Lab 10 vision and the eye study Flashcards
Eyes enable us to see in 3 dimensions with
stereoscopic vision
Sterioscopic vision - This describes the ability of the visual brain to register a sense of three-dimensional shape and form from visual inputs. In current usage, stereoscopic vision often refers uniquely to the sense of
depth derived from the two eyes.
Eyelids also called
palpebrae
Eyelids thin, skin-
covered folds that
protect eye anteriorly
Eyelids Separated at
palpebral fissure (slit)
Eyelids Meet in corners at
medial and lateral canthus (commissures)
Lacrimal caruncle located at medial commissure contains
oil and sweat glands
Lubricating glands associated with eyelids
Tarsal (Meibomian) glands
Tarsal (Meibomian) glands Modified sebaceous glands produce
oily secretion that lubricates lid and eye
Conjunctiva - Transparent mucous membrane that produces
a lubricating mucous secretion
Lacrimal gland is located in orbit above lateral end of eye and secretes
lacrimal secretion (tears)
lacrimal secretion (tears),
a dilute saline solution containing mucus, antibodies, and antibacterial lysozyme
Blinking spreads tears toward
medial commissure, where they enter lateral puncta
Flow
- the lacrimal gland produces and secretes tears (lacrimal secretions) 2. tears enter the conjunctival sac via the excretory ducts of the lacrimal gland 3. tears flow down and across the eyeball 4. tears enter the lacrimal canaliculi at openings called lacrimal puncta 5. tears drain into the lacrimal sac 6. from the lacrimal sac tears empty via the nasolacrimal duct into the inferior meatus of the nasal cavity
Six straplike extrinsic eye muscles Originate from
bony orbit and insert on eyeball
Extrinsic eye muscles Enable eye to
follow moving objects, maintain shape of eyeball, and hold it in orbit
Four rectus muscles originate from common tendinous ring; names indicate movements
Superior, inferior, lateral, and medial rectus
Two oblique muscles move eye in vertical plane and rotate eyeball
Superior and inferior oblique muscles
lateral rectus moves eye
laterally
lateral rectus muscle cotrols what cranial nerve
Vl (abducens)
Medial rectus moves eye
medially
Medial rectus muscle cotrols what cranial nerve
lll (oculomotor)
superior rectus elevates eye and turns it
medially
superior rectus muscle cotrols what cranial nerve
lll (oculomotor)
inferior rectus depresses eye and turns it
medially
inferior rectus muscle cotrols what cranial nerve
lll (oculomotor)
inferior oblique elevates eye and turns it
laterally
inferior oblique muscle cotrols what cranial nerve
lll (oculomotor)
superior oblique depresses eye and turns it
laterally
superior oblique muscle cotrols what cranial nerve
lV (trochlear)
Nasal cavity mucosa is continuous with mucosa of lacrimal duct system, so a cold or nasal inflammation often causes
lacrimal mucosa to swell
Swelling constricts the ducts and prevents tears from draining, causing
“watery” eyes
Wall of eyeball contains three layers
- Fibrous layer
- Vascular layer
- Inner layer
Internal cavity filled with fluids called
humors
Lens separates internal cavity into
anterior and posterior segments
Fibrous layer Outermost layer;
dense avascular
connective tissue
Fibrous layer Two regions
sclera and cornea
Sclera
Opaque posterior region
Sclera Protects and
shapes eyeball
Sclera Anchors
extrinsic eye muscles
Cornea Transparent anterior one-sixth of
fibrous layer
Cornea Forms clear window that lets light enter and
bends light as it enters eye
Numerous pain receptors contribute to
blinking and tearing reflexes
Vascular layer Middle pigmented layer of eye, also
called
uvea
Vascular layer Three regions
choroid, ciliary body, and iris
Choroid region Posterior portion of
uvea
Choroid region Supplies blood to
all layers of eyeball
Brown pigment absorbs light to prevent scattering of light, which would cause
visual confusion
Iris Colored part of eye that lies between
cornea and
lens, continuous with ciliary body
Pupil: central opening that regulates
amount of light entering eye
Close vision and bright light cause sphincter pupillae (circular muscles) to contract and pupils to constrict;
parasympathetic control
Distant vision and dim light cause dilator pupillae (radial muscles) to contract and pupils to dilate;
sympathetic control
Changes in emotional state—pupils dilate when subject matter is appealing or
requires problem- solving skills
Anteriorly, choroid becomes
Ciliary body
Ciliary body Thickened ring of
tissue surrounding lens
Consists of smooth muscle bundles
ciliary muscles, that control shape of lens
Capillaries of ciliary processes secrete fluid for
anterior segment of eyeball
Ciliary (suspensory ligament) extends from
ciliary processes to lens
• Holds lens in position
Retina originates as an
outpocketing of brain
Inner layer (retina) Contains: 3
- Millions of photoreceptor cells that transduce light energy
- Neurons
- Glial cells
Inner layer (retina) Delicate two-layered membrane
