WEEK TWO

Bismillahirrahmanirrahim.

As I promised, this week's post will be the 'lab session with me'. My supervisor told me to do the laboratory session for EOG test. The lab session was done on Wednesday 23rd of February. This lab session is to prove the polarity of the rolling eyes and the voltage differences. 

The lab session was not running smoothly actually. I went to the lab at 11 am. And I had class on 12 pm. So, I only have one hour to do the lab. But, in all time I took most of the time left to complete the EOG circuit with the help of my friend and the technician as I was not really prepared. As the circuit finished, I tried to get the result. Below are the pictures that I captured. 

result one

result two

result three

Result one, result two and result three show the results which I got on the 'lab session'. Result one shows the result when eyes were blinking simultaneously while result two shows the result when eyes were turning from right to left simultaneously. Result three shows the result when eyes were rolling from upward to downward simultaneously. The reading taken for each waveform is four to five readings. The result I got were not very good. 

applying the EOG electrode

In this experiment, I use four channel electrode configuration for taking the EOG reading. The horizontal electrodes were placed on my right and left eyes each while the vertical electrodes were placed on upper and lower of my right eye. The reference electrode was placed on the center of my forehead. 

I think I want to do this experiment again to check and re-check the waveform produced. Also, I want to take the voltage range for the EOG measurement. 

Barakallah.

WEEK ONE also

Bismillahirrahmanirrahim.

In this post, I will explain more about the EOG and how electrooculography works. Just for reminding, electrooculography (EOG) is a type of biomedical technique for measuring the resting potential of the retina while the electrooculogram is the resulting signals that comes from the potential difference caused by the eye movements.

The electrooculogram (EOG) is the electrical signal produced by the potential difference between the retina and the cornea of the eye. This difference is due to the large presence of electrically active nerves in the retina compared to the front of the eye. Many experiments show that the corneal part is a positive pole and the retina part is a negative pole in the eyeball. The movements of the eye create dipole which can be measured using bipolar electrodes to provide information about eye movements, e.g., angular amplitude and velocity.

The diagram above represents the schematic of the eye and the polarity of the potential difference (top). Angular deviation of eye position changes the vector of the dipole, resulting in amplitude changes in the EOG recording.

For EOG, there are two basic channel configurations. The first one is two channel configuration and the second is four channel basic configuration. 

Two Channel Configuration

In this configuration, the electrode is placed at the area between the eye and the hairline of both eyes. The electrodes must be centered to match the pupil of the subjects’ both eyes. Reference electrodes are placed at the in the middle of the subject's forehead. Because eye movements are largely binocularly synchronous in both sleeping and awake subjects, this electrode configuration will provide out-of-phase deflections on each electrode for most types of eye movements.

two channel configuration EOG electrode

Four Channel Configuration

For this configuration, the electrodes are placed at same position as two channel configuration but there are another two electrodes placed one above the eyelid and another below the eye. The advantage of this technique is that simultaneously recording vertical and horizontal eye movements allows for eye position and vector to be calculated.

four channel configuration EOG electrode

Positive or negative pulses will be generated when the eyes rolling upward or downward. The amplitude of pulse will be increased with the increment of rolling angle, and the width of the positive (negative) pulse is proportional to the duration of the eyeball rolling process.

When the eyes are stationary or when the eyes are looking straight ahead, there is no considerable change in potential and the amplitude of signal obtained is approximately zero.

When the eyes are made to move upwards, then there results an action potential, which when measured will give a value of -0.06v to +0.06v. Similarly a downward movement of the eyes will give a similar voltage but with opposite polarities to that obtained due to the left movement. The potential difference is differ depend on the subject. 

the graph represent the potential difference when the eyes
rolling upward, downward, left or right.

That's the basic of EOG. In the next post, I will show the lab test on the EOG. But using the EOG equipped in UniKL BMI's Medical Electronics Laboratory :)

Barakallah.

*updated*
For slide presentation given to students as guideline click here.

WEEK ONE

Bismillahirrahmanirrahim.

As the first week of s1’13 starts, I was assigned to build a project for my final year project. The first things-to-do are to find supervisor for my project. He, which I choose Sir Syazwan Md Yid will be advising me on and about the project. In this week also, there is the first briefing for all final year students for bachelor program and engineering design for diploma students.

This project is mainly about the electrooculography or EOG. EOG is a biomedical technique for measuring the resting potential of the retina while the electrooculogram is the resulting signals of the potential difference caused by the eye movements. This technique use recording the eye movements non-invasively using skin surface electrodes placed around the eyes. The main applications are in ophthalmological diagnosis and in recording eye movements. EOG interfaces also let users who can’t manipulate a mouse or track pad with their hands move a cursor on a computer screen.

The voltage difference is measured between the cornea and the retina. The resting potential ranges from 0.4mV to 1mV and a pair of electrodes are commonly used to detect this signal. Depending on the eyes' position, an electrode is more positive or negative with respect to the ground electrode. Therefore, the recorded signal is either negative or positive when moving the eyes.

This can be monitored using bipolar electrodes in two basic configurations which are two channel configuration and four channel configuration. The two channel configuration is designed to detect movement onset and direction in a single plane which is horizontal while four channels configuration is designed to detect movement onset and direction in any plane which is horizontal and vertical. However, the voltage differences when there is an eye movement can be just small microvolts. So, the EOG system must amplify the voltage in order to get a readable signal for the oscilloscope or CPU. This is because the oscilloscope and CPU cannot detect the small voltages from the EOG system. 

TWO CHANNEL ELECTRODE CONFIGURATION

I will explain more about EOG system in the next post :)

Barakallah.

INTRODUCTION

BISMILLAHIRRAHMANIRRAHIM.

Finally, I am in final year. Throughout this year, I will do my Final Year Project which I chose Sir Mohd Syazwan Md Yid as my supervisor. The tittle of this project is the Development of EOG Circuit for Controlling Mouse Cursor on Computer. I think the tittle of this project is something interesting. But I can't deny it is hard. I hope I can do this project with help of my supervisor and friends. Also the technicians. I will do my very best on this project, insya Allah. May Allah ease! 

(picture from here)

Picture above is on how I will try to measure the EOG of the subject. I will explain in detail in next post :)

Barakallah.