Eye Anatomy – Exeter Eye

The human eye is remarkable. Although it is small in size, the eye arguably provides us with the most important of the five senses – vision.

Vision occurs when light enters the eye through the pupil. With help from other important structures in the eye, like the iris and cornea, the appropriate amount of light is directed towards the lens.

Just like a lens in a camera sends a message to produce a film; the lens in the eye refracts incoming light onto the retina, where messages are encoded. The retina, which is made up by millions of specialised cells known as ‘rods’ and ‘cones’, transforms the image into electrical energy and this is sent to the optic disk on the retina, where it will be transferred via electrical impulses along the optic nerve to be processed by the brain.

The eyeball contains three layers:

• The outer layer, formed by the cornea and sclera
• The middle layer, holding the primary blood supply for the eye and containing the iris and pupil
• The inner layer, comprised of the retina

The eyeball also contains three chambers of fluid:

• Anterior chamber, between the cornea and iris
• Posterior chamber, between the iris and the lens
• Vitreous chamber, between the lens and the retina

The anterior and posterior chambers are filled with aqueous humour, which is a watery fluid that provides nourishment to the interior eye structures and helps to keep the eyeball inflated. The vitreous chamber is filled with a thicker fluid called vitreous humour, a transparent gel which is 99% water, which helps the eyes to stay inflated.

What makes up an eye?

• Choroid: the middle layer of the eye between the retina and the sclera. It also contains a pigment that absorbs excess light so preventing blurring of vision.

The choroid is the spongy middle layer of your eye located between the sclera and the retina. Filled with blood vessels, the choroid’s function is to nourish the outer layers of the retina.

• Ciliary body: the part of the eye that connects the choroid to the iris.

The ciliary body is located behind your iris, near the crystalline lens. This structure has two functions. The aqueous fluid that fills the front of your eye is made inside the ciliary body. Also, the ciliary body is made up of muscles that allow the eye to focus at different distances.

• Cone cells are the second type of light sensitive cells in the retina of the eye. The human retina contains between six and seven million cones; they function best in bright light and are essential for acute vision (receiving a sharp accurate image). It is thought that there are three types of cones, each sensitive to the wavelength of a different primary colour – red, yellow or blue. Other colours are seen as combinations of these primary colours.

• Cornea: the transparent circular part of the front of the eyeball. It refracts the light entering the eye onto the lens, which then focuses it onto the retina. The cornea contains no blood vessels and is extremely sensitive to pain.

The cornea is the clear front window, representing one-sixth of the outer layer of your eye. The primary function of the cornea is to focus and transmit light onto the retina.

• Conjunctiva: the thin, moist, clear membrane that covers the sclera – the white part of the eye. It is the skin that lines the eye socket and protects and lubricates the eyeball.

• Crystalline Lens: The transparent structure inside of the eye located directly behind your iris. The sole function of your lens is to focus light rays onto the retina.

• Fovea: forms a small indentation at the centre of the macula and is the area with the greatest concentration of cone cells. When the eye is directed at an object, the part of the image that is focused on the fovea is the image most accurately registered by the brain.

• Iris: regulates the amount of light that enters your eye. It forms the coloured, visible part of your eye in front of the lens. Light enters through a central opening called the pupil.

The iris is the colored portion of your eye. Located behind the cornea, and in front of the crystalline lens. This structure separates the anterior and posterior chambers of the eye. The function of the iris is to help regulate the amount of light that enters your eye.

• Lens: a transparent structure situated behind your pupil. It is enclosed in a thin transparent capsule and helps to refract incoming light and focus it onto the retina. A cataract is when the lens becomes cloudy, and a cataract operation involves the replacement of the cloudy lens with an artificial plastic lens.

• Macula: a yellow spot on the retina at the back of the eye which surrounds the fovea.

The macula is located roughly in the center of the retina. It is a small and highly sensitive part of the retina responsible for detailed central vision. The fovea is the very center of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such as reading or driving a car.

• Optic disc: the visible (when the eye is examined) portion of the optic nerve, also found on the retina. The optic disc identifies the start of the optic nerve where messages from cone and rod cells leave the eye via nerve fibres to the optic centre of the brain. This area is also known as the ‘blind spot’.

