Special Senses: The Eye and The Vision Flashcards
Includes the eyes and other accessory structures that aid in sight. These include muscles, glands, and protective layers
The visual system
Size and shape of the eye
2.5 cm in diameter and has a spherical shape
→ Positioned anterior to the eye
→ Together with eyelashes, they protect the eyes from foreign objects
Eyelids (palpebrae)
The space between the eyelids
Palpebral fissure
Where the eyelids meet at the corners
Lateral commissure (lateral canthus) & Medial commissure (medial canthus)
a reddish-pink mound found within the medial canthus, containing sebaceous and sweat glands
Lacrimal caruncle
→ Located in the tarsal plate, a crescent-shaped connective tissue that helps maintain eyelid shape.
→ Produces oily secretions that lubricate the eyes and prevent tears from overflowing.
Tarsal (Meibomian) Glands
- Located between the eyelashes and act as sweat glands.
- Their ducts open near the base of the eyelashes.
Ciliary glands (glands of moll)
→ A mucous membrane that lines the eyelids and covers the outer surface of the eyeball.
→ Secreted mucus to keep the eyes lubricated and moist.
Conjunctiva
Covers the anterior white surface of the eye, connecting to the transparent cornea
Bulbar conjunctiva
Lines the inner surface of the eyelids
palpebral conjunctiva
→ is the white part of the eye, a tough, fibrous outer layer that provides
structure and protection.
→ It helps maintain the shape of the eye and serves as an attachment point for the extrinsic eye muscles.
Sclera
Includes the lacrimal glands and ducts, which produce and drain lacrimal fluid (tears).
Lacrimal apparatus
Cleanse, protect, moisten, and lubricate the eyes.
Contains: Dilute salt solution, mucus, antibodies, lysozymes
Tears (lacrimal fluid)
Pathway of tears
Lacrimal gland → Lacrimal canaliculus → Lacrimal sac → Nasolacrimal duct → Empties into the inferior meatus of the nasal cavity.
These six muscles control the movement of the eyes
Extrinsic eye muscles
Moves the eye laterally
Lateral rectus
Moves the eye medially
Medial rectus
Elevates the eye and turns it medially
Superior rectus
Depresses the eye and turns it medially
Inferior rectus
Elevates the eye and turns it laterally
Inferior oblique
Depresses the eye and turns it laterally
Superior oblique
Three layers that form the wall of the eyeball
Tunic
3 layers of tunic
Fibrous, vascular, sensory
Are fluids that fill the interior of the
eyeball
Humors
Divides the eye into two chambers
Lens
Consists of the sclera and cornea
Fibrous layer
→ Thick, white connective tissue layer and anteriorly we see this as the white part of the eye
→ To help maintain the shape of the eyeball and to help protect the internal structures of the eyeball and to provide an attachment point for the muscles that moves the eyeball
Sclera
→ The transparent central anterior region of the eyeball
→ It is the area that is exposed and prone to damage but it can repair itself easily
→ It allows the light to pass through it
→ It is the only human tissue that can be transplanted without the fear of rejection. This is because it is less immunologically active.
Cornea
→ The term means “membrane.”
→ It is a relatively thin layer located at the posterior part of the vascular layer.
→ The choroid is a blood-rich layer containing dark pigment, which prevents light from scattering within the eye
Choroid
→ contains most of the blood vessels of the eyeball.
→ It consists of three main structures: the choroid, ciliary body, and iris.
Vascular layer
→ It is located in the anterior part of the vascular layer and is modified from the choroid into two smooth muscle structures.
→ It is attached to the lens via the zonules (zonular fibers).
→ The function of this is to change the shape of the lens when focusing on objects.
Ciliary body
Ciliary bodies are attached to the lens via
Zonules (zonular fibers)
It is the pigmented layer that gives
the eye its color, which varies among
individuals.
→ It is composed of circular and radial
smooth muscle fibers.
→ At the center of the iris is the pupil,
the opening through which light
passes.
→ It acts as a diaphragm that regulates the amount of light entering the eye by controlling the size of the pupil
Iris
In bright light or when focusing on close objects: The_______ contract, causing the pupil to constrict (get smaller).
Circular muscles
In dim light or when focusing on distant objects: The _______ contract, causing the pupil to dilate (get larger).
radial fibers
Composed of the retina.
Sensory layer
The retina consists of two main layers:
- Outer pigmented layer
- Inner neural layer
→ Composed of pigmented simple
cuboidal epithelial cells
→ Absorbs light: Prevents light from
scattering inside the eye.
→ Phagocytic activity: Acts as phagocytes to remove dead and damaged receptor cells.
