple manner.

For the quality of the measurement result of a generic eye measuring device, the discrimination of the excitation light relative to the scattered light is relevant.

It is therefore an object of the present invention to further develop an eye measuring device of the type mentioned at the beginning in such a way that the scattered light can be better discriminated against the scattered excitation light. This object is achieved by a device having the features specified in claim 1.

According to the invention, it has been recognized that a detection coupling-out mirror, which is embodied transmissively for the scattered light and reflective for the excitation light, offers the possibility of significantly improved discrimination between scattered light and excitation light. The excitation light is coupled via a reflection at the detection output mirror in the common beam axis of excitation light and scattered light. In this reflection, excitation light, which runs undesirably exactly along the path of the scattered light to be detected, is transmitted by the detection outcoupling mirror, thus it is thus not coupled into the common beam axis. Only scattered light can then run along the path of the scattered light to be detected, so that it is suppressed highly efficiently with respect to the excitation light. Compared to the beam guides described in the prior art, this leads to a qualitatively much improved and thus more meaningful measurement signal of the dynamic light scattering.

An antireflection coating according to claim 2 improves the maximum scattered light signal. In addition, such an antireflection layer improves the suppression of excitation light traveling on the scattered light path during the reflection at the detection outcoupling mirror. It is preferred if both sides of the detection coupling-out mirror carry an antireflection coating.

An excitation light selection mirror according to claim 3 can be designed with a coating equivalent to the coating of the detection coupling-out mirror. This reduces the effort in the production of Eye-measuring device, since the detection coupling-out mirror and the excitation light selection mirror can be used from the same coating batch.

A hollow beam according to claim 4 allows a highly efficient excitation, which is adapted to the optical geometry of the eye.

An annular reflective coating according to claim 5 enables a defined and efficient generation of the hollow beam. To avoid diffraction effects, the annular reflection coating of at least one of the mirrors which generate the hollow beam can be designed with a non-sharp-edged transition between the highly reflective ring and the transversive central area.

Beam angle according to claim 6 allow a survey also rearward regions of the eye, in particular the retina. A beam angle of 4.6 ° is preferred.

Scattering volumes according to claim 7 allow a good compromise between see the criticality of the adjustment and the maximum achievable scatter signal.

Embodiments of the invention will be explained in more detail with reference to the drawing. In this show:

1 shows schematically the beam guidance within an apparatus for eye measurement with the aid of dynamic light scattering; Fig. 2 shows the intensity course of the beam direction containing

Longitudinal section through a hollow excitation light beam, which is used in the apparatus of Figure 1;

FIG. 3 schematically shows the beam path of the excitation light beam and of a scattered light beam emanating from a scattering volume when the device according to FIG. 1 is used; FIG.

4 shows an example of a correlation function of the scattered light measured with the device according to FIG. 1; and

5, in a representation similar to FIG. 3, shows the beam path of excitation light and scattered light in a further embodiment of an eye measuring device with the aid of dynamic light scattering.

Fig. 1 shows schematically the beam path within a generally designated 1 device for eye measurement using dynamic light scattering. As a radiation source 2 for generating scattering excitation light 3 is a helium-neon laser. The emission from this first passes through a filter 4 and is then coupled via a laser-fiber coupler 5 in a monomode fiber 6. An entrance surface of the mono-mode fiber 6 is ground by 6 °, so that disturbing back reflections in the radiation source 2 are prevented. The monomode fiber 6 forces a Gaussian bundle cross-section of the scatter excitation light 3 after the exit of this from the monomode fiber 6 and a downstream collimator 7 with a focal length of 6.2 mm. After the collimator 7, the scattered excitation light 3 is reflected by a mirror 8 which is coated in an annular manner for the scattered excitation light 3 in the region of the annular coating and thus deflected by 90 °. After the reflection at the annular layer of the mirror 8, the scattered excitation light 3 is thus present as a hollow bundle 9. The transmitted by the mirror 8 central portion 10 of the scatter excitation light 3 is blocked in a defined manner. The mirror 8 represents an excitation light selection mirror for selectively separating the scattered excitation light 3 used for the measurement, that is to say the hollow bundle 9, from other excitation light, that is to say from the fraction 10.