• Optic nerve: leaves the eye at the optic disc and transfers all the visual information to the brain.

The optic nerve is located in the back of the eye. This structure is responsible for transmitting the images we see from the retina to the brain. The front surface of the optic nerve, which is visible on the retina, is called the optic disk. There are millions of nerve fibers that pass through the retina and converge to form the optic nerve. When light hits the retina it is converted into electrical impulses and carried along these fibers through the optic nerve and to the brain.

• Pupil: the circular opening in the centre of the iris through which light passes into the lens of the eye. The iris controls widening and narrowing (dilation and constriction) of the pupil.

The pupil is the dark center in the middle of the iris. The pupil’s function is to regulate how much light enters the eye. The pupil’s size is automatically varied to regulate the amount of light entering the eye.

• Retina: a light sensitive layer that lines the interior of the eye. It is composed of light sensitive cells known as rods and cones. The human eye contains about 125 million rods, which are necessary for seeing in dim light. Cones, on the other hand, function best in bright light. There are between six and seven million cones in the eye and they are essential for receiving a sharp accurate image and for distinguishing colours. The retina works much in the same way as film in a camera. The retina’s function is to sense light and create impulses that are sent through the optic nerve and to the brain.

• Rod cells are one of the two types of light-sensitive cells in the retina of the eye. There are about 125 million rods, which are necessary for seeing in dim light.

• Sclera: the white part of the eye, a tough covering with which the cornea forms the external protective coat of the eye.

The sclera is the white portion of your eye, making up the back five-sixth’s of the eyes outer layer. The function of the sclera is to provide protection for your eye, and to serve as the attachment for the extra ocular muscles which move the eye.

• Tear Layer: Understanding the structure of tears is important in order to understand how the tears and tear film provide the eye with a number of specialized functions.

Our tears are formed by tiny glands that surround the eye. Tears are comprised of three layers: oil, water, and mucous. The lower mucous layer serves as an anchor for the tear film and helps it adhere to the cornea. The middle layer is comprised of water and the outer layer seals the tear film and prevents evaporation. The tear film serves several purposes. It keeps the eye moist, creates a smooth surface for light to pass through the eye, nourishes the front of the eye, and provides protection from injury and infection. When we blink, the eyelids smooth and spread the tear film so that it is uniform across the surface of the cornea. Excess tears flow out of the eye into two tiny ducts, which then drain into the nasal passage.

• Vitreous Body: A clear, jelly-like substance that fills the center of the eye.

It is composed mainly of water and comprises about two thirds of the eye’s volume. The vitreous helps the eye maintain a round shape and is attached to the retina at various points, including the macula and the optic nerve.

• Zonules: a series of fine fibers that connect the crystalline lens to the ciliary body. The function of your zonules is to hold the lens in place in the eye.

If you are worried about the health of your eyes, take a look at the range of symptoms you may experience, call us on 01392 699969, arrange a call back or get in touch online.

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Eye Anatomy: The Front of the Eye

Did you know that the eye is made up of over 2 million parts, each contributing a distinct vital role in your ability to see?

The eye is a complicated organ (second in its complexity to the brain), and all of its parts need to work in perfect harmony to enable you to see the world around you.

The following ocular structures lie within the outer and middle layers of the eye, also known as the anterior area of the eye. 

Sclera

The outermost layer of the eye consists of the sclera, also known as the white part of the eye.

The sclera is made up of tough fibrous tissue and is responsible for giving the eye it’s round shape and protecting the inner structures of the eye. The sclera is thickest in the back of the eye as it provides extra protection to the area around the optic nerve.

The sclera consists of three parts:

• Episclera- the loose connective tissue located directly under the conjunctiva
• Sclera proper- the dense white tissue that gives the sclera its white color
• Lamina fusca- the innermost area that consists of elastic fibers

The sclera at the front of the eye is covered with a protective tissue called the conjunctiva.

Conjunctiva 

The conjunctiva is the thin, clear tissue that covers the sclera and cornea, and wraps around the entire front of the eye, connecting the eye to the underside of the eyelids.

The conjunctival connection of the sclera to the eyelids prevents any objects from “getting lost behind the eye”— a common concern of first time contact lens users.

