METHOD AND A SYSTEM FOR A NON-INVASIVE ASSESSMENT OF A RELATION BETWEEN AN INTRACRANIAL PRESSURE AND AN INTRAOCULAR PRESSURE

Abstract

Method and system for a non-invasive assessment of a relation between an intracranial pressure and an intraocular pressure. The method comprising the steps of recording a plurality of images of a retina part of an eye of a person, identifying at least one vein, determining a first plurality of characteristic vein diameters for the identified vein at a first vein location, determining whether the at least one vein has experienced a vein collapse during the first time period, and determining a relation between intraocular pressure and intracranial pressure during the first time period.

Claims

1. A method for a non-invasive assessment of a relation between an intracranial pressure and an intraocular pressure using an image recording device, comprising: recording, over a first time period, a plurality of images of a retina part of an eye of a person using the image recording device, identifying, in the plurality of images, at least one vein, determining, in a first set of images from the plurality of images recorded over the first time period, a first plurality of characteristic vein diameters for the at least one vein at a first vein location, determining, based on the first plurality of characteristic vein diameters, whether the at least one vein has experienced a vein collapse during the first time period, and determining the relation between the intraocular pressure and the intracranial pressure during the first time period, wherein if the at least one vein has experienced a vein collapse the intraocular pressure is determined to exceed the intracranial pressure.

2. The method of claim 1, wherein determining whether the at least one vein has experienced a vein collapse comprises: identifying, in the plurality of images, at least one artery associated with the at least one vein, determining, in the first set of images from the plurality of images recorded over the first time period, a first plurality of characteristic artery diameters for the at least one artery at a first artery location, determining, based on the first plurality of characteristic artery diameters, an artery diameter behaviour, determining, based on the first plurality of characteristic vein diameters, a vein diameter behaviour, comparing the vein diameter behaviour to the artery diameter behaviour, and determining, based on the comparison between the vein diameter behaviour and the artery diameter behaviour, whether the at least one vein has experienced a vein collapse during the first time period.

3. The method of claim 1, wherein the plurality of images of the retina part of the eye are also of an optic disc of the eye, and wherein determining whether the at least one vein has experienced a vein collapse comprises: determining, in the first set of images from the plurality of images recorded over the first time period, a location of the optic disc, determining, in the first set of images from the plurality of images recorded over the first time period, a second plurality of characteristic vein diameters for the at least one vein at a second vein location, wherein the second vein location is farther away from the optic disc than the first vein location, determining, based on the first plurality of characteristic vein diameters, a first vein diameter behaviour, determining, based on the second plurality of characteristic vein diameters, a second vein diameter behaviour, comparing the first vein diameter behaviour to the second vein diameter behaviour, and determining based on the comparison between the first vein diameter behaviour and the second vein diameter behaviour, whether the at least one vein has experienced a vein collapse during the first time period.

4. The method of claim 3, wherein the second vein location is at least a distance corresponding to a diameter of the optic disc away from the optic disc.

5. The method of claim 1, wherein determining whether the at least one vein has experienced a vein collapse comprises: determining, based on the first plurality of characteristic vein diameters, a change in vein diameter during the first time period, comparing the change in the vein diameter with a threshold value, and determining, based on the comparison between the change in the vein diameter and the threshold value, whether the at least one vein has experienced a vein collapse during the first time period.

6. The method of claim 1, further comprising: recording, over a second time period, a second plurality of images of the retina part of the eye of the person using the image recording device, identifying, in the second plurality of images, the at least one vein, determining, in a second set of images from the second plurality of images recorded over the second time period, a second plurality of characteristic vein diameters for the at least one vein at the first vein location, determining, based on the second plurality of characteristic vein diameters, whether the at least one vein has experienced a vein collapse during the second time period, and determining the relation between the intraocular pressure and the intracranial pressure during the second time period, wherein if the at least one vein has experienced a vein collapse the intraocular pressure is determined to exceed the intracranial pressure.

7. The method of claim 1, further comprising: identifying, in the plurality of images, at least one artery associated with the at least one vein, determining, in the first set of images from the plurality of images recorded over the first time period, a first plurality of characteristic artery diameters for the at least one artery at a first artery location, calculating an arteriovenous ratio based on the first plurality of characteristic artery diameters and the first plurality of characteristic vein diameters, and comparing the arteriovenous ratio to the relation between the intraocular pressure and the intracranial pressure during the first time period.

