Human eye - The retina (2023)

The retina is the part of the eye that receives the light and converts it into chemical energy. The chemical energy activates nerves that conduct the messages out of the eye into the higher regions of the brain. The retina is a complex nervous structure, being, in essence, an outgrowth of the forebrain.

Ten layers of cells in the retina can be seen microscopically. In general, there are four main layers: (1) Next to the choroid is the pigment epithelium, already mentioned. (2) Above the epithelium is the layer of rods and cones, the light-sensitive cells. The changes induced in the rods and cones by light are transmitted to (3) a layer of neurons (nerve cells) called the bipolar cells. These bipolar cells connect with (4) the innermost layer of neurons, the ganglion cells; and the transmitted messages are carried out of the eye along their projections, or axons, which constitute the optic nerve fibres. Thus, the optic nerve is really a central tract, rather than a nerve, connecting two regions of the nervous system, namely, the layer of bipolar cells, and the cells of the lateral geniculate body, the latter being a visual relay station in the diencephalon (the rear portion of the forebrain).

The arrangement of the retinal cells in an orderly manner gives rise to the outer nuclear layer, containing the nuclei of the rods and cones; the inner nuclear layer, containing the nuclei and perikarya (main cell bodies outside the nucleus) of the bipolar cells, and the ganglion cell layer, containing the corresponding structures of the ganglion cells. The plexiform layers are regions in which the neurons make their interconnections. Thus, the outer plexiform layer contains the rod and cone projections terminating as the rod spherule and cone pedicle; these make connections with the dendritic processes of the bipolar cells, so that changes produced by light in the rods and cones are transmitted by way of these connections to the bipolar cells. (The dendritic process of a nerve cell is the projection that receives nerve impulses to the cell; the axon is the projection that carries impulses from the cell.) In the inner plexiform layer are the axons of the bipolar cells and the dendritic processes of the ganglion and amacrine cells (see below). The association is such as to allow messages in the bipolar cells to be transmitted to the ganglion cells, the messages then passing out along the axons of the ganglion cells as optic nerve messages.

The photosensitive cells are, in the human and in most vertebrate retinas, of two kinds, called rods and cones, the rods being usually much thinner than the cones but both being built up on the same plan. The light-sensitive pigment is contained in the outer segment, which rests on the pigment epithelium. Through the other end, called the synaptic body, effects of light are transmitted to the bipolar and horizontal cells. When examined in the electron microscope, the outer segments of the rods and cones are seen to be composed of stacks of disks, apparently made by the infolding of the limiting membrane surrounding the outer segment; the visual pigment, located on the surfaces of these disks, is thus spread over a very wide area, and this contributes to the efficiency with which light is absorbed by the visual cell.

More From Britannicahuman nervous system: The eye

The arrangement of the retina makes it necessary for light to pass through the layers not sensitive to light first before it reaches the light-sensitive rods and cones. The optical disadvantages of this arrangement are largely overcome by the development of the fovea centralis, a localized region of the retina, close to the optic axis of the eye, where the inner layers of the retina are absent. The result is a depression, the foveal pit, where light has an almost unrestricted passage to the light-sensitive cells. It is essentially this region of the retina that is employed for accurate vision, the eyes being directed toward the objects of regard so that their images fall in this restricted region. If the object of interest is large, so as to subtend a large angle, then the eye must move rapidly from region to region so as to bring their images successively onto the fovea; this is typically seen during reading. In the central region of the fovea there are cones exclusively; toward its edges, rods also occur, and as successive zones are reached the proportion of rods increases while the absolute density of packing of the receptors tends to decrease. Thus, the central fovea is characterized by an exclusive population of very densely packed cones; here, also, the cones are very thin and in form very similar to rods. The region surrounding the fovea is called the parafovea; it stretches about 1,250 microns from the centre of the fovea, and it is here that the highest density of rods occurs. Surrounding the parafovea, in turn, is the perifovea, its outermost edge being 2,750 microns from the centre of the fovea; here the density of cones is still further diminished, the number being only 12 per hundred microns compared with 50 per hundred microns in the most central region of the fovea. In the whole human retina there are said to be about 7,000,000 cones and from 75,000,000 to 150,000,000 rods.

