WO2025114307A1

WO2025114307A1 - Confocal optical measurement apparatus and method of optically measuring a biomarker

Info

Publication number: WO2025114307A1
Application number: PCT/EP2024/083668
Authority: WO
Inventors: James Reynolds
Original assignee: Occuity Ltd
Current assignee: Occuity Ltd
Priority date: 2023-11-27
Filing date: 2024-11-26
Publication date: 2025-06-05
Anticipated expiration: 2026-05-27
Also published as: GB2635767A; GB202318067D0

Abstract

A confocal optical measurement apparatus (100) comprises a source of electromagnetic radiation (102) configured to emit electromagnetic radiation at an emission wavelength. The apparatus (100) also comprises a detector module (112) configured to receive electromagnetic radiation, and a dioptric optical system (138, 140) comprising a scannable intermediate optical element (138) and an achromatic objective (140), the scannable intermediate optical element (138) being disposed in an optical path between the detector module (112) and the achromatic objective (138). The apparatus (100) further comprises a multimode optical fibre (132) operably coupled between the detector module (112) and the dioptric optical system (138, 140).

Description

CONFOCAL OPTICAL MEASUREMENT APPARATUS AND METHOD OF OPTICALLY MEASURING A BIOMARKER

[0001] The present invention relates to a confocal optical measurement apparatus of the type that, for example, comprises an optical system having a scannable intermediate optical element. The present invention also relates to a method of optically measuring a biomarker, the method being of the type that, for example, scans a focus of an emitted beam of electromagnetic radiation through a region to be measured.

[0002] In the field of medical measurement devices, it is known to measure a metabolic parameter by analysing a property of an eye, for example a human eye. For example, blood glucose concentration in a patient can be measured by analysing the influence that the patient’s eye has on light propagating therethrough. In this example, the parameter is refraction of the light propagating through the aqueous humour of the eye.

[0003] Another biomarker relating to the metabolic condition known as diabetes mellitus (hereinafter referred to as “diabetes”), is the concentration of so-called Advanced Glycation End-products (AGEs) within a crystalline lens of the eye, which has been associated with diabetes and intermediate metabolic states between normal and diabetes (sometimes called prediabetes). In this regard, it has been discovered that the rate of increase of AGEs with age of a patient is greater in patients with diabetes than patients that are not metabolically deranged. It therefore follows that calculating an age-corrected AGE concentration can be indicative of a patient’s likelihood of being diabetic or pre-diabetic.

[0004] With particular reference to the lens of the eye, there is evidence that the distribution of AGEs within the lens varies with the depth of the lens. Indeed, it is known that the lens accretes cells over time and so it is expected that the concentration distribution of the AGEs with depth into the lens could indicate the progression of the metabolic disorder over time. Conversely, the concentration distribution of the AGEs in the lens could be indicative of the effect of any treatment or lifestyle changes on a patient becoming diabetic, and so it is desirable to be able to measure the change in concentration of AGEs with depth in the eye.

[0005] US patent no. 5,203,328 and US patent no. 6,088,606 describe dual-axis confocal optical systems for making measurements in respect of lens tissue within the eye. These systems excite a sample and detect from different axes, measuring intensity of backscatter and fluorescence at particular wavelengths. In the case of US 5,203,328, the system then determines whether a patient has diabetes and in the case of US 6,088,606 the system estimates the duration for which the patient has had diabetes. Whilst such optical systems minimise cross-talk well, the use of different axes is a fundamental flaw when striving to achieve high spatial resolution for measurements, because the different excitation and detection paths result in the measurements made being susceptible to errors caused by different optical aberrations within the eye. This is also true of US patent publication no. 2012/0203086 A1 , which also describes a dual-axis confocal measurement system employing a translatable system to make measurements, and a rotating filter mechanism to separate light at wavelengths associated with backscatter from light at wavelengths associated with fluorescence. The system is, like those of US 5,203,328 and US 6,088,606, sufficiently slow at making measurements that without a very reliable and accurate alignment subsystem, accuracy of measurements over a measurement period are inconsistent. Furthermore, the systems of US 5,203,328 and US 6,088,606 are unable to measure changes of AGEs with depth in lens tissue in the eye, because they possess insufficient spatial resolution.

[0006] Yu et al. (Journal of Biomedical Optics 1 (3), 280-288 (1996)) describes a system bearing similarities with the systems of US 5,203,328 and US 6,088,606 and appears to possess good spatial resolution. However, the system used by Yu et al. is bulky and power-hungry. It is also a dual-axis system and so is also prone to inaccuracies as a result of the different aberrations within the eye.

