Eyes

This image displays a detailed cross-sectional view of the cornea, which is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. The cornea, with its curved shape and clear structure, functions like a window that controls and focuses the entry of light into the eye.

The outermost layer, appearing as a thin, clear strip on the surface, is the epithelium. This layer serves as a barrier to protect the eye from dust, debris, and bacteria, and contains cells that have the ability to regenerate quickly, aiding in the rapid healing of superficial injuries.

Beneath the epithelium is Bowman’s layer. While it is not as distinct in this image, it is a tough layer composed of collagen fibers, which contribute to the cornea’s strength and elasticity.

The next layer, represented here by the thick, blue-colored region, is the stroma. It constitutes the bulk of the corneal thickness and is composed primarily of water and collagen fibers arranged in a precise, regular pattern. This arrangement allows the cornea to be transparent and lets light pass through without scattering.

Following the stroma is Descemet’s membrane, a thin sheet that serves as the modified basement membrane of the corneal endothelium. It’s not clearly demarcated in this image but it’s essential for maintaining the integrity and function of the endothelial cells.

The innermost layer seen here, lining the interior surface of the cornea, is the endothelium. This single layer of cells is responsible for pumping excess water out of the stroma to keep the cornea clear. If these cells are damaged or deteriorate, they do not regenerate, and the cornea may become swollen or opaque, losing its transparency and reducing vision.

The cross-sectional view also shows the uniform thickness of the corneal layers and the smooth curvature that is essential for refracting light appropriately onto the lens and subsequently onto the retina. This anatomical precision is critical for clear vision.

The image provided is a labeled diagram of the human eye, showcasing the anatomy and various structures integral to its function.

At the front of the eye, the cornea is shown as a transparent dome-like structure. It functions as the eye’s outermost lens, controlling and focusing the entry of light. Below the cornea, the anterior chamber is a fluid-filled space that provides nutrients to the eye and maintains intraocular pressure.

The iris, the colored part of the eye, controls the diameter and size of the pupil and thus the amount of light that enters the eye. The pupil is the opening in the center of the iris through which light passes to the lens. The lens is a transparent, biconvex structure that further focuses light onto the retina. The suspensory ligaments, also known as zonules, are tiny fibers that connect the ciliary body and muscle to the lens, enabling the lens to change shape for focusing, a process known as accommodation.

Behind the lens is the posterior chamber, which, like the anterior chamber, is filled with aqueous humor that nourishes the eye and carries away waste.

The large space in the posterior part of the eye is the vitreous chamber, filled with a gel-like substance called the vitreous humor, which helps maintain the spherical shape of the eye and also acts as a shock absorber.

The innermost layer lining the back of the eye is the retina, which contains the light-sensitive cells that convert light into electrical signals. The optic nerve and retinal blood vessels are visible entering the back of the eye, indicating the flow of visual information to the brain and the blood supply to the retina, respectively.

The macula lutea is a small central area of the retina that is responsible for high-acuity vision, while the fovea centralis, located within the macula, is the point of sharpest vision.

Surrounding the retina is the choroid, a layer rich in blood vessels that supply oxygen and nutrients to the retina.

The sclera is the white, fibrous outer layer of the eye that maintains the shape of the eye and offers protection.

Lastly, the extrinsic muscles of the eye, such as the lateral and medial rectus muscles, control the movements of the eyeball, enabling it to look in different directions.

The illustration effectively summarizes the complex structure and organization of the eye, a vital organ for vision.

The image illustrates the anatomy of the eye along with the changes occurring in macular degeneration, a common eye condition that affects the macula, the central part of the retina responsible for clear vision in your direct line of sight.

In the top part of the image, a cross-sectional diagram of the eye shows the main anatomical features. The outermost layer is the sclera, the white part of the eye. Below this is the choroid, which contains blood vessels that supply the eye with nutrients. The retina is the innermost layer where light-sensitive cells convert light into electrical signals to be processed by the brain.

The macula is highlighted, indicating its importance in providing sharp, central vision. The optic disc, also known as the blind spot, is where the optic nerve exits the eye; there are no photoreceptors here, so it is insensitive to light. The optic nerve carries visual information from the retina to the brain.

Below the main diagram are three smaller images that compare the normal macula with two types of macular degeneration:

  1. Normal: The macula appears uniform in color, indicating a healthy distribution of photoreceptor cells and absence of any abnormalities.

  2. “Wet” Macular Degeneration: This type is characterized by the presence of abnormal blood vessels that leak fluid or blood into the region of the macula, leading to blurred vision or blind spots. The diagram shows a blob-like distortion representing bleeding or fluid leakage.

  3. “Dry” Macular Degeneration: This more common type is depicted with yellowish spots known as drusen, which are deposits that form under the retina. Over time, these can lead to a gradual breakdown of the cells in the macula, resulting in blurred or diminished central vision.