8. The method of claim 6, further comprising: identifying, in the second plurality of images, at least one artery associated with the at least one vein; determining, in the second set of images from the plurality of images recorded over the second time period, a second plurality of characteristic artery diameters for the at least one artery at a first artery location, calculating an arteriovenous ratio based on the second plurality of characteristic artery diameters and the second plurality of characteristic vein diameters, determining a change in the arteriovenous ratio between the first time period and the second time period, and comparing the change in the arteriovenous ratio to the relation between the intraocular pressure and the intracranial pressure during the first time period and to the relation between the intraocular pressure and the intracranial pressure during the second time period.

9. The method of claim 6, wherein the first time period, the second time period, or both is at least equal to a duration of at least one heart pulse cycle of the person, a duration of at least one respiratory cycle for the person, or both.

10. The method of claim 9, further comprising: determining, based on the first plurality of characteristic vein diameters, the duration of at least one heart pulse cycle of the person, the duration of at least one respiratory cycle of the person, or both.

11. A system for performing a non-invasive assessment of a relation between an intracranial pressure and an intraocular pressure, comprising: an image recording device, configured to record, over a first time period, a plurality of images of a retina part of an eye of a person, and a processing unit communicatively connectable to the image recording device and configured to: receive the plurality of images recorded by the image recording device, identify, in the plurality of images, at least one vein, determine, in a first set of images from the plurality of images recorded over the first time period, a first plurality of characteristic vein diameters for the at least one vein at a first vein location, determine, based on the first plurality of characteristic vein diameters, whether the at least one vein has experienced a vein collapse during the first time period, and determine the relation between the intraocular pressure and the intracranial pressure during the first time period, wherein if the at least one vein has experienced a vein collapse the intraocular pressure is determined to exceed the intracranial pressure.

12. The system of claim 11, further comprising: a cardiac monitoring component configured to determine a heart pulse cycle of the person, wherein the processing unit is further configured to determine the first plurality of characteristic vein diameters for the at least one vein at the first vein location based on temporal information about the heart pulse cycle.

13. The system of claim 11, further comprising: a respiratory monitoring component configured to determine a respiratory cycle of the person, wherein the processing unit is further configured to determine the first plurality of characteristic vein diameters for the at least one vein at the first vein location based on temporal information about the respiratory cycle.

14. The system of claim 11, wherein, to determine whether the at least one vein has experienced a vein collapse, the processing unit is further configured to: identify, in the plurality of images, at least one artery associated with the at least one vein, determine, in the first set of images from the plurality of images recorded over the first time period, a first plurality of characteristic artery diameters for the at least one artery at a first artery location, determine, based on the first plurality of characteristic artery diameters, an artery diameter behaviour, determine, based on the first plurality of characteristic vein diameters, a vein diameter behaviour, compare the vein diameter behaviour to the artery diameter behaviour, and determine, based on the comparison between the vein diameter behaviour and the artery diameter behaviour, whether the at least one vein has experienced a vein collapse during the first time period.

15. The system of claim 11, wherein, the plurality of images of the retina part of the eye are also of an optic disc of the eye, and wherein, to determine whether the at least one vein has experienced a vein collapse, the processing unit is further configured to: determine, in the first set of images from the plurality of images recorded over the first time period, a location of the optic disc, determine, in the first set of images from the plurality of images recorded over the first time period, a second plurality of characteristic vein diameters for the at least one vein at a second vein location, wherein the second vein location is farther away from the optic disc than the first vein location, determine, based on the first plurality of characteristic vein diameters, a first vein diameter behaviour, determine, based on the second plurality of characteristic vein diameters, a second vein diameter behaviour, compare the first vein diameter behaviour to the second vein diameter behaviour, and determine based on the comparison between the first vein diameter behaviour and the second vein diameter behaviour, whether the at least one vein has experienced a vein collapse during the first time period.

16. The system of claim 11, wherein, to determine whether the at least one vein has experienced a vein collapse, the processing unit is further configured to: determine, based on the first plurality of characteristic vein diameters, a change in vein diameter during the first time period, compare the change in the vein diameter with a threshold value, and determine, based on the comparison between the change in the vein diameter and the threshold value, whether the at least one vein has experienced a vein collapse during the first time period.

