Method for Assessing Blood Flow in Segments of the Eye using

Multichannel Rheoophthalmography

Elena N. Iomdina

, Nina Yu. Kushnarevich

, Tatiana Yu. Larina

, Petr V. Luzhnov

Anna A. Kiseleva

and Elena P. Tarutta

Helmholtz National Medical Research Centre of Eye Diseases, Russia

Bauman Moscow State Technical University, Russia

Keywords: Rheoophthalmography, Electrical Impedance Signal, Contour Analysis, Automatic Differentiation,

Diagnostic Algorithm.

Abstract: The paper presents the issue of studying changes and redistribution of the blood flow level in different

segments of the eye using the electrical impedance method - rheoophthalmography. There are described and

considered the quantitative values using this method for the posterior segment of the eye and the retrobulbar

segment of the eye. Based on the obtained data, an algorithm for differentiation of disease stage for research

groups with myopia is proposed. The principle of its operation is described. The prospects for increasing the

efficiency of the developed algorithm are considered.

1 INTRODUCTION

Any changes in the blood supply to any organ or

tissue of the human body entail changes in its

functioning. It is also true for the human eyes

(Schmetterer L., 2012). The blood supply to the eye

covers both the area of the ciliary body in the

anterior segment of the eye and the area of the sclera

in the posterior segment of the eye. Determination of

the blood supply level to the eye segments is of

interest for many problems of ophthalmic

diagnostics (Golzan S.M., Avolio A., et al., 2012;

Michelson G., Gründler A., et al., 1994). It is known

that in ocular pathologies, in particular myopia, the

level of blood flow in different segments of the eye

changes. In this regard, particular interest to the

ophthalmologist is a study on the changes and

redistribution of blood flow in the eye segments

(Kunin V.D., Svirina T.A., 2002). This is especially

true for a group of patients with low myopia, who

are indicated for further therapy and correction.

Electrical impedance diagnostics is one of the

non-invasive methods for assessing the state of

blood flow in different areas of the human body with

minimal impact on it (Cybulski G., 2011; Vasilyeva

R.M., 2017; Bodo M., 2010). This diagnostic

method makes it possible to form diagnostic

information about the pulse blood filling of the

investigated body area, as well as information about

the biomechanical properties of blood vessels and

the level of blood flow in them. The electrical

impedance method is based on recording the

changes in total resistance during probing tissues

with high-frequency and low-amplitude current.

Currently, there are several rheoophthalmographic

(ROG) techniques for examining the eye (Avetisov

E.S., Katsnel'son L.A., et al., 1967; Lazarenko V.I.,

Kornilovsky I.M., et al., 1999). The most atraumatic

of them is the technique of transpalpebral

rheoophthalmography (TP ROG), in which

electrodes are applied to the closed upper eyelid

(Luzhnov P.V., Shamaev D.M., et al., 2017;

Luzhnov P.V., Shamaev D.M., et al. 2018). The

study of the eye blood flow during the progression

of myopia was carried out, the possibility of using

this technique for the early diagnosis of blood

supply disorders in myopic children was shown

(Luzhnov P.V., Shamaev D.M., et al. 2017;

Sokolova I.V., Yarullin K.K., et al., 1977). A feature

of signal analysis of myopic patients concerns

mainly the anterior segment of the eye.

In the general case, to assess the eye blood flow

during diagnosis, it is possible to operate with three

integral values of the blood flow level (Kiseleva

A.A., Luzhnov P.V., et al., 2020): in the anterior

segment of the eye, in the posterior segment of the

eye, and also in the retrobulbar segment of the eye

212

Iomdina, E., Kushnarevich, N., Larina, T., Luzhnov, P., Kiseleva, A. and Tar utta, E.

Method for Assessing Blood Flow in Segments of the Eye using Multichannel Rheoophthalmography.

DOI: 10.5220/0010988700003123

In Proceedings of the 15th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2022) - Volume 1: BIODEVICES, pages 212-216

ISBN: 978-989-758-552-4; ISSN: 2184-4305

(as input value relative to the eye). It is necessary to

develop a diagnostic algorithm for such a differential

assessment of blood flow in different parts and take

into account changes in the level of blood flow in

each segment of the eye, and the ratio of these

changes between segments.

2 MATERIALS AND METHODS

The method of electrical impedance diagnostics

allows an integral assessment of the blood flow state

in the eye vessels. At the same time, most other

diagnostic methods are based on determining the

blood filling of the eye vessels differentially.

Electrical impedance diagnostics makes it possible

to quantify blood supply not in individual arteries,

but in the vascular system of the eye as a whole. The

TP ROG technique allows a quantitative assessment

of blood supply at a level corresponding to the

anterior segment of the eye. It is achieved due to the

positioning peculiarities of the TP ROG electrodes

system (Luzhnov P.V., Shamaev D.M., et al. 2017).