The comparison between the normal macula and the affected ones in wet and dry macular degeneration provides a visual explanation of how this condition can impact vision. It underscores the importance of the macula in eye health and the potential severity of macular degeneration as a disease.

The image depicts two types of photoreceptor cells in the retina of the human eye: rod cells and cone cells. These cells are crucial for vision, converting light into electrical signals that the brain can interpret.

On the left, the rod cell is shown with its elongated, cylindrical shape, which is optimized for detecting low levels of light, making them crucial for night vision. The outer segment contains stacked discs, which are rich in the photopigment rhodopsin. This segment is where the initial photochemical reactions occur when light is absorbed.

Below the outer segment is the inner segment of the rod cell, which contains mitochondria. These organelles are the powerhouses of the cell, providing the energy required for the phototransduction process, which is the conversion of light into electrical signals.

The cell body contains the nucleus, which houses the cell’s genetic material. At the base of the rod cell is the synapse, where the photoreceptor cell communicates with the next neuron in the visual pathway by releasing neurotransmitters.

On the right, the cone cell is displayed with a conical outer segment. Cone cells are responsible for color vision and function best in bright light. Similar to rod cells, the outer segment of cone cells contains photopigments; however, they have different types of opsins that respond to different wavelengths of light, allowing for the perception of color.

Both rod and cone cells have a connecting cilium, which is a slender structure that links the inner and outer segments, facilitating the transport of molecules between these two compartments.

The nucleus of the cone cell is also located within the cell body, and it connects to the synapse at the bottom, similar to the rod cell, for neurotransmission.

This image succinctly illustrates the structural differences between rods and cones, correlating to their different functions in vision. Rods are more numerous and sensitive to light, contributing to vision in low-light conditions, while cones are less sensitive but essential for color vision and visual acuity.

This illustration provides a detailed view of the blood supply and anatomy of the eye, particularly focusing on the vascular system and the associated structures.

At the center, the iris is shown, which is the colored part of the eye that controls the size of the pupil and, consequently, the amount of light that enters the eye. Two arterial circles can be observed in the iris: the large arterial circle and the small arterial circle. These circles are part of the intricate vascular network that provides the iris with blood.

The ciliary body is an extension of the iris. The ciliary muscle within it adjusts the shape of the lens, allowing the eye to focus on objects at different distances, a process known as accommodation. This muscle is also involved in controlling the flow of aqueous humor into the eye’s anterior chamber.

The cornea, labeled at the front of the eye, is the transparent structure that refracts light entering the eye. It is avascular, meaning it has no blood vessels, and receives nutrients from tears and aqueous humor.

The sclera, the white part of the eye, is the outer protective layer that maintains the shape of the eyeball. It extends all the way around the eye and provides an attachment for the extrinsic eye muscles, which are responsible for moving the eye.

The choroid is a layer rich in blood vessels lying between the retina and the sclera; it provides oxygen and nutrients to the outer layers of the retina.

The optic nerve is responsible for transmitting visual information from the retina to the brain. It is represented as the thick band exiting the back of the eye.

The blood vessels are highlighted, with arteries depicted in red and veins in blue. The anterior ciliary artery supplies blood to the ciliary body and the iris. The recurrent branch of the anterior ciliary artery is shown looping back towards the front of the eye.

Posteriorly, the posterior short ciliary arteries penetrate the sclera around the optic nerve to supply the choroid and the optic disc. The posterior long ciliary artery also runs forward to supply the ciliary body and the iris.

Veins are shown as return pathways for deoxygenated blood, with the return vein and the portal vein indicated.

Overall, this image effectively demonstrates the complexity of the eye’s vascular network, highlighting how blood is delivered to and from the various tissues of the eye, ensuring their proper function.

The image presents a simplified view of the eye’s anatomy alongside a magnified section of the retina, offering insight into the cellular composition and arrangement within the retinal layer.

In the larger image on the left, the entire structure of the eye is encapsulated, with the retina marked along the back inner surface. The retina is the light-sensitive layer of tissue at the back of the eye, which is essential for vision as it receives light and converts it into neural signals for the brain to process.

The smaller image on the right zooms into the retinal layer, depicting the precise organization and types of cells that compose the retina. Starting from the bottom, the layers are as follows:

  1. Rod Cells: These are long, cylindrical cells responsible for vision at low light levels. They are highly sensitive to light and enable us to see in shades of gray in dim conditions.

  2. Cone Cells: These are shorter, tapering cells responsible for color vision and visual acuity. They function best in bright light and enable us to see fine details and rich color variations.

  3. Bipolar Cells: Positioned between the photoreceptors (rod and cone cells) and the ganglion cells, these cells act as direct relay cells that transmit signals from the rods and cones to the ganglion cells.

  4. Ganglion Cells: These cells receive signals from the bipolar cells. Their axons converge to form the optic nerve, which transmits visual information to the brain.

  5. Retinal Pigment Epithelium (RPE): This is a layer of pigmented cells adjacent to the photoreceptors. The RPE is essential for the maintenance and function of the photoreceptor cells. It helps absorb excess light to prevent light scattering, recycles visual pigments, and supplies nutrients to the retina.

