Electrooculography , Seminar Reports | PPT | PDF | DOC | Presentation |

Our window into the large universe has always been a fused two-piece unit called as the eye. The eye is a complex optical system which collects light from the surrounding environment, regulates its intensity and focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain. The new advancements in the field of biomedical electronics and in the field of electronics and communication system have changed the perception of eye from an ordinary sense organ which enables us to see , in to, an organ which generates trigger pulses to activate and control various electronic devices.

The new methods of efficient human machine interfaces by using the eye movements and eye blinks are realized by using a very new bio-electric signal processing technique called as Electrooculography (EOG). Electrooculography is a technique for measuring the resting and action potential of the retina. The resulting signal is called the electrooculogram. Usually, pairs of electrodes are placed either above and below the eye or to the left and right of the eye. If the eye is moved from the center position towards one electrode, this electrode "sees" the positive side of the retina and the opposite electrode "sees" the negative side of the retina. Consequently, a potential difference occurs between the electrodes. Assuming that the resting potential is constant, the recorded potential is a measure for the eye position.

The hardware components generally required to detect the EOG signals are four to five electrodes, and   the amplifiers and filters are required for amplification and filtering processes respectively. The signals are processed using controllers or dsp processors depending up on the complexity of the application. Some of the important applications of EOG are in electrooculographic guidance of a wheel chair, retina controlled mouse, eye controlled switching on and off of electronic and electric devices, interactive gaming systems etc. The use of EOG for guiding of missiles in the battle field is a new project under research by the defense systems.

Bioelectricpotentials refers to the electrical, magnetic or electromagnetic fields produced by living cells, tissues or organisms. Bioelectric potentials are generated by a variety of biological processes and generally range in strength from one to a few hundred millivolts. Biological cells use bioelectricity to store metabolic energy, to do work or trigger internal changes and to signal one another. Bioelectricity is the electric current produced by action potentials along with the magnetic fields they generate through the phenomenon of electromagnetism. Bioelectric potentials are identical with the potentials produced by devices such as batteries or generators. In nearly all cases, however, a bioelectric current consists of a flow of ions (i.e., electrically charged atoms or molecules), whereas the electric current used for lighting, communication, or power is a movement of electrons.

 If two solutions with different concentrations of an ion are separated by a membrane that blocks the flow of the ions between them, the concentration imbalance gives rise to an electric-potential difference between the solutions. In most solutions, ions of a given electric charge are accompanied by ions of opposite charge, so that the solution itself has no net charge. If two solutions of different concentrations are separated by a membrane that allows one kind of ion to pass but not the other, the concentrations of the ion that can pass will tend to equalize by diffusion, producing equal and opposite net charges in the two solutions.

In living cells the two solutions are those found inside and outside the cell. The cell membrane separating inside from outside is semi permeable, allowing certain ions to pass through while blocking others. In particular, nerve- and muscle-cell membranes are slightly permeable to positive potassium ions, which diffuse outward, leaving a net negative charge in the cell. The bioelectric potential across a cell membrane is typically about 50 mill volts; this potential is known as the resting potential. All cells use their bioelectric potentials to assist or control metabolic processes, but some cells make specialized use of bioelectric potentials and currents for distinctive physiological functions, such as the nerve cell.