Multiple electrodes systems should be used to

diagnose blood flow in multiple parts of the eye. The

areas of study corresponding to the anterior,

posterior and retrobulbar regions are shown in Fig.1.

The corresponding positioning schemes for the ROG

measuring electrodes are shown in the figure on the

right.

Figure 1: The areas of study corresponding to the anterior

(AP), posterior (PP) and retrobulbar (RB) parts in the

multichannel rheoophthalmography technique.

To study the anterior segment of the eye, it is

advisable to use the TP ROG technique (Luzhnov

P.V., Shamaev D.M., et al. 2017), which proved itself

in the diagnosis of various stages of myopia in

children and adolescents (Luzhnov P.V., Shamaev

D.M., et al., 2015; Iomdina E.N., Luzhnov P.V., et al.,

2014). To study the posterior segment of the eye, the

method was previously used to determine blood flow

parameters in groups of patients with glaucoma. For

the study of the input blood flow, the method (Bodo

M., 2010; Sokolova I.V., Yarullin K.K., et al., 1977)

is known, which was used for the study of cerebral

circulation. In our work, the data on TP ROG

diagnostics were taken from (Luzhnov P.V., Shamaev

D.M., et al., 2015). ROG signals for the posterior and

retrobulbar segments were recorded in groups of

patients with various degrees of myopia.

To register the electrical impedance signals of

the ROG, a two-channel tetrapolar measurement

technique was used. For each channel, two pairs of

electrodes were used: two current and two

measuring. The axis of electrodes symmetry of the

posterior segment was located vertically (the first

channel). The measuring electrodes were located

along the edge of the orbit above and below the eye.

The distance between them was 4.5 cm. Measuring

electrodes of the second channel were located at the

temple. The distance between the measuring

electrodes was 2.5 cm. The second channel probing

area included the area of the ophthalmic and internal

carotid arteries. In the study we used standard self-

adhesive electrodes for functional diagnostics. The

distance between the electrodes was controlled by

measuring the distance between their centers, or the

attachment points of the lead cable. The frequency

of the probing current was 100 kHz, the amplitude

was 3 mA. Two-channel registration of the ROG

signals with a sampling rate of 200 Hz was carried

out. Then the ROG signals were filtered.

The primary analogue filtering was carried out

using a combined bandpass filter with cutoff

frequencies of 0.15 Hz and 100 Hz. It allowed

selecting the component of the ROG signal, which

reflected the process of pulse blood filling. Its

amplitude was determined by the rheographic index

(RI). The second component of the signal, called the

base impedance (BI), was formed by a low-pass

filter with a cutoff frequency of 0.15 Hz and

reflected the level of general blood filling in the

examined part of the eye.

Thus, the ROG signal was available for

calculations for each patient, from which the RI and

BI values could be determined. The average values

of RI and BI for the study group were also

calculated. Then it was possible to calculate the

relative changes in these parameters comparing the

study and the control groups. Based on these data, it

became possible to build an algorithm for

diagnosing and determining the blood supply

disorders specific for the stage of the myopic

process. This sequence implied the algorithm

development for assessing blood flow in one part of

the eye and the subsequent comparison of the data

obtained in different parts of the eye using the

signals analysis from multichannel ROG.

Method for Assessing Blood Flow in Segments of the Eye using Multichannel Rheoophthalmography

213

At the first step of the algorithm, one recorded

signal was processed. In our work, the duration of

the ROG signal was chosen to be 20 seconds.

During this period, with calm breathing, several

complete breathing cycles passed. It eliminated the

influence of breathing phases on the one signal

processing result. The computation started with a

contour analysis of the ROG signal. The contour

analysis used automatic detection of the onset of the

systole phase with a period of rapid blood filling. It

was used the threshold method used on the first

derivative of the signal. The second point of the

contour analysis was the systolic wave amplitude. It

was determined by the position of the signal local

extremum. The value of the RI amplitude was

determined by the difference in the levels of these

points. Then this stage of the algorithm was repeated

for all whole periods of cardiac cycles presented in

the analyzed signal record.

At the next step of the algorithm, the amplitude

of the ROG signal was determined as the arithmetic

mean of the amplitudes of all pulse waves included

in the 20-second recording period. The RI value

determined in this way corresponded to one value of

the BI, since the BI change in time during the

recording of the ROG signal was negligible. One

ROG signal was represented by the resulting RI-BI

score pair. For the second channel, the calculation

was done using the same step. As a result, there

were two pairs of RI-BI values for a two-channel

ROG recording in a single patient study. One pair

characterized the posterior segment of the eye, the

other pair characterized the retrobulbar segment of

the eye.

