Eye Health: Anatomy of the Eye - VisionAware Eye Health: Anatomy of the Eye Eye Health: Anatomy of the Eye About the Eye and How It Works Diagram of the eye, viewed from the side. National Eye Institute To understand this diagram of the eye, try to picture it as being split in two, like an apple that's been cut in half. Imagine yourself looking into the eye from the cut side. The Cornea The cornea is a transparent dome-shaped tissue that forms the front part of your eye. It functions as a window and allows light to enter your eye. It also begins the process of focusing light rays that allow you to see words and images clearly. The cornea does not contain any blood vessels, but instead contains many nerve endings that make it extremely sensitive. That is why a scratch or a loose eyelash is so painful. Jake Whalen: Living and Coping with Keratoconus Jake Whalen is a freelance copywriter who has struggled for most of his life with keratoconus . Keratoconus is a degenerative condition of the cornea , a transparent dome-shaped tissue that forms the front part of the eye.

Keratoconus gradually causes the cornea to thin, bulge/protrude outward, and become cone-shaped. This creates an abnormal curvature of the eye that can cause blurred vision, glare problems, light sensitivity, and even extreme pain. Learn more about the basics of effective eye care, including: Questions to ask when you see an eye care specialist. Check out our Getting Started Kit for more ideas to help you live well with low vision. Sign up with VisionAware to receive free weekly email alerts for more helpful information and tips for everyday living with vision loss. Aqueous Humor Aqueous humor is a clear, watery fluid contained in a chamber behind the cornea that helps bring nutrients to the eye tissue. It is made behind the lens and flows to the front of the eye, where it is drained by a tissue called the trabecular meshwork. Problems with the flow of the aqueous fluid can lead to problems with the pressure inside the eye, such as glaucoma . The Sclera The sclera is a tough white outer coating of fibrous tissue that covers your entire eyeball (all the way around) except for the cornea. The muscles that move the eye are attached to the sclera.

The name sclera comes from the Greek word "skleros," which means "hard." The Iris and the Pupil The iris is a tissue inside the eye that has a hole in the center called the pupil. The iris contains muscles that allow the pupil to become larger (open up or dilate) and smaller (close up or constrict). The iris regulates the amount of light that enters your eye by adjusting the size of the pupil opening. In bright light, the iris closes (or constricts) and makes the pupil opening smaller to restrict the amount of light that enters your eye. The iris in bright light In dim light, the iris opens (or dilates) and makes the pupil opening larger to increase the amount of light that enters your eye: The iris in dim light In addition, it is the iris that determines your eye color. People with brown eyes have heavily pigmented irises, while people with blue or lighter-colored eyes have irises with less pigment. The Lens The lens is composed of transparent, flexible tissue and is located directly behind the iris and the pupil. It is the second part of your eye, after the cornea, that helps to focus light and images on your retina.

Because the lens is flexible and elastic, it can change its curved shape to focus on objects and people that are either nearby or at a distance. The ciliary muscles, which are part of the ciliary body, are attached to the lens and contract or release to change the lens shape and curvature. The lens becomes more rounded to focus on near objects (see Figure 1): Fig. 1: A more rounded lens can focus on near objects. The lens becomes more elongated (or stretched) to focus on objects that are far away (see Figure 2): Fig. 2: A more elongated/stretched lens can focus on far objects Over time, the lens loses some of its elasticity and therefore loses some of its ability to focus on near objects. This is called presbyopia and explains why people need reading glasses as they become older. The Choroid The choroid is a dark brown membrane that is rich with blood vessels, located between the sclera and the retina. It supplies blood and nutrients to the retina and nourishes all of the other structures within the eye. The Vitreous The vitreous is the jelly-like substance that fills the inside of the back part of the eye.

Over time, the vitreous becomes more liquid and can detach from the back part of the eye, which can create floaters . If you notice new floaters or flashing lights, it is important to see your eye doctor, because a detached vitreous can cause a hole (a condition called a macular hole ) to develop in the retina. The Retina and Optic Nerve The retina is the light-sensitive tissue that lines the inside surface of the eye, much like wallpaper. Cells in the retina convert incoming light into electrical impulses. These electrical impulses are carried by the optic nerve (which resembles your television cable) to the brain, which finally interprets them as visual images. The macula is the small sensitive area in the center of the retina that provides clear central vision. The fovea is located in the center of the macula and provides the sharpest detail vision. Additional Eye Diagrams You can get a closer look at different parts of eye with this interactive eye diagram from the National Eye Institute. Healthline.com provides an interactive Human Eye in 3D online tool that can help you understand how the parts of the eye work in relation to each other.

More Information You can learn more about the parts of the eye and refractive errors, including myopia (nearsightedness), hyperopia (farsightedness), and astigmatism (both near and far blurriness) at Refractive Error and Astigmatism and A Guide to Eye Conditions . Retina | definition of Retina by Medical dictionary Retina | definition of Retina by Medical dictionary Related to Retina: Retina Display retina [ret´ĭ-nah] the innermost of the three tunics of the eye , surrounding the vitreous body and continuous posteriorly with the optic nerve. The retina is composed of light-sensitive neurons arranged in three layers; the first layer is made up of rods and cones and the other two transmit impulses from the rods and cones to the optic nerve . The rods are sensitive in dim light, and the cones are sensitive in bright light and are responsible for color vision. Disorders of the Retina. retinopathies are pathologic conditions of the retina; they occur in conjunction with certain systemic disorders, such as hypertension, nephritis, toxemia of pregnancy, and diabetes mellitus.

detachment of the retina is complete or partial separation of the retina from the choroid, the middle coat of the eyeball. It occurs most often in persons with myopia (nearsightedness), but it also can result from trauma to the head. Structure of the retina showing the rods and cones. From Applegate, 2000. ret·i·na (ret'i-nă), [TA] Grossly, the retina consists of three parts: optic, ciliary, and iridial. The optic part, the physiologic portion that receives the visual light rays, is further divided into two parts, the pigmented part (pigment epithelium) and the nervous part, which are arranged in the following ten layers: pigmented layer; layer of inner and outer segments (of rods and cones); outer limiting layer (actually a row of junctional complexes); outer nuclear layer; outer plexiform layer; inner nuclear layer; inner plexiform layer; ganglionic (cell) layer; layer of nerve fibers; and inner limiting layer. Layers 2-10 comprise the neural layer.