[0007] According to a first aspect of the present invention, there is provided a confocal optical measurement apparatus comprising: a source of electromagnetic radiation configured to emit electromagnetic radiation at an emission wavelength; a detector module configured to receive electromagnetic radiation; a dioptric optical system comprising a scannable intermediate optical element and an achromatic objective, the scannable intermediate optical element being disposed in an optical path between the detector module and the achromatic objective; and a multimode optical fibre operably coupled between the detector module and the dioptric optical system.

[0008] The scannable intermediate lens may be configured to scan, when in use, a focus of the electromagnetic radiation emitted by the source of electromagnetic radiation.

[0009] The detector module may comprise: a scatter detector; and a fluorescence detector.

[0010] The detector module may comprise a dichroic beamsplitter. The detector module may comprise a detector module housing having an input/output port, a scatter detector port for receiving the scatter detector and a fluorescence detector port for receiving the fluorescence detector. The dichroic beamsplitter may be disposed in the detector module housing and configured to separate the scatter detector port from the fluorescence detector port. A first optical filter may be disposed between the scatter detector port and the dichroic beamsplitter. A second optical filter may be disposed between the fluorescence detector port and the dichroic beam splitter.

[0011] The scatter detector may be configured to generate a first amplitude signal in response to first received electromagnetic radiation. The fluorescence detector may be configured to generate a second amplitude signal in response to second received electromagnetic radiation.

[0012] The scatter detector may be configured to detect the received electromagnetic radiation when a wavelength of the received electromagnetic radiation is substantially the same as the emission wavelength; and the fluorescence detector may be configured to detect the electromagnetic radiation when a wavelength of the received electromagnetic radiation is longer than the emission wavelength.

[0013] The detector module may comprise a scatter detector. The scatter detector may be configured to detect the received electromagnetic radiation when a wavelength of the received electromagnetic radiation is substantially the same as the emission wavelength.

[0014] The detector module may comprise a fluorescence detector. The fluorescence detector may be configured to detect the electromagnetic radiation when a wavelength of the received electromagnetic radiation is longer than the emission wavelength.

[0015] The achromatic objective may comprise a first doublet and a second doublet disposed opposite the first doublet.

[0016] The apparatus may further comprise: an optical circulator operably coupled to the source of electromagnetic radiation, the detector module and the scannable intermediate optical element.

[0017] The optical circulator may be a multimode optical circulator. The multimode optical fibre may couple the optical circulator to the dioptric optical system; the optical fibre may define a pinhole.

[0018] The apparatus may further comprise: a collimator disposed between the optical circulator and the scannable intermediate optical element.

[0019] The apparatus may further comprise: a housing; the housing may contain the source of electromagnetic radiation, the detector module, the dioptric optical system and the multimode fibre. The housing may be a handheld housing.

[0020] The housing may comprise a window configured to provide irradiative access to a region to be measured located at a substantially static target location external to the housing. [0021] The apparatus may further comprise: processing circuitry operably coupled to the detector module and configured to calculate selectively scatter and/or fluorescence.

[0022] The processing circuitry may be configured to calculate a function of fluorescence and scatter.

[0023] The scatter may be in respect of a reflection from a surface within an anterior chamber of the eye, for example a surface of a cornea of an eye, such as an anterior surface and/or a posterior surface of the cornea of the eye. The scatter in respect of the reflection from the surface within the anterior chamber of the eye may be employed to determine adequacy of alignment of the achromatic objective with an optical axis of the eye. In other examples, the reflection may be in respect of an anterior surface or posterior surface of the lens of the eye.

[0024] The function may be a ratio of fluorescence to scatter. The function may be a ratio of measured peak fluorescence to peak scatter in respect of the lens of the eye. The function may be a ratio of measured peak fluorescence to peak specular reflection by the cornea of the eye. The ratio may be a ratio of measured peak scatter in respect of the lens of the eye to peak specular reflection by the cornea of the eye.

[0025] The processing circuitry may be configured to record the first amplitude signal as a function of position of the scannable intermediate optical element. The processing circuitry may be configured to record the second amplitude signal as a function of position of the scannable intermediate optical element.

[0026] The processing circuitry may be operably coupled to the fluorescence detector and the scatter detector.

[0027] The processing circuitry may be configured to translate, when in use, the scannable intermediate optical element in order to scan a focus of the achromatic objective through a substantially static target region and to calculate a variation of the function with depth. [0028] The apparatus may further comprise: an optical system comprising the dioptric optical system and the multimode optical fibre; wherein the optical system may be a single-axis confocal optical system.

