1

IES LAS MUSAS

TRABAJO DE INVESTIGACIÓN

LUTEIN AND ZEAXANTHIN AS

PROTECTORS AGAINST AGE RELATED

MACULAR DEGENERATION

Authors: Lorena Rodríguez Bravo and Bárbara Rodríguez Sarrión

Tutors: J. Carlos Ortega Lázaro and Mª Elvira López-Oliva Muñoz

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INDEX

Appreciations ............................................................................................................................... 3

Personal motivation ...................................................................................................................... 3

Objectives .................................................................................................................................... 3

Abstract ........................................................................................................................................ 4

Introduction .................................................................................................................................. 5

Eye anatomy................................................................................................................................. 5

Age-Related Macular Degeneration ........................................................................................... 15

Causes ................................................................................................................................ 15

Symptoms .......................................................................................................................... 16

Diagnosis ........................................................................................................................... 16

Risk factors ........................................................................................................................ 20

Treatment ........................................................................................................................... 21

Prevention .......................................................................................................................... 22

Macular pigments; Lutein and Zeaxanthin ................................................................................. 23

Functions ................................................................................................................................ 23

Roles in visual health ............................................................................................................. 24

Dietary sources ....................................................................................................................... 26

Measurement .......................................................................................................................... 27

Absorption .............................................................................................................................. 27

Transport and tissue distribution ............................................................................................ 28

Roles in Age-Related Macular Degeneration ......................................................................... 28

Recommended intake values ................................................................................................. 29

Conclusion ................................................................................................................................. 30

Lecture cited............................................................................................................................... 31

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APPRECIATION This work would not have been possible without the help of several people. We would like to

thank our inner tutor of the project, Carlos Ortega for helping and guiding us throughout the

whole investigation of this project and our English teacher, Mª Ángeles Martín Llantino, for

helping us to express our research in the language of English. We want to show our gratitude as

well to Maria Elvira López Muñoz, our external tutor and teacher in the Pharmacy faculty of the

Complutense University of Madrid for her involvement in the project. Her help, dedication and

experience have been essential in the development of this study. Moreover, we would like to

stand out the task of the Complutense University of Madrid for allowing us to work there and

live such a satisfying experience. To sum up, we would like to thank the high school IES Las

Musas for all the effort made to give us the opportunity to work and research on such an

interesting project.

PERSONAL MOTIVATION One of the main reasons we have carried out this work is because of the desire of doing

something different in Bachillerato. We certainly believe that the investigation projects are

highly beneficial for the students, as they are given the chance of working in a more practical

and professional way on something that causes us curiosity. Furthermore, this project will

prepare us for the future and therefore we will be able to face better this kind of works.

Personally, we have been interested in the human eye for a long time and when we saw we

could investigate and increase our knowledge of this organ we did not hesitate. As our external

tutor is an expert of nutrients, we decided that it could be interesting to unite her knowledge and

our passion about the eye and we came up with the idea of investigating the role of some

antioxidants against a very serious ocular disease which is the Age-Related Macular

Degeneration.

OBJECTIVES There are several aims to be accomplished in this project. First of all, it is necessary the

acquisition of the knowledge of ocular anatomy, Age- Related Macular Degeneration, Lutein

and Zeaxanthin. Afterwards, the information learned before will be used to fulfill the main

objective of this study which is the analysis of the roles of Lutein and Zeaxanthin. In the case

they are beneficial for the eye, the intake values recommended will be calculated in order to

improve the condition of all the people who have AMD.

4

Abstract: The retina is a light sensitive tissue whose central part is the macula, the main part

of our vision camp. There is an ocular disease called Age Related Macular Degeneration(AMD)

which produces visual disturbances as it gradually destroys the macula. This sickness is so

aggressive that is the leading cause of vision loss in people over 60 years old. This disease has

two types; the Dry AMD, provoked by the accumulation of extracellular metabolism waste

products in the macula, called drusen and the Wet AMD caused by the abnormal growth of new

blood vessels behind the macula. While the Wet AMD is treated with laser technology, the Dry

AMD has no specific treatment, but a nutritional therapy. It has been suggested that the addition

of antioxidants like Lutein and Zeaxanthin may have some protective effect for the eye against

the AMD. L and Z are antioxidants that form the macular pigment(MP), a region of the macula

responsible for fine-feature vision. In this study, it will be analyzed if a nutritional

supplementation with L and Z has a positive effect in people with AMD and if it protects people

who does not have this ocular disorder.