At the posterior pole of the visual axis is the macula, in the center of which is the fovea, the area of acute vision. Here, layers 6-9 and blood vessels are absent, and only elongated cones are present. About 3 mm medial to the fovea is the optic disc, where axons of the ganglionic cells converge to form the optic nerve. The ciliary and iridial parts of the retina are forward prolongations of the pigmented layer and a layer of supporting columnar or epithelial cells over the ciliary body and the posterior surface of the iris, respectively. [Mediev. L. prob. fr. L. rete, a net] retina /ret·i·na/ (ret´ĭ-nah) [L.] the innermost tunic of the eyeball, containing the neural elements for reception and transmission of visual stimuli. retina (rĕt′n-ə) n. pl. retinas or retinae (rĕt′n-ē′) A delicate, multilayered, light-sensitive membrane lining the inner eyeball and connected by the optic nerve to the brain. ret′i·nal adj.

[ret′inə] Etymology: L, rete, net a 10-layered, delicate nervous tissue membrane of the eye, continuous with the optic nerve, that receives images of external objects and transmits visual impulses through the optic nerve to the brain. The retina is soft and semitransparent and contains rhodopsin. It consists of the outer pigmented layer and the nine-layered retina proper. These nine layers, starting with the most internal, are the internal limiting membrane, the stratum opticum, the ganglion cell layer, the inner plexiform layer, the inner nuclear layer, the outer plexiform layer, the outer nuclear layer, the external limiting membrane, and the layer of rods and cones. The outer surface of the retina is in contact with the choroid, the inner surface with the vitreous body. The retina is thinner anteriorly, where it extends nearly as far as the ciliary body, and thicker posteriorly, except for a thin spot in the exact center of the posterior surface where focus is best.

The photoreceptors end anteriorly in the jagged ora serrata at the ciliary body, but the membrane of the retina extends over the back of the ciliary processes and the iris. The retina becomes clouded and opaque if exposed to direct sunlight. See also Jacob x membrane, macula, optic disc . Layers of the retina: A, nerve fiber layer; B, ganglion cell layer; C, inner nuclear layer; D, outer nuclear layer; E, rods and cones Retina ret·i·na (ret'i-nă) [TA] The light-sensitive membrane forming the innermost layer of the eyeball. Grossly, the retina consists of three parts: optic part of retina, ciliary part of retina, and iridial part of retina.

The optic part, the physiologic portion that receives the visual light rays, is further divided into two parts, pigmented part (pigment epithelium) and nervous part, which are arranged in the following layers: 1) pigment epithelium; 2) layer of rods and cones; 3) external limiting lamina, actually a row of junctional complexes; 4) external nuclear lamina; 5) external plexiform lamina; 6) internal nuclear lamina; 7) internal plexiform lamina; 8) ganglionic cell lamina; 9) lamina of nerve fibers; 10) internal limiting lamina. Layers 2-10 comprise the nervous part. At the posterior pole of the visual axis is the macula, in the center of which is the fovea, the area of acute vision. Here layers 6-9 and blood vessels are absent, and only elongated cones are present. About 3 mm medial to the fovea is the optic disc, where axons of the ganglionic cells converge to form the optic nerve.

The ciliary and iridial parts of the retina are forward prolongations of the pigmented layer and a layer of supporting columnar or epithelial cells over the ciliary body and the posterior surface of the iris, respectively. [Mediev. L. prob. fr. L. rete, a net] retina A retina having a spotted or striped appearance, seen in retinitis pigmentosa. retina The complex membranous network of nerve cells, fibres and photoreceptors that lines the inside of the back of the eye and converts optical images formed by the lens system of the eye into nerve impulses. The retina contains colour-blind but very sensitive rods and colour-sensitive cones and a computing system that refines the signals produced by these. The impulses leave each retina by way of about one million nerve fibres that form the optic nerve. Fig. 269 Retina. retina the lining of the interior of the vertebrate eye containing a concentration of photoreceptor cells known as rods and cones that are connected to the optic nerve via BIPOLAR CELLS . The retina lies immediately in front of the vascular choroid layer which nourishes it.

Retina Light sensitive layer of the eye, that consists of four major layers: the outer neural layer, containing nerve cells and blood vessels, the photoreceptor layer, a single layer that contains the light sensing rods and cones, the pigmented retinal epithelium (PRE) and the choroid, consisting of connective tissue and capillaries. Mentioned in: Cataract Surgery , Cataracts , Color Blindness , Eye and Orbit Ultrasounds , Eye Examination , Eye Glasses and Contact Lenses , Eye Muscle Surgery , Glaucoma , Hyperopia , Macular Degeneration , Microphthalmia and Anophthalmia , Myopia , Photorefractive Keratectomy and Laser-Assisted In-Situ Keratomileusis , Radial Keratotomy , Retinal Artery Occlusion , Retinal Vein Occlusion , Retinoblastoma , Uveitis , Vitiligo retina light-sensitive membrane at the back of the eyeball, formed of specialized nerve cells (rods and cones) and vascular tissue retina The light-receptive, innermost nervous tunic of the eye.

It is a thin transparent membrane (about 125 μm near the ora serrata, 350 μm near the macula and 560 μm near the optic disc). The retina proper has an area of about 266 mm2. It lies between the vitreous body and the choroid, and extends from the optic disc to the ora serrata. Near the posterior pole and temporal to the optic disc is the macula, at the centre of which is the foveola which provides the best visual acuity. The retina contains at least 10 distinct layers, of which there are two synaptic layers.

They are from the outermost layer to the innermost: (1) the pigment epithelium; (2) the layer of rods and cones; (3) the external limiting membrane; (4) the outer nuclear layer; (5) the outer molecular (outer plexiform) layer; (6) the inner nuclear layer (which contains the bipolar, amacrine and horizontal cells and nuclei of the fibres of Mueller); (7) the inner molecular (inner plexiform) layer; (8) the ganglion cell layer; (9) the nerve fibre (layer stratum opticum); and (10) the internal limiting membrane. The two synaptic layers where visual signals must synapse as they emerge from the rods and cones on their way to the optic nerve are the two molecular layers (5 and 7) (Fig. R9). The blood supply to the retina is composed of the capillaries from the central retinal artery, which supply the inner two-thirds of the retina up to the outer plexiform layer, and the choriocapillaris, which supplies the outer one-third. There is no retinal circulation in the foveola (avascular zone).

