3.1.4 QUIZ

PLTW HBS 3.2.4 MORE THAN MEETS THE EYE QUIZ STUDY GUIDE 

1. Eye anatomy and structure: You will need to identify and know the functions of the following terms related to the eye: 

Pupil - regulating the amount of light that enters the eye, which is crucial for maintaining optimal vision under varying light conditions

 Retina- sensory tissue lining the back of the eye, containing photoreceptor cells that convert light into electrical signals, which are then transmitted to the brain via the optic nerve for visual processing

 Aqueous Humor - clear fluid that fills front portion of the eye providing nutrients and oxygen to the surrounding tissues, maintaining intraocular pressure, and aiding the refractive properties of the cornea and lens for clear vision

Vitreous Humor- transparent gel-like substance that fills the space between the lens and the retina in the posterior segment of the eye. Its main functions include maintaining the shape of the eye, providing mechanical support to the retina, helping to transmit light to the retina, and contributing to the eye's refractive properties

Lens - flexible structure located behind the iris and pupil. Its primary function is to focus light onto the retina by adjusting its shape through a process called accommodation. This process enables the eye to form clear images of objects at various distances, contributing to visual acuity and sharpness.

Ciliary body -  ciliary body is a muscular structure located behind the iris in the eye. Its main function is to control the shape of the lens through the suspensory ligaments, a process crucial for adjusting the eye's focus on objects at different distances, known as accommodation. Additionally, the ciliary body produces aqueous humor, contributing to the maintenance of intraocular pressure and nourishment of the eye's tissues.

suspensory ligaments-  zonular fibers, are thin, fibrous strands that connect the ciliary body to the lens in the eye. Their primary function is to hold the lens in place and suspend it behind the iris. Additionally, these ligaments play a crucial role in adjusting the shape of the lens during the process of accommodation, allowing the eye to focus on objects at different distances for clear vision.

 Cornea- ransparent, dome-shaped outermost layer of the eye. Its primary function is to refract (bend) and focus light onto the retina, which is essential for creating clear and sharp images. Additionally, the cornea serves as a protective barrier, shielding the eye from dust, debris, and pathogens, while also contributing to the eye's structural integrity and maintaining its shape.

 Choroid- choroid is a highly vascular layer located between the retina and the sclera (the white outer layer) of the eye. Its main function is to supply oxygen and nutrients to the outer layers of the retina, including the photoreceptor cells responsible for vision. Additionally, the choroid helps regulate the temperature of the eye and absorbs excess light, preventing glare and maintaining visual clarity.

 Sclera- tough, fibrous outer layer of the eye, commonly known as the "white of the eye." Its primary function is to provide structural support and protection to the inner delicate structures of the eye, including the retina, choroid, and the aqueous and vitreous humors. Additionally, the sclera helps maintain the shape of the eye and serves as an attachment site for the extraocular muscles, which control eye movement.

 Macula- small, specialized area in the center of the retina responsible for central vision and detailed visual tasks, such as reading and recognizing faces. Its main function is to contain a high concentration of cone photoreceptor cells, which are essential for color vision and visual acuity. The macula also houses the fovea, a tiny depression within it, which is the region of highest visual acuity due to its dense concentration of cones and minimal presence of other retinal layers.

Iris-  iris is the colored part of the eye located between the cornea and the lens. Its primary function is to regulate the amount of light entering the eye through the pupil by controlling its size. The iris accomplishes this through the contraction or relaxation of its muscles in response to varying light conditions, thus adjusting the size of the pupil. Additionally, the iris plays a role in determining eye color and protecting the internal structures of the eye from excessive light exposure.

Optic disc (where is it and how is it related to the blind spot)-  also known as the optic nerve head, is the area in the retina where the optic nerve exits the eye. Its main function is to transmit visual information from the retina to the brain via the optic nerve fibers. The optic disc lacks photoreceptor cells, making it the blind spot in the visual field. However, it serves as a vital entry point for blood vessels that supply nutrients to the retina and optic nerve. Additionally, the appearance of the optic disc is crucial in diagnosing and monitoring various eye conditions, such as glaucoma, as changes in its size, shape, or color can indicate underlying pathology.

optic nerve -  primary pathway for transmitting visual information from the retina to the brain. Comprised of a bundle of nerve fibers, it connects the eye to the visual centers in the brain, specifically the thalamus and the occipital lobe of the cerebral cortex. Its main function is to relay electrical signals generated by photoreceptor cells in the retina in response to light stimuli, allowing the brain to interpret and process visual images. The optic nerve plays a crucial role in vision, as any damage or impairment to its structure can result in visual deficits or blindness.

2. Path of light as it travels through the eye from the cornea till the occipital lobe of the brain ( in the correct order) 

Cornea: Light enters the eye through the transparent outer layer called the cornea.

Aqueous humor: The light passes through the aqueous humor, a clear fluid that fills the space between the cornea and the lens.