The illustration provides a clear depiction of the retinal cells and their connectivity, emphasizing the complex processing that occurs within the eye before visual information is even sent to the brain. The arrangement of these cells in layers reflects the sequential processing and filtering of visual data, from the initial photodetection by rods and cones to the complex signal integration and transmission by bipolar and ganglion cells.

The image offers an educational comparison of a normal eye and one affected by glaucoma, highlighting the mechanisms behind this eye condition.

On the left, the top and bottom illustrations depict a normal eye. The eye has a clear fluid called aqueous humor that flows in and out of the anterior chamber, providing nutrients and maintaining intraocular pressure. The fluid drains through the trabecular meshwork, located in the angle where the iris and cornea meet. The illustration shows an unobstructed flow of aqueous humor, which is crucial for maintaining healthy eye pressure.

In the middle, the eye with glaucoma is shown. The top image indicates a blocked drainage channel, which prevents the aqueous humor from flowing out of the eye properly. As a result, as seen in the bottom image, there’s an increase in intraocular pressure, indicated by the red arrows pushing outwards. This pressure buildup can damage the optic nerve, which is responsible for transmitting visual information from the retina to the brain.

On the right, the progression of glaucoma is further illustrated by showing changes in the optic nerve due to this increased pressure. The optic nerve appears to be compressed and damaged, which can lead to vision loss. The change in coloration and the disorganized appearance of the optic nerve fibers signify the severity of damage that glaucoma can cause, potentially leading to blindness if untreated.

This visual comparison serves as a powerful tool for understanding glaucoma’s impact on eye anatomy and the importance of proper aqueous humor drainage for ocular health.

The image presents a two-part illustration focused on the optic nerve and its connection to the eye.

On the left, we see a cross-sectional view of the human eye, with the optic nerve extending from the back of the eyeball. This nerve is crucial for vision; it is composed of retinal ganglion cell axons and glial cells, and it carries visual information from the retina to the brain for processing.

The central retinal artery and vein can be seen entering and exiting the eye alongside the optic nerve, providing essential blood supply to and from the retinal tissues. These blood vessels are vital for the delivery of oxygen and nutrients to the retina and the removal of metabolic waste.

The larger image on the right provides a magnified view of the optic nerve, showing the intricate

network of blood vessels that supply it. The axons within the optic nerve are bundled together, and each is insulated by a myelin sheath, which is not explicitly shown here but is vital for the rapid conduction of electrical signals.

The optic nerve fibers are shown in yellow, illustrating how they are organized into a cohesive bundle that transmits visual information. The surrounding blood vessels ensure the nerve receives sufficient oxygen and nutrients to function properly.

The image highlights the optic nerve’s critical role in vision and the complexity of its vascular supply, emphasizing the significance of the optic nerve in maintaining healthy eyesight. It’s a clear and informative visual representation of the anatomy and importance of the optic nerve within the visual system.

The image provides a comparative visual overview of various conditions affecting the fundus, which is the interior surface of the eye opposite the lens, including the retina, optic disc, macula, fovea, and posterior pole.

The first illustration depicts a healthy fundus with a clear, bright appearance of the retina, unobstructed and well-defined blood vessels, and a sharp optic disc where the optic nerve enters the retina.

The second illustration shows retinitis, characterized by the presence of white infiltrates and a hazy appearance, suggesting inflammation of the retina. The blood vessels appear engorged or sheathed, and there may be a slight blurring around the optic disc.

The third illustration presents retinal detachment, where the retina has pulled away from the back of the eye, indicated by the elevated sections of the retinal tissue. This detachment disrupts the normal architecture and placement of the retina.

The fourth illustration depicts an epiretinal membrane, where a thin, translucent layer has formed on the surface of the retina, causing a wrinkling or distortion of the retinal tissue that can impact vision.

The final illustration shows retinal vascular thrombosis, which is the blockage of a retinal vein, leading to hemorrhages seen as red spots and blotches, and may also cause swelling and white patches where the retina is deprived of oxygen.

Each condition illustrated can lead to vision changes or loss and requires medical attention. These depictions are valuable for educational purposes, illustrating how diseases of the fundus can alter the appearance of the eye’s interior and affect ocular health.

This image is an infographic depicting the anatomy of the right eye as viewed from above, providing a comprehensive look at both the external and internal structures.

Starting with the external parts, the upper portion shows the eye lid, which protects the eye and helps distribute tear fluid across the surface of the eye. The lacrimal caruncle is a small, pink, globular nubbin of flesh located at the inner corner of the eye, which contains glands that produce a portion of the tear film. Adjacent to this is the tear duct, also known as the nasolacrimal duct, which drains tears from the eye into the nasal cavity.