A blood-retina barrier is created by the walls of the retinal capillaries which restrict the movement of molecules, which could be damaging to neural tissue or interfere with function, from the inside to the outside of the capillaries. The blood-retina barrier in the outer third of the retina is formed by the tight junctions of the retinal pigment epithelium cells. See astrocytes ; optic cup ; optic disc ; ectoderm ; ocular fundus ; fibre layer of Henle; macula ; neurotransmitter ; neurosensory retina; retinitis ; retinopathy ; rhodopsin ; transduction . converse retina See inverted retina. fleck retina Term referring to a retina with multiple, small or yellow spots, which are seen in various conditions: actinic keratopathy, drusen, fundus albipunctatus, fundus flavimaculatus. inverted retina Term referring to the fact that the retina of vertebrates is orientated so that the light has to pass through all the neuronal layers before reaching the photo-receptors.

However, the retina of invertebrates is normally orientated so that light passes first through the photoreceptors as it traverses the retina: such a retina is called a verted or converse retina. lattice degeneration of the retina A vitreoretinal degeneration usually found between the equator and the ora serrata leading to a thinning of the retina and characterized by a lesion made up of fine white lines and some pigmentation. It may result in holes or tears and in rhegmatogenous retinal detachment by which time the patient usually complains of floaters. The condition is most common in myopes and often found in patients with Marfan's syndrome. See retinal break ; retinal detachment ; retinoschisis ; Marfan's syndrome . centre of disc 4.6 mm or 15.5 *The figures given for the size of the disc are those corresponding to the blind spot. Anatomically the optic disc is slightly smaller. ret·i·na (ret'i-nă) [TA] Grossly, section of eye that consists of three parts: optic, ciliary, and iridial.

The optic part, the physiologic portion that receives the visual light rays, is further divided into two parts, the pigmented part (pigment epithelium) and the nervous part. [Mediev. L. prob. fr. L. rete, a net] retina (ret´ənə), n a 10-layered, delicate nervous-tissue membrane of the eye, continuous with the optic nerve, that receives images of external objects and transmits visual impulses through the optic nerve to the brain. retina the innermost of the three tunics of the eyeball, surrounding the vitreous body and continuous posteriorly with the optic nerve. The retina is composed of two parts: an optical part in the fundus of the eye that is sensitive to light, and a nonsensitive pigmented part that lines the ciliary body and iris. The light-sensitive neurons are arranged in three layers; the first layer is made up of rods and cones and the other two transmit impulses from the rods and cones to the optic nerve The rods are sensitive to dim light of a variety of wavelengths, and the cones are sensitive to bright light of more restricted wavelengths and are responsible for color vision. Visual acuity is greatest in the central part of the retina.

See also eye . Retina of the dog. By permission from Aspinall V, O'Reilly M, Introduction to Veterinary Anatomy and Physiology, Butterworth Heinemann, 2004 silent retina syndrome see sudden acquired retinal degeneration. How The Eye Works The CORNEA The cornea is the transparent window at the front of the eye that allows light to pass into the eye. The PUPIL The pupil is like the aperture of a camera. Light enters here, then passes through the lens. Liquid flowing through the pupil, called aqueous fluid, is absorbed through channels in front of the iris. This fluid provides nourishment to the lens, iris and cornea. Pressure within the eye depends on the delicate balance between the body's production and absorption of this fluid. The IRIS With a camera, you can enlarge or reduce the aperture to control the amount of light that enters. Similarly, the iristhe colored portion of the eye, automatically opens (dilates) or closes (constricts) the pupil to adapt to the surrounding light. The LENS The lens in the healthy eye is flexible or deformable. The ring-shaped ciliary muscle surrounding it contracts or relaxes to adjust its shape according to visual need.

The lens bends or "refracts" light rays to focus on near or far objects. The light rays pass through the transparent gel that fills the inside of the eyeballthe vitreous gel, and come to a focus on the surface of the retina. The RETINA The retina is a light-sensitive tissue that lines the back of the eye, comparable to film in a camera. The retina receives the picture formed by the light rays and sends the image to the brain through a cable known as the optic nerve. The MACULA The central part of the retina, which processes detailed vision, is called the macula. It is here that the optic nerve collects and transmits visual images to the brain for processing. The brain combines the separate images produced by the eyes into a single, composite neural image. The VITREOUS SIU SOM Histology SSB Online slides of eye -- normal | pathology These specimens at the Virtual Slidebox (University of Iowa Department of Pathology ) may be examined with full range of magnification and movement. Requires Java and fast internet connection. Overview / Basic structure of the eyeball The eyeball consists of three principal layers. The outer layer, or sclera, consists of dense fibrous connective tissue.

The sclera is "white" of the eye. The sclera is continuous with the transparent substantia propria of the cornea . The exposed front surface of the eye, including the cornea, is also covered by a thin, non-keratinized stratified squamous epithelium. The next layer, or choroid, consists of heavily pigmented loose connective tissue, including many melanocytes. The choroid is normally not visible behind the "white" of the sclera. The choroid is continuous with the iris ; together the choroid and iris are called the uvea. A hole in this layer, the pupil, allows light to pass through. The inner layer, or retina , includes two portions. The neural retina is the photoreceptive, imaging-processing tissue. The pigmented epithelium lies behind the neural retina; it also extends forward to line the hidden side of the iris. The lens is a specialized epithelial structure, suspended behind the pupil. The anterior chamber, a space filled with aqueous humor , lies between the iris and the cornea. The posterior chamber lies behind the iris.

Cornea The cornea consists of a thin surface epithelium ( non-keratinized stratified squamous ) overlying a layer of dense fibrous connective tissue , called substantia propria. Although the corneal tissues are made of the same tissue elements as other body parts (i.e., epithelial cells, collagen, fibroblasts, etc.), the cornea is quite unlike most tissues in that it is perfectly transparent. Compare and contrast the tissue layers of the cornea with those of other body surfaces: Trachea The features which distinguish corneal tissues from those of other body surfaces are all related to its transparency . The epithelium of the cornea is continuous with the epithelium of the conjunctive, both that of the eyeball itself and that of the inside of the eyelid, which in turn is continuous with the epidermis of skin on the exposed surface of the eyelid. Corneal epithelium is very thin (only a few cells thick). Notably (i.e., unlike most other stratified squamous epithelial), corneal epithelium lies flat against the underlying substantia propria.