[0029] According to a second aspect of the present invention, there is provided a biomarker measurement apparatus for a lens of an eye, the apparatus comprising: the confocal optical measurement apparatus as set forth above in relation to the first aspect of the invention.

[0030] The biomarker may be an advanced glycation end-product.

[0031] The scannable intermediate optical element may be configured to scan, when in use, a focus through the eye.

[0032] According to a third aspect of the present invention, there is provided a method of optically measuring a metabolic parameter, the method comprising: launching a source beam of electromagnetic radiation at an emission wavelength into a first end of a multimode optical fibre, a second end of the multimode optical fibre constituting a pinhole; illuminating a region to be measured; receiving electromagnetic radiation from the region to be measured in response to illumination by the beam of electromagnetic radiation; confocally and achromatically collecting and launching the received electromagnetic radiation into the second end of the multimode optical fibre; measuring the received electromagnetic radiation; and calculating a measure of the metabolic parameter using the measured received electromagnetic radiation.

[0033] The method may further comprise: focussing the source beam of electromagnetic radiation exiting the second end of the multimode optical fibre, and scanning a focus of the focussed beam of electromagnetic radiation through a region to be measured.

[0034] It is thus possible to provide a confocal optical measurement apparatus that is sufficiently compact to enable provision in a hand-held housing. The apparatus and the method of optically measuring a biomarker can make measurements sufficiently rapidly for the measurements not to be influenced by movement of the eye, and with sufficient resolution in order to be able to measure changes of backscatter and/or fluorescence with depth of focus in, for example, the eye. The method and apparatus are non-contact and so also obviates or at least mitigates the need for drawing blood from a patient or performance of a biopsy.

[0035] At least one embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is schematic diagram of a confocal optical measurement apparatus constituting an embodiment of the invention;

Figure 2 is a schematic diagram of a part of the apparatus of Figure 1 in greater detail;

Figure 3 is a schematic diagram of a detector module of Figure 1 in greater detail; and

Figure 4 is a flow diagram of a method of optically measuring a biomarker constituting another embodiment of the invention.

[0036] Throughout the following description identical reference numerals will be used to identify like parts.

[0037] Referring to Figure 1 , a confocal optical measurement apparatus 100, for example for measuring a biomarker such as a metabolic parameter, comprises a source of electromagnetic radiation 102, for example a laser source such as a laser diode, operably coupled to a first port 104 of a multimode optical circulator 106 by a first connecting optical fibre 108. In this example, the first connecting optical fibre 108 has a diameter of about 50 m. An input/output port 110 of an optical detector module 112 is operably coupled to a second port 113 of the multimode optical circulator 106 by a second connecting optical fibre 114.

[0038] In this example, the optical detector module 112 comprises a detector module housing 116 having a first detector port 118 and a second detector port 120 disposed perpendicularly with respect to each other. A scatter detector 122, to detect backscatter, is sealingly fitted in the first detector port 118 and a fluorescence detector 124 is sealingly fitted in the second detector port 120. As a result of the relative positioning of the first and second detector ports 118, 120 in the detector module housing 116, sensing elements of the scatter detector 122 and the fluorescence detector 124, respectively, reside in planes perpendicular to each other.

[0039] The detector module housing 116 comprises a beamsplitter, for example a dichroic beamsplitter 126, arranged within the detector module housing 116 to reside between the first and second detector ports 118, 120 and thus between the scatter detector 122 and the fluorescence detector 124. However, in other embodiments, a multi-mode Wave Division Multiplexer (WDM) can be employed in place of the dichroic beamsplitter 126.

[0040] A third port 128 of the multimode optical circulator 106 is operably coupled to a collimator 130 by a third connecting optical fibre 132, a first end 134 of the third connecting optical fibre 132 being coupled to the third port 128 of the multimode optical circulator 106, and a second end 136 of the third connecting optical fibre 132 being coupled to the collimator 130 via an interfacing glass rod portion 135 to prevent back reflections, when in use. In this example, the diameter of the third connecting optical fibre 132 is about l OO ^z m, for example about 105 Az m. The second end 136 of the third connecting optical fibre 132 serves as a pinhole for the collimated optical measurement apparatus 100. The first, second and third optical fibres 108, 114, 132 are multimode optical fibres.

[0041] A scannable optical element, for example an intermediate optical element, such as a scannable lens 138 or lens system, carried by a linearly translatable carriage 137, for example as described in UK patent publication no. GB-A-2 607 286 (the content of which are incorporated herein in its entirety), is located opposite the collimator 130. Although not shown, the linearly translatable carriage 137 can comprise or be operably coupled to a position encoder in order to enable the position of the scannable lens 138 to be determined.