The conjunctiva lubricates the eyeball and allows the eyelids to easily slide over the surface of the eye upon blinking. This tissue is highly vascularized and can become inflamed or infected easily.

When the conjunctival vessels become swollen, the eye appears red or pink— this is generally caused by an infection called conjunctivitis, also known as “pink eye”.

Often, the conjunctiva can become red from other conditions as well, such as dry eyes and eye allergies.

If you suspect you have an eye condition, contact an eye doctor near you, who can diagnose and treat the condition.

SEE RELATED: Eye Anatomy: External Parts of the Eye

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Cornea

The cornea is the clear outer layer of the eye that protects the eye from harmful particles and ultraviolet rays.

This part of the eye is also responsible for bending the light that enters the eye. The cornea’s shape or curvature determines the eye’s focusing abilities for both near and distant objects.

The cornea is the area of the eye that contact lenses are positioned, and the tissue that LASIK surgery is performed on.

The cornea receives its oxygen from the environment and does not contain any blood vessels (avascular). This enables light to easily pass through for clear vision.

The cornea consists of five layers:

• Epithelium- As the outermost layer of the cornea, this layer prevents harmful particles from entering the eye and absorbs oxygen and nutrients from the tears.
• Bowman’s layer- This layer maintains the cornea’s shape.
• Stroma- As the central layer of the cornea, this layer is by far the thickest. It is made up of collagen fibers, water and proteins that give the cornea an elastic but solid and strong consistency.
• Descemet’s membrane- This layer is the resting layer for endothelial cells.
• Endothelium- This layer works as a pump, removing the waste products and excess water from the cornea and depositing them into the fluid of the anterior chamber to prevent vision problems.

Corneal disease or infection can affect the cornea’s ability to function normally, and cause vision loss and even blindness.

Anterior chamber

The anterior chamber is located between the cornea and the iris.

The anterior chamber is filled with a clear fluid called aqueous humor which helps to maintain the shape of the eye and provide nourishment to the ocular structures.

The aqueous humor flows out of the anterior chamber through the trabecular meshwork. As new fluid is produced, the “old” fluid drains out. If there is a problem within the trabecular meshwork and the fluid cannot drain properly, or the fluid is being produced faster than it can drain out, the pressure within the eye can increase. 

When this happens, a serious eye disease called glaucoma, can develop.

Trabecular meshwork

The trabecular meshwork is made up of connective tissue and is located between the iris and the cornea.

This tissue is responsible for draining the aqueous fluid from the front of the eye into the veins of the eye, and eventually into the bloodstream. 

Glaucoma surgery is typically focused on the trabecular meshwork, with the goal of opening up any blockages and reducing eye pressure.

Pupil

The pupil is the black hole in the center of the iris through which light can enter the eye. 

The pupil controls the amount of light that enters the eye by widening and constricting in response to the intensity of the light. The size of the pupil is controlled by the muscles in the iris around it.

If the pupil does not dilate or constrict in response to light, it may signal a neurological problem.

During an eye exam, the pupils are dilated with the use of special eye drops in order to allow the eye doctor to examine the inner structures and the retina in the back of the eye.

Iris

The iris is the pigmented part of the eye that encompasses the pupil. The iris contains muscles that adjust the pupil’s size in response to light intensity.

The color of the iris is what gives us green, blue, hazel, brown or dark colored eyes.

The color of the iris is also determined by the amount of pigment cells in the muscles— a higher amount of pigment leads to a darker iris, less pigment leads to a lighter iris. As a result, people with lighter eyes are more sensitive to light, as their eyes don’t contain the dark pigment that protects them from bright lights that enter the eye.

Ciliary body

The ciliary body is a muscle that is located behind the iris.

This muscle is responsible for focusing, also known as accommodation, and changes the shape of the eye’s lens. 

This response allows us to shift our focus between near and distant objects.

The ciliary body also contains cells that produce the aqueous humor (fluid) located in the anterior chamber. If the ciliary body produces too much fluid, or if the fluid does not drain out of the anterior chamber fast enough, the pressure within the eye can rise. High pressure within the eye can cause glaucoma.

Uvea

The uvea is responsible for transporting blood to the retina, and consists of the three inner structures beneath the sclera: the iris, ciliary body, and the choroid. 

