Visual field in the context of Floater

Visual hierarchy, according to Gestalt psychology, is a pattern in the visual field wherein some elements tend to "stand out," or attract attention, more strongly than other elements, suggesting a hierarchy of importance. While it may occur naturally in any visual field, the term is most commonly used in design (especially graphic design and cartography), where elements are intentionally designed to make some look more important than others. This order is created by the visual contrast between forms in a field of perception. Objects with highest contrast to their surroundings are recognized first by the human mind.

Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Some people experience a gradual worsening of vision that may affect one or both eyes. While it does not result in complete blindness, loss of central vision can make it hard to recognize faces, drive, read, or perform other activities of daily life. Visual hallucinations may also occur.

Macular degeneration typically occurs in older people, and is caused by damage to the macula of the retina. Genetic factors and smoking may play a role. The condition is diagnosed through a complete eye exam. Severity is divided into early, intermediate, and late types. The late type is additionally divided into "dry" and "wet" forms, with the dry form making up 90% of cases.

In neuroanatomy, the optic tract (from Latin tractus opticus) is a part of the visual system in the brain. It is a continuation of the optic nerve that relays information from the optic chiasm to the ipsilateral lateral geniculate nucleus (LGN), pretectal nuclei, and superior colliculus.

It is composed of two individual tracts, the left optic tract and the right optic tract, each of which conveys visual information exclusive to its respective contralateral half of the visual field. Each of these tracts is derived from a combination of temporal and nasal retinal fibers from each eye that corresponds to one half of the visual field. In more specific terms, the optic tract contains fibers from the ipsilateral temporal hemiretina and contralateral nasal hemiretina.

The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. The area of the visual cortex that receives the sensory input from the lateral geniculate nucleus is the primary visual cortex, also known as visual area 1 (V1), Brodmann area 17, or the striate cortex. The extrastriate areas consist of visual areas 2, 3, 4, and 5 (also known as V2, V3, V4, and V5, or Brodmann area 18 and all Brodmann area 19).

Both hemispheres of the brain include a visual cortex; the visual cortex in the left hemisphere receives signals from the right visual field, and the visual cortex in the right hemisphere receives signals from the left visual field.

The mental world or mindscape is an ontological category in metaphysics, populated by nonmaterial mental objects, without physical extension (though possibly with mental extension as in a visual field, or possibly not, as in an olfactory field) contrasted with the physical world of space and time populated with physical objects, or Plato's world of ideals populated, in part, with mathematical objects.

A blind spot, scotoma, is an obscuration of the visual field. A particular blind spot known as the physiological blind spot, "blind point", or punctum caecum in medical literature, is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the optic nerve passes through the optic disc. Because there are no cells to detect light on the optic disc, the corresponding part of the field of vision is invisible. Via processes in the brain, the blind spot is interpolated based on surrounding detail and information from the other eye, so it is not normally perceived.

Although all vertebrates have this blind spot, cephalopod eyes, which are only superficially similar because they evolved independently, do not. In them, the optic nerve approaches the receptors from behind, so it does not create a break in the retina.

The accommodation reflex (or accommodation-convergence reflex) is a reflex action of the eye, in response to focusing on a near object, then looking at a distant object (and vice versa), comprising coordinated changes in vergence, lens shape (accommodation) and pupil size. It is dependent on cranial nerve II (afferent limb of reflex), superior centers (interneuron) and cranial nerve III (efferent limb of reflex). The change in the shape of the lens is controlled by ciliary muscles inside the eye. Changes in contraction of the ciliary muscles alter the focal distance of the eye, causing nearer or farther images to come into focus on the retina; this process is known as accommodation. The reflex, controlled by the parasympathetic nervous system, involves three responses: pupil constriction, lens accommodation, and convergence.

A near object (for example, a computer screen) subtends a large area in the visual field, i.e. the eyes receive light from wide angles. When moving focus from a distant to a near object, the eyes converge. The ciliary muscle constricts making the lens thicker, shortening its focal length. The pupil constricts in order to prevent strongly diverging light rays hitting the periphery of the cornea and the lens from entering the eye and creating a blurred image.