The absence of connective tissue papillae (compare with skin, where the basal surface of the epidermis is indented by many dermal papillae). The basement membranes between corneal epithelium and substantia propria is exceptionally thick and is called Bowman's membrane. Like most dense fibrous connective tissue, the substantia propria of the cornea is mostly collagen and ground substance , with fibroblasts as the most common cell type. Quite unlike most other dense, fibrous connective tissue, the corneal connective tissue is perfectly transparent. Collagen of the cornea is organized into extremely regular layers. All the collagen fibers in one layer arranged in parallel, and alternating layers run in different directions. Corneal connective tissue has no blood vessels. (You don't need a microscope to confirm this; just look in a mirror.) Even though cells of the cornea are not very active metabolically, they still need oxygen and nutrients. As long as the cornea is in direct contact with air, oxygen can be absorbed directly. Nutrients can diffuse into cornea from aqueous humor. Cells of corneal connective tissue are limited to fibroblasts.

There is no immune-system component, hence the relative ease with which corneal tissue can be transplanted without need for careful tissue typing. At the inner surface of the cornea, a thick basal lamina (Decemet's membrane) separates the substantia propria from a cellular layer, resembling a simple low cuboidal epithelium, called corneal endothelium. (This is a unique use of the term endothelium; it is not related to vascular endothelium .) It is believed that this corneal endothelium is essential for maintaining corneal transparency , by regulating the composition of ground substance in the substantial propria. Corneal epithelium contains free nerve endings. Since pain seems to be the only sensory modality that functions for corneal tissue, biologists long ago decided that free nerve endings elsewhere may also represent pain fibers. Corneal transparency. The tissue elements of the cornea are specialized for transparency. The effectiveness of this design can be readily seen by looking in the mirror and comparing cornea with sclera (the white of the eye). However, apart from the cornea's obvious absence of blood vessels, its tissue composition appears almost identical to that of the sclera.

Yet unlike the sclera, the cornea is marvellously transparent. The transparency of the cornea is based primarily on the regularity of its tissue components, which minimizes the number of surfaces where light can be refracted or reflected. At the limbus (the edge of the cornea, where the cornea meets the sclera), it is apparent that the epithelium of the sclera is almost identical to that of the cornea, except for a slightly less regular basal layer. Similarly, collagen of the corneal substantia propria is not noticably different from collagen of the sclera, except for being slightly more uniform in arrangement. But these small differences are significant; the cornea is transparent while the sclera is opaque. The effect is rather like the difference between packed snow and crystalline ice -- both have the same composition (frozen water), but one is opaque (by scattering the light off the surfaces of many tiny snow crystals) while the other is crystal clear. Although most cells and fibers are colorless, the surfaces of these elements can scatter light when irregularly arranged. Similarly, light scattered from colorless and transparent ice crystals produce the familiar whiteness of winter snow.

Such scattering (together with absorption of light by pigments such as melanin and hemoglobin) prevents light from passing freely through most tissues. Features of the cornea which minimize the scattering of light include the following: Both outer and inner surfaces of the corneal epithelium are smooth. The collagen fibers of the substantia propria are arranged into uniform layers with parallel fibers within each layer (unlike the more irregular texture of collagen in the sclera and in the dermis of the skin). Collagen fibers are formed extracellularly, self-assembling from tropocollagen molecules (secreted as procollagen by fibroblasts). The regulatory machinery responsible for the regular arrangement of collagen fibers in the cornea remains unknown. The water content of the ground substance is carefully regulated, to maintain uniform spacing among collagen fibers. The low cuboidal cells which form the cornea's innermost layer, the so-called corneal endothelium, actively pump ions and water from the corneal ground substance into the aqueous humor, to prevent excess water from disturbing the regularity of the collagen layers and causing opacity. Iris Functionally, the iris is a rather simple opaque ring surrounding and controlling the diameter of its central aperture -- the pupil.

However, the iris does have some peculiar histological features. The iris is the only internal organ which is clearly visible from outside the body. The visible surface of the iris consists of loose connective tissue and includes blood vessels. The color of the iris ("eye color") results both from scattering of light by its trabecular meshwork of collagen fibers and from absorption of light by melanin granules in scattered melanocytes. Variation in eye color result from individual differences in the distribution and density of melanocytes and trabecular meshwork. The posterior (hidden) surface of the iris is an intensely pigmented extension of the embryological optic cup (the same tissue which forms the retina and the pigmented epithelium ). This tissue continues as the ciliary processes around the perimeter of the iris. A ring of smooth muscle surrounding the pupil comprises the pupillary sphincter. The pupillary dilator is not ordinary smooth muscle but rather contractile extensions of myoepithelial cells of the deep layer of the two-layered pigmented epithelial tissue that comprises the posterior surface of the iris. Additional iris images . Lens Histologically, the lens is bizarre.

It is an isolated island of epithelial tissue with an anterior layer that is simple cuboidal and a posterior layer consisting of extravagantly elongated cells, called lens fibers, that are packed with lens protein. This pattern is most readily understood by considering the embryology of the eye. The lens forms as a vesicle that pinches in from surface ectoderm. In basic plan, it is therefore a "bubble" of epithelial tissue. The cells on the posterior of this bubble then grow incredibly long until they extend across almost the entire thickness of the lens, save only a thin layer of cuboidal epithelium that remains on the lens' anterior surface. At the edge of the lens, one can see where these two different epithelial cell shapes meet one another. The shape of the lens (and hence its focal length) is determined by tension exerted through the suspensory fibers , controlled by smooth muscle of the ciliary body . Additional lens images Ciliary body and suspensory fibers (zonules) Deep to the limbus (i.e., the cite where the cornea meets the sclera ), the choroid layer is thickened into the ciliary body.