17. The system of claim 11, wherein the processing unit is further configured to: record, over a second time period, a second plurality of images of the retina part of the eye of the person using the image recording device, identify, in the second plurality of images, the at least one vein, determine, in a second set of images from the second plurality of images recorded over the second time period, a second plurality of characteristic vein diameters for the at least one vein at the first vein location, determine, based on the second plurality of characteristic vein diameters, whether the at least one vein has experienced a vein collapse during the second time period, and determine the relation between the intraocular pressure and the intracranial pressure during the second time period, wherein if the at least one vein has experienced a vein collapse the intraocular pressure is determined to exceed the intracranial pressure.

18. The system of claim 17, wherein the processing unit is further configured to: identify, in the second plurality of images, at least one artery associated with the at least one vein; determine, in the second set of images from the plurality of images recorded over the second time period, a second plurality of characteristic artery diameters for the at least one artery at a first artery location, calculate an arteriovenous ratio based on the second plurality of characteristic artery diameters and the second plurality of characteristic vein diameters, determining a change in the arteriovenous ratio between the first time period and the second time period, and compare the change in the arteriovenous ratio to the relation between the intraocular pressure and the intracranial pressure during the first time period and to the relation between the intraocular pressure and the intracranial pressure during the second time period.

19. The system of claim 11, wherein the processing unit is further configured to: identify, in the plurality of images, at least one artery associated with the at least one vein, determine, in the first set of images from the plurality of images recorded over the first time period, a first plurality of characteristic artery diameters for the at least one artery at a first artery location, calculate an arteriovenous ratio based on the first plurality of characteristic artery diameters and the first plurality of characteristic vein diameters, and compare the arteriovenous ratio to the relation between the intraocular pressure and the intracranial pressure during the first time period.

20. The system of claim 11, wherein the processing unit is further configured to: determine, based on the first plurality of characteristic vein diameters, a duration of at least one heart pulse cycle of the person, a duration of at least one respiratory cycle of the person, or both.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] For exemplifying purposes, the disclosure will be described in closer detail in the following with reference to examples thereof illustrated in the attached drawings, wherein:

[0113] FIGS. 1a and 1b depict cross-sections of arteries and veins within an eye at different pressures and different relations between IOP and ICP.

[0114] FIG. 2 depicts a simplified pressure block model of a human body.

[0115] FIG. 3 depicts an example of a system according to the disclosure.

[0116] FIG. 4 depicts cross-sections of a vein and an associated artery during a cardiac cycle under two different relations between ICP and IOP.

[0117] FIG. 5 depicts a collapsed vein exiting the optic disc and two cross-sections of the vein at a first vein location and a second vein location.

[0118] FIG. 6 depicts a graph showing the characteristic vein diameter as a function of time and ICP.

[0119] FIGS. 7a and 7b depict graphs of measurements of AVR as a function of ICP.

[0120] FIG. 8 depicts a block diagram according to an example of the first aspect of the disclosure.

DETAILED DESCRIPTION

[0121] In the following detailed description, examples of the present disclosure will be described. However, it is to be understood that features of the different examples are exchangeable between the examples and may be combined in different ways, unless anything else is specifically indicated. It may also be noted that, for the sake of clarity, the dimensions of certain elements illustrated in the drawings may differ from the corresponding dimensions in real-life implementations.

[0122] Referring initially to FIGS. 1a and 1b, depicting cross-sections of arteries 2 and veins 1 within an eye at different pressures and different relations between IOP and ICP. FIG. 1a depicts the situation where the ICP exceeds the IOP. The vein 1 has a first characteristic vein diameter dv1 and the artery 2 has a first characteristic artery diameter da1. As depicted on FIG. 1a the characteristic vein diameters dv1, dv2 normally exceeds the characteristic artery diameters da1, da2, because of the lower strength of the walls of the vein 1, though exceptions may occur. When the vessel pressure increases both the artery 2 and the vein 1 experiences a uniform increase in their cross-sections, consequently also an increase in their characteristic diameters.