Resumen: La retina es un tejido sensible a la luz cuya parte central es la mácula, el centro de

nuestro campo visual. Existe una enfermedad ocular llamada Degeneración Macular asociada a

la Edad (DME) que produce alteraciones visuales a medida que gradualmente va destruyendo la

mácula. Esta enfermedad es tan agresiva que es la principal causa de la pérdida de visión en

personas de más de 60 años. Esta enfermedad tiene dos tipos; la DME seca, la cual está

provocada por la acumulación de productos de desecho del metabolismo extracelular llamados

drusas y la DME húmeda, causada por el crecimiento anormal de nuevos vasos sanguíneos por

detrás de la mácula. Mientras que la DME húmeda es tratada con tecnología láser, la DME seca

no tiene ningún tratamiento específico excepto una terapia nutricional. Se ha planteado el hecho

de que la adición de unos antioxidantes llamados, Luteína(L) y Zeaxantina(Z), pueda tener un

efecto protector para el ojo frente a la DME. La L y Z son antioxidantes que forman el pigmento

macular(PM), una región de la mácula que es responsable de la visión en detalle. En este

estudio, se analizará si una suplementación nutricional con L y Z tiene un efecto positivo en

personas con DME y si protege a las personas que no tienen esta enfermedad ocular.

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INTRODUCTION

It is known that the eye is the main organ of the sense of sight, that receives the pictures of what

we are seeing and it transforms them into electric signs which go through the optic nerve to the

brain. There, after these electric signs are interpreted, we receive the information about the

things we are looking at. The eye is a complex organ whose correct functioning depends on the

collaboration of its multiple parts. In particular, the retina is a light sensitive tissue responsible

for the image formation processing and its central part, the macula is essential for the fine-

feature vision. Any kind of alteration in the retina can have serious consequences like in the

Age-Related Macular Degeneration as we will see later.

ANATOMY OF THE EYE

It is known that the eye is the main organ of the sense of sight, that receives the pictures of what

we are seeing and it transforms them into electric signs which go through the optic nerve to the

brain. There, after these electric signs are interpreted, we receive the information about the

things we are looking at.

The eye is a sphere, approximately 25 mm in diameter with a weight of 8 grams. The eye lies in

the bony orbit of the skull. Anatomically, the eye can be divided in two compartments, the

anterior segment (including the cornea, iris, lens, anterior and posterior chamber) and the

posterior segment (the remainder of the eye).

The eye contains a huge number of factors that protect it from any damage. One of these, is a

regulated complement system that is continuously activated protecting some compartments of

the eye. Another example, is the multiple blood-ocular barriers formed by tight junctions in the

uvea, the endothelial cells of the capillaries located in the retina and the cornea. Therefore, if

these ocular barriers are broken or downregulated, the eye becomes really vulnerable to any

attack, for instance, the invasion of non-resident immune cells which can cause tissue damage.

[1]

Moreover, the eye has several functional layers, which can be divided in this way:

6

Cornea: it is an avascular and transparent protective barrier that covers the anterior

ocular surface. It is about 0.5 mm in thickness and protects the eye against infections

and injuries. However, its main purpose is to transmit and focus light into the eye. The

external surface of the cornea is covered by a tear film , and the internal is in contact

with the aqueous humor. This is a transparent liquid whose function is to nourish the

cornea. Moreover, the cornea can be divided into five main layers, which are; the

corneal epithelium (the most superficial layer), the Bowman’s layer, the corneal stroma

Figure 1

7

(constituting 90% of the cornea), the Descemet’s layer and the corneal endothelium (the

most internal layer). [1]

Limbus: the corneal edge or limbus, is a band that encircles the peripheral cornea. It is

a transitional zone between the cornea and the sclera, and the cornea and the

conjunctiva. It is formed by cells derived from its adjacent tissues. In addition, the stem

cells of the limbus maintain and renew the corneal epithelium cell layers. [1]

Sclera: this is a white opaque collagen-enriched layer that helps to maintain the shape

of the eye, and the muscles attached to it, control the movements of the eye. This layer

is known as the “white of the eye”. [1]

Figure 4

Figure 5

Figure 3

Figure 2

8

Conjunctiva: it is a thin, translucent, vascularized mucus secreting membrane. It can

be divided into the bulbar area (on the eye surface) and the palpebral area (lining the

posterior surface of the eyelids). The superficial conjunctival epithelium has mucin-

producing goblet cells, which in combination with lymphoid cells and resident T-cells,

have an important role in the ocular defense and immunological protection of the tear

film. [1]