The ciliary body is a ring of smooth muscle fibers arranged concentrically around the opening in which the lens is suspended. The lens is suspended from the ciliary body by thin fibers of collagen, called suspensory fibers or zonules. Together, the ciliary body and suspensory fibers control the shape of the lens . When smooth muscle is in a relaxed state, the elasticity of the eyeball (sclera) puts tension on the suspensory fibers, which in turn stretch the lens radially and make it thinner. In this condition, the lens brings distant objects into focus on the retina. When the smooth muscle of the ciliary body contracts, the opening in which the lens is suspended becomes (slightly) smaller and tension on the suspensory fibers is relaxed. The lens is then allowed to adopt its "resting" shape, which is more round. In this condition, the lens brings nearby objects into focus on the retina. Note that a stretched lens, for distant focus, is maintained by a relaxed muscle. Hence eyes at rest are focussed for distance vision. Conversely, a contracted muscle is responsible for a relaxed lens, for near focus.

Close work is tiring because the ciliary body must remain in contraction to maintain focus. Ciliary processes and aqueous humor The surface of the ciliary body is covered by an extension of the embryonic optic cup ( the same tissue which forms the retina and the pigmented epithelium ). Small projections of this tissue form the ciliary processes, which secrete the aqueous humor. Aqueous humor flows from its site of formation in the posterior chamber (i.e., behind the iris) through the pupil into the anterior chamber. From there it drains into the canal of Schlemm and hence into venous drainage. Clinical note: An imbalance between the formation and drainage of aqueous humor can create increased pressure. Increased fluid pressure inside the eyeball reduces blood flow into the eyeball, leading to glaucoma. Canal of Schlemm The canal of Schlemm is a network of connective tissue spaces at the edge (limbus) of the cornea, through which aqueous humor can escape from the anterior chamber; from here the fluid seeps into venous drainage. The retina consists of two fundamentally distinct layers, the neural retina (often called simply "the retina") and the pigmented epithelium .

These two layers derive, respectively, from the front and back ectodermal surfaces of the embryonic optic cup . The neural retina is the light-sensitive tissue of the eye. The retina is famously built "upside down". That is, the photoreceptor cells (rods and cones) are located in the back of the retina, so light must pass through all of the layers of the neural retina before getting to the receptors. Even worse, the blood vessels which serve the retina are spread across the front surface, so light on its way to the receptors must also pass by the blood vessels. (Evidently, our visual system is designed to ignore the blood vessels; otherwise every view of the world would have a superimposed array of branching blood vessels and coursing red blood cells.) As one final insult, the nerve fibers which eventually travel from the eye through the optic nerve must pass through the layers of the retina, leaving a " blind spot " where they do so. (And once again, our visual system is designed to ignore the blind spot, filling in the corresponding "hole" in the visual field with whatever color and texture does the best job of hiding the blind spot.) [ How to "see" your own blind spot .

] Cells comprising the neural retina give the appearance of several layers. The innermost layer is the inner limiting membrane, a basal lamina separating nervous tissue of the retina from connective tissue of the vitreous humor . The layer of nerve fibers contains axons from ganglion cells which travel across the retina to the optic nerve and hence past the optic chiasm into the optic tract and into lateral geniculate nucleus of the thalamus. The ganglion cell layer contains the cell bodies of ganglion cells , the cells whose axons project to the brain. The inner plexiform layer contains dendrites of ganglion cells synapsing with axons of bipolar cells . The inner nuclear layer contains the cell bodies of bipolar cells The outer plexiform layer contains dendrites of bipolar cells synapsing with axons of photoreceptor cells . The outer nuclear layer contains the cell bodies of receptor cells . Between the outer nuclear layer and the receptor layer is the site of the outer limiting membrane, a basal lamina bounding the neural retina. The outer segments (rods and cones) of the receptor cells penetrate the outer membrane to contact the pigmented epithelium . The receptor layer contains the photoreceptive outer segments (rods and cones) of receptor cells .

The pigmented epithelium is the outermost layer of the retina, consisting of cuboidal epithelial cells derived from the outer layer of the embryonic optic cup . The dense melanin pigment of this layer absorbs light not captured by photoreceptors. The cells of the pigmented epithelium also contribute to the maintenance of photoreceptors, "recycling" membranes that are shed from rod and cone outer segments. Clinical note: Although cells of the pigmented epithelium are intimately associated with outer segments (rods and cones) of receptor cells , this surface where the neural retina contacts the pigmented epithelium is inherently extremely fragile and is the site where retinal detachment can occur. Three principal cell types comprise the neural retina. Click on the thumbnail below for a diagrammatic representation of these cells. Photoreceptor cells come in two types, rods and cones. The names "rod" and "cone" are descriptive of the shapes, as seen microscopically, of the outer segments of the photoreceptors. Each outer segment is a highly-modified cilium, with many sheet-like folds of membrane arranged in a tall stack. Rods are sensitive to dim light and provide night vision. Rods are more numerous in the peripheral retina.

Cones need brighter light and provide daytime color vision. Cones are more prevalent in the vicinity of the fovea. Three different pigments, in three different types of cones, are each optimally sensitive to different wavelength of light. Bipolar cells are small neurons named for their shape, with two short processes extending away from the cell body. One process receives synapses from photoreceptors; the other process conveys signals to ganglion cells. Ganglion cells are the neurons whose axons travel in the optic nerve. The dendrites of ganglion cells receive synapses from bipolar cells and provide first-order analysis of the visual image. Several additional cell types are also found in the retina (there are horizontal cells and amacrine cells, and the retinal glia are called Mueller's cells), but the three above are the most familiar. The retina has received intensive research investigation, so a great deal of information is available about the structures and functions of its cells. For additional details, consult your print resources or search the web. The journal Nature recently published a report (Helmstaedter, M. et al.

Nature 500, 168�174 , 2013) presenting detailed 3D description of neural connections in the retina of the mouse. A video might be found here (if Nature maintains public accessiblity for this link). Embryology of neural retina and pigmented epithelium The retina forms from the optic cup , which evaginates from the neuroectodermal diencephalic vesicle . The optic vesicle remains attached to developing brain; the connection between optic and diencephalic vesicles becomes the optic nerve. The optic vesicle itself collapses into a cup. The front surface of this vesicle (the hollow of the cup) becomes the neural retina , while the back surface becomes the retina's pigmented epithelium . Clinical note: The embryonic separation between front and back epithelia of the retina disappears as the retina develops, so that the pigmented epithelium becomes intimately associated with outer segments (rods and cones) of receptor cells . However, this embryonic separation can reappear as retinal detachment if the eye is subjected to stress.