[0123] In the context of the disclosure a vessel pressure is to be understood as the pressure inside of a blood vessel. The increase in the characteristic diameter leads to the artery 2 having a second characteristic artery diameter da2 and the vein 1 having a second characteristic vein diameter dv2. Furthermore, since the strength of the vein 1 is in general lower than that of the artery 2, the increase in the characteristic diameter is larger for the vein 1. When the vessel pressure decreases both the artery 2 and the vein 1 experiences a uniform decrease in their cross-sections, resulting in a decrease in their characteristic diameters. The decrease in the characteristic diameter leads to the artery 2 returning to the first characteristic artery diameter dal and the vein 1 returning to the first characteristic vein diameter dv1. FIG. 1b depicts the situation where the IOP exceeds the ICP. The general behaviour of the artery 2 does not change when the IOP exceeds the ICP. However, the behaviour of the vein 1 changes. When the vessel pressure decreases it results in the vein 1 collapsing. The collapse of the vein 1 leads to the vein 1 approaching an elliptical cross-section, wherein the characteristic vein diameter is measured along the semi major axis of the ellipse, resulting in the vein 1 having a third characteristic vein diameter dv3. The third characteristic diameter dv3 of the vein 1 in the collapsed state exceeds that of the first characteristic diameter dv1 and the second characteristic diameter dv2. Generally, the characteristic diameter of the vein in the collapsed state exceeds the characteristic diameter of the vein in the non-collapsed state.

[0124] Although cross-sections of the vein 1 and the artery 2 at different situations are shown, it is important to understand the change in the artery 2 and vein 1 happens continuously over time, thereby giving rise to a plurality of different cross-section for both the vein 1 and the artery 2.

[0125] Referring to FIG. 2, which depicts a simplified pressure block model of a human body. To understand the nature of why a vein 1 collapses in the eye, it is highly relevant to understand the different pressures involved and how they interact. The depicted pressure block model has been simplified to only include a heart 5, a cranium 4, an eye 3, an artery 2, and a vein 1. The pressure within the veins 1 and arteries 2 are generated by the heart 5 pumping blood through the circulatory system. The pumping of the heart 5 generates a pressure wave, which drives the blood through the circulatory system and assures blood circulation within the vessels. The pressures in the blood vessels generated by the heart 5 causes the vessels to expand and contract as depicted in FIGS. 1a and 1b. To start of blood is pumped from the heart 5 to the cranium 4 through the artery 2. The artery 2 and vein 1 within the cranium 4 of a person experiences an external pressure exerting a pressure onto the vein 1 and the artery 2 in the cranium 4. The external pressure in the cranium 4 is known as ICP. From the cranium 4 the blood travels into the eye 3 via the artery 2. The artery 2 and the vein 1 within the eye 3 also experiences an external pressure. The external pressure in the eye 4 is known as IOP. ICP and IOP are rarely equal and in most cases differs from each other. When the blood is circulated back from the eye 3 it is done via the vein 1. The vein 1 travels from the eye 3 and back into the cranium 4 and then back to the heart 5. What is important to understand is that the blood vessels are not rigid tubes, but expand and contract, especially the vein 1 experience changes in size, as the strength of the vein is lower than that of the artery 2. Thus, it would be more accurate to view the blood vessels, in particular the vein 1, as a flexible tube capable of deforming. Thus, when either of the external pressures, IOP or ICP, pressing onto the vein 1 exceeds the pressure within the vein 1, the vein 1 collapses. Furthermore, for blood to flow from the eye 3 and into the cranium 4 through the vein 1, the pressure within the vein 1 must exceed the ICP otherwise a blood flow into the cranium 4 would not be present. The pressure generated by the pumping of the heart 5 ensures the blood pressure within the vein 1 exceeds the ICP and ensures a blood flow from the eye 3 and into the cranium 4. The pressure generated by the heart 5 may be described by the cardiac cycle. The pressure generated by the heart can be viewed as a pressure wave, which can roughly be split into systole where the blood pressure is high and diastole where the blood pressure is low. In a situation where the ICP exceeds the IOP, the vein 1 does not collapse since the blood pressure within the vein 1 will exceed the IOP, otherwise a proper blood flow would not be present. However, in the situation where the IOP exceeds the ICP, the blood pressure within the vein 1 may fall below the IOP causing a collapse of the vein 1, because of the external pressure, i.e. IOP, pressing down on the vein 1. However, the IOP may in some cases exceed the ICP without a vein collapse occurring, as the IOP needs to exceed the pressure within the vein in order for a vein collapse to occur. Consequently, if the pressure within the vein exceeds the IOP, the IOP may exceed ICP without a vein collapse occurring. Thus, only when the vein collapses may it be assured that the IOP exceeds the ICP. The collapse of the vein 1 will normally happen during diastole when the blood pressure is low. With the vein 1 returning from its collapse during systole. Of course, the higher the IOP is in relation to ICP, the larger is the amount of time the vein 1 will spend in a collapsed state during the cardiac cycle, as the blood pressure will fall below the IOP sooner during the pressure wave.