Moving to the internal anatomy, the sclera is the white, fibrous outer layer of the eyeball; its main function is to provide structure, strength, and flexibility to the eye. The cornea is the transparent, dome-shaped surface that covers the front of the eye and, together with the lens, helps to refract and focus light onto the retina.

The iris is the colored part of the eye that surrounds the pupil, the central opening that regulates the amount of light entering the eye. The lens sits just behind the iris and pupil, and it is held in place by suspensory ligaments attached to the ciliary body, which contains the muscle that alters the shape of the lens for focusing, a process known as accommodation.

Between the cornea and the lens are the anterior and posterior chambers, which are filled with a clear fluid called the aqueous humor. This fluid maintains intraocular pressure and provides nutrients to the avascular structures of the eye.

The vitreous body is the clear gel that fills the space between the lens and the retina, helping to maintain the spherical shape of the eye and offering support to the retina. The retina itself is the thin layer of tissue that lines the back of the eye, containing the photoreceptor cells that convert light into electrical signals.

The fovea centralis, located in the center of the macula of the retina, is responsible for sharp central vision. The hyaloid canal is a small channel that runs through the vitreous body, which in the fetal eye allows the passage of nutrients from the optic nerve to the developing lens.

Finally, the optic nerve is depicted exiting the back of the eye. This nerve is responsible for transmitting visual information from the retina to the brain. Accompanying the optic nerve are the retinal blood vessels, which supply the retinal tissue with nutrients and oxygen.

The muscles illustrated are the lateral rectus muscle, which moves the eye outward away from the nose, and the medial rectus muscle, which moves the eye inward towards the nose.

Overall, the infographic serves as an educational tool, providing a clear and detailed visual representation of the various components of the eye and their respective roles in the complex process of vision.

The image is a detailed representation of human eye anatomy, with a primary focus on the sectional view of the eye and a magnified inset detailing the layers of the retina.

The main illustration shows a cross-section of the eye, with labels for the sclera, the tough outer layer that forms the white of the eye, and the cornea, the clear front surface that covers the iris, pupil, and anterior chamber. The anterior chamber lies between the cornea and the iris, and is filled with aqueous humor, which nourishes the eye and maintains pressure.

The iris, the colored part of the eye, regulates the size of the pupil, the opening that controls the amount of light entering the eye. Behind the iris is the lens, which focuses light onto the retina. The ciliary body, attached to the lens, contains the muscle that changes the shape of the lens for focusing. The vitreous body, a clear gel filling the large space behind the lens, maintains the eye’s shape and supports the retina.

The retina is the light-sensitive layer at the back of the eye that converts light into electrical signals. The macula is the central part of the retina, responsible for detailed vision, and within the macula is the fovea, which provides the sharpest vision. The choroid beneath the retina is a layer containing blood vessels that supply the retina with nutrients and oxygen.

The optic nerve is the pathway that transmits visual signals from the retina to the brain, and the optic disc is the point on the retina where the optic nerve fibers exit the eye, also known as the blind spot because it lacks photoreceptors.

The inset magnifies the retinal layers, starting from the outermost part of the retina adjacent to the vitreous body. The layers are as follows:

  1. Internal Limiting Membrane: the innermost surface of the retina, facing the vitreous body.
  2. Nerve Fiber Layer: contains the axons of the ganglion cells that form the optic nerve.
  3. Ganglion Cell Layer: contains the cell bodies of ganglion cells.
  4. Inner Plexiform Layer: location of synapses between bipolar cell axons and ganglion cell dendrites.
  5. Inner Nuclear Layer: contains the nuclei and cell bodies of bipolar, horizontal, and amacrine cells.
  6. Outer Plexiform Layer: site of synapses between photoreceptor cells and bipolar cells.
  7. Outer Nuclear Layer: contains the cell bodies of the photoreceptors, rods, and cones.
  8. Outer Segments of Photoreceptors: the light-sensitive parts of rods and cones where phototransduction occurs.
  9. RPE (Retinal Pigment Epithelium): a layer of pigmented cells that nourishes the retinal visual cells and is critical for the regeneration of photoreceptor outer segments.

The illustration also denotes Bruch’s membrane, which separates the choroid from the RPE, and the choroidal vessels, which supply blood to the outer retina.

This comprehensive image serves as an excellent visual aid for understanding the complex structure of the eye and the retina’s specialized layers, crucial for the perception of visual images.

The image is an explanatory diagram contrasting the effects of vitreous floaters on vision compared to a normal eye.

In the top half of the diagram, a side cross-section of a normal eye is shown, indicating how light passes through the eyeball without obstruction, resulting in clear vision. This is represented by a circular field of vision that is completely unobstructed.

The bottom half of the diagram illustrates an eye affected by vitreous floaters. Here, the cross-section shows the interior of the eyeball containing various shapes labeled as “floaters.” These floaters represent debris within the vitreous humor—the clear gel that fills the space between the lens and the retina. The text explains that the passage of light through the eyeball is hindered by the presence of the vitreous floaters, which generate shadows on the retinal surface. This is visually represented by a circular field of vision with multiple shadowy shapes corresponding to the floaters, indicating disturbed vision.

