MODULE 2 Vision Process The stimulus received by the sense of sight (eyes) is light. Light entering through the cornea will be transmitted as follows: Light → Aqueous humor → Pupil → Lens → Vitreous humor → Retina If the incoming light is too bright, the pupil will narrow or constrict. When the light is dim, the pupils will dilate or become dilated. Light reflected into the eye enters the retina, especially at the fovea (yellow spot). This light can be focused into the fovea because it is controlled by the lens. The eye lens has the ability to flatten and convex. The muscles attached to the lens and choroidal walls are called the ciliary muscles. This muscle functions to change the shape of the lens. If the lens is used to see objects at close range, the lens of the eye will be convex, the shape of the lens will be flattened when used for seeing remote objects. The retina contains 2 types of cells, namely rod cells and cone cells. These cells are mostly located in the fovea and function to receive images with weak light, and the images that are formed or perceived are black and white. If your view becomes dark when you enter a room from a brightly lit room outside. This can happen because when you are outside (there is sunlight) the cone cells do their job of conveying images to the brain. Meanwhile, the rhodopsin pigments in the stem cells will break down so that the stem cells cannot work properly. If you suddenly enter a dark room, the rhodopsin pigments that are broken down in the rod cells will reform, and the rod cells will take over the task of the cone cells in conveying images to the brain. The formation of rhodopsin pigments occurs gradually. This causes a person to not be able to immediately see clearly when entering a dark room. The length of time required for the rhodopsin formation process is called the rhodopsin adaptation time. Apart from containing rod cells, the retina also contains cone cells or cone cells. The function of cone cells is to receive red, blue and green stimuli. Each cone cell contains one of the three pigments. If the retina of the eye only has one pigment or one cone cell, you will experience color blindness. People who only have two types of cone cells are called dichromats. Meanwhile, people who only have one type of cone cell are called monochromats. In monochromats, the only colors visible to the eye are black and white and shades of gray. All parts of the retina contain rod cells and cone cells, except where the optic nerve is located. The area where the eye nerve is located is so small that it resembles just a point. These small spots are called blind spots. The ability of the lens to focus images on the retina varies. The following is an image of the lens when focusing the image. Apart from having light, the condition for the eyes to see well is that the eyes must be in a normal condition. Normal eyes (emetropy) are eyes that can accommodate well. The farthest point (punctum remotum) is as far away as possible. The closest point (punctum proximum) is at the ideal reading distance (25 cm) in front of the eye.