[0042] An objective 140, for example an objective optical system 140, is disposed opposite the scannable lens 138 so that the scannable lens 138 is disposed between the collimator 130 and the objective optical system 140. The scannable lens 138 is disposed to one side of the objective optical system 140 and a region to be measured 142 is located at an opposite side of the objective optical system 140.

[0043] Signal processing circuitry 144 is operably coupled to, inter alia, the source of electromagnetic radiation 102, the optical detector module 144 and the linear translatable carriage 137. The signal processing circuitry 144 can comprise control circuitry or such control circuitry can be provided separate to the digital processing circuitry. The control circuitry is operably coupled to the linearly translatable carriage 137.

[0044] The confocal optical measurement apparatus 100 comprises a device housing 146, which in this example is a handheld housing 146. The device housing 146 serves to contain the source of electromagnetic radiation 102, the multimode optical circulator 106, the optical detector module 112, the collimator 130, the scannable lens 138 and the linear translation carriage 137, the objective optical system 140, the signal processing circuitry 144, the optical fibres 108, 114, 132 and any other sundry components or elements to ensure functioning of the confocal optical apparatus 100, for example a power source, memory, and a display amongst other items.

[0045] The objective optical system 140 has a sample-facing side, the handheld housing 146 comprises an aperture 147. An end 149 of the objective optical system 140 on the sample-facing side is, in this example, sealingly fitted within and flush with the aperture 147 in order to close the aperture 147 and provides irradiative access to the region to be measured 142 for electromagnetic radiation emitted from within the handheld housing 146, and also for light emanating from the region to be measured 142 to optical components within the handheld housing 146. In this example, the region to be measured is substantially static and external to the handheld housing 146.

[0046] Referring to Figure 2, although not shown in Figure 1 , the collimator 130 and the scannable lens 138 are separated from the objective optical system 140 by a fold mirror 150 in order to facilitate compact arrangement of the parts of the optical system of the confocal optical measurement apparatus 100 within the device housing 146.

[0047] A free-space optical path 152 (dashed line) extends from the second end 136 of the third optical fibre 132 to the fold mirror 150 where the free-space optical path 152 folds and extends to the region to be measured 142 (not shown in Figure 2), which in this example overlaps a lens 154, such as a crystalline lens, in an eye 156. In this example, the objective optical system 140 is provided in the portion of the free-space optical path 152 between the fold mirror 150 and the lens 154 of the eye 156.

[0048] The objective optical system 140 is achromatic and comprises a doublet pair 158 disposed between a first plano-convex lens 160 and a second planoconvex lens 162. The doublet pair 158 comprises a first doublet 164 disposed opposite a second doublet 166. In this example, the lens 154 of the eye 156 is disposed in the region to be measured 142 shown in Figure 1 , opposite the second plano-convex lens 162. The combination of the first and second plano-convex lenses 160, 162 with the doublet pair 158 serves to make the objective optical system 140 an achromatic optical system.

[0049] The scannable lens 138 and the objective optical system 140 in combination constitute a dioptric optical system and so not comprise any reflective components. The dioptric optical system and the third connecting optical fibre 132 constitute a single-axis confocal optical system. [0050] Turning to Figure 3, as mentioned above, the detector module 112 comprises the scatter detector 122 and the fluorescence detector 124 respectively residing in planes perpendicular to each other, with the dichroic beamsplitter 126 disposed between the scatter detector 122 and the fluorescence detector 124.

[0051] Between the dichroic beamsplitter 126 and the scatter detector 122, the detector module 112 also comprises a first filter 168, a third plano-convex lens 170 and a first detector window 172 of the scatter detector 122. The first filter 168 is disposed opposite the dichroic beamsplitter 126 and the third plano-convex lens 170 is disposed between the first filters 168 and the first detector window 172 of the scatter detector 122. The first filter 168 is configured to accept electromagnetic radiation in a first range corresponding to backscattered electromagnetic radiation but not electromagnetic radiation generated through fluorescence.

[0052] Between the dichroic beamsplitter 126 and the fluorescence detector 124, the detector module 112 also comprises a second filter 174, a fourth plano-convex lens 176 and a second detector window 178 of the fluorescence detector 124. The second filter 174 is disposed opposite the dichroic beamsplitter 126 and the fourth plano-convex lens 176 is disposed between the second filter 174 and the second detector window 178 of the fluorescence detector 124. The second filter 174 is configured to accept electromagnetic radiation in a second range of wavelengths corresponding to electromagnetic radiation generated through fluorescence, but not backscattered electromagnetic radiation.