The lens: the lens is called crystalline. It consists of stiff, elongated, prismatic cells

tightly packed together. It is biconvex and it is attached to the ciliary process by zonular

fibers called, Zinn’s zonulas. Moreover, the crystalline is avascular, colourless and

transparent and its mission is to focus the light rays on the retina. [1]

In addition, through a process called accommodation, we are able to focus on objects

located at different distances, as the curvature of the lens is modified due to the

contractions od the ciliary muscle. Therefore, as we can see in the picture, the light from

a distant object, and from a nearby object, strikes in the same point of the retina thanks

to the modification of the curvature of the lens .[1]

Figure 6

Figure 7

9

Iris: this is a highly vascularized, coloured, smooth muscle portion of the uvea, located

between the cornea and the crystalline with the pupil in its center. It divides the anterior

segment into posterior and anterior chambers. The colour of the iris depends of the

amount and the distribution of melanin. The iris is responsible for regulating the amount

of light that enters into the eye, through the sphincter muscle of the pupil, which adapts

to the intensity of light. In this way, when the light is intense, the pupil contracts

(miosis) in order to reduce the light that enters in the eye. On the contrary, when light is

scarce, the pupil dilates (mydriasis) to capture the maximum possible light. [1]

Ciliary body: this is a structure formed by melanocytes, muscle cells, fibroblasts,

epithelium and pigmented epithelial cells and it is the anterior continuation of the

choroid and retina. It is responsible for the thickness of the lens and its curvature during

the process explained before called accommodation. [1]

Figure 9

Figure 10

Figure 8

10

Choroid: it is a highly vascular layer located between the sclera and the retina. Its

structure can be divided into Bruch’s membrane( the most internal layer), the choroidal

stroma, the network of the choriocapillaris, and the outer suprachoriod lamina. The

choroid, is responsible for regulating the retinal temperature and the exchange of

catabolites, fluids, nutrients, oxygen, and blood between the choroid and the retina. [1]

Vitreous humor: this is a transparent gel placed behind the lens occupying most of

the inside of the eye and it is also in contact with the retina. Anatomically, it can be

divided into the central vitreous, the basal vitreous, the vitreous cortex, the vitreoretinal

interface and the zonule. It is composed by 98% of water and 2% of collagen fibrils and

its mission is to help the eye maintain its shape.[1]

Figure 11

Figure 12

11

Retina: it is a light sensitive tissue located on the inner surface of the eye. The light

that hits the retina, produces various chemical and electric phenomena which are

translated into nerve impulses that are subsequently sent to the brain through the optic

nerve. [2]

The retina can be divided into some macroscopic parts:

o Papilla or optical disc: it is a pink disc approximately 2x1.5 mm. The optic

nerve going through this disc and therefore, going through the sclera, choroid

and retina is able to enter into the eyeball. As the optical disc does not receive

any light, it does not have any photoreceptors, and as a result it is considered a

blind spot.

o Fovea: this is a small structure placed in the center of the retina and surrounded

by the macula. The fovea is responsible for detailed vision.

o Ora serrata: it is the most anterior and peripheral portion of the retina, and it is

in contact with the ciliary body.

o Macula: this is the central area of the retina, and it surrounds the fovea.

o Peripheral retinal area: this zone has less activity of photoreception, as it has

less photoreceptors.

Figure 13

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On the microscopic structure of the retina, we find ten parallel layers which are:

o Retinal pigment epithelium: it is a monolayer of hexagonal cells which have

pigment, especially, melanin granules and it is located in the outside of the

retina. It is anchored to the choroid, specifically to the Bruch’s membrane. It

has many functions, such as, nourish the photoreceptors and the maintenance of

retinal adhesion, light adsorption, phagocytosis of the outer segments of the

photoreceptors, relying on nutrition from the choroidal blood flow to the retina

and the participation in the blood-retina barrier. [5]

o Layer of photoreceptor cells: it consists of the extremes of the segments of the

photoreceptors.

o Outer limiting layer: it is a group of intercellular junctions between the cells

photoreceptors and the Muller cells.

o Nuclear layer or granular external: it is composed by the nuclei of the cons and

rods.