The fovea is sometimes referred to as the macula lutea (“yellow spot”); actually this term defines a rather vague area, characterized by the presence of a yellow pigment in the nervous layers, stretching over the whole central retina—i.e., the fovea, parafovea, and perifovea.

The blind spot in the retina corresponds to the optic papilla, the region on the nasal side of the retina through which the optic nerve fibres pass out of the eye.

Although the rods and cones may be said to form a mosaic, the retina is not organized in a simple mosaic fashion in the sense that each rod or cone is connected to a single bipolar cell that itself is connected to a single ganglion cell. There are only about 1,000,000 optic nerve fibres, while there are at least 150,000,000 receptors, so that there must be considerable convergence of receptors on the optic pathway. This means that there will be considerable mixing of messages. Furthermore, the retina contains additional nerve cells besides the bipolar and ganglion cells; these, the horizontal and amacrine cells, operate in the horizontal direction, allowing one area of the retina to influence the activity of another. In this way, for example, the messages from one part of the retina may be suppressed by a visual stimulus falling on another, an important element in the total of messages sent to the higher regions of the brain. Finally, it has been argued that some messages may be running the opposite way; they are called centrifugal and would allow one layer of the retina to affect another, or higher regions of the brain to control the responses of the retinal neurons. In primates the existence of these centrifugal fibres has been finally disproved, but in such lower vertebrates as the pigeon, their existence is quite certain.

The pathway of the retinal messages through the brain is described later in this article; it is sufficient to state here that most of the optic nerve fibres in primates carry their messages to the lateral geniculate body, a relay station specifically concerned with vision. Some of the fibres separate from the main stream and run to a midbrain centre called the pretectal nucleus, which is a relay centre for pupillary responses to light.

The transparent media

Within the cavities enclosed by the three layers of the globe described above there are the aqueous humour in the anterior and posterior chambers; the crystalline lens behind the iris; and the vitreous body, which fills the large cavity behind the lens and iris.

The aqueous humour

The aqueous humour is a clear colourless fluid with a chemical composition rather similar to that of blood plasma (the blood exclusive of its cells) but lacking the high protein content of the latter. Its main function is to keep the globe reasonably firm. It is secreted continuously by the ciliary body into the posterior chamber, and flows as a gentle stream through the pupil into the anterior chamber, from which it is drained by way of a channel at the limbus; that is, the juncture of the cornea and the sclera. This channel, the canal of Schlemm, encircles the cornea and connects by small connector channels to the blood vessels buried in the sclera and forming the intrascleral plexus or network. From this plexus the blood, containing the aqueous humour, passes into more superficial vessels; it finally leaves the eye in the anterior ciliary veins. The wall of the canal that faces the aqueous humour is very delicate and allows the fluid to percolate through by virtue of the relatively high pressure of the fluid within the eye. Obstruction of this exit, for example, if the iris is pushed forward to cover the wall of the canal, causes a sharp rise in the pressure within the eye, a condition that is known as glaucoma. Often the obstruction is not obvious, but is caused perhaps by a hardening of the tissue just adjacent to the wall of the canal—the trabecular meshwork, in which case the rise of pressure is more gradual and insidious. Ultimately the abnormal pressure damages the retina and causes a variable degree of blindness. The normal intraocular pressure is about 15 mm (0.6 inch) of mercury above atmospheric pressure, so that if the anterior chamber is punctured by a hypodermic needle the aqueous humour flows out readily. Its function in maintaining the eye reasonably hard is seen by the collapse and wrinkling of the cornea when the fluid is allowed to escape. An additional function of the fluid is to provide nutrition for the crystalline lens and also for the cornea, both of which are devoid of blood vessels; the steady renewal and drainage serve to bring into the eye various nutrient substances, including glucose and amino acids, and to remove waste products of metabolism.

The vitreous body

The vitreous body is a semisolid gel structure that is remarkable for the small amount of solid matter that it contains. The solid material is made up of a form of collagen, vitrosin, and hyaluronic acid (a mucopolysaccharide). Thus, its composition is rather similar to that of the cornea, but the proportion of water is much greater, about 98 percent or more, compared with about 75 percent for the cornea. The jelly is probably secreted by certain cells of the retina. In general, the vitreous body is devoid of cells, in contrast with the lens, which is packed tight with cells. Embedded in the surface of the vitreous body, however, there is a population of specialized cells, the hyalocytes of Balazs, which may contribute to the breakdown and renewal of the hyaluronic acid. The vitreous body serves to keep the underlying retina pressed against the choroid.