Vitreous floaters are often seen as small dark spots, lines, or cobwebs in a person’s field of vision, particularly when looking at a plain, bright background like a blue sky or a white wall. They are usually harmless and are a common part of the eye’s aging process, but a sudden increase in floaters can also indicate more serious eye conditions, such as retinal detachment.

This visual tool effectively communicates how vitreous floaters can interfere with normal vision by casting shadows on the retina, leading to the perception of floating spots or threads in the visual field.

This image is an annotated illustration of the human eye, specifically focusing on the external anatomy and the structures associated with the conjunctiva.

The key parts labeled in this diagram are:

  • Ciliae: Commonly known as eyelashes, they protect the eye from debris.
  • Pupilla (Pupil): The central opening of the iris that allows light to enter the eye.
  • Iris: The colored part of the eye that controls the size of the pupil.
  • Angulus oculi lateralis (Lateral canthus): The outer corner where the upper and lower eyelids meet.
  • Tunica conjunctiva bulbi: The conjunctiva as it covers the sclera (the white of the eye).
  • Limbus posterior palpebrae: The border of the eyelid near the conjunctival fornix.
  • Fornix conjunctivae inferior (Inferior conjunctival fornix): The space between the palpebral conjunctiva and the bulbar conjunctiva on the lower eyelid.
  • Palpebra superior (Upper eyelid): Protects the anterior part of the eye and contains the superior conjunctival fornix.
  • Sulcus sclerae (Scleral sulcus): A groove or space which can refer to the area between the cornea and the sclera.
  • Plica semilunaris conjunctivae: A small fold of conjunctiva that allows for movements of the eyeball.
  • Caruncula lacrimalis (Lacrimal caruncle): A small, pink, globular nodule at the inner corner of the eye that contains glands producing a portion of the tear film.
  • Angulus oculi medialis (Medial canthus): The inner corner where the upper and lower eyelids meet.
  • Papilla lacrimalis: This term typically refers to a small elevation or bump in the conjunctiva where the lacrimal duct opens, though it is not conventionally at the inner corner.
  • Limbus anterior: The junction between the cornea and the sclera.
  • Tunica conjunctiva (Conjunctiva): A clear mucous membrane that lines the inside of the eyelids (palpebral conjunctiva) and covers the sclera (bulbar conjunctiva).
  • Palpebra inferior (Lower eyelid): Protects the anterior part of the eye and contains the inferior conjunctival fornix.

The illustration provides a detailed view of the eye’s external and accessory structures, emphasizing the conjunctival elements which play a role in eye lubrication and protection. 

The image provides an intricate diagram of the human eye, focusing specifically on the lacrimal system and the anatomy surrounding the orbit.

Key structures labeled in the diagram are:

  • Septum orbitale: A membrane that helps form the boundary between the eyelid and orbital fat.
  • Musculus levator palpebrae superioris: The muscle responsible for lifting the upper eyelid.
  • Glandula lacrimalis, pars palpebralis: The part of the lacrimal gland associated with the eyelid, responsible for tear production.
  • Glandula lacrimalis, pars orbitalis: The portion of the lacrimal gland situated in the orbit, also involved in tear production.
  • Conjunctiva: The mucous membrane that covers the front of the eye and lines the inside of the eyelids.
  • Ampulla canaliculi lacrimalis: The dilated part of the lacrimal canaliculus into which tears drain.
  • Septum orbitale: A thin, fibrous structure that separates the eyelid from the orbit.
  • Vagina bulbi oculi (Tenon’s capsule): A membrane enveloping the eyeball, providing a socket for movement.
  • Plica semilunaris: A small fold of conjunctiva that allows for movements of the eyeball.
  • Canaliculus lacrimalis: Part of the lacrimal drainage system that carries tears from the lacrimal punctum towards the lacrimal sac.
  • Fornix sacci lacrimalis: The upper fold or arch of the lacrimal sac where the canaliculi drain into.
  • Saccus lacrimalis (Lacrimal sac): The upper dilated end of the nasolacrimal duct that collects tears from the canaliculi.
  • Papilla lacrimalis: A small elevation in the conjunctiva where the lacrimal duct opens to release tears onto the eye surface.
  • Ductus nasolacrimalis (Nasolacrimal duct): The duct that carries tears from the lacrimal sac into the nasal cavity.
  • Sinus maxillaris (Maxillary sinus): One of the large cavities in the bones of the face, connected to the nasal cavity.
  • Concha nasi inferior (Inferior nasal concha): A structure within the nasal cavity that helps to filter and humidify the air breathed through the nose.
  • Meatus nasi inferior (Inferior nasal meatus): A passage within the nasal cavity below the inferior nasal concha, where the nasolacrimal duct drains.

This diagram provides a detailed overview of the lacrimal apparatus and associated orbital anatomy, showing how tears are produced and drained through the nasolacrimal system, ultimately leading to the nasal cavity.