Figure 14

Figure 15

13

o Outer plexiform layer: it is the region of the synaptic connection between cells

photoreceptors and bipolar cells.

o Nuclear layer or granular internal layer: it is formed by the nuclei of the bipolar

cells, horizontal cells and amacrine cells.

o Inner plexiform layer: this is the area of the synaptic connection between

bipolar cells , amacrine cells and ganglion cells.

o Layer of ganglion cells: it is composed by the nuclei og the ganglion cells.

o Optic nerve fiber layer: it is formed by the axons of the ganglion cells that also

form the optic nerve.

o Inner limiting layer: this is the layer which separates the retina from the

vitreous humor. [2]

The retina has three types of cells:

o Pigmented cells: they are responsible for the metabolism of the photoreceptors.

o Neurons:

- Photoreceptor cells: they are the cons and rods. They transform the

light into electric signals. The human retina has 6.5 million cones and

120 million rods. The rods work in low light conditions and provide the

vision in black and white. On the contrary, the cones are adapted to

situations with great

luminosity and they provide

the color vision. [3]

Figure 16 Figure 17

14

- Bipolar cells: of the retina: they connect the photoreceptors with the

ganglion cells.

- Amacrine cells and horizontal cells: they are modulating interneurons.

- Ganglion cells: the optic nerve goes from these cells to the retina and

then to the brain.

o Supportive cells:

- Astrocytes: they sheath superficial blood vessels in the inner retina.

- Muller cells: they are essential for maintaining the cellular micro-

environment and the stability of the entire retinal sheet. [4]

Optic nerve: it is the second cranial nerve that starts in the optic nerve head and

reaches the brain. As we know, the light is captured by the photoreceptors, as it enters

into eye and it is reflected in the retina thanks to the accommodation. Then, the light is

transformed into electric signs that are transported to the visual cortex in the brain by

the optic nerve. There, they will be analyzed and we will receive the information about

what we are seeing. [5]

Figure 18

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AGE-RELATED MACULAR DEGENERATION

Age-Related Macular Degeneration (AMD) is the leading cause of vision loss in people over 60

years old. It is a chronic ocular disorder that produces visual disturbances as it affects the

macula, which is the central part of the retina and it is the main part of our vision field. [6]

Causes: its origin may be due to multiple factors. There are two types of AMD:

o Dry AMD: it is the common one. In this type, a series of extracellular

metabolism waste products called drusen accumulates under the retina, between

the retinal pigmentary epithelium (RPE) and the Bruch membrane. As time

goes by, the drusen gradually alter the RPE causing not only its death but also

the loss of the photoreceptors in the retina, the cones and rods. This leads to

vision becoming more and more blurred until it is lost in its entirety. It has three

stages;

- Early AMD: in this phase, patients have some small or medium-sized

drusen, however there is no vision loss.

- Middle AMD: in this case, patients have many medium-sized drusen or

few large drusen, causing sometimes, the appearance of a big blurred

spot in the centre of the visual field. Moreover, in this phase, some

patients may need more light for tasks like reading.

- Advanced AMD: at this stage, patients have a large number of drusen

and their RPE , their photoreceptors and their retinal supporting tissues

are broken. Furthermore, a large blurred spot appears in the centre of

the visual field (the macula) and with the passage of time, it can

increase its size and get darker. All this causes a total loss of the central

vision in the long term. [7]

Figure 19 Figure 20

16

o Wet AMD: it is produced when blood vessels grow behind the macula as the

RPE and the photoreceptors are dying. Firstly, the Bruch membrane starts to

break near the drusen and new blood vessels are formed and they start to grow.

This growth is known as neo-vascularization. The new blood vessels are really

fragile and they start leaking liquid and blood which turns out in the

cicatrisation of the macula. Moreover, this causes permanent damage to the

photoreceptors, which die and create blind spots in the retina. In this way,

straight vision can be distorted or lost in its entirety during a brief period of

time, sometimes days or weeks. This type represents 10% of the cases of AMD.

It does not have any stages, since this sort of AMD is considered advanced. [7]

Symptoms: in the early stages of AMD, symptoms may not be detected. The first sign

usually noticed is a gradual or sudden alteration in the quality of the vision. Dark, blurry

spots or straight lines might appear causing the deterioration of the visual ability.

However, all these signs may not be caused by this disease, therefore, the patient must

go to the doctor to analyse the visual problem and to be given a diagnosis.[8]

Diagnosis: as we know, the first stages of AMD usually start without symptoms,

therefore, only an eye exam can detect this disease. The exam may be formed by

different test, some of them are:

o Visual acuity test: in order to measure the visual ability from different

distances. [9]

Figure 21 Figure 22

17

o Dilated eye exam: the ophthalmologist puts eye drops in the patients eyes to

dilate the pupils to have a better view of the back of the eye. Then using a

special magnifying lens, the ophthalmologist examines the retina and the optic

nerve for signs of AMD and other eye problems. With this process the dry

AMD can be detected, and if it is so, the patient may have to try the Amsler

grid next to check for macular degeneration symptoms and therefore, confirm

the diagnosis.