[0126] Referring to FIG. 3, which depicts an example of a system 6 according to the disclosure. The system 6 comprises an image recording device 61 connected to a processing unit 63. The image recording device 61 may be a smart phone provided with an add-on configured for ophthalmology measurements or a camera specifically configured for ophthalmology measurements. The connection 62 between the image recording device 61 and the processing device 63 may be a wired connection or a wireless connection. In some examples the image recording device 61 and the processing device may also be comprised in the same device, e.g. a smart phone, or other dedicated devices. The processing device 63 may further comprise a display 65 for displaying results determined by the processing unit 63. The display 65 may be connected to the processing unit 63 via a wired or wireless connection 64. The image recording device 61 is configured for recording images for of a retina part of an eye 3. Images are recorded through a lens 32 of the eye 3. The images recorded are meant for imaging veins 1 and arteries 2 on the retina part of the eye 3. In some examples the recorded images may also comprises images of an optic disc 31 of the eye 3. The characteristic diameters of veins and/or arteries determined from the recorded images is the diameter of the veins 1 and/or arteries 2 extending across the retina part of the eye 3. Consequently, when the veins 1 collapse they collapse against the retina part of the eye 3, thus resulting in an increase in the diameter of the veins 1 extending across the retina part of the eye 3, resulting in an increase in the characteristic vein diameter.

[0127] Referring to FIG. 4, which depict cross-sections of a vein 1 and an associated artery 2 during a cardiac cycle under two different relations between ICP and IOP. On FIG. 4 a graph 7 is depicted having time along a first axis and pressure within a vein 1 along a second axis. The graph 7 depicts the pressure within the vein 1 during the cardiac cycle. The pressure within the vein 1 shown on the graph 7 substantially follow the same trend as the arterial pressure during the cardiac cycle, other pressure behaviours within the vein 1 are also possible. During the cardiac cycle the pressure within the vein 1 changes significantly, the maximum pressure within the vein 1 happens at a systolic blood pressure 71. At the systolic blood pressure 71 the pressure within the artery 2 and the vein is at the maximum. In the situation where ICP exceeds IOP both the vein 1 and artery 2 have their maximum characteristic diameter at the systolic blood pressure 71. As the blood pressure decreases the characteristic diameters of both the artery 2 and the vein 1 decreases, until reaching their minimum characteristic diameter at a diastolic blood pressure 72. Thus, both the artery 2 and the vein 1 exhibits a matching behaviour when ICP exceeds IOP. In the situation where IOP exceeds ICP the behaviour of the artery 2 does not change. However, the behaviour of the vein 1 changes. As the blood pressure decreases towards the diastolic blood pressure 72, the vein 1 collapses as a result of the blood pressure within the vein 1 being exceeded by the IOP. The collapse of the vein 1 leads to an increased characteristic diameter at the diastolic blood pressure 72 which is opposed to what is observed for the artery 2, which will have a decreased characteristic diameter at the diastolic blood pressure 72. Thus, the artery 2 and the vein 1 exhibits differing behaviours. The characteristic diameter of the vein 1 resulting from the collapse of the vein 1, normally exceeds even the characteristic diameter of the vein 1 at the systolic blood pressure 71. Thus, by observing, determining and comparing the diameter behaviour of both the vein 1 and the artery 2, and subsequently comparing these to each other it is possible to determine, whether the vein 1 has undergone a collapse, since if the behaviours differs between the artery 2 and the vein 1, it signals that the vein 1 has undergone a collapse.