The image is a schematic representation of the structure of the retina, showcasing the two primary types of photoreceptor cells: rods and cones.

At the top layer of the diagram, the pigment epithelium is shown. This layer of the retina is vital for the health of the photoreceptor cells, as it absorbs excess light, thereby preventing light scatter that can affect visual acuity. It also plays a role in the recycling of visual pigments after phototransduction.

Below the pigment epithelium are the rod cells. Rods are illustrated here in red and are more numerous in the human retina than cones. They are highly sensitive to light and enable vision in low-light conditions but do not support color vision. Rods are responsible for peripheral vision and motion detection.

Next to the rods are the cone cells, depicted in various colors (blue, green, and red) to represent the three types of cones sensitive to different wavelengths of light: S-cones (blue light), M-cones (green light), and L-cones (red light). Cones are responsible for high-acuity central vision and color vision and are densely packed in the macula, particularly in the fovea—the region of the retina that provides the sharpest vision.

Each photoreceptor cell has an outer segment where phototransduction—conversion of light into electrical signals—takes place, an inner segment containing the cell’s organelles, a cell body with the nucleus, and a synaptic terminal that communicates with other neurons in the retina.

The arrangement of rods and cones in the image illustrates their distribution within the retina, which is a crucial factor in how we perceive light and color in various lighting conditions. This diagram is typically used for educational purposes to explain the complex process of vision and the specialized functions of different photoreceptor cells in the retina.

The image provides a comparative visualization of common corneal conditions alongside a depiction of a normal cornea.

  • Normal: The first illustration shows a standard, healthy cornea with a smooth, dome-like shape that is essential for proper vision. The cornea’s transparency and curvature are crucial for focusing light onto the retina.

  • Keratoconus: The second illustration depicts keratoconus, a condition where the cornea thins and begins to bulge into a cone-like shape, distorting vision. This irregular curvature disrupts the focus of light entering the eye, leading to visual impairment.

  • Bullous Keratopathy: The third illustration shows bullous keratopathy, characterized by fluid blisters (bullae) on the cornea, which result from endothelial cell damage and dysfunction. The endothelium’s primary role is to pump excess fluid out of the cornea, and its failure leads to corneal swelling and blistering, causing pain and vision distortion.

  • Corneal Scarring: The fourth illustration represents corneal scarring, where the transparent tissue has become opaque due to injury, infection, or inflammation. Scarring can cause the cornea to lose its clarity and smooth surface, leading to visual disturbances.

The diagram effectively educates on how various corneal conditions can alter the structure of the cornea and the potential impact on vision. Each condition depicted requires medical attention, and the treatments vary from corrective lenses in the early stages of keratoconus to corneal transplantation in severe cases of scarring or keratopathy.

The image is a detailed cross-sectional illustration of the human eye, providing an extensive overview of its anatomy and internal structure.

Starting from the front of the eye:

  • Cornea: The clear, dome-shaped tissue that covers the front of the eye and helps focus incoming light.
  • Anterior Chamber: The fluid-filled space between the cornea and the iris.
  • Iris: The colored part of the eye, which controls the size of the pupil and thus the amount of light that enters the eye.
  • Pupil: The adjustable opening at the center of the iris through which light passes.
  • Lens: A clear, flexible structure that works with the cornea to focus light onto the retina.
  • Suspensory Ligament: A series of fibers that connect the ciliary body to the lens, helping to hold it in place and adjust its shape for focusing.
  • Schlemm’s Canal: A circular channel in the eye that collects aqueous humor from the anterior chamber and delivers it into the bloodstream.
  • Limbus: The border between the cornea and the sclera.
  • Ciliary Body: Contains the ciliary muscle and ciliary processes, which produce aqueous humor and alter the shape of the lens.
  • Ciliary Muscle and Ciliary Process: The muscle adjusts lens shape for focusing, while the processes are involved in aqueous humor production.

Moving further back in the eye:

  • Vitreous Chamber: The large space filled with a clear, gel-like substance called vitreous humor.
  • Retina: The light-sensitive layer of cells at the back of the eye that converts light into electrical signals.
  • Fovea Centralis: The small depression in the retina where visual acuity is highest.
  • Optic Disc Area (Blind Spot): The point on the retina where the optic nerve fibers exit the eye; it lacks photoreceptors and is thus insensitive to light.
  • Optic Nerve (Cranial Nerve II): Transmits visual information from the retina to the brain.
  • Central Retinal Blood Vessels: The blood vessels that supply the retina with nutrients and oxygen.
  • Choroid: The vascular layer of the eye, lying between the retina and the sclera, supplying the outer retina with blood.
  • Sclera: The white, outer layer of the eyeball, providing protection and structure.
  • Ora Serrata: The serrated junction between the retina and the ciliary body.
  • Hyaloïd Canal: A small channel running through the vitreous body, a remnant of the fetal arterial system.

