An ophthalmoscope is used for viewing the retina.
The picture that human beings see when they look at an object requires a complex network: the manipulation of light with contact lenses or glasses, structural clarity of the eyeball, neurological integrity of the eyeball, and neurological integrity of the visual system in the brain. The rod and cone cells in the eyeball form the basis for the neurological integrity of the eyeball.
Retina
The retina is the neurological tissue that lines the inner surface of the eyeball at the back of the eyeball. There are 10 retinal layers; the two layers that pertain to the rods and cones are the outer nuclear layer, containing the rod and cone inner segments, and the photoreceptor layer, where the outer segments of the rods and cones are located.
Rod and Cone Inner Segments
The inner segment of the rods and cones contain the cell's nucleus, mitochondria, golgi apparatus, and all of the other elements of the cell that allow it to function properly. The processes that occur in the inner segment of the rods and cones make the processes that occur in the rod and cone outer segments possible.
Rod and Cone Outer Segments
The outer segments of the rods and cones contain a protein known as opsin. Retinal is a specific portion of the opsin protein that is affected by light. When a particle of light comes into contact with the retinal portion of the opsin, the retinal undergoes a chemical change. This chemical change is temporary. When the change happens, it causes the rod and cone outer segments to send an electrical impulse through the rod or cone cell. This is where the visual signal actually begins in the eyeball.
Path of the Eyeball's Electrical Impulse
The electrical impulse generated from the rod and cone outer segments is conducted through seven of the remaining eight layers of the retina. When the electrical impulse reaches the optic nerve, it is transmitted through that nerve into the brains' visual system. The visual portion of the brain is located in the occipital lobe at the back of the brain; this is where the picture that a human sees is formed.
Functional Difference Between Rods and Cones
Rods are designed to be stimulated more easily by smaller amounts of light. However, they lack the ability to detect color differences or to see in fine detail. They function better in the dark for detecting movement. The cone cells are much smaller and are responsible for providing fine detail and color vision.
Tags: outer segments, rods cones, neurological integrity, chemical change, cone cells, cone outer