As we know, the pupils, open wide allowing the ophthalmologist to see the

retina, the optic nerve and the macula, for instance (Figure 7). If the patient had

AMD, the doctor would see yellow spots beneath the retina which are known as

drusen. (Figure 8) This would mean the patient has dry AMD. [9]

Figures 24 and 25

Figure 27

Figure 26

Figure 23

18

o Amsler grid: this is a pattern of straight black horizontal and vertical lines that

form multiples white squares. If the patient sees some wavy lines instead of

straight lines or if some of the lines are missing for the patient, it could be a

sign of AMD. [10]

o Optical coherence tomography(OCT): this device is used for obtaining 3D high

resolution images of the retina, which allows the ophthalmologist to analyse the

state of the retina parts. This process is similar to ultrasound technology except,

the image is performed by light instead of sound. [11]

o F

Figure 28

Figure 31

Figure 29 Figure 30

19

luorescein angiography: in this procedure, the ophthalmologist injects a dye

into a vein of the patient’s arm. Afterwards, when the dye has reached the eye

and flowed through the blood vessels of the retina, the doctor takes some

photographs. In this way, the resultant images are able to show new vessels or

vessels that are leaking fluid or blood in the macula, which is the cause of wet

AMD. [10]

Figure 33

Figure 34

Eye with

Wet AMD Other case of Wet

AMD

Figure 32

20

Risk factors:

o Advanced age: although AMD may occur earlier, the risk of this disease

increases with age. Therefore, people over 60 are at greater risk than those who

are younger. [12]

o Race: AMD is more prevalent in the Caucasian population than in other races

with more darkly pigmented skin, hair and eye color. Therefore, Europeans are

more likely to develop AMD than Africans, Asians, and Hispanics. [13]

o Gender: it is known that women are statistically more likely to develop AMD,

however some studies, such as the Beaver Damn Eye Study, the Blue

Mountains Eye Study and the Rotterdam Study revealed that there are not any

differences between genres in relation to AMD risk. [13]

o Family History: this disease has multiple inherited risk factors, including one

major genetic risk locus on chromosome 1, along with other minor genetic risk

factors. [13]

o Cigarette smoking: smoking increases the possibilities of having AMD, as the

retina has a high rate of oxygen consumption, anything that affects the oxygen

delivery, causes damage to the vision. Moreover, smoking causes oxidative

damage, which contributes to the progression of this disease. [14]

o Oxidative stress: this refers to cellular damage caused by reactive oxygen

species (ROS), which have free radicals, peroxides and other products from the

oxygen metabolism. As time goes by, the RPE, accumulates lipofuscin which

acts as a photosensitizer, generating ROS. The problem is that the retina is

really susceptible to oxidative stress because of its high oxygen consumption

and the high exposure to light. As we age, the oxidative damage increases and

the antioxidant capacity to stop this damage decreases. It is believed that these

oxidative age-related changes indicate an early AMD, which, in combination

with heredity susceptibility and other retinal modifiers, can turn out into the

advanced AMD. Later on, some antioxidants such as lutein and zeaxanthin will

be studied in order to see if they can reduce oxidative damage and therefore the

risk of AMD. [13]

21

o Excessive light exposure: it can be an AMD risk factor, since it aggravates

oxidative damage. [13]

o Diet: people whose diets are elevated in fat, cholesterol and high- glycemic

index foods, and low in antioxidants and green leafy vegetables may be more

likely to develop AMD. However, low-glycemic diets can lower the risk of

AMD by stabilizing blood sugar levels. [14]

o High blood pressure: this leads to the narrowing of the blood vessels that

nourish the retina and therefore, it causes the restriction of the oxygen flow.

[14]

o Inactivity: in dry AMD the retina does not receive adequate oxygen, leading to

the death of cells of the RPE. In this case, exercise may help, as it improves

cardiovascular health. [14]

Treatment

o Dry AMD: the treatment for this type of AMD is based on a nutritional therapy.

