From en.wikipedia.org:
[Oval-shaped pigmented area near the center of the retina] [the macula of the
eye] [date=April 2017] {{Infobox anatomy | Name = Macula | Latin = macula
lutea | Image = Blausen 0389 EyeAnatomy 02.png | Caption = The macula is the
central part of the retina of the human eye, its center slightly shifted to
the temporal side. (The location in the image is misleading: it looks as if
the macula were far removed from the center which is not the case.) | Image2 =
| Caption2 = | Precursor = | System = | Artery = | Vein = | Nerve = | Lymph =
| part_of = Retina of human eye | system = Visual system }}
The MACULA ([ˈ])[1] or MACULA LUTEA is an oval-shaped pigmented area in the
center of the retina of the human eye and in other animals. The macula in
humans has a diameter of around [5.5] and is subdivided into the umbo,
foveola, foveal avascular zone, fovea, parafovea, and perifovea areas.[2]
The anatomical macula at a size of [5.5] is much larger than the clinical
macula which, at a size of [1.5], corresponds to the anatomical
fovea.[3][4][5]
The macula is responsible for the central, high-resolution, color vision that
is possible in good light. This kind of vision is impaired if the macula is
damaged, as in macular degeneration. The clinical macula is seen when viewed
from the pupil, as in ophthalmoscopy or retinal photography.
The term macula lutea comes from Latin _macula_, "spot", and _lutea_,
"yellow".
** Structure
The macula is an oval-shaped pigmented area in the center of the retina of the
human eye and other animal eyes. Its center is shifted slightly away from the
optical axis (laterally, by 5°=1.5 mm).[6] The macula in humans has a diameter
of around [5.5] and is subdivided into the umbo, foveola, foveal avascular
zone, fovea, parafovea, and perifovea areas.<ref name="Project Orbis
International"/> An even smaller central region of highest receptor density
(40–80 μm) is sometimes referred to as the _foveal bouquet_.[7][8][9][10] The
anatomical macula at [5.5] is much larger than the clinical macula which, at
[1.5], corresponds to the anatomical fovea.<ref name="Yanoff2009"/><ref
name="Small1994"/><ref name="PeymanMeffert2000"/>
The clinical macula is seen when viewed from the pupil, as in ophthalmoscopy
or retinal photography. The anatomical macula is defined histologically in
terms of having two or more layers of ganglion cells.[11] 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's receptor layer
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 and zeaxanthin, which are yellow xanthophyll 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 macular
degeneration. 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.[12]
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.[13]
*** Regions
- Fovea – [1.55]
- Foveal avascular zone (FAZ) – [0.5 to 0.6]
- Foveola – [0.35]
- Umbo – [0.15]
** 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 macular degeneration.[14]
** Clinical significance
{{multiple image | direction = horizontal | width = 150 | footer = Fundus
photographs of the right eye (left image) and left eye (right image), seen
from front so that left in each image is to the person's right. The gaze is
into the camera, so in each picture the macula is in the center of the image,
and the optic disc is located towards the nose. | image1 = Fundus photograph
of normal right eye.jpg | alt1 = | caption1 = | image2 = Fundus photograph of
normal left eye.jpg | alt2 = | caption2 = }} 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 known as
macular degeneration 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.<ref
name="Macular Degeneration"/>
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 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
(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.[15] 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 is an unlikely outcome of the infarction, as too much of
the lateral geniculate nucleus is, proportionally, devoted to macular-stream
processing.[16]
** Additional images
<gallery> 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.
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) </gallery>
** See also
[Anatomy-terms] [colwidth=30em]
- Macular degeneration
- Macular edema
- Macular pucker ( epiretinal membrane )
- Cherry-red spot
- Macular hypoplasia
- Photic retinopathy
- Intermediate uveitis
[Div col end]
** References
[Reflist]
** External links
- [Macula lutea]
- [002252]
[Eye] [Authority control]
Category:Human eye anatomy