→ Storage of Vitamin A: Essential for vision
Outer pigmented layer
Contains different receptor cells
known as photoreceptors
Inner neural layer
2 types of photoreceptors
Rods and cones
How many cones do we have?
Approx. 6 to 7 million
Respond to light, enabling vision
Photoreceptors
→ Location: Primarily found on the
edges of the retina
→ Function:
○ Enable vision in dim light
○ Provide peripheral vision
→ do not perceive color; they are more sensitive to light.
Rods
How many rods do we have?
Approx. 12 million
→ Location: Densely concentrated in the center of the retina, particularly in the fovea centralis
→ Function:
○ Allow for detailed color vision
→ There are three types, each sensitive to different wavelength of light (red, green, and blue)
Cones
Electric signals generated by
photoreceptors are transmitted via a two-neuron pathway, which includes:
Bipolar cells and Ganglion cells
The signals from these cells (bipolar and ganglion) converge
and travel through the ______ to reach the brain.
optic nerve
where the neural layer of the retina meets and optic nerves
Optic disc
It is a crucial structure in the retina
where:
○ The central retinal artery
enters
○ The central retinal vein exits
○ Optic nerve exits the eye
optic disc
Images focused on the optic disc cannot be seen because it lacks photoreceptors, creating a
blind spot
→ Location: Lateral to the blind spot in the retina.
→ It is the area where light is most focused when looking directly at an object.
→ It contains only cone cells, which are more densely packed than in other areas of the retina.
→ This high concentration of
photoreceptors results in the greatest visual acuity or sharpest vision.
Fovea centralis
→ Sensitive to short wavelengths of light.
→ Responds best to light around 420 nm (nanometers), which appears as blue.
blue cones
→ Sensitive to medium wavelengths of light.
→ Most responsive to light around 530 nm, corresponding to green light.
Green cones
→ Sensitive to long wavelengths of light.
→ Responds strongly to light around 560 nm, which is perceived as red.
→ Can also detect some yellow and
orange hues due to overlapping wavelengths with green cones
Red cones
○ This is a flexible, crystal-like structure.
Lens
What is the anterior side of the lens made of?
Layer of cuboidal epithelial
What is the posterior side of the lens made of?
Long columnar epithelial cells known as lens fibers
The lens is held in place by _______ attached to the ciliary body.
suspensory ligaments
→ Located anterior to the lens
→ Contains aqueous humor, a clear,
watery fluid.
Anterior segment (aqueous segment)
→ Located posterior to the lens.
→ Contains vitreous humor, a gel-like
substance.
Posterior segment (Vitreous segment)
Location: Found in the anterior segment of the eye (aqueous segment). Watery fluid found between lens and cornea
Similar to blood plasma Composition:99.9% water (similar to blood plasma).
Helps maintain intraocular pressure (the pressure inside the eye). Provides nutrients for the lens and cornea , which are avascular (lack blood supply). Drains into the venous blood through the scleral venous sinus (canal of Schlemm) to prevent pressure buildup, which can lead to vision loss. Should be supplied at and drained at an equal rate to prevent build up of pressure that can cause vision loss
Aqueous humor
Location: Found in the posterior segment of the eye (vitreous segment). Gel-like substance posterior to the lens
→ Prevents the eye from collapsing
→ Helps maintain intraocular pressure
→ Cannot be regenerated or actively
replenished.
Vitreous humor
→ Instrument used to illuminate the
interior of the eyeball
→ Can detect diabetes, arteriosclerosis, degeneration of the optic nerve and
retina
→ Allows visualization of the retina,
optic disc, and internal blood vessels at the fundus (posterior wall of the eye).
Ophthalmoscope
Bundle of axons that exit the back of
the eye carrying impulses from the retina to the brain
Optic nerve
→ The location where optic nerves cross.
→ Fibers from the medial side of each eye cross over to the opposite side of the brain
Optic chiasma
→ Fibers from the medial side ofeach
eye cross over to the opposite side of
the brain.
→ These tracts synapse with neurons in the thalamus.
Optic tracts
Axons from the thalamus run to the
occipital lobe, synapsing with cortical cells where visual interpretation occurs (seeing).
Optic radiation
→ Each eye perceives a slightly different view.
→ The field of viewoverlaps for both
eyes, enabling binocular vision.
Visual field
Two-eyed vision provides depth
perception (three-dimensional vision) by fusing the two slightly different images into one.
Binocular vision
A reflexive movement where the eyes
move medially when focusing on a close object
Convergence
The pupils constrict in response to
bright light to protect photoreceptors.
Photopupillary reflex
The pupils also constrict when viewing close objects to improve focus.
Accomodation pupillary reflex
