A visual field encompasses the entire area one can see, including both central and peripheral vision, while looking straight ahead. The temporal visual field specifically refers to the outer portion of this visual area, located towards the temples of each eye. This region of vision allows individuals to perceive and interpret visual information from their side view.
How the Temporal Visual Field is Processed
Light from the temporal visual field enters the eye and strikes the nasal (inner) half of the retina. This is because the eye’s lens inverts the image, so objects from the outer visual field are projected onto the inner retinal surface. The axons from the nasal retina then gather to form part of the optic nerve.
These nerve fibers travel from the eye towards the brain. At the optic chiasm, located at the base of the brain, fibers from the nasal half of each retina cross to the opposite side. This means information from the left temporal visual field travels to the right side of the brain, and information from the right temporal visual field travels to the left side.
After the optic chiasm, these crossed and uncrossed fibers form the optic tracts. The visual information then continues its journey, synapsing in the lateral geniculate nucleus (LGN) of the thalamus. From the LGN, axons project to the primary visual cortex, located in the occipital lobe at the back of the brain. Here, visual signals are processed and interpreted.
The Role of the Temporal Visual Field in Vision
The temporal visual field is highly involved in detecting motion and perceiving the broader visual environment. It is responsible for noticing objects and movements in the periphery, which helps individuals respond to potential threats or other stimuli outside their direct line of sight.
This outer vision contributes to depth perception and spatial relationships, helping us understand where objects are in relation to ourselves and each other. It also assists in guiding eye movements and coordinating head and body movements, allowing for fluid navigation through an environment. For instance, when driving, peripheral vision helps monitor road edges and other traffic, even if not directly fixated.
The temporal visual field also plays a role in balance and overall awareness of our surroundings. Without sufficient peripheral awareness, the context of visual space can be lost, making it difficult to distinguish objects from their background.
Conditions Impacting the Temporal Visual Field
Various medical conditions and injuries can specifically affect the temporal visual field, leading to distinct patterns of vision loss. One prominent example is bitemporal hemianopsia, a condition characterized by the loss of vision in the outer (temporal) halves of both the right and left visual fields.
Bitemporal hemianopsia commonly arises from compression of the optic chiasm, where the nerve fibers from the nasal retinas cross. Since the pituitary gland is located directly beneath the optic chiasm, pituitary tumors are a frequent cause of this condition. As the tumor grows, it can press on these crossing fibers, disrupting the visual signals.
Other causes of optic chiasm compression include meningiomas and craniopharyngiomas, which are other types of tumors, or aneurysms. The extent and specific pattern of temporal visual field loss can vary depending on the size and exact location of the compression.
Detecting Problems in the Temporal Visual Field
Eye care professionals use specific tests to detect and diagnose issues within the temporal visual field. A common method is perimetry, also known as visual field testing, which helps create a map of a person’s entire visual field. This non-invasive test is part of a comprehensive eye examination and can reveal vision problems linked to eye diseases or brain disorders.
One type of perimetry is the automated static perimetry test, where a patient looks into a bowl-shaped instrument called a perimeter. While focusing on a central point, flashing lights of varying sizes and brightness appear in different parts of the visual field. The patient presses a button when they see a light, allowing the machine to map areas of vision and any deficits.
Another screening method is the confrontation visual field test, where the examiner holds up a varying number of fingers in the patient’s side vision while the patient looks straight ahead. The patient then reports how many fingers they see. This simpler test is often used as an initial check for visual field problems.