Uveitis is a condition that can occur when the uvea becomes inflamed, and is typically caused by an autoimmune disease, viral infection, or eye injury.

In most cases, uveitis does not cause any serious problems, but vision loss can occur if severe cases are left untreated.

Lens 

The lens is located behind the iris and is responsible for bending the light it receives from the cornea, and focusing that light onto the retina.

The lens changes its shape to enable you to shift focus and see clear images at all distances.

As we age, the crystalline lens begins to harden and lose its flexibility, causing presbyopia— the reason why many people wear reading glasses as they get older.

Additionally, over time, the lens becomes cloudy, causing a condition called cataracts. Cataracts usually develop slowly over time and can be treated with cataract surgery as they begin to impact daily living.

LEARN MORE:  Guide to Eye Health

Schedule an appointment with an eye doctor for a comprehensive eye exam, and to discuss any questions you may have about your eyes and eye health.

Sparks in the eyes | Articles

Small sparkling dots before the eyes – sparks – are familiar to many. This symptom indicates a violation in the work of the retina. Doctors refer to this phenomenon as photopsy – false light perceptions.

Sparks before the eyes are also spoken of in cases where dots of white, yellow or golden color appear in the field of view. They are especially noticeable in sunny weather, in bright light. If you look at a white surface (for example, a wall) on a sunny day, it will be covered with bright “sparks”. In some cases, patients complain of manifestations that occur with their eyes closed.

Why do sparks appear in the eyes?

• Destruction of the vitreous body. This pathology is the most common cause of the appearance of sparks before the eyes. Their occurrence is accompanied by the appearance of floating spots, various in shape and size.
• Vitreous detachment. In people older than 50 years, wrinkling of the vitreous body is often diagnosed – the most complex pathology of the vitreous body. This deformation leads to severe tension at the attachment points to the retina of the vitreous body. As a result, when the eye moves, sparks appear. They are especially noticeable with closed eyes.
• Vascular anomalies. Often the appearance of sparks before the eyes accompanies hypertension, diabetes mellitus and other diseases associated with vascular damage. Spasms occur in the eyes, which cause the appearance of foreign objects.
• Retinal breaks. In some cases, the appearance of sparks is associated with damage to the retina. Against the background of its rupture, a rupture of the vessel may occur. As a result, blood enters the eye cavity and hemophthalmos occurs. This condition is accompanied by the appearance of a veil over the entire field of vision and a decrease in the visual acuity of the world. Retinal tear can cause retinal detachment. This is fraught with serious consequences for vision. If sparks occur, you should immediately seek help from an ophthalmologist.
• Retinal detachment. This disease is one of the most dangerous in ophthalmology, as it can lead to complete and irreversible loss of vision. With retinal detachment, sparks of red and purple colors, as well as dark shades, appear before the eyes. The intensity of objects increases over time. All this is accompanied by an active deterioration of vision.
• Eye injuries. Sparks occur directly at the moment of injury – impact or other mechanical impact. If the contusion was mild, over time, all unpleasant symptoms disappear.
• Head injury. Visual centers are located in the occipital part of the brain. A blow to this area may be accompanied by a sensation of sparks “falling” from the eyes.
• Pressure on the eye. With gentle pressure, a light spot may appear in the field of view. This phenomenon is called mechanophosphene. When the pressure stops, it disappears, so this condition is not a pathology.
• Tumors inside the eyes. If a tumor develops inside the organs of vision, over time it can lead to the appearance of sparks. This is due to the fact that in the process of growth, it begins to put pressure on the surrounding tissues.

Treatment

Sparks in the eyes are not a disease, but only a symptom of a pathology. Eliminating the cause often leads to instant relief from this manifestation. If sparks appear before the eyes, the nature of which is not completely clear or is caused by physical overstrain or severe stress, it is necessary to seek help from a specialist. The ophthalmologist will conduct an examination, assess the condition of the organs of vision and exclude (or confirm) serious eye pathologies. Examination is important, as many ophthalmic diseases are irreversible. Remember: the occurrence of sparks can be associated with retinal detachment, which leads to blindness.

