The
macula or
macula lutea (from
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
macula, "spot" +
lutea, "yellow") is an oval-shaped highly pigmented
yellowYellow is the color evoked by light that stimulates both the L and M cone cells of the retina about equally, with no significant stimulation of the S cone cells. Light with a wavelength of 570–590 nm is yellow, as is light with a suitable mixture of red and green...
spot near the center of the
retinaThe vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
of the
human eyeThe human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
. It has a diameter of around 5 mm and is often histologically defined as having two or more layers of
ganglion cellA retinal ganglion cell is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and amacrine cells...
s. Near its center is the
foveaThe fovea centralis, also generally known as the fovea , is a part of the eye, located in the center of the macula region of the retina....
, a small pit that contains the largest concentration of
cone cellCone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
s in the eye and is responsible for central, high resolution vision. The macula also contains the parafovea and perifovea.
Because the macula is yellow in colour it absorbs excess blue and ultraviolet light that enter the eye, and acts as a natural sunblock (analogous to sunglasses) for this area of the retina. The yellow colour comes from its content of
luteinLutein is a xanthophyll and one of 600 known naturally occurring carotenoids. Lutein is synthesized only by plants and like other xanthophylls is found in high quantities in green leafy vegetables such as spinach and kale...
and
zeaxanthinZeaxanthin is one of the most common carotenoid alcohols found in nature. It is important in the xanthophyll cycle. Synthesized in plants & some micro-organisms, it is the pigment that gives paprika , corn, saffron, and many other plants & microbes their characteristic color.The name is derived...
, which are yellow
xanthophyllXanthophylls are yellow pigments that form one of two major divisions of the carotenoid group. The name is from Greek xanthos + phyllon , due to their formation of the yellow band seen in early chromatography of leaf pigments...
carotenoidCarotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s, derived from the diet. Zeaxanthin predominates at the macula, while lutein predominates elsewhere in the retina. There is some evidence that these carotenoids protect the pigmented region from some types of
macular degenerationAge-related macular degeneration is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults...
.
Structures in the macula are specialized for high
acuityVisual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....
vision. Within the macula are the
foveaThe fovea centralis, also generally known as the fovea , is a part of the eye, located in the center of the macula region of the retina....
and
foveolaThe foveola is located within a region called the macula, a yellowish, cone photo receptor filled portion of the human retina. The foveola is approximately 0.35 mm in diameter and lies in the center of the fovea and contains only cone cells, and a cone-shaped zone of Müller cells...
which contain a high density of
conesCone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
(photoreceptors with high acuity).
Clinical significance
Whereas loss of
peripheral vision Peripheral vision is a part of vision that occurs outside the very center of gaze. There is a broad set of non-central points in the field of view that is included in the notion of peripheral vision...
may go unnoticed for some time, damage to the macula will result in loss of central vision, which is usually immediately obvious.
The progressive destruction of the macula is a
diseaseA disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
known as
macular degenerationAge-related macular degeneration is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field because of damage to the retina. It occurs in “dry” and “wet” forms. It is a major cause of blindness and visual impairment in older adults...
and can sometimes lead to the creation of a macular hole. Macular holes are rarely caused by trauma, but if a severe blow is delivered it can burst the blood vessels going to the macula, destroying it.
Visual input to the macula occupies a substantial portion of the brain's visual capacity. As a result, some forms of visual field loss can occur without involving the macula; this is termed
macular sparing. (For example, visual field testing might demonstrate
homonymous hemianopia with macular sparing.).
In the case of Occipitoparital ischemia owing to occlusion of elements of either
posterior cerebral artery-External links: - Posterior Cerebral Artery Stroke* at strokecenter.org* at State University of New York Upstate Medical University* at psyweb.com* at neuropat.dote.hu...
, patients may display cortical
blindnessBlindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...
(which involves blindness that the patient denies having, as seen in
Anton's SyndromeAnton–Babinski syndrome is a rare symptom of brain damage occurring in the occipital lobe. People who suffer from it are "cortically blind", but affirm, often quite adamantly and in the face of clear evidence of their blindness, that they are capable of seeing. Failing to accept being blind...
), yet display sparing of the macula. This selective sparing is due to the collateral circulation offered to macular tracts by the
middle cerebral artery
.. Neurological examination that confirms macular sparing can go far in representing the type of damage mediated by an infarct, in this case, indicating that the caudal visual cortex (which is the principal recipient of macular projections of the optic nerve) has been spared. Further, it indicates that cortical damage rostral to. and including,
lateral geniculate nucleusThe lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
is an unlikely outcome of the infarction, as too much of the lateral geniculate nucleus is, proportionally, devoted to macular-stream processing .