The Atlantic mudskipper (Periophthalmus barbarus) is a species of mudskipper native to fresh, marine, and brackish waters of the tropical Atlantic coasts of Africa, including most offshore islands. The Greek scientific name Periophthalmus barbarus is named after the eyes that provide the Atlantic mudskipper with a wide field of vision. The Atlantic mudskipper is a member of the genus Periophthalmus, which includes oxudercine gobies that have one row of canine-like teeth.

The Atlantic mudskipper can grow up to 25 cm (9.8 in) in body length. Similar to other members of the genus, it has dorsally positioned eyes and pectoral fins that aid in locomotion on land and in water. Atlantic mudskippers can skip, crawl, and climb on land using their pelvic and pectoral fins.

The Accipitrinae are the subfamily of the Accipitridae often known as the "true" hawks. The subfamily contains 73 species that are divided into 11 genera. It includes the genus Accipiter which formerly included many more species. The large genus was found to be non-monophyletic and was split into several new or resurrected genera. The birds in this subfamily are primarily woodland birds that hunt by sudden dashes from a concealed perch, with long tails, broad wings and high visual acuity facilitating this lifestyle.

Hawks, including the accipitrines, are believed to have vision several times sharper than humans, in part because of the great number of photoreceptor cells in their retinas (up to 1,000,000 per square mm, against 200,000 for humans), a very high number of nerves connecting the receptors to the brain, and an indented fovea, which magnifies the central portion of the visual field. Eagles, such as the bald eagle in the family Buteoninae, are also included in this family.

Peripheral vision or indirect vision is vision as it occurs outside the point of fixation (i.e., away from the center of gaze) or, when viewed at large angles, in (or out of) the "corner of one's eye". The vast majority of the area in the visual field is included in the notion of peripheral vision. "Far peripheral" vision refers to the area at the edges of the visual field, "mid-peripheral" vision refers to medium eccentricities, and "near-peripheral", sometimes referred to as "para-central", vision, exists adjacent to the center of gaze.

Illusory palinopsia is a subtype of palinopsia, a visual disturbance defined as the persistence or recurrence of a visual image after the stimulus has been removed. Palinopsia is a broad term describing a heterogeneous group of symptoms, which is divided into hallucinatory palinopsia and illusory palinopsia. Illusory palinopsia is likely due to sustained awareness of a stimulus and is similar to a visual illusion: the distorted perception of a real external stimulus.

Illusory palinopsia is caused by migraines, hallucinogen persisting perception disorder (HPPD), prescription drugs, and head trauma, but is also sometimes idiopathic. Illusory palinopsia consists of afterimages that are short-lived or unformed, occur at the same location in the visual field as the original stimulus, and are often exposed or exacerbated based on environmental parameters such as stimulus intensity, background contrast, fixation, and movement. Illusory palinopsia symptoms occur continuously or predictably, based on environmental conditions. The term is from Greek: palin for "again" and opsia for "seeing".

Visual snow syndrome (VSS) is an uncommon neurological condition in which the primary symptom is persistent flickering white, black, transparent, or colored dots across the whole visual field. It is distinct from the symptom of visual snow itself, which can also be caused by several other causes; these cases are referred to as "VSS mimics."

Other common symptoms are palinopsia, enhanced entoptic phenomena, photophobia, and tension headaches. The condition is typically always present and has no known cure, as viable treatments are still under research. Astigmatism, although not presumed connected to these visual disturbances, is a common comorbidity. Migraines and tinnitus are common comorbidities that are both associated with a more severe presentation of the syndrome.

The foveal avascular zone (FAZ) is a region within the fovea centralis at the centre of the retina of the human eye that is devoid of retinal blood vessels. The geometric centre of the FAZ is often taken to be the centre of the macula and thus the point of fixation.

The FAZ is an important anatomical landmark in fluorescein angiography. Its diameter is 0.5mm, the central 1.5 degrees of an individual's visual field.