The fovea centralis is a very specialized section of the retina, which is the photosensitive lining of the eye. Based on its name, it is located in the center of the retina and has a pit shape. It is an avascular region of the retina and is responsible for the central vision of each eye. Lastly, the fovea centralis contains the highest number of cones—light-sensitive receptors that are responsible for the ability to see colors—within its region compared to the rest of the retina.
Anatomy and Physiology
The visual system’s external organ is the eye, and light entering the eye begins the process of sight. The eye is a complex organ that acts like a camera as it uses the laws of optics, which are based in physics. The eye uses light from an external object to focus an image onto its photoreceptors—rod and cone cells. These photoreceptors are found at the posterior portion of the eye in the retina. To help focus the light and project the image, the eye will refract the incoming light first through the cornea. The light then passes through the pupil and is refracted again via the lens. Together, the cornea and the lens act like a compound lens to project the image upside down onto the retina.
The definition of central vision or the central visual field is the central 10 degrees of a visual angle. Basically, it is the visual field that is seen when a person is looking straight ahead and does not move the eyes. For mapping images to the retina, scientists have measured that 1 degree of a visual angle maps to about 0.3 millimeter (mm) of the retina. Thus, 10 degrees would map to about 3 mm of the central retina or the area within a 1.5 mm radius from the exact center—0 degree eccentricity. This 3 mm region contains the macula, which looks yellow in color under an ophthalmoscope. Within the middle of the macula is where the fovea centralis is located. It is about 1 mm in diameter and forms a depression or pit within the macula. This depression occurs because there are no blood vessels in the fovea centralis. Instead it is densely packed with cone cells and contains the majority of cone cells within the entire retina. The number of cones drastically decreases in number as you move away from the fovea centralis and toward the periphery of the retina.
Cone cells have a faster response time to light stimuli compared to rod cells, thus allowing details of objects to be viewed and/or perceived. Because activation of cone cells is used to identify details of an object, they need plenty of light to be stimulated. In rare cases, cones can be damaged, resulting in a type of cone dystrophy, which is a general term to describe rare disorders that affect cone cells.
Today, macular degeneration is the leading cause of central vision loss and blindness among Americans who are age 65 and older. Symptoms start with center vision becoming blurred and colors may become muted in this region. Over time, gray spots may appear in the central vision.
Jennifer L. Hellier
See also: Blind Spot; Color Blindness; Cones; Hubel, David H.; Retina; Rods; Sensory Receptors; Visual Fields; Visual Perception; Wiesel, Torsten N.
Bear, Mark F., Barry W. Connors, & Michael A. Paradiso. (2007). Neuroscience exploring the brain (3rd ed.). Baltimore, MD: Lippincott Williams & Wilkins.
Provis, Jan M., Adam M. Dubis, Ted Maddess, & Joseph Carroll. (2013). Adaptation of the central retina for high acuity vision: Cones, the fovea and the avascular zone. Progress in Retinal and Eye Research, 35, 63—81.