Optic nerve The optic nerve is properly considered a tract of the central nervous system, rather than a peripheral nerve, since the retina itself is derived from the embryonic diencephalon (i.e., from neuroectoderm). The axons in the optic nerve come from ganglion cells in the retina and project through the optic chiasm and optic tract to the lateral geniculate nucleus. Vitreous humor The vitreous humor is a peculiar connective tissue extracellular matrix, essentially cell-free after its formation from embryonic mesenchyme. The light sensitive tissue lining the inner surface of your eye - Specialty Retina Center The light sensitive tissue lining the inner surface of your eye 05 May, 2014 The light sensitive tissue lining the inner surface of your eye, known as the retina, acts in a similar way to film in a traditional camera.[/caption]Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged.

It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.The light sensitive tissue lining the inner surface of your eye, known as the retina, acts in a similar way to film in a traditional camera.[/caption]Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. The light sensitive tissue lining the inner surface of your eye, known as the retina, acts in a similar way to film in a traditional camera.[/caption]Lorem Ipsum is simply dummy text of the printing and typesetting industry.

Lorem Ipsum has been the industry’s standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum. Add a comment Allowed HTML tags: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong> Name Retina light sensitive tissue lining the inner surface of the - ENV - 115 View Full Document Retina- light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera Macula lutea- is the yellow oval spot at the center of the retina (back of the eye).

It is responsible for sharp, detailed central vision Iris- is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. Eye color Fovea centralis- center of the eye's sharpest vision and the location of most color and most acute vision Lens- helps to refract light to be focused on the retina. functions to change the focal distance of the eye so that it can focus on objects at various distances Optic nerve- transmits visual information from the retina to the brain Cornea- s the transparent front part of the eye that covers the iris, pupil, and anterior chamber Definitions: Recessive- refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in a homozygous genotype (an organism that has two copies of the same This is the end of the preview. Sign up to access the rest of the document. TERM Distinguish between mafic and felsic mineralsFelsic- light colored minerals Mafic- mo lab practical Retina Anatomy: Overview, Gross Anatomy, Microscopic Anatomy Microscopic Anatomy Overview Overview The retina is the light-sensitive tissue that lines the inside of the eye.

The retina functions in a manner similar to film in a camera. The optical elements within the eye focus an image onto the retina of the eye, initiating a series of chemical and electrical events within the retina. Nerve fibers within the retina send electrical signals to the brain, which then interprets these signals as visual images. [ 1 ] Next: Gross Anatomy The human retina is located on the inner surface of the posterior two-thirds to three-quarters of the eye. The eye itself is a mostly hollow organ, roughly spherical in shape. In adults, the eye measures approximately 22 mm in diameter. The walls of the eye consist of the firm outermost coat, comprised of the white sclera in the posterior three-quarters of the eye and the clear cornea in the anterior one-quarter of the eye. The middle layer consists of the uveal tract made up of the choroid posteriorly and the ciliary body and iris anteriorly. The retina is the innermost layer. It lines the entire posterior portion of the eye with the exception of the area of the optic nerve and extends anteriorly to end 360 degrees circumferentially at the ora serrata. The total area of the retina is approximately 1,100 mm2 ­­.

The circumferential diameter at the equator of the adult eye averages 69 mm. The retinal distance circumferentially passing posteriorly from a point on the ora serrata to a point on the ora serrata 180 degrees away is approximately 50 mm. The average healthy retina is 250-µm thick immediately adjacent to the temporal margin of the optic nerve. The retina thickens to approximately 400 µm in the macular area around the fovea and thins to 150 µm in the fovea. This difference in thickness in the central and noncentral portions of the macula can be appreciated when the eye is examined with an ophthalmoscope. The retina thins as it approaches the equatorial region of the eye and further thins to 80 µm at the ora serrata. Retinal nerve fibers exit the eye through the optic nerve, located nasally and on the same plane as the anatomical center of the retina. There is no retinal tissue overlying the optic nerve head. The optic nerve head or optic disc is oval in shape and measures approximately 1.75 mm. vertically and 1.5 mm horizontally.

The center of the optic disc is located 4.5 mm to 5 mm nasal to the anatomical center of the retina. The center of the retina provides the greatest resolving power of the eye. This area, responsible for central vision, is known as the macula. The center of the macula is called the fovea. The inner surface of the retina is adjacent to the vitreous of the eye. The outermost layer of the retina, the retinal pigment epithelium, is tightly attached to the choroid. Assuming that the ocular media (cornea, anterior chamber, lens, and vitreous) are not cloudy, the living retina can be examined using a direct or indirect ophthalmoscope or a retinal lens at the slit lamp. In addition, the retina may be photographed using a retinal camera. The arterioles and venules of the retina are the only blood vessels whose wall can be directly examined in the living human without an incision. The retina, with the exception of the blood vessels coursing through it, is transparent to the examiner up to its outer layer, the retinal pigment epithelium. The transparent portion of the retina is known as the neurosensory retina.

The examiner sees the neurosensory retina against the background orange color of the melanin containing retinal pigment epithelium and blood-filled choroidal layer of the eye. The neuroretina is tightly attached to the underlying retinal pigment only at the margins of the optic nerve and at the ora serrata. There is a potential space between the neurosensory retina and the retinal pigment epithelium. In a retinal detachment, this space fills with fluid and detaches the neurosensory retina from the underlying retinal pigment epithelium. The living retina may be imaged using fluorescein angiography, polarimetry, or optical coherence tomography. Blood Supply of the Retina There are two circulations to the retina, both supplied by the ophthalmic artery, the first branch of the internal carotid artery on each side. The outer and middle retinal layers, including the outer plexiform and outer nuclear layers, the photoreceptors, and the retinal pigment epithelium, are nourished by branches of the posterior ciliary arteries, which enter the back of the eye outside the optic nerve. These vessels also supply the choroidal layer, external to the retina.