[0053] A fifth plano-convex lens 180 is disposed between the input/output port 110 of the detector module 112 and the dichroic beamsplitter 126. It should be appreciated that although in this example plano-convex lenses are provided in the detector module 112, other types of optical element can be employed, for example different kinds of lenses.

[0054] In operation (Figure 4), the source of electromagnetic radiation 102 is powered up (Step 200) and the confocal optical measurement apparatus 100 is placed opposite a tissue to be scanned, for example the lens 154 of the eye 156, so that the tissue is within a scanning range of the confocal optical measurement apparatus 100, for example by holding the housing 146 to the eye of a patient and positioned the confocal measurement apparatus 100 adequately using, for example any suitable alignment system, for example as described in UK patent application no. 2208731.6 (the content of which is incorporated herein by reference). Upon initiation of a measurement, first electromagnetic radiation (hereafter referred to as “first light”) is emitted by the source of electromagnetic radiation 102. In this example, the wavelength of the first light (the emission wavelength) is in the blue range of the electromagnetic spectrum, for example between about 400nm and about 500nm, such 450nm or 488nm. In the exemplary context of measuring AGEs, the emission wavelength is selected as an excitation wavelength for AGEs.

[0055] The first light propagates within the first connecting optical fibre 108 to the multimode optical circulator 106, which directs (Step 202) the first light into the third connecting optical fibre 132. The first light then propagates through the third connecting optical fibre 132 to the pinhole of the second end 136 of the third connecting optical fibre 132. The first light emitted (Step 204) from the pinhole of the second end 136 of the third connecting optical fibre 132 is launched into the collimator 130, the first light being collimated (Step 206) as the first light propagates through the collimator 130. Upon exiting the collimator 130, the collimated first light is incident upon the scannable lens 138, which focusses (Step 208) the collimated first light to an intermediate focus 182 before propagating further towards the objective optical system 140. The objective optical system 140 focusses (Step 210) the received first light from the intermediate focus 182 to a focal point 184 within the region to be measured 142 and, in particular, the lens 154 of the eye 156.

[0056] The singlets (the first and second plano-convex lenses 160, 162) and the achromatic doublet pair 158 act together to form the achromatic objective optical system 140. The combination serves to minimise spherical aberration across the range of scanning of the scannable lens 138 and also compensates for chromatic aberration of the collimator 130 and the scannable lens 138.

[0057] The linearly translatable carriage 137 translates (Step 224) to-and-fro in an oscillatory manner along a portion of the free-space optical path 152, thereby scanning the intermediate focus 182 and thus the focal point 184 through the region to be measured 142 and thus the lens 154 of the eye 156. In the lens 154 of the eye 156, part of the first light incident upon the material from which the lens 154 is formed backscatters (Step 212) and another part of the first light incident upon the lens material causes fluorescence (Step 212), second light generated by the fluorescence process being partly emitted towards the objective optical system 140. Likewise, some of the backscattered first light, constituting third light, is scattered toward the objective optical system 140. The wavelength of the second light generated by the fluorescence process is different to the wavelength of the first light, the wavelength of the third light being backscattered is the same as the wavelength of the first light.

[0058] The second and third light propagate back to the objective optical system 140 where they are focussed (Step 214) by the objective optical system 140 to the intermediate focus 182 before propagating (Step 216) onwards to the scannable lens 138 where the second and third light are collimated by the scannable lens 138 before propagating to the collimator 130.

[0059] Thereafter, the collimated second and third light are focussed and launched (Step 218) by the collimator 130, operating in a reverse manner owing to the direction of propagation of the second and third light, into the pinhole of the second end 136 of the third connecting optical fibre 132. The second and third light then propagate through the third connecting optical fibre 132 to the multimode optical circulator 106, which directs the second and third light into the second connecting optical fibre 114. The second and third light then propagate (Step 220) through the second connecting optical fibre 114 and are launched into the input/output port 110 of the optical detector module 112.

[0060] The second and third light entering the optical detector module 112 are then incident upon the fifth plano-convex lens 180, the fifth plano-convex lens 180 collimating the second and third light. The collimated second and third light then propagate to the dichroic beamsplitter 126 whereupon the second light in respect of the fluorescence process that occurred in the eye 156 is folded and directed (Step 222) by the dichroic beamsplitter 126 towards the fluorescence detector 124. The third light in respect of backscatter propagates through (Step 222) the dichroic beamsplitter 126 towards the scatter detector 122.

