The macula (/ˈmakjʊlə/) or macula lutea is an oval-shaped pigmented area in the center of the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

of the human eye and in other animals. The macula in humans has a diameter of around and is subdivided into the umbo, foveola, foveal avascular zone,

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy * Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head *Trochlear fovea of the f ...

, parafovea, and

perifovea Perifovea is a region in the retina that circumscribes the parafovea and fovea and is a part of the macula lutea. The perifovea is a belt that covers a 10° radius around the fovea and is 1.5 mm wide. The perifovea ends when the Henle's fiber laye ...

areas. The anatomical macula at a size of is much larger than the clinical macula which, at a size of , corresponds to the anatomical fovea. The macula is responsible for the central, high-resolution, color vision that is possible in good light; and this kind of vision is impaired if the macula is damaged, for example in

macular degeneration 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. Over time, however, som ...

. The clinical macula is seen when viewed from the pupil, as in ophthalmoscopy or retinal photography. The term macula lutea comes from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''macula'', "spot", and ''lutea'', "yellow".

Structure

The macula is an oval-shaped pigmented area in the center of the

of the human eye and other animal

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

s. Its center is shifted slightly away from the optical axis (laterally, by 5°=1.5 mm). The macula in humans has a diameter of around and is subdivided into the umbo, foveola, foveal avascular zone,

, parafovea, and

areas. An even smaller central region of highest receptor density (40–80 μm) is sometimes referred to as the ''foveal bouquet''. The anatomical macula at is much larger than the clinical macula which, at , corresponds to the anatomical fovea. The clinical macula is seen when viewed from the pupil, as in

ophthalmoscopy Ophthalmoscopy, also called funduscopy, is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope (or funduscope). It is done as part of an eye examination and may be done as par ...

or retinal photography. The anatomical macula is defined histologically in terms of having two or more layers of ganglion cells. The umbo is the center of the foveola which in turn is located at the center of the fovea. The fovea is located near the center of the macula. It is a small pit that contains the largest concentration of

cone cell Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Con ...

s. The retina contains two types of photosensitive cells, the

rod cell Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in p ...

s and the cone cells.

Color

Because the macula is yellow in color 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 color comes from its content of

lutein Lutein (;"Lutein"

zeaxanthin Zeaxanthin is one of the most common carotenoids in nature, and is used in the xanthophyll cycle. Synthesized in plants and some micro-organisms, it is the pigment that gives paprika (made from bell peppers), corn, saffron, goji (wolfberries), ...

, which are yellow

xanthophyll Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek (, "yellow") and (, "lea ...

carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, cor ...

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

. A formulation of 10 mg lutein and 2 mg zeaxanthin has been shown to reduce the risk of age-related macular degeneration progressing to advanced stages, although these carotenoids have not been shown to prevent the disease. After death or enucleation (removal of the eye), the macula appears yellow, a color that is not visible in the living eye except when viewed with light from which red has been filtered.

Regions

Fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy * Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head *Trochlear fovea of the f ...

– * Foveal avascular zone (FAZ) – * Foveola – * Umbo –

Function

Structures in the macula are specialized for high- acuity vision. Within the macula are the fovea and foveola that both contain a high density of cones, which are nerve cells that are photoreceptors with high acuity. In detail, the normal human eye contains three different types of cones, with different ranges of spectral sensitivity. The brain combines the signals from neighboring cones to distinguish different colors. There is only one type of rod, but the rods are more sensitive than the cones, so in dim light, they are the dominant photoreceptors active, and without information provided by the separate spectral sensitivity of the cones it is impossible to discriminate colors. In the fovea ''centralis'', cones predominate and are present at high density. The macula is thus responsible for the central, high-resolution, color vision that is possible in good light; and this kind of vision is impaired if the macula is damaged, for example in

Clinical significance

The clinical macula is seen when viewed from the pupil, as in ophthalmoscopy or retinal photography. Whereas loss 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

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

known as

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 from the macula occupies a substantial portion of the brain's visual capacity. As a result, some forms of visual field loss that occur without involving the macula are termed macular sparing. (For example,

visual field testing A visual field test is an eye examination that can detect dysfunction in central and peripheral vision which may be caused by various medical conditions such as glaucoma, stroke, pituitary disease, brain tumours or other neurological deficits. ...

might demonstrate '' homonymous hemianopsia with macular sparing''.) In the case of occipitoparietal ischemia owing to occlusion of elements of either posterior cerebral artery, patients may display cortical

blindness Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...

(which, rarely, can involve blindness that the patient denies having, as seen in

Anton's Syndrome Anton syndrome, also known as Anton's blindness and visual anosognosia, is a rare symptom of brain damage occurring in the occipital lobe. Those who have it are cortically blind, but affirm, often quite adamantly and in the face of clear evidenc ...

), 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 nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral proj ...

is an unlikely outcome of the infarction, as too much of the lateral geniculate nucleus is, proportionally, devoted to macular-stream processing.

Additional images

File:Retinography.jpg, A fundus photograph showing the macula as a spot to the left. The optic disc is the area on the right where blood vessels converge. The grey, more diffuse spot in the centre is a shadow

artifact Artifact, or artefact, may refer to: Science and technology * Artifact (error), misleading or confusing alteration in data or observation, commonly in experimental science, resulting from flaws in technique or equipment ** Compression artifact, a ...

. File:Retina-OCT800.png, Time-Domain OCT of the macular area of a retina at 800 nm, axial resolution 3 µm File:SD-OCT Macula Cross-Section.png, Spectral-Domain OCT macula cross-section scan. File:Macula Histology OCT.jpg, alt=macula histology (OCT), macula histology (OCT)

References

External links

* * {{Authority control Human eye anatomy