The inner retina is supplied by the central retinal artery, the branch of the ophthalmic artery that enters the optic nerve 4 mm posterior to the eye. The central retinal artery has 4 main branches within the retina. These vessels emerge from the optic nerve head and run radially away from the optic nerve. The temporal vessels curve towards and around the fovea. The macular vessels arise from branches of the superior temporal and inferior temporal arteries. There is a blood vessel-free and capillary-free zone of approximately 500 µm in diameter in the area of the fovea. In about 1 out of 5 people, the inner layer of the macula is dually supplied by cilioretinal arteries branching from the posterior ciliary arteries. Retinal blood vessels maintain the blood-retinal barrier due to nonfenestration of the vascular endothelium. Choroidal endothelial vascular cells are fenestrated. The arterial intraretinal branches then supply capillary networks, which subsequently drain into venules and then into the central retinal vein. The arterial circulation emanating from the posterior ciliary arteries drain out of the eye through one or two vortex veins in each of the 4 quadrants of the eyeball.

The vortex veins penetrate the sclera and merge into the ophthalmic vein. Previous Macula Pucker Macula Pucker Problems & Diseases Definition The retina is the light-sensitive tissue that lines the inside wall of the eye and enables sight. The macula is the central part of the retina that is responsible for seeing straight ahead. A macular pucker is scar tissue that forms on the surface of the macula. Other names for this condition include: epiretinal membrane, pre-retinal membrane, cellophane maculopathy, and surface wrinkling retinopathy. Macular pucker can cause blurry and distorted central vision. This can be a significant problem because a healthy macula is needed to see the fine detail required for reading and driving. A macular pucker is not related to macular degeneration, these are two different problems. A macular pucker should not be considered a precursor to a macular hole. Causes and Associations We know that development of macular pucker is often related to age. They are most common in patients over 50. The most common cause of macular pucker relates to traction from the vitreous, which is a gel-like substance that fills the center of the eye.

The vitreous gel is normally clear and is mildly adherent to the retina lining the back of the eye. As we age, the vitreous gradually shrinks and pulls away from the back of the eye wall. This is a normal process and the eye produces natural, clear fluid that fills the areas where the vitreous has contracted. Sometimes patients see floaters when the vitreous begins to pull away from the retina. Sometimes when the vitreous pulls away from the retina there is microscopic damage to the retinal surface. The retina may respond to this insult by forming scar tissue or an epiretinal membrane on the surface of the retina. When this scar tissue contracts, it causes the retina to wrinkle or pucker, which distorts central vision. In addition, development of macular pucker can be more likely in patients who have had trauma, retinal tears or detachments, retinal vein occlusion, diabetic retinopathy or inflammation in the eye. Symptoms Problems from a macular pucker usually occur gradually. The first symptoms are often blurry and distorted central vision. Straight lines might look wavy, distorted or have missing segments. There may be a gray area in the central vision.

Sometimes a patient does not notice a problem for some time because they do not cover their good eye and realize that they have a problem looking with the eye containing the macular pucker. Reading often becomes difficult. Examination & Testing It is important to be examined by an ophthalmologist who can often diagnosis a macular pucker by examining the eye. Visual Acuity Testing visual acuity is one way to measure the functional severity of macular pucker. An Amsler grid is similar to a piece of graph paper that patients can use to detect subtle changes in their central vision. Patients look at the grid with each eye individually and report to their doctor if there are any missing areas or the lines look distorted or wavy. 2. Optical Coherence Tomography (OCT) In addition, the ophthalmologist may obtain a scan using optical coherence tomography (OCT). OCT uses light to produce images of the retina. The resolution of the images is very fine, and doctors can see problems that exist above, below, and within the retina. During an OCT, a patient will sit and place their head in a chin rest while looking into a machine. The patient will see lights moving around. Nothing touches the patient and there is no pain.

Doctors can use the OCT images to determine the presence and severity of macular pucker. What the Doctor Sees When a doctor examines the patient, he or she will use a slit lamp thatprojects a bright light into the eye and use a lens to focus the light on the macula. Usually the doctor can see the macular pucker. The doctor may note swelling of the retina that can result from macular pucker. Prognosis For most people, visual problems from macular pucker progress slowly and vision can remain stable for a long time. Most instances of macular pucker require no treatment. People often adapt to the mild visual distortion and can continue to perform their usual activities of daily living. Occasionally, the scar tissue forming the macular pucker can lift off the retina, permitting the retina to smooth out with improvement of visual symptoms. Because peripheral vision remains intact, patients will not go completely blind from a macular pucker alone. If one eye has a macular pucker, there is only a small chance that pucker will develop in the other eye. Some patients wonder if the “strain” placed on the good eye can contribute to poor vision in that eye, but this is not the case.

When vision worsens to the point that a patient is very bothered by the macular pucker, the treatment is surgical. Prevention Generally, there is nothing that can be done to avoid developing macular pucker. Diet and exercise do not contribute to the formation of macular pucker. There are no eye drops or vitamins that can prevent macular pucker. Occasionally covering each eye to test the fellow eye alone is the best way of detecting a change in central vision. In addition, having a regular, annual eye exam is the best way to catch macular pucker in its early stages. Treatment The treatment is surgical. Surgeons will perform a vitrectomy, a procedure in which the vitreous gel is removed from the center of the eye. During a vitrectomy the surgeon makes three small ports in the eye wall: one for an infusion of fluid to maintain the eye’s shape, one for a small fiber-optic light, and one for an instrument such as forceps, a laser probe, or a vitrector which removes the vitreous gel. The surgeon uses an operating microscope and lenses to look through the patient’s pupil to the retina.

After the vitreous is removed, the surgeon will peel away the scar tissue on the surface of the retina. The procedure is normally performed under local anesthesia and as an outpatient. There is usually very little postoperative pain. Many surgeons employ 23- or 25-gauge instrumentation which does not require any sutures. Most patients appreciate an improvement in vision after the surgery, but few would say that their vision returned to “normal”. Often the most significant improvement is a reduction in central visual distortion, rather than in measured visual acuity . Visual recovery usually occurs gradually and can take up to three months. It is important to note that having a vitrectomy accelerates the formation of a cataract. Sometimes, it is not until after a patient has had their cataract removed months after surgery that the patient realizes his or her best vision. Risks Risks of any eye surgery include infection, retinal detachment, and worse vision than before the surgery. It is possible that the scar tissue on the retinal surface will not be completely removed. Because this type of surgery is delicate and challenging, many doctors will wait until visual acuity is 20/50 or worse before suggesting surgical treatment. Macular Pucker Author: Allen C.