The crystalline lens

The lens is a transparent body, flatter on its anterior than on its posterior surface, and suspended within the eye by the zonular fibres of Zinn attached to its equator; its anterior surface is bathed by aqueous humour, and its posterior surface by the vitreous body. The lens is a mass of tightly packed transparent fibrous cells, the lens fibres, enclosed in an elastic collagenous capsule. The lens fibres are arranged in sheets that form successive layers; the fibres run from pole to pole of the lens, the middle of a given fibre being in the equatorial region. On meridional (horizontal) section, the fibres are cut longitudinally to give an onion-scale appearance, whereas a section at right-angles to this—an equatorial section—would cut all the fibres across, and the result would be to give a honeycomb appearance. The epithelium, covering the anterior surface of the lens under the capsule, serves as the origin of the lens fibres, both during embryonic and fetal development and during infant and adult life, the lens continuing to grow by the laying down of new fibres throughout life.


What is in the human retina? ›

The retina is a layered structure with ten distinct layers of neurons interconnected by synapses. The cells subdivide into three basic cell types: photoreceptor cells, neuronal cells, and glial cells.

How many retinas are in the human eye? ›

The entire retina contains about 7 million cones and 75 to 150 million rods. The optic disc, a part of the retina sometimes called "the blind spot" because it lacks photoreceptors, is located at the optic papilla, where the optic-nerve fibres leave the eye.

What happens if retina is damaged? ›

Damage to the retina often leads to vision loss. Medical experts explain that when the retina is injured through disease or an accident, blood vessels are affected. The veins carry neurons between the optic nerve and the brain. When they are damaged, neurons die, and the brain doesn't receive visual information.

Can the retina regenerate? ›

Unlike in fish and frogs, the human retina doesn't regenerate, and the vision loss caused by damage to cells in the back of the eye – be it genetic or physical – can rarely be fixed. But new research suggests that regrowing the retina may not be science fiction after all.

Can you still see without a retina? ›

People need a healthy retina to be able to see clearly. At first, detachment might only affect a small part of the retina. Without treatment, however, the whole retina can peel off, and a person risks losing the vision from that eye.

Do both eyes have same retina? ›

Each eye looks at an item from a slightly different angle and registers a slightly different image on its retina (the back of the eye). The two images are sent to the brain where the information is processed. In a fraction of a second our brain brings one three-dimensional image to our awareness.

What is the purpose of retina? ›

The retina is a layer of photoreceptors cells and glial cells within the eye that captures incoming photons and transmits them along neuronal pathways as both electrical and chemical signals for the brain to perceive a visual picture.

Can you go blind with retina? ›

The symptoms of retinal detachment often come on quickly. If the retinal detachment isn't treated right away, more of the retina can detach — which increases the risk of permanent vision loss or blindness.

Can you fix retina damage? ›

Yes, in many cases an eye doctor can repair a damaged retina. While a patient may not experience completely restored vision, retinal repair can prevent further vision loss and stabilize vision. It's important that patients get treatment for their damaged retinas as soon as possible.

What causes damage to your retina? ›

The most common causes of retina damage are those related to old age, light damage or trauma. Retinal disorders can damage this vital tissue. They can affect your vision, and some can be serious enough to cause blindness.

Can retina be corrected? ›

Laser surgery can repair a retinal tear or hole. Your surgeon uses a laser to heat small pinpoints on the retina. This creates scarring that usually binds (welds) the retina to the underlying tissue. Immediate laser treatment of a new retinal tear can decrease the chance of it causing a retinal detachment.

How long does it take for a retina to heal? ›

In fact complete healing after retinal surgery often takes 6 months. In most cases, the visual acuity at 6 months will be the final vision. There is normal swelling of the eye after retina surgery, which initially, will limit the vision.

How long does it take to recover from retina? ›

On average, the expected recovery timeline is 2 to 4 weeks, but it can take up to several months for vision to fully recover. Vision will likely be blurry for a few weeks and it may still be up to 3 to 6 months before vision improves.

