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 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 ...

, fovea, parafovea, and perifovea 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 of the ...

''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 eyes. 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,

, fovea, parafovea, and perifovea 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 part ...

or retinal photography. The anatomical macula is defined

histologically Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...

in terms of having two or more layers of

ganglion cell {{stack, A ganglion cell is a cell found in a ganglion. Examples of ganglion cells include: * Retinal ganglion cell (RGC) found in the ganglion cell layer of the retina * Cells that reside in the adrenal medulla, where they are involved in the ...

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

carotenoids, 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 – *

Foveal avascular zone 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 ...

(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 A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...

, 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 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 th ...

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 The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...

that occur without involving the macula are termed macular sparing. (For example, visual field testing 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), yet display sparing of the macula. This selective sparing is due to the collateral circulation offered to macular tracts by the

middle cerebral artery The middle cerebral artery (MCA) is one of the three major paired cerebral arteries that supply blood to the cerebrum. The MCA arises from the internal carotid artery and continues into the lateral sulcus where it then branches and projects to ma ...

. 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 projec ...

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 Fundus photography involves photographing the rear of an eye, also known as the fundus. Specialized fundus cameras consisting of an intricate microscope attached to a flash enabled camera are used in fundus photography. The main structures that ...

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. 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