According to the patient’s condition, supplements will be prescribed in order to

add the quantities needed of certain vitamins, minerals and antioxidants to

increase healthy pigments and support the cell structure.[15].

o Wet AMD: there are multiple techniques to treat this form of AMD;

- Anti-VEGF (vascular endothelial growth factor) Therapy : nowadays, it

is the most effective treatment for wet AMD. It is a periodic intravitreal

injection of “anti-VEGF”. VEGF is a molecule that is made by the RPE

and it supports the growth of new blood vessels, so it is healthy for our

body. Nevertheless, in the case of macular health , this molecule

promotes the growth of new, weak blood vessels in the choroid which

start leaking blood, lipids and serum into the retinal layers, and this

leads to the death of the RPE and the photoreceptors. In this way, an

intraocular injection of “anti-VEGF” drugs inhibits the formation of

the new blood vessels and may avoid the leakage. The effect usually

lasts for about a month. High rates of success with anti-VEGF

injections have been reported, including, receding blood vessels behind

22

the retina, a slower development of the disease, and in some patients,

improvements in vision capacity. [16]

- Laser therapy: in this method, the pupil is dilated using drops and an

anesthetic is given to numb the surface of the eye and in some cases to

keep the eye from moving. Afterwards, a high-energy laser beam is

aimed at the leaking blood vessels in order to seal them and to stop

them from growing. Depending on how close the abnormal vessels are

to the center of the macula, the patient may experience some permanent

blurring. Usually the patient needs a retreatment after four years. [15]

- Photodynamic Therapy (PDT): this technique is based on two steps.

Firstly, a drug called “Visudyne” is injected intravenously into the

patient’s arm in order to help direct the laser to the affected area. It

travels to the abnormal vessels which are causing the wet AMD. Then,

the drug is activated by shining a low energy non-thermal laser light

and this leads to the destruction of the unwanted leaking vessels. This

procedure seals off the leaking vessels while leaving the healthy ones

intact. This technique needs to be applied multiple times to complete

the treatment. [16]

Prevention: there are many ways that may help protect vision and reduce the risk of

developing AMD.

o Do not smoke.

o Take a balanced diet that includes green leafy vegetables, yellow and orange

fruit and fish.

o Take a balanced multivitamin supplement.

o Do exercise regularly.

o Keep the blood pressure and the levels of cholesterol under control.

o Avoid long sun exposure.

o Wear sunglasses to block UV and blue light that may cause eye damage.

o Have regular eye exam.

[17]

23

MACULAR PIGMENTS; LUTEIN AND ZEAXANTHIN

As we know one of the causes of AMD is the oxidative stress in the retina. Current evidence

suggests that some supplements such as lutein and zeaxanthin, as they are antioxidants, they

have a protective effect by reducing this stress and therefore they contribute to the improvement

of people with AMD.

Lutein (L) and zeaxanthin (Z) are two antioxidants that belong to the class of carotenoids called

xanthophylls. L, Z and their isomer called meso-zeaxanthin(MZ) form the macular pigment

(MP) which is a region of the macula that is responsible for fine-feature vision. There are

between 20 and 30 carotenoids in the human body, however, only L ,Z, and MZ are in the eye,

specifically, in the macula. [18]

MZ is the dominant carotenoid at central part of the macula (the fovea) and the radio of Z to L

declines and concentration of Z decreases with increasing the distance away from the fovea. In

this way, MZ is the dominant carotenoid at the central part, Z at the mid-periphery and L at the

periphery of the macula. [19]

FUNCTIONS

These carotenoids carry out some functions such as:

Light absorption: L and Z absorb between 40-90% of blue light, reducing the light

scatter and protecting indirectly this way the retina from oxidative damage. They act as

an internal sunglasses preventing the blue light from reaching the photoreceptors of the

retina, the cons and rods. However, the 78% of the population of USA for example,

does not have the optimal MP to protect the eye from this light. And as a result, it is

Figure 35

24

common to take supplements of L and Z in the diet, to help the MP protect the retina.

[19,20]

Protection against inflammation: L protects the eye from inflammation, which is a

pathogenic mechanism that can affect many regions in the eye and it appears in order to

prevent the increase of oxidation induced cytokines for instance. Moreover, L reduces

systemic inflammation by decreasing factor D(an enzyme that activates inflammation).

[21]

Oher functions: some evidence suggests that these carotenoids may play an important

role in cell-to-cell communication and the presence of L and Z in the neural retina and

brain may improve the transmission of visual impulses to the brain. [21]

ROLES IN VISUAL HEALTH

These antioxidants also contribute enhancing visual performance.

Visual acuity: this is the ability to resolve objects that are in high contrasts to their

background. It is measured by the ability to recognize small letters at a certain distance.