How can I strengthen my retina? ›

Fortunately, there are steps you can take to help support your retinal health:
  1. Regular dilated eye exams. ...
  2. Eat plenty of vitamin and nutrient-rich foods. ...
  3. Quit smoking. ...
  4. Control blood sugar, pressure and cholesterol. ...
  5. Know your family history. ...
  6. Protect your eyes from UV rays.
Jun 29, 2022

What is the best food for retina health? ›

Dark green leafy vegetables such as Spinach, Kale Mustard Greens, Collard Greens, Chard are rich source of lutein and zeaxanthin. Besides, add Vitamin C rich fruits like oranges, sweetlime, grapes etc as well. Nuts are also abundant source of Vitamin E like walnut, almonds, hazelnuts etc.

Can you live with a torn retina? ›

Living with the effects of retinal detachment can be daunting at first. Treatment is available, but its success can depend on how quickly it happens – and how much damage has already occurred. However, most people live independently with a good level of vision following retinal detachment surgery.

What happens to the retina after death? ›

Most researchers believe that human retinal neurons become swiftly non-functional after death. In the study, researchers confirmed this rapid loss of retinal function in mice, using a method called electroretinography (ERG) to track the decline in retinal neuron activity in the minutes after death.

Can a retina be reattached? ›

Most of the time, the retina can be reattached with one operation. However, some people will need several surgeries. More than 9 out of 10 detachments can be repaired. Failure to repair the retina always results in loss of vision to some degree.

Can you watch TV with a detached retina? ›

During the recovery period, patients should avoid certain activities including watching TV, driving and heavy lifting. Patients with nonactive jobs can typically return to work after two weeks. If not treated quickly, a retinal detachment can cause partial or total vision loss so prompt treatment is essential.

Can you fly with a detached retina? ›

Retinal detachment can occur for any number of reasons, including advanced disease (diabetic retinopathy), trauma (a sudden blow to the head) or from aging (the most common cause). Following retinal detachment surgery, it is important that flying is completely avoided until your eye has fully healed.

Can your retina detach twice? ›

It's possible to get a detached retina more than once. You may need a second surgery if this happens. Talk to your provider about preventive steps you can take to protect your vision. If you notice symptoms returning, call your provider right away.

Which eye is dominant? ›

Most people have a dominant eye that corresponds to their dominant hand. For example, if you are left-handed, you are more likely to have a dominant left eye. Right-handed people can also have a dominant left eye, but it is not as common.

Why is my left eye not as clear as my right? ›

There are a number of causes of blurry vision in one eye. Among the most common ones are refractive errors, which can lead to long- or short-sightedness. Other possible causes include infections, migraine, and cataracts. Most causes of blurry vision are not serious.

What is retina in simple words? ›

(REH-tih-nuh) The light-sensitive layers of nerve tissue at the back of the eye that receive images and sends them as electric signals through the optic nerve to the brain.

Does the retina need oxygen? ›

The same lack of regulation allows choroidal PO2 to increase dramatically during hyperoxia, offering the potential for O2 to be used therapeutically in retinal vascular occlusive diseases and retinal detachment. Oxygen (O2) is essential for retinal function.

How serious is retinal tear? ›

Retinal tears can lead to a retinal detachment, which requires immediate attention. Retinal tears can be a very serious condition that can impact your vision, so if you are experiencing any symptoms associated with a torn retina, contact our offices as soon as possible.

Can you drive with one eye? ›

Your horizontal field of vision must be 150° or more. If you have sight in one eye only, you must have a visual acuity (with corrective lenses, where necessary) of at least 0.6 (6/10), an unrestricted field of vision in the eye concerned and your monocular vision must have existed for enough time to allow you to adapt.

How long can a retina be detached before blindness? ›

A retinal detachment may cause permanent blindness over a matter of days and should be considered an eye emergency until evaluated by a retina specialist. Most retinal detachments occur suddenly and can threaten the central vision within hours or days.

How can I check my retina at home? ›

Cover one eye. Hold the grid about 10 inches away from the eye you are testing. Look at the center dot keeping your eye focused on it at all times. While looking directly at the center, and only the center, be sure that all the lines are straight and all the small squares are the same size.

Can stress cause retina problems? ›

The simple answer is no, stress cannot cause retinal detachment. Retinal detachment is due to tears in the peripheral retina. Retinal detachment occurs in less than 1 in 10,000 people and can occur at any age but is more likely to affect people over age 40.

