Eye Movement (sensory) - Varieties and Purpose of Movement

Varieties and Purpose of Movement

There are three main basic types of eye movements:

• Vergence Movements or convergence are the movements of both eyes to make sure that the image of the object being looked at falls on the corresponding spot on both retinas.

This type of movement helps in the depth perception of objects

• Saccades are the rapid movement of eyes that is used while scanning a visual scene. In our subjective impression, the eyes do not move smoothly across the printed page during reading. Instead, our eyes make short and rapid movements called saccades. During each saccade the eyes move as fast as they can and the speed cannot be consciously controlled in between the stops. The movements are worth a few minutes of arc, moving at regular intervals about three to four per second. One of the main uses for these saccadic eye movements is to be able to scan a greater area with the high resolution fovea of the eye.
• Pursuit Movements or Smooth pursuit are the movements that the eyes make while tracking an object's movement, so that its moving image can remain maintained on fovea.

Additionally, the eyes are never completely at rest. They make fast random jittering movements even when we are fixated on one point. The reason for these random movements are the photoreceptors and the ganglion cells. It appears that a constant visual stimulus can make the photoreceptors or the ganglion cells to become unresponsive; on the other hand a changing stimuli will not. Therefore, these random eye movements constantly change the stimuli that fall on the photoreceptors and the ganglion cells making the image more clear.

Saccades are faster than vergence and pursuit eye movements.