In the Center for Vision Restoration, the examination is carried out using modern diagnostic equipment. Based on the results, you will receive a comprehensive consultation of an experienced ophthalmologist. We work for you every day from 8:00 to 20:00, we accept patients of any age. Our doctors will identify the objective cause of eye pathology and prescribe competent treatment. Thousands of patients come to us every year. We give them all healthy vision!

Are you interested in the cost of diagnostics and treatment at the Vision Restoration Center? Do you want to make an appointment?

Read also:

Laser cataract removal at the best price.

SHASHORINA Svetlana Alexandrovna
Ophthalmologist, candidate of medical sciences. Oculist.

Exercise for the eyes – exercises for relaxation and improvement of vision – clinic Krugozor in Moscow

Every day we “absorb” a large amount of information. Many vision problems arise from overexertion, so we experience discomfort, dryness, and fatigue. These seemingly minor symptoms are the first signs of visual impairment.

To avoid problems with vision, it is necessary to perform “Eye exercises ”. It is advisable to do exercises in the morning or in the evening (before going to bed), after removing glasses or contact lenses. Movements should be smooth, without jerks, it is also useful to blink between exercises.

“GYMNASTICS FOR THE EYES”

* Starting position (hereinafter referred to as i.p.).

Exercise No. 1 “Big Eyes”:

i.p. – sitting. Close your eyes tightly for 3-5 seconds, and then open your eyes for 3-5 seconds, repeat 6-8 times. This exercise strengthens the muscles of the eyelids. Promotes blood circulation and relaxation of eye muscles.

Exercise #2:

i.p. – standing. Look straight ahead for 2-3 seconds. Place the finger of the right hand on the midline of the face at a distance of 25-30 cm from the eye, look at the end of the finger and look at it for 3-5 seconds. Give up. Repeat 10-12 times. Exercise relieves fatigue, facilitates visual work at close range.

Exercise No. 3 “Shutters”:

i.p. – sitting. Blink rapidly for 1-2 minutes. Helps improve blood circulation.

Exercise #4:

i.p. – standing. Stretch your arms forward, look at the end of the finger of the outstretched hand, placed on the midline of the face, slowly bring the finger closer, keeping your eyes on it until the finger begins to double. Repeat 6-8 times. Makes working at close range easier.

Exercise No. 5:

i.p. – sitting. Close the eyelids, massage them with circular movements of the finger. Repeat for 1 minute. Exercise relaxes muscles and improves blood circulation.

Exercise #6:

i. p. – standing. Place the finger of the right hand along the midline of the face at a distance of 25-30 cm from the eye, look with both eyes at the end of the finger for 3-5 seconds, cover the eye with the palm of the left hand for 3-5 seconds, remove the palm, look with both eyes at the end of the finger for 3-5 seconds. Place the finger of the left hand in the middle line at a distance of 25-30 cm, cover the right eye with the palm of the right hand for 3-5 seconds, remove the palm, look at the wallpaper with the eyes at the end of the finger for 3-5 seconds. Repeat 5-6 times. The exercise strengthens the muscles of both eyes (binocular vision).

Exercise #7:

i.p. – standing. Take your hand to the right side, slowly move the finger of the half-bent hand from right to left and, with a motionless head, follow the finger with your eyes, slowly move the finger of the half-bent hand from left to right and, with a motionless head, follow the finger with your eyes. Repeat 10-15 times. This exercise strengthens the horizontal eye muscles and improves their coordination.

Exercise No. 8:

i.p. – sitting. With three fingers of each hand, it is easy to press on the upper eyelid, after 1-2 seconds. Remove fingers from eyelids. Repeat 3-4 times. Exercise strengthens the circulation of intraocular fluid.

Exercise No. 9 “Mark in glass”:

Make a dot from plasticine and sculpt on glass. We select a distant object outside the window, look into the distance for a few seconds, then look at the point. Later, you can complicate the loads – focus on four objects at different distances.

Exercise No. 10 “Massage”:

With three fingers of each hand, lightly press the upper eyelids, after 1-2 seconds, remove the fingers from the eyelids. Repeat 3 times. Improves the circulation of intraocular fluid.

Exercise No. 11 “Hydromassage”:

Twice a day, in the morning and in the evening, rinse the eyes.