In a longitudinal section containing the beam direction of the hollow bundle 9, the hollow bundle 9 has an intensity distribution shown in FIG. The x-scale in mm refers to a hollow bundle section which lies 88 mm behind the center of a focusing lens 1 1, which in its function is still to be described, in front of a scattering volume 12. Shown in FIG. 2 is an intensity measurement curve 13 I = f (x), measured transversely to the beam direction of the hollow bundle 9, together with a step function 14 idealizing the intensity profile and a Gaussian distribution 15. A slight increase in intensity 16, which does not apply to the light scattering measurements is distracting caused by diffraction at the coating edges of the reflective coating of the mirror 8. This diffraction effect can be reduced if instead of a level of reflectivity on the mirror 8 a gentler, z. B. continuous, reflectivity transition between the reflective ring coating and surrounded by this central, transmissive region is selected.

After reflection on the mirror 8, the hollow bundle 9 is parallelized by a further lens 17 with a focal length of 120 mm. After the other lens 17, the hollow beam 9 is reflected by a detection output mirror 18. The detection outcoupling mirror 18 is coated in a highly reflective manner in the same way as the mirror 8 in the region of the impinging hollow bundle 9. In the central area surrounded by this reflective coating, the detection output mirror 18 is highly transmissive to the scattered excitation light. Excitation light components 19 in the region of the intensity increase 16 produced by diffraction are therefore transmitted by the detection output mirror 18 and are subsequently blocked in a defined manner.

After the reflection at the detection output mirror 18, the hollow beam 9 is deflected by a deflection mirror 20 and subsequently focused by means of the focusing lens 11 with focal length f = 105 mm into the scattering volume 12. About the deflection mirror 20, the coupling of an observation microscope microscope with observation direction 20a is possible. The scattering volume 12 lies in a retina 21 of an eye 22 to be measured, as shown in FIG. Depending on the distance of the eye 22 from the focusing lens 11 and depending on the focal length of the focusing lens 11 used, the scattering volume 12 at other positions of the eye 22 gene gene, z. B. preretinal, posterior to a vitreous humor 23 of the eye, in the center of the vitreous body 23, posterior to an eye lens 24, in the center of the eye lens 24, anterior to the lens 24, in the middle of an anterior chamber 25 or in the region of a cornea 26 of the An angle α _s in air in front of the scattering volume 12 of the hollow bundle 9 to the beam axis 28, ie to the central excitation beam path, is 4.6 ° in the beam path for scattering at the scattering volume 12 in the retina 21. Other angles between 2 ° and 8 ° are possible, depending on the position of the scattering volume to be measured in the eye 22. The scattering volume 12 has a size of 640 μm ³ in air. Other sizes between 50 and 800 microns ³ are possible.

In the scattering volume 12, scattered light 27 is generated by dynamic light scattering. The latter is only shown in the drawing, as far as it is actually detected with the eye-measuring device 1. In fact, the scattered light 27 is radiated in many spatial directions. The scattered light 27 leaves the eye through the eye lens 24 and the cornea 26 and passes through the focusing lens 11 centrally. Subsequently, the scattered light 27 is deflected in the deflection mirror 20 and subsequently passes through the detection output mirror 18. The detection output coupling mirror 18 has an anti-reflection layer for the scattered light 27 centrally.

Between the detection output mirror 18 and the scattering volume 12, an excitation beam path of the scatter excitation light 3 and a detection beam path of the scattered light 27 extend along or parallel to a common beam axis 28. In this beam path section between the detection output mirror 18 and the scattering volume 12, the beams of the scattered excitation light 3 and the scattered light 27 are spaced apart from each other.

After passing through the detection output mirror 18, the scattered light 27 is coupled via a collimator 29 into a detection monomode fiber 30. The collimator 29 has a focal length of 20 mm.

After passing through the detection monomode fiber 30, the scattered light 27 is directed onto a single-photon avalanche diode (SPAD) 31. The latter has an internally stabilized high voltage supply and a dead time of 30 ns. The measurement signal received by the SPAD 31 is from a digital correlator 32 according to the multiple-tau schemes known from the technical article by K. Schätzel "Noise in photon correlation data: I. Autocorrelation functions", Quantum Opt. 1990, 2: 287-305 A correlation curve g ₂ (τ) obtained as a function of a correlation delay time τ is shown as measurement curve 33 in FIG. 4. Between the delay times τ i and τ _2, for example at τ _m This drop as well as other temporal details of measured correlation curves are characteristic of size distributions and compositions of the dynamic scattering objects in the scattering volume 12. scattering particles which play a significant role for the measurement curve 33 in the dynamic light scattering in the eye, are, for example, hemoglobin and melanin pigments, therefore the information can be obtained from the measurement curve 33 whether the measured litter volume 12 is in a normal, healthy or diseased state.