How successful is retina surgery? ›

Retinal detachment surgery involves reattaching the retina to the back of the eye and sealing any breaks or holes in the retina. The treatment success rate is high, with around nine out of 10 retinas able to be reattached.

Does retina changes with age? ›

With aging, there is diffuse thickening of the internal limiting membrane of the retina and diminution of neural elements with gliosis in the peripheral retina. These changes lead to disorganization in the area of the ora serrata, and the RPE may migrate into the sensory retina in this area.

What cells make up the retina? ›

There are five types of neurons in the retina: photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells.

What are the three parts of the retina? ›

Retina is primarily made up of three layers of nerve cells, these are ganglion cells, bipolar cells and photoreceptor cells.

What is unique about the human retina? ›

The retina's cones differentiate varied wavelengths in light to produce different colors. The outer layer of the retina is pigmented to prevent the back reflection of light that would decrease vision clarity. Everyone has a blind spot known as the optic disc.

Is retina actually brain tissue? ›

The retina is actually an extension of the brain, formed embryonically from neural tissue and connected to the brain proper by the optic nerve. The retina is a complex transparent tissue consisting of several layers, only one of which contains light-sensitive photoreceptor cells.

What happens when light hits the retina? ›

When light hits the retina (a light-sensitive layer of tissue at the back of the eye), special cells called photoreceptors turn the light into electrical signals. These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images you see.

What nerve supplies the retina? ›

The retina is supplied by the central retinal artery and the short posterior ciliary arteries (Fig 2.3). The central retinal artery travels in or beside the optic nerve as it pierces the sclera then branches to supply the layers of the inner retina (i.e., the layers closest to the vitreous compartment).

What is the retina responsible for? ›

The retina is a layer of photoreceptors cells and glial cells within the eye that captures incoming photons and transmits them along neuronal pathways as both electrical and chemical signals for the brain to perceive a visual picture.

What is the most important part of the retina? ›

The macula (macular zone, yellow spot) is the most important part of the retina. The macula ensures central vision since it contains numerous photo receptors – namely the cones.

Which part of the retina is affected by Best disease? ›

Best disease is an inherited disease that affects the retinas of your eyes. It causes the macula, which is the central part of the retina, to degrade. This means that you can have problems with your central vision, or seeing things that are right in front of you. Best disease may not affect peripheral (side) vision.

What are 3 facts about the retina? ›

The retina can tear in a very small area and lead to a large retinal detachment. The retina is about the size of a postage stamp. The retina has a cell layer that has the same pigment seen in skin cells known as melanin. The retinal image created by your eye is upside down and back to front.

What happens if you have no retina? ›

The areas where the retina detaches lose their blood supply and stop working, causing you to lose vision. The most common cause of rhegmatogenous detachment is aging.

Why is the retina the most important part of the eye? ›

One of the most important parts of the eye is the retina. But why is it so important? Your retina only has one job, but it is a very important one: convert the light that the eye has captured into electric signals that the brain can process.

What keeps the retina in place? ›

The vitreous also comes in contact with the retina (the light-sensitive tissue at the back of the eye that acts like the film of a camera). The pressure of the vitreous humour helps to keep the retina in place.

How does the retina see the world? ›

Light passes through the lens at the front of your eye and hits the retina. Photoreceptors — cells inside your retina that react to light — change light energy into an electrical signal. This signal travels through your optic nerve and into your brain to become the picture of the world you see.

How does a retina look like? ›

The retina most often looks red or orange because there are many blood vessels right behind it. An ophthalmoscope allows a health care provider to see through your pupil and lens to the retina.

Top Articles
Latest Posts
Article information

Author: Rubie Ullrich

Last Updated: 19/12/2023

Views: 6257

Rating: 4.1 / 5 (72 voted)

Reviews: 95% of readers found this page helpful

Author information

Name: Rubie Ullrich

Birthday: 1998-02-02

Address: 743 Stoltenberg Center, Genovevaville, NJ 59925-3119

Phone: +2202978377583

Job: Administration Engineer

Hobby: Surfing, Sailing, Listening to music, Web surfing, Kitesurfing, Geocaching, Backpacking

Introduction: My name is Rubie Ullrich, I am a enthusiastic, perfect, tender, vivacious, talented, famous, delightful person who loves writing and wants to share my knowledge and understanding with you.