[0128] Referring to FIG. 5, which depicts a collapsed vein 1 exiting the optic disc 31 and two cross-sections of the vein 1 at a first vein location 11 and a second vein location 12. When the vein 1 collapses it has been observed to collapse close to the optic disc 31. The collapse of the vein 1 close to the optic disc 31 results in a pressure increase upstream of the collapse, which hinders the collapse from propagating to the rest of the vein 1. On FIG. 5 the vein has collapsed at a first vein location 11 close to the optic disc 31, the collapse results in the vein 1 having an elliptical cross-section A-A at the first vein location 11. Farther away from the optic disc 31, at the second vein location 12 no collapse has occurred as a result of the increased pressure caused by the collapse. Since no collapse occurs at the second vein location 12, the cross-section of the vein 1 at the second vein location is circular as seen from cross-section B-B. Since the cross-section B-B retains a circular cross-section, the characteristic diameter of the cross-section B-B will develop in accordance with the vessel pressure, i.e. whenever the vessel pressure decreases the characteristic diameter will decrease, and whenever the vessel pressure increases the characteristic diameter will increase. Whereas, at the cross-section A-A a decrease in vessel pressure may result in a collapse, which leads to an increase in the characteristic diameter. Thus, by observing, determining, and comparing the behaviour of the vein 1 at a first vein location 11 and a second vein location 12, it is possible to determine, whether the vein 1 has undergone a collapse, since if the behaviours differs between the first vein location 11 and the second vein location 12, it signals that the vein 1 has undergone a collapse.

[0129] Referring to FIG. 6, which depict a graph showing measurements of the characteristic vein diameter as a function of time and ICP. The measurements show that the characteristic vein diameter at low ICPs undergoes large changes over time. The large changes are caused by the vein collapsing. The vein collapsing results in a large change in the characteristic vein diameter, which corresponds to the large fluctuations seen on the graph. As the ICP increases the changes in the characteristic vein diameter becomes less pronounced, this is because the ICP starts to exceed the IOP, which leads to the vein not collapsing. However, small fluctuations are still present because of the changing blood pressure within the vein. The larger changes in characteristic vein diameter have been measured by the applicant to correspond to a relative change in the characteristic vein diameter above 2-3%, while the less pronounced changes correspond to a relative change in the characteristic vein diameter of 2-3% or below.

[0130] Referring to FIGS. 7a and 7b, which depict graphs 8 showing measurements of AVR as a function of ICP. On FIG. 7a two example measurements 81, 82 are shown of the AVR of a person. For both measurements 81, 82 the ICP was lower than the IOP. The first measurement 81 was performed for a first time period, and the second measurement 82 was performed for a second time period subsequent the first time period. Both measurements 81, 82 were carried out by recording a plurality of images and identifying one vein and at least one artery associated with said vein, then determining a first plurality of characteristic artery diameters for the identified artery at a first artery location and determining a first plurality of characteristic vein diameters for the identified vein at a first vein location. Based on the determined characteristic diameters of the vein and artery the AVR was calculated as a ratio between the determined characteristic diameters of the artery and the vein. The AVR may be calculated as a median or average AVR over the recorded time period. The AVR is normally a value between one and zero, as the vein generally exhibits a larger characteristic diameter than the artery. In the situation where ICP exceeds IOP, an increase in the AVR suggests a decrease in the ICP of a person. The reason why an increase in the AVR corresponds to a decrease in the ICP of a person, if ICP exceeds IOP, is that the vein deforms to a larger extent with pressure than the artery. Thus, when ICP falls the vein deforms to a smaller extent, thereby more closely resembling the artery and leading to an AVR close to one. However, the opposite is observed when IOP exceeds ICP, as is observed between the first measurement 81 and the second measurement 82, where the increase in the AVR corresponds to an increase in the ICP. In the situation where IOP exceeds ICP an increase in the AVR suggests an increase in the ICP. This behaviour is observed because of the vein collapsing. The collapse of the vein gives rise to a large change in characteristic diameter, thus giving a large difference between the vein and the artery. Consequently, the reason why the AVR increases between the first measurement 81 and the second measurement, even though the ICP increases, is that the time the vein is in the collapsed state during the cardiac cycle decreases as the ICP increases. Thus, the vein starts to resemble the artery more and more as the ICP starts to increase towards the IOP. Therefore, if a person is in a situation where IOP exceeds the ICP a false impression of the development of ICP may be developed if one is not aware of the relation between IOP and ICP.