[0061] The redirected second light propagates through the second filter 174 (Step 226) and then through the fourth plano-convex lens 176, the second filter 174 blocking wavelengths of light that are not within a predetermined range of wavelengths associated with a biomarker, for example a metabolite, of interest. The parts of the second light remaining are focussed by the fourth plano-convex lens and propagate through the second detector window 178 for sensing by photosensitive elements of the fluorescence detector 124.

[0062] The third light propagates through the first filter 168 (Step 228), the first filter 168 conversely blocking the components of the third light of the predetermined range of wavelengths mentioned above. The parts of the third light remaining are focussed by the third plano-convex lens 170 and propagate through the first detector window 172 for sensing by photosensitive elements of the scatter detector 122.

[0063] In response to incidence of the portion of the second light within the predetermined range of wavelengths, generated as a result of the fluorescence process in the eye 156, upon the fluorescence detector 124, the fluorescence detector 124 generates (Step 230) a first electrical output signal proportional to the intensity of the portion of the second light incident upon the fluorescence detector 124. Similarly, in response to incidence of the portion of the third light outside the predetermined range of wavelengths, generated as a result of the backscatter process in the eye 156, upon the scatter detector 122, the scatter detector 122 generates (Step 232) a second electrical output signal proportional to the intensity of the portion of the third light incident upon the fluorescence detector 124. In this example, the first and second electrical output signals are amplitude signals. The first electrical output signal is a measure of received electromagnetic radiation in respect of fluorescence and the wavelength of the second light received in respect of the fluorescence is longer than the emission wavelength, the emission wavelength being an excitation wavelength in the context of fluorescence. In contrast, the wavelength of the third light is substantially the same as the emission wavelength, the third light having simply experienced scattering.

[0064] The first and second filters 168, 174 of the detector module 112 serve to reduce crosstalk in the between the optical signals that are the received second and third light.

[0065] The control circuitry component of the signal processing circuit 144 then determines (Step 234) whether further scans of the lens 154 of the eye 156 need to be performed. If the further scans are required, the control circuitry controls performance of the above-described steps again (Steps 200 to 232). Otherwise, if no further scans are required, the measurement process is halted.

[0066] The signal processing circuity 144 can then process the first and second output signals in accordance with any desired manner, for example by calculating a function of the first electrical signal and the second electrical signal, and thus a function of the amplitude of the intensity of the portion of the second light and the amplitude of the intensity of the portion of the third light incident upon the fluorescence detector 124 and the scatter detector 122, respectively. The signal processing circuitry 144 can be configured to isolate different portions of the first and second electrical output signals, respectively, by analysis of position in the scan signal and extent. For example, specular reflections from the anterior and/or posterior cornea, and/or specular reflection from the anterior and/or posterior lens and/or fluorescence originating from the lens.

[0067] In this example, in order to detect AGEs effectively a ratio is calculated of the intensities of the portion of the second light to the intensity of the portion of the third light using the amplitudes of the first and second electrical signals. Of course, however, other calculations can be performed depending upon the biomarker being measured. Furthermore, the function is calculated and the position of the scannable lens 138 is recorded, for example using the position encoder mentioned above, as a measure of scanning depth associated with the measurements of intensity. This enables the changes of concentration of AGEs or measures of other biomarkers with depth of focus to be determined and thus, in this example, position within the lens 154 of the eye 156.

[0068] In some examples, the calculated ratio can be compared to values in a lookup table, for example stored in a memory or other data store operably coupled to the signal processing circuitry 144 or remote from the confocal optical measurement apparatus 100, to determine a possible risk factor for a patient. In this regard, the data stored can comprise information concerning variation of concentration of AGEs with depth of focus and age of a patient, and possibly other relevant factors, for example gender. This data is accessed either by the signal processing circuitry 144, assuming an age of a patient has been provided to the signal processing circuitry 144 through any suitable input/output interface of the confocal optical measurement apparatus 100 by the operator.

[0069] In another embodiment, the confocal optical measurement apparatus 100 can be configured, for example by adaptation of the functionality of the control circuitry, to measure selectively only fluorescence or backscatter. This can be achieved, for example, by only analysing signals generated by the fluorescence detector 124 or the scatter detector 122. In such an embodiment, the signal processing circuitry 144 records the position of the scannable lens 138 and hence records an indication of depth of the focal point 184 for the measured fluorescence or backscatter.