Basically, the following procedure is used to diagnose an eye disease:

First, the correlation signal g ₂ (τ) of the scattered beam at a certain delay time, z. B. at the time τ _m , determined, with a measuring scattering volume 12 is measured.

Subsequently, z. B. by displacement of the eye or by appropriate adjustment of the beam axis 28, the scattering volume 12 to be measured shifted towards a reference scattering volume spaced therefrom within the eye. The reference scattering volume is chosen so that there with sufficient certainty healthy eye tissue is present. The reference litter volume may also be in the other, healthy eye of a patient. Now again the correlation signal g ₂ (τ) is determined at the same delay time τ _m . Since τ _{m is} in a range that is sensitive to an anomaly of the eye, the two correlation signals are different if there is diseased eye tissue in the measured scattering volume.

Now the difference of the two correlation signals is formed. This difference is then significantly different from 0 if diseased ocular tissue is present in the measured scattering volume. This can be determined by evaluating the difference value, wherein an eye disease is then reported as soon as the difference absolute value is above a predetermined threshold.

Sensitivity refers to the ability of the dynamic light scattering on the eye to recognize a disease correctly, ie to respond positively to an actual anomaly of the eye. Selectivity refers to the ability of the measurement to actually identify healthy patients as healthy, ie to reject them positively in healthy patients. If an absolute threshold value of 0.05 is chosen for the difference between the correlation signals g ₂ (τ _m ), measured on the measured scattering volume and on the reference scattering volume, the sensitivity of the diagnostic method is 78%. The selectivity of the diagnostic procedure is then 72%.

One such sensitive eye anomaly is age-related macular degeneration (AMD). This can be diagnosed especially at a very early stage. In particular, it is significant for AMD that in the case of dynamic light scattering measurements on the central retina on the one hand and on the peripheral retina on the other hand, there is a clear difference in the measured curve at τ _m in the healthy eye, whereas this difference is smaller or even completely absent from an AMD-containing measured eye is missing.

The eye measurement device 1 can be used for dynamic light scattering both in vitro and in vivo.

5 shows a variant of the beam guidance in a further embodiment of an eye measurement device. Components and reference quantities which correspond to those which have already been explained above with reference to FIGS. 1 to 4 bear the same reference numerals and will not be discussed again in detail.

In the beam guide according to FIG. 5, the scattered excitation light 3 is not provided in the form of a hollow beam but in the form of an excitation light beam guided parallel to the beam axis 28 in front of the focusing lens 11. The distance of the beam path of the scattered excitation light 3 from the beam axis 28, along which the scattered light 27 passes, is as large as the radius of the hollow beam 9 in the beam guidance according to FIGS. 1 to 4.

Claims

claims

1. Device (1) for eye measurement with the aid of dynamic light scattering - with a radiation source (2) for generating scattered light

Excitation light (3) having a detection device (29 to 32) for detecting scattered light (27) emanating from a scattering volume (12), an excitation beam path of the scatter excitation light (3) and a detection beam path of the scattered light (27) in a

Scattering volume (12) adjacent beam path portion (18, 20, 11, 12) parallel to a common beam axis (28), wherein a detection Auskoppelspiegel (18) for coupling out the scattered light (27) is provided from the excitation beam path, characterized in that the detection outcoupling mirror (18) is designed to be transparent to the scattered light (27) and highly reflective to the scattered excitation light (3).

2. Apparatus according to claim 1, characterized in that the detection Auskoppelspiegel (18) in particular on both sides of an anti-reflection layer for the scattered light (27).

3. Apparatus according to claim 1 or 2, characterized by a

Excitation light selection mirror (8) for selectively separating the scattered excitation light (9) used for the measurement from the other excitation light (10), wherein the scattered excitation light (9) used for the measurement is reflected by the excitation light selection mirror (8).

4. Device according to one of claims 1 to 3, characterized in that the scattered excitation light (3) in the form of a hollow beam (9) is provided.

5. Device according to claim 4, characterized in that the detection-outcoupling mirror (18) and, if present, also the excitation light-detection mirror (10) has an annular reflection coating.

6. Device according to one of claims 1 to 5, characterized by a guide of scattered excitation light (3) and scattered light (27) such that in air before the scattering volume (12) the particular hollow scatter excitation light (3, 9) for Detection beam path (27, 28) occupies an angle (α _s ) between 2 ° and 8 °.

7. Device according to one of claims 1 to 6, characterized by a guide of scattered excitation light (3) and scattered light (27) such that the scattering volume (12) in air has a size between 50 and 800 microns ³ .