[0131] On FIG. 7b another two example measurements 83, 84 are shown of the AVR of a person. The third measurement 83 was performed for a third time period, and the fourth measurement 84 was performed for a fourth time period subsequent the third time period. Both measurements 83, 84 were carried out in a similar manner as described in relation to the measurements 81, 82 of FIG. 7a. However, for both measurements the ICP exceeded the IOP. The result of the ICP exceeding the IOP is that the vein does not collapse. Therefore, the AVR decreases as the ICP increases, since the vein will start to deform more and more relative to the artery with increasing ICP. Thus, from FIGS. 7a and 7b the importance to know the relation between ICP and IOP is underlined, since it is needed to know the relation between IOP and ICP in order to correctly determine how the development in the AVR correlates to a development in the ICP.

[0132] Referring to FIG. 8, which depicts a block diagram 100 according to an example of the first aspect of the disclosure. In a first step 10 a patient is prepared. The preparation of the patient may be voluntarily and is not a necessary step to carry out. In the preparation it may be desirable to dilate the pupil of an eye of the patient in order to record good quality images of a fundus of an eye of the patient. In a hospital environment there may be time and personnel for chemically dilating the pupil by e.g. dripping the patient's eye with belladonna. This could for instance be the case if the patient is known to suffer from specific conditions, such as hydrocephalus patients, patients with neurosurgical conditions, liver patients, kidney patients, or patients being observed for concussion. If, on the other hand, the patient is a victim of an accident and there is little time available, but an ambulance crew or paramedics suspect a head trauma, such as a developing hematoma, there may only be time for placing the patient in a dark environment, and e.g. ask him to look into the darkness over the shoulder of the person recording the image. The preparation of the patient may also comprise having the patient sitting/lying still for an amount of time in a recording position before initiating recording, which may allow a blood flow of the patient to normalize before starting recording. The amount of time may vary but is preferably 5-300 seconds.

[0133] In a second step 11 a plurality of images of the retina part of the eye of the person is recorded over a first time period. The recording of the images is carried out by using an image recording device. The recorded images should preferably be of the fundus of the eye with the optic disc in the middle of which the arteries and veins enter and exit the eye, respectively, along the optic nerve, and from which they branch out in all directions across the fundus. In principle, the recorded images may be recorded using any suitable device. This could be a dedicated device for this specific purpose. It could also be a digital camera with suitable optics, preferably in combination with a data processing device, such as a personal computer, PC, for inter alia processing the image data according to the method, and possibly providing storage capacity for the recorded images, at least temporarily. In particular, however, the image recording device could be the built-in camera of a smart phone fitted with a suitable lens adapter. The smart phone could thus be used both for the recording of the images, and the subsequent image data processing according to the method, as well as providing storage capacity for the recorded images. Suitable lens adapters for recording eye images are commercially available, such as the iExaminer™, from Welch Allyn, Inc., 4341 State Road, Skaneateles Falls, N.Y. 13153, USA. In general, but particular when using a smart phone as the image recording device, it should be noted that the image recording device should record the images in an uncompressed format, such as Bitmap (.bmp), Tagged Image File (.tiff), JPEG2000 in lossless setting (.JP2, .JPF, .JPX). Compression may blur images and therefore adversely affect the subsequent image data processing of the method according to the disclosure and is therefore not desirable.

[0134] In a third step 12 at least one vein is identified in the recorded plurality of images. The method is of course not limited to one vein, a plurality of veins may also be identified and analysed in a same manner as the at least one vein. The at least one vein may be identified manually by personnel analysing the plurality of recorded images. Alternatively, or in combination, the identification of the at least one vein may be carried out by a processing unit using appropriate image analysis software.

[0135] In a fourth step 13 a first plurality of characteristic vein diameters for the identified vein at a first vein location is determined, in a first plurality of images from the plurality of images recorded over the first time period.

[0136] In a fifth step 14 it is determined, based on the first plurality of characteristic vein diameters, whether the at least one vein has experienced a vein collapse during the first time period. The determination of whether the least one vein has experienced a vein collapse during the first time period may be carried out in plethora of ways. In the block diagram three different methods 141-146, 147-1412, 1413-1415 of determining whether the vein has collapsed in the first time period is presented. The different method may be carried all in parallel with each other, a combination of the methods may be chosen to be carried out in parallel, or just a single of the presented methods may be used.