[0070] In some embodiments, particularly but not exclusively where the optical system is a single-axis optical system, electromagnetic radiation received from a part of the region to be measured 142, for example light scattered by the lens 154 of the eye 156 contains noise caused by crosstalk from the light emitted by the source of electromagnetic radiation 102. Also, the amplitude of the portion of the second electrical output signal attributable to the light scattered by the lens 154 of the eye 156, and the amplitude of the first electrical output signal attributable to fluorescence caused by the lens 154 of the eye 156 are dependent upon alignment of the objective optical system 140 with the optical axis of the eye 156 as a result of aberrations within the anterior chamber of the eye 156 having an influence at the resolution at which the confocal optical measurement apparatus 100 scans. The presence of noise in the second electrical output signal generated by the scatter detector 122 can be mitigated by analysing a different portion of the second electrical output signal caused by specular reflection of the first light by the anterior surface of the cornea (not shown and hereafter referred to as the cornea anterior) of the eye 156. The reflection of the first light by the cornea anterior is detectable, because the scatter detector 122 operates at the same wavelength as the wavelength of the electromagnetic radiation emitted by the source of electromagnetic radiation 102 and is thus present in the second electrical output signal. The portion of the second electrical signal caused by the specular reflection from the cornea anterior is of a greater amplitude than the portion of the second electrical output signal attributable to the third light scattered by the lens 154 of the eye 156 and so is little affected by noise at the levels of noise experienced. Furthermore, like the first electrical output signal and the portion of the second electrical output signal attributable to the light scattered by the lens 154 of the eye 156, the amplitude of the portion of the second electrical output signal attributable to the light reflected by the cornea anterior is dependent upon alignment of the objective optical system 140 with the optical axis of the eye 156.

[0071] The function, for example the calculation of the ratio described above using the first and second electrical output signals, can be modified, because both the amplitude of the portion of the second electrical output signal attributable to the light reflected by the cornea anterior and the amplitudes of the first optical output signal attributable to fluorescence and the portion of the second electrical output signal attributable to the backscatter caused by the lens 154 of the eye are similarly dependent upon alignment of the objective optical system 140 with the optical axis of the eye 156. As such, the function calculated, for example the ratio mentioned above, is reasonably insensitive to alignment and so the signal processing circuitry 144 can analyse the portion of the second electrical output signal attributable to the specular reflection caused by the cornea anterior instead of the backscatter caused by the lens 154, and the amplitude of the portion of the second electrical output signal attributable to the specular reflection caused by the cornea anterior, for example peak amplitude, can be employed for the function mentioned above instead of the portion of the second electrical output signal attributable to the backscatter from the lens 154.

[0072] Similarly, in examples mentioned above where only the second electrical output signal generated by the scatter detector 122 is employed, for example when trying to detect cataracts or amyloid plaques, the portion of the second electrical output signal attributable to the specular reflection from the cornea anterior can be used to evaluate a function, for example a ratio between the portion of the second electrical output signal attributable to the specular reflection caused by the cornea anterior, for example peak amplitude, and the portion of the electrical output signal caused by the light backscattered by the lens 154, for example peak amplitude thereof.

[0073] The above examples can employ reflections from other surfaces within the anterior chamber of the eye 156, for example the posterior surface of the cornea and/or indeed the posterior and/or anterior surface of the lens 154 of the eye 156. These can be used for within the function mentioned above and/or for the assessment of alignment.

[0074] In some embodiments, a thresholding technique can be employed using the portion of the second electrical output signal caused by the specular reflection from the cornea anterior, or another surface from within the anterior chamber of the eye 156, in order to determine whether to accept a measurement made or reject the measurement. A threshold level can be set, above which the measurement is considered to have been made on a sufficiently optically aligned basis (alignment of the optical axis of the objective optical system 140 with the optical axis of the eye 156) to be accepted, otherwise the objective optical system 140 is considered insufficiently aligned with the optical axis of the eye 156 and thus the measurement is inadequate.

[0075] It should be appreciated that references herein to “light”, other than where expressly stated otherwise, are intended as references relating to the optical range of the electromagnetic spectrum, for example, between about 300 nm and about 500 nm, such as between about 400 nm and about 500 nm for applications involving the eye. However, for other applications, these wavelengths can vary.

[0076] Although in the above examples, measurement has been described with respect to the lens 154 of the eye 156, it should be appreciated that the confocal optical measurement apparatus 100 can be configured and employed to make measurements in respects of other parts of the eye 156. Indeed, it should be further appreciated that the application of the confocal optical measurement apparatus 100 is not limited to the eye 156 and measurements in relation to other tissue is intended, the measurements typically being in vivo.