The obtained values were averaged for the entire

group of studies. The resulting averaged value made

it possible to assess the change of the indicators

value in comparison with a certain value (for

example, the norm). It also allowed comparing the

diagnostic results in different groups. To visualize

such comparison, the resulting parameters were

presented graphically on the RI-BI plane. This

presentation of the results made it possible to

analyze the obtained diagnostic data. In addition, on

the RI-BI plane, it became possible to build an

algorithm for differentiation by disease stages.

To test the developed algorithm on the basis of

the department of refraction pathology, binocular

vision and ophthalmoergonomics of Helmholtz

National Medical Research Center of Eye Diseases,

a study of the ROG signals of several groups of

patients with myopia was carried out. Simultaneous

registration of the ROG signals of the posterior and

retrobulbar parts of the eye was carried out using a

two-channel measuring transducer. During the

examination, the patient was in a horizontal position

at rest. In total, ROG signals were analyzed in 21

patients (42 eyes). When carrying out two-channel

registration, 4 groups of patients were formed:

conditionally healthy with normal vision (refraction

more than - 1.0 diopter), a group with low myopia

(from -1.0 to -3.0 diopters), a group with moderate

myopia (from -3.0 up to - 6.0 diopters) and a group

with high myopia (- 6.0 diopters and more). The first

group included 6 subjects (11 eyes) with an average

age of 23.7 years. The group with low myopia

consisted of 7 people (13 eyes) with an average age

of 14.0 years. The group with moderate myopia was

4 people (8 eyes) with an average age of 17.2 years.

The group with high myopia consisted of 5 people

(10 eyes) with an average age of 16.2 years. This

study was performed in accordance with the

Declaration of Helsinki and was approved by the

Local Committee of Biomedical Ethics of the

Helmholtz National Medical Research Center of Eye

Diseases. A written informed consent was obtained

from all participants.

3 RESULTS

The relative change in pulse blood filling in groups

with myopia was determined as the difference

between the mean value of the parameter in the

myopic group and in the group with normal

refraction (normal group), divided by the mean

value of the parameter for the normal group. In this

case, RI(PP) and BI(PP) determine the indicators for

the posterior segment, RI(RB) and BI(RB)

determine the indicators for the retrobulbar segment.

To use the developed algorithm, the norm group

was used as a control group. The magnitude of the

relative change was calculated as the difference

between the mean parameter in the group and the

mean parameter in the control group, normalized to

the mean parameter in the control group (in

percents). This value was determined for each

channel separately. The calculation results are

shown in Table 1.

Table 1: Relative change in parameters for two-channel

registration of ROG signals in percents.

Myopia

ree

RI(PP) BI(PP) RI(RB) BI(RB)

Low 4.1 22.4 5.0 29.5

Moderate -6.0 -23.6 -9.7 -2.9

High -2.6 10.0 -5.6 8.3

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The result of the algorithm is presented

graphically in Fig.2. For each patient of the groups

with myopia, two values of diagnostic parameters

were obtained, presented by a pair of points on the

RI-BI plane.

Figure 2: The diagnostic parameters, presented by a pair of

points on the RI-BI plane for different stages of myopia.

Red markers on the graph (see Fig.2) show the

parameters of the retrobulbar segment of the eye,

orange markers show the parameters of the posterior

segment of the eye.

4 DISCUSSION

The obtained results indicate a simultaneous

increase in indicators in the temporal region and the

region of the posterior segment of the eye for a low

myopia. The points position on the graph with

moderate myopia indicates an increase in the BI

value against the background of a decrease in the

blood supply to the posterior segment. In high

myopia, it describes a decrease in the blood supply

to the posterior segment of the eye with a

simultaneous decrease in the total blood supply. This

result suggests that with a low degree of myopia, a

compensatory response from the vascular system is

observed, which manifests itself in a relative

increase in blood flow parameters.

In this work, the values of the control group were

selected as the basis for the calculation results of the

algorithm. However, the efficiency of the algorithm

can be improved if other values are used as the

origin of the RI-BI plane. It can be, for example,

parameters reflecting blood flow in the anterior

segment of the eye. The question of choosing the

origin of coordinates to achieve maximum efficiency

of the algorithm has not been fully resolved and

requires further research, including other diagnostic

methods, such as optical coherence tomography

(Iomdina E.N., Kiseleva A.A., et al., 2020) for the

posterior segment of the eye.

5 CONCLUSIONS

The use of the developed algorithm makes it

possible to present for analysis and present

graphically large data sets in multichannel ROG

studies. The use of the algorithm for groups of

patients with different myopia degrees showed the

fundamental possibility of automatic differentiation

according to the severity of the blood supply

disorders. Along with the possibility of early

diagnosis of these disorders, this will make it

possible to study blood flow disorders of the eye in

different segments with the possibility of

quantitative comparison of these disorders. With the

help of the developed algorithm, it becomes possible

to implement it within the framework of one

diagnostic technique for different ophthalmic

diseases.

ACKNOWLEDGEMENT

The authors declare that they have no conflict of

interest.

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