[0137] In the first method 141-146 at least one artery associated with said vein is identified 141. The artery may be identified in a corresponding manner as the vein. A first plurality of characteristic artery diameters for the identified artery at a first artery location is determined 142 in the first plurality of images from the plurality of images recorded over the first time period. Based on the first plurality of characteristic artery diameters an artery diameter behaviour is determined 143. Based on the first plurality of characteristic vein diameters a vein diameter behaviour is determined 144. The vein diameter behaviour is compared 145 to the artery diameter behaviour. Based on the comparison between the vein diameter behaviour and the artery diameter behaviour, it is determined 146, whether the at least one vein has experienced a vein collapse during the first time period. The workings behind the first method 141-146 is presented in higher detail in relation to FIG. 4.

[0138] In the second method 147-1412 the location of the optic disc is determined 147 in the first plurality of images. A second plurality of characteristic vein diameters for the identified vein at a second vein location is determined 148 in the first plurality of images from the plurality of images recorded over the first time period. Based on the first plurality of characteristic vein diameters a first vein diameter behaviour is determined 149. Based on the second plurality of characteristic vein diameters a second vein diameter behaviour is determined 1410. The first vein diameter behaviour is compared 1411 to the second vein diameter behaviour. Based on the comparison between the first vein diameter behaviour and the second vein diameter behaviour, it is determined 1412, whether the at least one vein has experienced a vein collapse during the first time period. The workings behind the second method 147-1412 is presented in higher detail in relation to FIG. 5.

[0139] In the third method 1413-1415 a change in vein diameter during the first time period is determined 1413, based on the first plurality of characteristic vein diameters. The change in vein diameter is compared 1414 with a threshold value. Based on the comparison between the change in vein diameter and the threshold value it is determined 1415, whether the at least one vein has experienced a vein collapse during the first time period. The workings behind the third method 1413-1415 is presented in higher detail in relation to FIG. 5.

[0140] Thus, the determination made in the fifth step 14 rely on the first method 141-146, the second method 147-1412, the third method 1413-1415, or any combination of these, e.g. if it was not possible to identify an artery in the recorded images the second method 147-1412 and/or the third method 1413-1415 may still be used to determine whether the at least one vein has experienced a vein collapse. Alternatively, if an artery was identified but the image quality was only sufficient to measure a characteristic vein diameter at a first vein location, the first method 141-146 and/or the third method may be used. Being able to rely on several methods allows for verification of results and lowers the requirements on the recorded images.

[0141] In a sixth step 15 a relation between IOP and ICP during the first time period is determined. The determination is made based on whether the at least one vein has collapsed during the first time period, where if the at least one vein has experienced a vein collapse the IOP is determined to exceed the ICP.

[0142] In a non-mandatory seventh step 16 the previous steps 10-15 may be repeated for a second time period, allowing for the monitoring of a patient over a longer duration of time.

[0143] In parallel with determining the relation between IOP and ICP during the first time period, an AVR for the patient.

[0144] In an eight step 17 at least one artery associated with said vein is identified in said plurality of images. This step may in some case be skipped if the first method 141-146 is applied, as the first method involves identifying 141 at least one artery associated with the least one vein.

[0145] In a ninth step 18 a first plurality of characteristic artery diameters for the identified artery at a first artery location is determined in the first plurality of images from the plurality of images recorded over the first time period. Similarly, to the eight step 17, the ninth step 19 may also be skipped if the first method 141-146 is applied, as the first method involves determining 142 the first plurality of characteristic artery diameters for the identified artery at the first artery location.

[0146] In a tenth step 19 an AVR is calculated based on the first plurality of characteristic artery diameters and the first plurality of characteristic vein diameters. The calculated AVR may be calculated as a mean or median value based on the determined characteristic diameters.

[0147] In an eleventh step 20 the calculated AVR is compared to the relation between IOP and ICP, determined in the sixth step 15.

[0148] In a twelfth step 21 the eight step 17, ninth step 18, and tenth step 19 may be repeated for a second time period in order to determine an AVR for the second time period.

[0149] In a thirteenth step 22 the change in AVR between the first time period and the second time period is determined.

[0150] In a fourteenth step 23 the change in AVR is compared to the relation between IOP and ICP during the first time period and to the relation between IOP and ICP during the second time period.

[0151] Specific examples of the disclosure have now been described. However, several alternatives are possible, as would be apparent for someone skilled in the art. Such and other modifications must be considered to be within the scope of the present disclosure, as it is defined by the appended claims.