- Outer pigmented layer
* Inner neural layer
Inner layer (retina) Pigmented layer of the retina Functions: 3
- Absorbs light and prevents its scattering
* Phagocytizes photoreceptor cell fragments • Stores vitamin A
Neural layer of the retina
Transparent layer that runs anteriorly to margin of ciliary body
Neural layer of the retina Composed of three main types of neurons
Photoreceptors, bipolar cells, ganglion cells
Signals spread from photoreceptors to
bipolar cells to ganglion cells
Ganglion cell axons exit eye as
optic nerve
Retinal Modifications: Optic disc
Site where optic nerve leaves eye
Optic disc Lacks photoreceptors, so referred to as
blind spot
Retina has quarter-billion photoreceptors that cannot
respond to light
Internal chambers and fluids 2
Posterior segment Anterior segment
Anterior segment Iris divides
anterior segment into two chambers
the two chambers
- Anterior chamber
* Posterior chamber
Entire anterior segment contains
aqueous humor
aqueous humor a plasma like fluid continuously formed by
capillaries of ciliary processes
Drains via scleral venous sinus (canal of Schlemm) Supplies nutrients and oxygen mainly to lens and cornea but also to
retina, and removes wastes
circulaiton of aqueous humor 3
- aqueous humore forms by filtration from the capilaries in the ciliary processes 2. aqueous humor flows from the posterior chamber through the pupil into the anterior chamber some also flow through the vitreous humor 3. aqueous humor is reabsorbed into the venous blood by the scleral venous sinus
Posterior segment Contains
vitreous humor
vitreous humor a fluid that 4
- Transmits light
- Supports posterior surface of lens
- Holds neural layer of retina firmly against pigmented layer
- Contributes to intraocular pressure
Lens
Biconvex, transparent, flexible, and avascular
Lens Changes shape to precisely focus light on
retina
Lens two regions
Lens epithelium
Lens fibers
Lens epithelium
anterior region of cuboidal cells that differentiate into lens fiber cells
Lens fibers
form bulk of lens
Lens fibers are continually added, so lens becomes
more dense, convex, and less elastic with age
Clouding of lens
Consequence of aging, diabetes mellitus, heavy
smoking, frequent exposure to intense sunlight
Clouding of lens 3
- Some congenital
- Crystallin proteins clump
- Lens can be replaced surgically with artificial lens
Refraction
bending of light rays
Light travels in straight lines (rays) at a constant speed until it
reaches a medium with a different density
Light rays bend (refraction) during passage through structures of
differing density
n eye, light is bent (refracted) three times – passing through these structures and the vitreous and aqueous humor
- Entering cornea or air
2. Entering lens from cornea 3. Leaving lens
Refraction – illustration – going from
air (less dense) to water (more dense)
Lens highly
elastic
Lens Shape can change via contractions of
ciliary smooth muscles
Lens Accommodates for light from
different distances
Looking at close objects, Ciliary muscles
contract, decrease tension suspensory ligaments
Problems associated with refraction related to eyeball shape 3
Myopia
hyperopia
astigmatism
Myopia (nearsightedness)
Eyeball is too long, so focal point is in front of retina
Corrected with a concave lens
hyperopia (farsightedness)
Eyeball is too short, so focal point is behind retina Corrected with a convex lens
astigmatism
Unequal curvatures in different parts of cornea or lens
Corrected with cylindrically ground lenses or laser procedures
Axons of retinal ganglion cells form
optic nerve
Medial fibers from each eye cross over at the
optic chiasma
The lateral field of vision fibers do not cross over at the
optic chiasma
After leaving the optic chiasm they continue on as
optic tracts
which means each optic tract: 2
- Contains fibers from lateral (temporal) aspect of eye on same side and medial (nasal) aspect of opposite eye, and
- Each carries information from same half of visual field
Paired Optic Tracts run posteriorly around
hypothalamus sending axons to synapse with neurons in Lateral Geniculate Nuclei of thalamus
Function: balance and combine retinal input for
delivery to visual cortex
Axons of Lateral Geniculate Nuclei form Optic Radiation of fibers in
white matter
Optic radiation of fibers project to primary visual cortex in
occipital lobes
Rods and Cones are
photoreceptors
photoreceptors are
modified neurons
Rods are more numerous; used for
dim light and peripheral vision
Cones used for bright light and provide for
high-resolution and color vision
Responsible for understanding common eye disorders pointed out in lab manual
• Find referred to in textbook
• Understand dark and light adaptation referred to in lab manual
• Understand other homeostatic imbalances associate with eye in lab book pg. 204
• I may use any of the figures in this presentation in the lab practical with the exception of figure 15.19a (visual pathway – will use the one from the lab manual)