[0077] In the examples set forth above, the light emitted by the source of electromagnetic radiation 102 is scanned through the tissue being measured. However, in other examples, it should be appreciated that the light emitted by the source of electromagnetic radiation 102 can be used to flood illuminate the tissue being measured.

[0078] Although, in the above examples, the multimode optical circulator 106 has been employed to direct emitted and received electromagnetic radiation, the skilled person should appreciate that this is not the only implementation for directing the emitted and received light and the multimode optical circulator 106 can be replaced with an appropriately configured beam splitter. In one example, the replacement beam splitter and the source of electromagnetic radiation 102 can be integrated into the optical detector module 112, thereby creating a tri-directional transceiver module with a single input-output port. This arrangement allows a more compact optical system overall. However, it should be noted that optical isolation between the source of electromagnetic radiation and the scatter detector 122 and the fluorescence detector 124 is less effective than employing the multimode optical circulator 106 and so may result in crosstalk between the source of electromagnetic radiation 102 and detectors 122, 124 and thus the overall optical system may exhibit poorer Signal to Noise Ratio (SNR) performance than when using the multimode optical circulator 106. [0079] In the examples set forth above, the application of the confocal optical measurement apparatus 100 has primarily been described in relation to a metabolite such as AGE. However, it should be appreciated that applications of the confocal optical measurement apparatus 100 is not limited to this specific metabolite or indeed only metabolites and measurements can more generally be made in relation to biomarkers. In this regard, the biomarkers can be endogenous biomarkers or other molecules, for example and not exclusively amyloid plaques, and/or exogenous biomarkers.

Claims

1 . A confocal optical measurement apparatus comprising: a source of electromagnetic radiation configured to emit electromagnetic radiation at an emission wavelength; a detector module configured to receive electromagnetic radiation; a dioptric optical system comprising a scannable intermediate optical element and an achromatic objective, the scannable intermediate optical element being disposed in an optical path between the detector module and the achromatic objective; and a multimode optical fibre operably coupled between the detector module and the dioptric optical system.

2. An apparatus as claimed in Claim 1 , wherein the detector module comprises: a scatter detector; and a fluorescence detector.

3. An apparatus as claimed in any one of the preceding claims, wherein the achromatic objective comprises a first doublet and a second doublet disposed opposite the first doublet.

4. An apparatus as claimed in any one of the preceding claims, further comprising: an optical circulator operably coupled to the source of electromagnetic radiation, the detector module and the scannable intermediate optical element.

5. An apparatus as claimed in Claim 4, wherein the optical circulator is a multimode optical circulator.

6. An apparatus as claimed in Claim 4 or Claim 5, wherein the multimode optical fibre couples the optical circulator to the dioptric optical system, the optical fibre defining a pinhole.

7. An apparatus as claimed in Claim 6, further comprising: a collimator disposed between the optical circulator and the scannable intermediate optical element.

8. An apparatus as claimed in any one of the preceding claims, further comprising: a housing, the housing containing the source of electromagnetic radiation, the detector module, the dioptric optical system and the multimode fibre.

9. An apparatus as claimed in Claim 8, wherein the housing is a handheld housing.

10. An apparatus as claimed in Claim 8 or Claim 9, wherein the housing comprises a window configured to provide irradiative access to a region to be measured located at a substantially static target location external to the housing.

11. An apparatus as claimed in any one of Claims 1 to 9, further comprising: processing circuitry operably coupled to the detector module and configured to calculate selectively scatter and/or fluorescence.

12. An apparatus as claimed in Claim 11 , wherein the processing circuitry is configured to calculate a function of fluorescence and scatter.

13. An apparatus as claimed in Claim 12, wherein the processing circuitry is configured to translate, when in use, the scannable intermediate optical element in order to scan a focus of the achromatic objective through a substantially static target region and to calculate a variation of the function with depth.

14. An apparatus as claimed in any one of the preceding claims, further comprising: an optical system comprising the dioptric optical system and the multimode optical fibre; wherein the optical system is a single-axis confocal optical system.

15. A method of optically measuring a metabolic parameter, the method comprising: launching a source beam of electromagnetic radiation at an emission wavelength into a first end of a multimode optical fibre, a second end of the multimode optical fibre constituting a pinhole; illuminating a region to be measured; receiving electromagnetic radiation from the region to be measured in response to illumination by the beam of electromagnetic radiation; confocally and achromatically collecting and launching the received electromagnetic radiation into the second end of the multimode optical fibre; measuring the received electromagnetic radiation; and calculating a measure of the metabolic parameter using the measured received electromagnetic radiation.