Some studies prove that there are improvements in visual acuity when L and/or Z are

supplemented alone or with other antioxidants. Furthermore, these upgrades have been

found even in people with early or advanced AMD, or with diabetic retinopathy and not

only has improved visual acuity but also L and Z have had an protective effect. Besides,

Figure 36

25

apart from the improvement in visual acuity caused by the MP in indoors test, it can

help us see further . It is believed that a person with 1.0 density unit of MP can see 26%

further than someone with little or no MP. [22]

Contrast sensitivity: it is the ability to recognize contrasts in levels of lightness and

darkness between certain objects and the background. This is correlated with orientation

and mobility, reading speed and driving. People who have been taking supplements that

contain L and Z, for three months to three years, have improved contrast sensitivity .

Among these individuals, some of them are young and healthy, others have early or

advanced AMD or diabetes but all of them have been benefited. Besides, L and Z,

protect the eye from age- and disease-related changes in long terms. [22]

Photo stress recovery and glare reduction: high levels of MP help the eye by:

o Reducing the impact of bright light as it reduces the time needed to recover

from it.

o Enhancing the ability to see in conditions of glare.

o Enhancing visual performance as it increases the range over which vision task

can be comfortably performed.

Therefore, the supplementation of L and Z helps on glare disability. [22]

Visual processing speed: as we know, the light captured by the photoreceptors is

transformed into electric signs that are transported through the optic nerve to the visual

cortex of the brain. There, it will be interpreted and we will receive the information

about what we are seeing. Some studies have revealed the possibility that high MP

levels based on the supplementation of L and Z, may improve visual processing speed.

[22]

Dark adaptation: it has been studied the possibility that MP may protect against

impairments in rod dark adaptation, which is essential for the contrast sensitivity. These

impairments occur because of the accumulation of hydrophobic lipids in the RPE,

which creates a barrier that slows the delivery of nutrients to rods, provoking they do

not work efficiency. [22]

26

DIETARY SOURCES OF LUTEIN AND ZEAXANTHIN In the beginning, L and Z were measured together because the techniques were not able to

separate the quantification of each carotenoids in an individual way. As we can see in the table,

vegetables sources contain only L, whereas corn and eggs contain both, L and Z.

Nowadays, the L and Z content has been individually studied. Moreover, some studies

revealed the possibility that MZ may be present in small amounts I the food supply, for

example in the egg yolk.

Figure 37

Figure 38

27

The availability of carotenoids from different type of food allows having a more varied and

easily maintainable diet. [23]

MEASUREMENT There are several techniques to measure L and Z. Most of them use the unit of “optical density”

that is equivalent to 0.025 ng MP over a 1mm^2 area of retinal tissue.

The levels of L and Z vary in each person which makes dietary, metabolic and genetic

differences on L and Z absorption, transport in blood and accumulation in the eye. Dietary

supplementation containing L and Z has been given for 6 to 24 months to individuals whose

macular pigment optical density (MPOD)has been increased but in different quantities. It is

believed that there are many influences on the uptake, transport, and retinal capture of L and Z

which provokes those differences. [24]

ABSORPTION It varies according to the food preparation methods, the bioavailability of L and Z and the

proteins that absorb these carotenoids. Consuming aliments with high concentration of L and Z

increases blood response. These antioxidants are more available in aliments like eggs and many

types of brightly coloured fruits and vegetables typical of a western diet. [25]

However, the bioavailability also depends on the proteins that influence the cholesterol uptake

into the intestinal lumen, because L is transported by cholesterol transporter proteins. Once L is

in the intestinal lumen, these proteins modulates the uptake of L and Z. Moreover, the

absorption of L and Z depends on the intake of beta-carotene and the activity of the enzyme

beta-carotene oxygenase 1(BCO1). The availability of these components in the diets reduces

the absorption of L and Z, as we can see in a recent trial. In this study, adding L and Z to a high

dose of antioxidant that contained beta-carotene did not lower the AMD progression, except in

individuals who took a supplementation without beta-carotene. Besides, five years later, the

levels of L and Z were higher in people who did not take beta-carotene than people who did.

Therefore, with this experiment, it has been verified that beta-carotene reduces the absorption of

L and Z, their levels in the organism and as a result, these low levels of L and Z were obviously

not effective enough to protect the eye from AMD in people who take beta-carotene. [26]

28

TRANSPORT AND TISSUE DISTRIBUTION

L and Z are transported by the secretion of the enterocytes in chylomicrons who take them to

the liver. There, they are repackaged into lipoproteins and then they are distributed throughout

the body.