Ho, M.D. Andrew Lam, MD What Is an Artificial Lens? - VisionAware What Is an Artificial Lens? What Is an Artificial Lens? By Tina D. Turner, M.D. Once the natural lens in the eye has been removed, the eye loses its ability to focus light and images clearly on to the retina , the light-sensitive tissue that lines the inside surface of the eye. Before the development of artificial lenses, hard contact lenses or very thick eyeglasses were the only options for correcting vision after cataract surgery. Artificial Intraocular Lenses Artificial intraocular (within the eye) lenses were developed in the early part of the 20th century, and Dr. Harold Ridley implanted the first artificial lens in 1949 in London. In 1952, the first artificial lens was implanted in the United States at Wills Eye Hospital in Philadelphia. Since that time, cataract surgery and artificial lenses have continued to evolve and develop. In most cases, the natural lens is removed and the artificial lens is implanted during the same surgery. The artificial lens is usually placed within the lens capsule, which is the small "sac" or membrane that once enclosed the natural lens and held it in place.

Artificial lenses are made of inert (or non-reactive) materials, such as PMMA , silicone, and acrylic. Just like natural lenses, artificial lenses have refractive power, or the ability to bend light, which helps to focus light rays and images on the retina. Because of this refractive power, it is now possible to correct nearsightedness and farsightedness with artificial lenses. An artificial intraocular lens Monofocal Lenses At present, monofocal lenses are the type most commonly implanted. Since "mono" means "one," monofocal lenses provide one type of focused, or clear, vision. They provide clear vision either at distance or near, but not both. Most patients who select monofocal lenses choose to have good distance vision and use reading glasses to help with near visual tasks, such as reading , computer work , or sewing . Some patients, however, may choose to have better near vision and use eyeglasses that will help correct distance vision. Monofocal lenses are typically covered by insurance and Medicare, and usually require no additional out-of-pocket payment. Astigmatic Lenses Astigmatic lenses (or toric lenses) are monofocal lenses that can correct astigmatism .

Because astigmatic lenses can correct astigmatism, they may reduce the need for an astigmatism correction in the patient's eyeglasses after surgery. Astigmatic lenses are not fully covered by insurance and Medicare, and usually require a substantial out-of-pocket patient contribution. Monovision It is possible, however, to implant a monofocal lens in one eye for distance vision and a monofocal lens in the other eye for reading vision. This technique is called monovision and can provide clear vision at both distance and near after cataract surgery. Monovision works very well for some patients, while other patients do not tolerate it well. If a patient has used monovision contact lenses in the past, with one eye corrected for distance and the other for near, the same type of monovision can be created with cataract surgery. If a patient has never experienced monovision, but is interested in learning more, it is recommended that he or she experiment with monovision eyeglasses or contact lenses prior to cataract surgery and determine if monovision is an appropriate solution.

Multifocal Lenses Since "multi" means "more than one," multifocal lenses provide more than one type of focused, or clear, vision. They attempt to provide clear vision both at distance and near simultaneously. Because multifocal lenses correct both distance and reading vision, they can reduce the patient's dependence on eyeglasses and contact lenses. Multifocal lenses are not fully covered by insurance and Medicare, and usually require a substantial out-of-pocket patient contribution. Multifocal lenses can present problems, however. The American Academy of Ophthalmology notes that "...pilots, night drivers, or those who spend a lot of time in front of the computer may not be good candidates for multifocal lenses. Patients who are intolerant of a small amount of glare and/or halos around lights, especially at night, may not be good candidates for these types of lenses." Also, patients who have significant astigmatism or macular disease should not have multifocal lenses. You can learn more about artificial lenses at Multifocal Intraocular Lenses: Frequently Asked Questions from the UCLA Laser Refractive Center. Read Paul and Dorothy Johnson's story, written by their adult daughter.

Dorothy had cataracts and Paul had macular degeneration and diabetes. Learn how the Johnsons and their daughter made the decision to live together. Announcements Anatomy and Structure of the Eye | BrightFocus Foundation Anatomy of the Eye Glossary of Terms Anterior chamber: The region of the eye between the cornea and the lens that contains aqueous humor. Aqueous humor: The fluid produced in the eye. Bruch's membrane: Located in the retina between the choroid and the retinal pigmented epithelium (RPE) layer; provides support to the retina and functions as the 'basement' membrane of the RPE layer. Ciliary body: Part of the eye, above the lens, that produces the aqueous humor. Choroid: Layer of the eye behind the retina, contains blood vessels that nourish the retina. Cones: The photoreceptor nerve cells present in the macula and concentrated in the fovea (the very center of the macula); enable people to see fine detail and color. Cornea: The outer, transparent structure at the front of the eye that covers the iris, pupil and anterior chamber; it is the eye's primary light-focusing structure.

Drusen: Deposits of yellowish extra cellular waste products that accumulate within and beneath the retinal pigmented epithelium (RPE) layer. Fovea: The pit or depression at the center of the macula that provides the greatest visual acuity. Iris: The colored ring of tissue behind the cornea that regulates the amount of light entering the eye by adjusting the size of the pupil. Lens: The transparent structure suspended behind the iris that helps to focus light on the retina; it primarly provides a fine-tuning adjustment to the primary focusing structure of the eye, which is the cornea. Macula: The portion of the eye at the center of the retina that processes sharp, clear straight-ahead vision. Optic nerve: The bundle of nerve fibers at the back of the eye that carry visual messages from the retina to the brain. Photoreceptors: The light sensing nerve cells (rods and cones) located in the retina. Pupil: The adjustable opening at the center of the iris through which light enters the eye. Retina: The light sensitive layer of tissue that lines the back of the eye.

Retinal Pigmented Epithelium (RPE): A layer of cells that protects and nourishes the retina, removes waste products, prevents new blood vessel growth into the retinal layer and absorbs light not absorbed by the photoreceptor cells; these actions prevent the scattering of the light and enhance clarity of vision. Rods: Photoreceptor nerve cells in the eyes that are sensitive to low light levels and are present in the retina, but outside the macula. Sclera: The tough outer coat that protects the entire eyeball. Trabecular meshwork: Spongy tissue located near the cornea through which aqueous humor flows out of the eye. Vitreous: Clear jelly-like substance that fills the eye from the lens to the back of the eye. Disease:

Question: What light-sensitive tissue lines the inner surface of the eye?
Answer: Retina