This diagram serves as an educational tool to explain the complex structures within the eye and their roles in the process of vision. It highlights the intricate interplay of optical components and the vascular system necessary for maintaining eye health and function.

The image provides a cross-sectional illustration of the human eye, highlighting the condition known as retinal detachment.

The key structures of the eye are labeled, including:

  • Ciliary Body: The part of the eye that releases the aqueous humor and contains the ciliary muscle, which controls the shape of the lens for focusing.
  • Sclera: The white, outer layer of the eyeball that provides protection and maintains the shape of the eye.
  • Choroid: A layer rich in blood vessels located between the retina and the sclera, supplying nutrients to the eye.
  • Retina: The innermost layer of the eye, which contains light-sensitive cells that convert light into neural signals.
  • Fovea Centralis: The small pit in the macula that provides the clearest vision of all.
  • Optic Disc (Blind Spot): The location on the retina where the optic nerve fibers exit the eye; this area does not contain any photoreceptor cells and is thus insensitive to light.
  • Blood Vessels: These provide essential nutrients and oxygen to the retinal cells.
  • Optic Nerve: The nerve that transmits visual information from the retina to the brain.
  • Iris: The colored part of the eye that controls the amount of light entering the eye by adjusting the size of the pupil.
  • Pupil: The opening in the center of the iris that allows light to enter the eye.
  • Cornea: The clear, dome-shaped surface that covers the front of the eye and contributes to the eye’s focusing power.
  • Lens: The transparent structure inside the eye that focuses light rays onto the retina.
  • Suspensory Ligament: The series of fibers that connect the ciliary body to the lens, helping to hold it in place.

The illustration also shows an arrow indicating the area where the retina has detached. In a normal eye, the retina is attached to the choroid layer, but in the case of retinal detachment, the retina peels away, leading to a potential loss of vision if not promptly treated. The area of detachment can be identified by the separation between the retina and the back wall of the eye, which can cause symptoms like an increase in floaters, flashes of light, or a shadow over the visual field.

The image illustrates the differences between normal vision, hyperopia (farsightedness), myopia (nearsightedness), and how these conditions can be corrected using lenses.

The top left illustration shows Normal Vision, where light rays entering the eye are focused precisely on the retina, resulting in a clear image.

The middle left illustration depicts Hyperopia, a condition where the eye is too short, causing light rays to focus behind the retina. This often leads to difficulty focusing on close objects, while distant objects may be clear.

The middle right illustration shows Hyperopia Corrected with the use of a converging lens, typically a biconvex lens. This lens bends the light rays so they converge more by the time they reach the retina, correcting the focal point to fall on the retina for clear vision.

The bottom left illustration shows Myopia, a condition where the eye is too long, causing light rays to focus in front of the retina. This results in clear vision for close objects but blurred vision for objects that are far away.

The bottom right illustration demonstrates Myopia Corrected with the use of a diverging lens, typically a biconcave lens. This lens spreads out the light rays slightly before they enter the eye, ensuring they focus directly on the retina rather than in front of it.

The term “Focal Plane” refers to the location where the light rays converge to form a clear image. In a normal eye, this is directly on the retina, but in hyperopic and myopic eyes, the focal plane is misplaced, leading to blurred vision which requires optical correction for clarity. The image serves as an educational diagram to explain common refractive errors and their corrections with lenses.

The image is a diagram illustrating the visual projection pathway, which is the route that visual information takes from the eyes to the visual cortex in the brain where it is interpreted.

At the top, two color-coded fields represent the left visual field (green) and the right visual field (red). These correspond to the areas of the external world that are visible to each eye when looking straight ahead.

The visual pathways from each eye start with the eyes themselves. The diagram shows how light from each visual field is projected onto the retina of both eyes. Notably, information from the right visual field is detected by the left side of both retinas, and vice versa for the left visual field.

The optic nerves from each eye carry the visual information towards the optic chiasm, where there is a partial crossing-over of nerve fibers. Fibers from the nasal (inner) halves of each retina cross to the opposite side of the brain, while fibers from the temporal (outer) halves remain on the same side. This crossing ensures that all information from the left visual field is processed by the right cerebral hemisphere, and all information from the right visual field is processed by the left cerebral hemisphere.

After the optic chiasm, the pathways continue as the optic tracts, which then synapse in several brain structures, including the lateral geniculate nucleus of the thalamus (shown in purple) and the superior colliculus (shown in blue). The lateral geniculate nucleus is the primary relay center for visual information on its way to the visual cortex.

From the lateral geniculate nucleus, the visual information travels through the optic radiations to the visual cortex located in the occipital lobe of the brain. This is where the visual information is interpreted, leading to visual perception.

The pretectal nuclei (shown in yellow) are involved in the reflex control of the pupil and lens.

The superior colliculus is involved in the orientation of the eyes and head towards visual stimuli.