Pupil: The light then passes through the pupil, which is the opening in the center of the iris that regulates the amount of light entering the eye.

Lens: The lens focuses the light onto the retina by changing its shape through a process called accommodation.

Retina: The light reaches the retina, which contains photoreceptor cells (rods and cones) that convert light into electrical signals.

Optic nerve: Electrical signals from the retina are transmitted through the optic nerve, a bundle of nerve fibers, towards the brain.

Optic chiasm: Some fibers from each optic nerve cross over at the optic chiasm, where they merge with fibers from the opposite eye.

Optic tract: The fibers continue their path as the optic tract, carrying visual information towards the thalamus.

Thalamus: Visual signals are relayed from the optic tract to the lateral geniculate nucleus (LGN) in the thalamus.

Optic radiation: From the LGN, visual signals travel via the optic radiation to the visual cortex in the occipital lobe of the brain.

Visual cortex: The occipital lobe processes visual information, allowing us to perceive and interpret the images that we see.

3. 6 muscles of the human eye, their names and locations 

Medial rectus muscle: This muscle is located on the inner side of the eye and is responsible for moving the eye inward towards the nose. It is controlled by the oculomotor nerve (cranial nerve III).

Lateral rectus muscle: Positioned on the outer side of the eye, the lateral rectus muscle is responsible for moving the eye outward away from the nose. It is innervated by the abducens nerve (cranial nerve VI).

Superior rectus muscle: Situated above the eye, the superior rectus muscle primarily elevates the eye, moving it upward. It is innervated by the oculomotor nerve (cranial nerve III).

Inferior rectus muscle: Located below the eye, the inferior rectus muscle primarily depresses the eye, moving it downward. It is innervated by the oculomotor nerve (cranial nerve III).

Superior oblique muscle: This muscle runs along the upper, outer side of the eye and is responsible for intorsion (rotating the top of the eye inward towards the nose) and depression (moving the eye downward). It is innervated by the trochlear nerve (cranial nerve IV).

Inferior oblique muscle: Positioned along the lower, outer side of the eye, the inferior oblique muscle primarily extorts (rotates the top of the eye outward away from the nose) and elevates the eye (moving it upward). It is innervated by the oculomotor nerve (cranial nerve III).

4. What are Rods and Cones and where are they located? 

Rods:

• Rods are photoreceptor cells that are highly sensitive to light and are primarily responsible for vision in low-light conditions (scotopic vision).

• They do not detect color but are instead sensitive to shades of gray.

• Rods are more abundant in the peripheral regions of the retina, making them essential for peripheral vision and night vision.

• Rods contain the pigment rhodopsin, which is sensitive to low levels of light.

Cones:

• Cones are photoreceptor cells that are responsible for color vision and high visual acuity in bright-light conditions (photopic vision).

• There are three types of cones, each containing a different photopigment that is sensitive to specific wavelengths of light, corresponding to red, green, and blue light.

• Cones are concentrated mainly in the central region of the retina, particularly in the macula and fovea, which are crucial for detailed and central vision.

• Cones provide the ability to perceive colors and discriminate fine details in visual stimuli.

5. Different eye conditions (description, treatment and causes): Onchocerciasis, Trachoma, Loiasis, Retinitis Pigmentosa, Traumatic Iridodialysis and Retinitis Pigmentosa 

Onchocerciasis (River Blindness):

Description: Onchocerciasis is a parasitic infection caused by the filarial worm Onchocerca volvulus, transmitted to humans through the bites of infected blackflies. It primarily affects the skin and eyes, leading to skin lesions and visual impairment, including blindness.

Treatment: Treatment typically involves the use of oral medications such as ivermectin, which kills the larvae of the parasite and prevents further transmission. Additionally, efforts to control the blackfly population and prevent bites are essential for disease prevention.

Causes: Onchocerciasis is caused by the parasitic infection of Onchocerca volvulus, which is transmitted to humans through the bites of infected blackflies (genus Simulium).

Trachoma:

Description: Trachoma is a contagious bacterial infection caused by Chlamydia trachomatis. It affects the conjunctiva and cornea of the eye, leading to symptoms such as eye irritation, pain, and eventually visual impairment or blindness if left untreated.

Treatment: Treatment involves antibiotic therapy to eliminate the bacterial infection, along with hygiene measures to prevent transmission. In advanced cases, surgery may be required to correct eyelid deformities or manage complications such as corneal scarring.

Causes: Trachoma is caused by the bacterium Chlamydia trachomatis, which is transmitted through direct contact with infected eye or nasal discharge, as well as through contaminated hands, towels, or other fomites.

Loiasis (African Eye Worm):

Description: Loiasis is a parasitic infection caused by the filarial worm Loa loa, transmitted to humans through the bites of infected deer flies or mango flies. It can lead to symptoms such as subcutaneous nodules, itching, and sometimes migration of the worm across the eye, causing visual disturbances.

