5 Major Eye Movements

Sight is one of the special senses and it is accomplished with an organ called the eye. The eye receives light and transforms the photon signal into an electrical signal that the brain interprets. This transformation of information is done via the photoreceptor cells found at the back of the eye on the retina. The photoreceptors, rods and cones, are distributed across the back of the eye to capture all light with a higher concentration found in the fovea for fine vision. The light stimulates rods and cones resulting in a change in their membrane potential. This change results in a cascade of signals via sensory nerve cells along an optic nerve to the visual cortex. The image that is seen is focused on via the use of both intraocular and extraocular

These two pathways result in the excitation of two different muscle fiber types that the extraocular muscles are composed of (Sadeh and Stern, 1984). These fibers are the fibrillary structure and plain structure muscle fibers. The fibrillary structure is under phasic innervation whereas the plain structures are under tonic innervation (Sadeh and Stern, 1984). Therefore, some muscles have finer control and are only called upon when needed while others are constantly excited. The innervation of these muscles result in 5 major eye

Saccadic eye movements are quick movements that enable the eye to rapidly focus the fovea on a scene (Chen and Epps, 2013). In general, the light enters the eye and then we attempt to foveate it to see the object in great detail (Whittaker and Cummings, 1990). Pursuit is a smooth eye movement that keeps the fovea focused on a moving object (Laurenceau, 2012). Before this is obtained the eye follows the object with saccadic movements to focus on the moving object. This is due to the fact that the motor neurons that result in pursuit motion are innervated via a long and complex pathway, taking more time to result in smooth pursuit motion (Lauenceau, 2012). The vestibular ocular reflex (VOR) is a reflex where the eye will be stabilized so that the retina will stay focused on an object or scene while the head moves from the center of the image. The velocity of the eye movement matches the speed with which the head is rotated, and it moves in the opposite direction (Kawato and Gomi, 1992). Vergence is composed of two eye movements which are made when the eye focuses from a near to distant object, and vice-versa, in the same line of view (Erkelens, 2011). Vergence is accomplished this while the eyes are rotating in opposite directions (Cullen and Van Horn, 2011).The optokinetic reflex (OKR) is another reflex that allows the eye to follow a field of motion