Carotenoids are stored in a tissue called, adipose tissue. Nevertheless, their distribution in this

tissue varies depending on the metabolic status of the individuals. For instance, obesity and

diabetes are associated with lower levels of serum carotenoids and lower MPOD. In addition,

there is an inverse relationship between MPOD and metabolic syndrome phenotypes. There are

three possible explanations for lower levels of L and Z in serum and MPOD in people with

those phenotypes. As they are associated with high oxidative stress and inflammation, the

turnover of carotenoids may vary. The second is reason is that large body fat can shift the

distribution, provoking the settlement of L and Z y the adipose tissue and not in the blood and

the retina. And the third reason is that there are some enzymes that directly influence adiposity.

[26]

ROLES OF LUTEIN AND ZEAXANTHN IN AMD The Age-Related Eye Disease Study 2 (AREDS2), a clinical trial done in the US suggests that

L and Z intake may provide protection against the AMD. The original Age-Related Eye

Disease Study(AREDS1) declared that the daily supplementation with vitamins C and E, β-

carotene, zinc and copper at levels higher than the recommended reduced the risk of progression

to a more advanced AMD by about 25%.[27] In AREDS2, 10mg of Lutein and 2mg of

zeaxanthin were added to the supplementation [28] obtaining the next results:

L and Z supplementation lowered the progression of advanced AMD in people with low

dietary of L and Z.

In people with median intake of 696 µg of L and Z per 1000 calories per day, the

supplementation reduced the risk of having the AMD.

In people with median intake of 1134 µg of L and Z per 1000 calories per day, the

supplementation had no additional impact of progression of the disease when the

background was sufficient in L and Z.

This suggests that a median intake of 2268 µg of L and Z per 2000 calories per day may have a

protective effect against advanced AMD.

According to the Blue Mountains Eye Study(BMES) and Rotterdam Study(RT), L and

Z intake reduced more than 20% the risk of dry AMD in people with high genetic risk.

29

L and Z intake also affects the visual performance in people with AMD, causing

improvements in the visual acuity and contrast sensitivity in a dose-response manner.

Moreover, along with these progresses, the MPOD increases which means an

improvement of the fine-feature vision. It is thought that MPOD levels may impact

AMD. A 2016 meta-analysis of 20 randomized controlled trials found that L, Z and MZ

supplementation improves MPOD in healthy people and in people with AMD.

[29]

RECOMMENDED INTAKE VALUES FOR LUTEIN AND ZEAXANTHIN Although there are no official recommended dietary intake levels of L and Z, an intake of 5 to 6

mg per day is associated with lowering the risk of developing AMD and 12 mg per day with the

deceleration of AMD progression. However, it is not clear if these levels could have adverse

consequences over the decades and if they would differ in certain parts of the population.

Therefore, until these aspects remain unresolved, it is recommended to increase the

consumption of lutein-rich vegetables and fruits and moderately increase egg intake as well, for

healthy people. And for people with AMD, it is counselled to promote the daily intake of

antioxidants containing 12 mg of L and Z. [30]

Figure 39

30

CONCLUSION

To sum up it is clear that the eye is a complex organ whose correct functioning depends on the

collaboration of all its parts. In particular, the retina is a light sensitive layer that is responsible

for the image formation process and its central part, the macula, it essential for fine feature

vision. As a result, any alteration produced in this layer can have serious consequences such as

blindness like in the case of AMD, which is a really serious disease. The preventive measures

specified before need to be followed in order to reduce the risk of having this ocular disease. In

spite of the fact that there is no specific treatment for the dry AMD, the supplementation of L

and Z in the diet is beneficial for the eye, as they help its condition either by reducing the

progress of AMD in those who have it or by lessening the risk of having this disease up to 20%.

Moreover, L and Z have other positive effects such as they absorb blue light, protect us against

inflammation and improve our visual acuity and processing speed, the contrast sensitivity and

the photo stress.

Although, the values of intake of Lutein and Zeaxanthin are not determined, it is highly

recommended for healthy people and people with AMD to have a diet rich in green vegetables

and all type of food that contains L and Z as they are essential because as we have seen not only

enhance they the visual performance but also they have a protective effect in AMD.

As we can see the objectives of investigating about the anatomy of the eye, the AMD and the

macular pigments have been accomplished. Although it has not been possible to determine

specific values of L and Z, it is clear that these carotenoids are important for the eye health and

for the recovery of people with macular degeneration.

31

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33

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