Treatment: Treatment typically involves the use of antiparasitic medications such as diethylcarbamazine (DEC) or ivermectin to kill the adult worms. Surgical removal may be necessary in cases of severe ocular involvement.

Causes: Loiasis is caused by the parasitic infection of Loa loa, transmitted to humans through the bites of infected deer flies or mango flies (genus Chrysops).

Retinitis Pigmentosa:

Description: Retinitis pigmentosa (RP) is a group of inherited retinal disorders characterized by progressive degeneration of the photoreceptor cells in the retina, leading to night blindness, peripheral vision loss, and eventual central vision impairment or blindness.

Treatment: Currently, there is no cure for RP. Treatment focuses on managing symptoms and slowing disease progression through measures such as vitamin supplementation, low-vision aids, and gene therapy in some cases.

Causes: Retinitis pigmentosa is primarily caused by genetic mutations that affect the function of photoreceptor cells in the retina. It can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner.

Traumatic Iridodialysis:

Description: Traumatic iridodialysis is a condition characterized by a separation or detachment of the iris from its attachment to the ciliary body, typically resulting from blunt trauma to the eye. It can lead to symptoms such as eye pain, photophobia, and visual disturbances.

Treatment: Treatment options vary depending on the severity of the condition but may include observation, pharmacological therapy to manage symptoms, and surgical repair to reattach the iris to the ciliary body.

Causes: Traumatic iridodialysis is caused by blunt trauma to the eye, such as from sports injuries, accidents, or assaults, which can result in mechanical disruption of the iris tissue.

6. Differences between Human and Horse eyes 

7. Differences between Myopia and Hyperopia and corrective lenses for each 

Myopia (Nearsightedness):

• Description: Myopia is a refractive error where distant objects appear blurry while close objects can be seen clearly. It occurs when the eyeball is too long or the cornea is too curved, causing light rays to focus in front of the retina rather than directly on it.

• Corrective Lenses: Corrective lenses for myopia are concave (minus) lenses, which diverge light rays before they enter the eye, thus shifting the focal point backward onto the retina. These lenses help to focus distant objects onto the retina for clearer vision.

Hyperopia (Farsightedness):

• Description: Hyperopia is a refractive error where close objects appear blurry while distant objects can be seen more clearly. It occurs when the eyeball is too short or the cornea has too little curvature, causing light rays to focus behind the retina rather than directly on it.

• Corrective Lenses: Corrective lenses for hyperopia are convex (plus) lenses, which converge light rays before they enter the eye, thus shifting the focal point forward onto the retina. These lenses help to focus close-up objects onto the retina for clearer vision.

8. What does 20/20 vision mean? How to read the Snellen Eye chart 

• if a person can read the 20/40 line, it means they can see at 20 feet what a person with normal vision could see at 40 feet. If a person can read the 20/20 line, it indicates normal or "perfect" vision. If they can read smaller letters, such as the 20/15 or 20/10 lines, it suggests better-than-normal vision. Conversely, if a person cannot read the 20/20 line and requires larger letters, it indicates impaired visual acuity.

9. What is astigmatism? 

•  common refractive error of the eye that causes blurred or distorted vision at all distances. It occurs when the cornea (the clear, front surface of the eye) or the lens (located behind the cornea) has an irregular shape, rather than being perfectly spherical like a basketball.

10. What is the Fovea Centralis? 

The fovea centralis is a small, specialized area located in the center of the macula within the retina of the eye. It is responsible for the sharpest and most detailed vision, particularly when focusing on objects directly in front of us.

Key characteristics of the fovea centralis include:

1. High Concentration of Cones: The fovea contains the highest concentration of cone photoreceptor cells in the retina. Cones are responsible for color vision and high visual acuity, making the fovea essential for detailed and central vision.

2. Minimal Presence of Other Retinal Layers: Unlike other parts of the retina, the fovea has a thinning or absence of other retinal layers, such as ganglion cells and blood vessels. This arrangement allows light to pass directly to the cones without obstruction, enhancing visual acuity.

3. Location of Fixation: When we focus on an object, the light from that object falls directly onto the fovea centralis. This area is where the clearest and most detailed images are formed, enabling us to discern fine details, such as small print or intricate patterns.

Due to its high concentration of cones and minimal retinal layers, the fovea centralis plays a crucial role in tasks that require precise vision, such as reading, driving, and recognizing faces. Any damage or impairment to the fovea can lead to central vision loss or impairment, affecting the ability to see fine details and perform daily activities.

11. How does accommodation happen in the eye?

Accommodation in the eye involves the contraction and relaxation of the ciliary muscles, which adjust the shape of the lens to refract incoming light rays appropriately. When viewing distant objects, the ciliary muscles relax, causing the lens to flatten and reduce its refractive power. Conversely, when focusing on near objects, the ciliary muscles contract, allowing the lens to become thicker and more rounded, increasing its refractive power. This dynamic process enables the eye to maintain clear vision at various distances by ensuring that light rays are properly focused onto the retina.