This visual pathway is crucial for visual processing, and any damage along this pathway can result in visual field defects, which are areas of lost or reduced vision within the visual fields. The diagram serves as an educational tool, providing a simplified overview of the complex process of visual information transmission from the eyes to the brain.

The image is an anatomical illustration showing the lateral view of the muscles of the eye, also known as the extraocular muscles. These muscles are responsible for moving the eyeball and are crucial for binocular vision.

The muscles labeled in the diagram include:

  • Superior Oblique: This muscle is located at the top part of the eye and is involved in downward and outward eye movement. It passes through a fibrous loop, known as the trochlea, before attaching to the top of the eyeball.

  • Superior Rectus: Situated above the eye, this muscle primarily moves the eye upward. It works in coordination with the inferior oblique to control elevation of the eye.

  • Medial Rectus: Located on the side of the eye closest to the nose (medial side), this muscle moves the eye inward, towards the nose.

  • Lateral Rectus: This muscle is found on the outer side (lateral side) of the eye and is responsible for moving the eye outward, away from the nose.

  • Inferior Rectus: Positioned below the eye, this muscle primarily moves the eye downward. It coordinates with the superior oblique for depression of the eye.

  • Inferior Oblique: This muscle is located beneath the eye and helps to move the eye upward and outward. It works opposite the superior oblique muscle.

These muscles are attached to the sclera of the eye and extend back to their respective origins in the orbit. They are innervated by cranial nerves III (oculomotor nerve), IV (trochlear nerve), and VI (abducens nerve). The oculomotor nerve innervates the superior, medial, and inferior recti, as well as the inferior oblique muscle. The trochlear nerve innervates the superior oblique muscle, and the abducens nerve controls the lateral rectus muscle.

TermDefinition
Arm (brachium)The part of the upper limb located between the shoulder and the elbow.
Elbow jointThe joint connecting the arm and the forearm, comprising the articulation between the humerus and the two forearm bones, ulna, and radius.
Brachial arteryThe major blood vessel of the upper arm that continues from the axillary artery to supply blood to the arm.
RadiusOne of the two bones of the forearm, extending from the lateral side of the elbow to the thumb side of the wrist.
UlnaThe longer and larger of the two bones of the forearm, placed on the side opposite to the thumb.
CorneaThe transparent front part of the eye that covers the iris, pupil, and anterior chamber.
IrisThe colored part of the eye, controlling the size of the pupil and thus the amount of light reaching the retina.
LensThe transparent structure inside the eye that focuses light rays onto the retina.
RetinaThe light-sensitive layer of tissue at the back of the inner eye, which translates light into neural signals for vision.
Fovea centralisA small central pit in the macula of the retina, composed of closely packed cones that is responsible for sharp central vision.
Optic nerveThe nerve that transmits visual information from the retina to the brain.
MaculaAn area near the center of the retina that is responsible for central vision and high visual acuity.
Vitreous humorThe clear gel that fills the space between the lens and the retina in the eyeball.
PhotoreceptorsCells in the retina that respond to light; they include rods, which are responsible for vision in low light, and cones, for color vision and detail.
ScleraThe white outer layer of the eyeball that provides protection and form.
ChoroidThe vascular layer of the eye between the retina and the sclera, supplying nutrients and oxygen to the eye.
Anterior chamberThe fluid-filled space inside the eye between the cornea and the iris.
Posterior chamberThe fluid-filled space directly behind the iris but in front of the lens.
ConjunctivaA clear mucous membrane that lines the inside of the eyelids and covers the sclera.
Lacrimal glandThe gland responsible for producing tears; it is situated in the upper outer region of the orbit, above the eyeball.
Aqueous humorThe clear, watery fluid that fills the space between the cornea and the iris.
MyopiaA common vision condition also known as nearsightedness, where distant objects appear blurred.
HyperopiaA vision condition also known as farsightedness, where close objects appear blurred.
AstigmatismA common imperfection in the curvature of the eye's cornea or lens, causing blurred or distorted vision.
Retinal detachmentA serious condition where the retina peels away from its underlying layer of support tissue.
Macular degenerationAn eye disease that may result in blurred or no vision in the center of the visual field due to damage to the macula.
GlaucomaA group of eye conditions that damage the optic nerve, often associated with increased pressure in the eye.
CataractsA condition characterized by clouding of the lens in the eye, leading to a decrease in vision.
ConjunctivitisAn eye condition diagnosed by irritation or infection of the conjunctiva, often resulting in redness and swelling.
KeratoconusA progressive eye disease where the normally round cornea thins and begins to bulge into a cone-like shape.
Bullous KeratopathyA condition causing swelling and blistering of the cornea due to endothelial cell dysfunction.
Corneal scarringOpacity or scarring of the cornea often resulting from injury, infection, or inflammation.
Extraocular musclesThe muscles that control the movements of the eye and the elevation of the eyelid.
Vitreous floatersSmall flecks or threads of collagen that float in the vitreous humor and cast shadows on the retina, often seen as floaters by the individual.

Practice Quiz