2.1 Role of Eye blinks in CVS
Blinking, best described as the predominantly involuntary rapid closure of the eyelids is one of many physiological functions of humans that have been described. In addition to its safety function, of protecting the eye from potentially dangerous external interferences and desiccation, it has also been discovered to play a vital role in cognitive high-order functioning . The eye blink is said to be primarily under the control of the Central Nervous System (CNS), especially the Globus pallidus area, with dopamine being the main transmitter involved  . In terms of higher order functioning, blinking and its frequency have been linked with attention, intelligence, and overall day-to-day functioning  . In a clinical research study carried out in Holland by Chermahini and Hommel, Eye Blink Rate (EBR) was found to be negatively associated with convergent thinking (‘Remote Association Task”) which had a positive relationship with intelligence. Whereas they found out that divergent thinking (“alternative uses” task) was mainly associated with average EBR . Several studies have also found a relationship between higher EBR, fatigue and sleepiness especially in the context of automobile crashes  . The average blink rate is 12-20 per minute with each blink lasting between 0.1 to 0.4 seconds  . As this rate and duration increase, the likelihood of automobile crashes has been said to increase significantly. While the importance of EB and its variability has been extensively studied with regards to automobiles, the relationship between EB variability and CVS has continued to gain more attention especially with the increasing use of digital electric screens and or visual display terminals.
2.2 Symptoms of CVS
CVS is a constellation of signs and symptoms associated with the use of computers and or digital devices. These include; eye strain (Asthenopia), diplopia, dry eyes, red eyes and blurred vision among others and it is usually due to computer/screen glare, poor lightning, inappropriate viewing distances, pre-existing visual abnormalities or a combination of any of these  . With symptoms increasing significantly with increased screen usage, especially greater than 4 hours of use, CVS is said to affect about 67.4%-90% of the population  . It is also said to be slightly more commonly reported by females, with eye strain and headache being the most prevalent symptoms  .
CVS is multidirectional as it affects individual of different age groups and gender differently with different associated symptoms. They have been broadly classified into three categories by ophthalmologists 
1. Accommodative or asthenopic symptoms
2. Ocular surface related symptoms
3. Extra Ocular symptoms
They further classified different symptom categories into specific symptoms in Table 1. Asthenopic symptoms are those eye accommodation problems that are already present in the individual but does not cause any discomfort to them, however with a prolonged exposure to VDTs they start having such symptoms as eye strain, dry eyes etc.
Ocular Surface related symptoms refer to disorders of the surface of the cornea – the transparent layer that forms the front of the eye examples are dry eye, Meibomian gland dysfunction blepharitis, chemical burns, thermal burns etc.
Extra Ocular Symptoms refers to physical posture of the VDT user when using the devices. It includes angle of view of the computer due to the height of the seat, poor or excessive lighting etc. 
Computer related ocular symptoms and diagnosis
|Ocular Surface related Symptoms
Contact Lens Problems
Poor focusing change
|Extra Ocular symptoms
2.3 EEG Overview
Electroencephalography (EEG) is a bio signal technique used in recording the electrical potential by the activities of the brain cortex which reflects the state of the brain in real-time . EEG belongs to a group of electro biological measurements techniques such as Electrocardiography (ECG) for measurement of heart beat, electromyography (EMG) for measurement of muscular contractions, electro-optigraphy (EOG) for eye dipole field measurement and other imaging techniques based on physical principles such as magnetic resonance imaging (MRI), and computer tomography (CT). Study of EEG is important in brain computer interface design. EEG is defined as alternating type of electrical activity recorded by a conductor or metal electrode from the scalp surface of the head . It is a non-invasive technique and poses virtually no health risk to the patients both in adults and children .
EEG involves the summed electrical activities of neutrons. Neutrons are excitable cells with characteristic intrinsic electrical properties and their activity produces electrical and magnetic fields. These fields are recorded by means of electrodes at a short distance from the cortal surface . The brain can be classified into three sections from the anatomical view point: cerebrum, cerebellum and the brain stem. The cerebrum is the principal and the most anterior part of the brain, it consists of the left and right hemisphere and the surface is referred to as the cerebral cortex and here is where the EEG electrodes record the electrical signals from . The cerebrum is an important part of the CNS and sensation, complex analysis, emotion etc. are controlled by this art of the brain. The cerebellum is responsible for maintaining balance and voluntary movement of muscles and the brain stem regulates heartbeat, controls hormone secretion and respiration . A layout of the electrodes on the scalp is shown in figure 1.
There are two internationally recognized nomenclatures to describe the different scalp locations of electrodes.
• The 10-20 naming system: This is an internationally recognized nomenclature; the 10-20 name was derived from the spacing of electrodes from one another with either 10% to 20% front to back electrode spacing or 10% to 20% left to right electrode spacing. Each electrode location is denoted by an alphabet and a number. F stands for frontal; T stands for Temporal; C stands for central (it has no real purpose asides just for identification); P stands for Parietal and O for occipital and odds numbers (1,3,5,7) stands for positions on the left hemisphere of the head and even numbers (2,4,6,8) stands for positions on the right hemisphere of the head.
• The Modified Combinatorial Nomenclature: The need for this aroused when it was required to add more electrodes to more accurate recordings. This system uses the intermediate points between the different electrode locations in 10-20 naming system. AF stands for the intermediate location between Fp and F electrodes; FC stands for the intermediate location between F and C; FT stands for the intermediate location between F and T; TP stands for the intermediate location between T and P; CP stands for the intermediate location between C and P; PO stands for the intermediate location between P and O; T7, T8, P7, P8 on the modified combinatorial nomenclature stands for T3, T4, T5, T6 respectively on the 10-20 system.
EEG is one of the hardest bio signals to read because of its low amplitude which normally ranges between 0.5 µV to 100µV . However, it has great advantage of speed as complex brain patterns can be recorded in real-time. EEG waves are an aggregation of multiple potential of different neutrons and it has been classified into different bands of frequency shown in table 2 and pictorially in figure 2. These different band of frequency represents human activities. The beta waves characterized with high frequencies with lower amplitude than the gamma waves indicate wakefulness, high alert, anxiety. Alpha wave has amplitudes lower than that of the beta waves and indicates awake, relaxed, learning. Theta waves indicates rapid eye movement (REM) sleep, meditation, day-dreaming and delta waves are the slowest and they have the highest amplitude and indicates non-rapid eye movement (NREM) sleep and gamma waves occur during sensory processing of sound and light.
Frequency bands of EEG signals 
||(30 - 100) Hz
||(12 - 30) Hz
||(8 -12) Hz
||(4 - 7) Hz
||(0.5 - 4) Hz