Eye 1 Flashcards
what % of sensory receptors in the human body are located in the eyes
over 50%
Name the 3 main components of the eye
bony orbit
accessory structures
eyeball itself
Describe the bony orbit
the eyeball is a sphere - 2.5cm in diameter, suspended within a cavity in the skull = bony orbit - by muscles controlling its movements, consists of a roof, floor and medial & lateral walls (superior orbital wall, medial orbital wall, inferior orbital wall, lateral orbital wall, apex region)
Describe the role of periorbital fat
partially cushions eyeball, thick layer, protects it during movement
Name 5 accessory structures of the eye
eyelid eyelashes eyebrows lacrimal apparactus extrinsic eye muscles
Describe the roles of the Eyelids
upper and lower eyelids (Palpebrae), shade the eyes during sleep, protect the eyes from excessive light and foreign objects, spread lubricating secretions over the eyeballs
Describe the tarsal plate within the eyelids
a thick fold of connective tissue within the eyelid that gives its form and support, embedded n each tarsal plate are rows of sebaceous glands known as tarsal or Meibomian glands - secrete a fluid that helps keep the eyelids from adhering to each other
Describe the conjunctiva of the eyelids
a thin, protective mucous membrane, lines the inner aspect of the eyelids and the surface of the eyeball, it covers the sclera but not the cornea
over the sclera the conjunctiva is vascular
Describe the role of eyelashes
protect the eye from debris
sebaceous ciliary glands at the base of the hair follicles release a lubricating fluid onto the lashes
Describe the role of the eyebrows
help protect the eyeballs from foreign objects perspiration direct rays of the sun provide facial expression
Describe the lacrimal apparatus
the lacrimal glands produce and secrete about 1ml of lacrimal fluid (tears) per day, the tears drain into the lacrimal ducts and out onto the surface of the conjunctiva of the upper lid, the tears then pass medially over the anterior surface of the eyeball, the tears then enter 2 small openings called lacrimal puncta, from the puncta the tears pass into the lacrimal canals which lead into the lacrimal sac and then into the nasolacrimal duct
Describe which lacrimal fluid contains
salts, some mucus and lysozyme - a protective bactericidal enzyme
What is the function of tears
to protect, clean, lubricate and moisten the conjunctiva and corneal epithelium
Describe the extrinsic eye muscles
extend from the walls of the bony orbit to the sclera of the eye, surrounded in the orbit by a significant quantity of orbital fat, capable of moving the eye in almost any direction
Name the 6 extrinsic eye muscles that move each eye
superior rectus muscle inferior rectus muscle lateral rectus muscle medial rectus muscle superior oblique rectus muscle inferior oblique rectus muscle
Which cranial nerves are the extrinsic eye muscles supplied by
Oculomotor (III) - supplies the superior, medial, inferior and inferior oblique rectus muscles
Trochlear (IV) - supplies the superior oblique rectus muscle
Abudcens (VI) - supplies the lateral rectus muscle
Name the 3 layers of the eyeball
Fibrous tunic - superficial layer
Vascular tunic - middle layer
Retina - inner layer
Describe the cornea of the eyeball
a transparent coat that covers the coloured iris, its curved and so helps focus light onto the retina
Describe the sclera of the eyeball
‘white of the eye’, covers entire eyeball except the cornea, gives shape to the eyeball, makes it more rigid, protect its inner parts, serves as a site of attachment for the extrinsic eye muscles
Desciribe the fibrous tunic layer of the eyeball
consists of the anterior cornea and posterior sclera
Describe the vascular tunic or uvea layer of the eyeball
composed of 3 parts
Choroid
Ciliary Body
Iris
Describe the choroid
lines most of the internal surface of the sclera, produces the pigment melanin - absorbs stray light rays, preventing reflection and scattering of light within the eyeball - ensures image cast on retina remains sharp and clear
Describe the anterior portion of the vascular tunic eyeball
the choroid becomes the ciliary body - contains the ciliary muscle, suspensory ligaments (zonules) extends from the ciliary body and attach to the lens
contraction or relaxation of the ciliary muscle changes the tightness of the suspensory ligaments which alters the shape of the lens, adapting it for near or far vision
Describe what happens for near vision
ciliary muscles contract and the central lens thickness increases to increase its power
Describe the iris within the vascular tunic layer of the eyeball
coloured portion of the eyeball, suspended between the cornea and the lens, attached at its outer margin to the ciliary suspensory ligaments (zonules), iris consists of muscle fibres which function to regulate the amount of light entering the eyeball through the pupil in response to light levels
Describe what happens in bright/dim light
bright light causes a decrease in the size of the pupil (constriction)
dim light causes an increase in the pupil’s size (dilation)
What determines eye colour
the amount of melanin in the iris
Describe the Retina
lines the posterior 3/4 of the eyeball, and is the beginning of the visual pathway, consists of a pigmented layer and a neural layer
the melanin in the pigmented layer helps absorb stray light rays
neural (sensory) layer processes visual data before sending it as a nerve impulse to the occipital lobe of the brain via the optic nerve
Describe the neural layer of the retina
contains neutrons called photoreceptors - specialised cells that begin the process of converting light rays to nerve impulses
2 types = rods and cones
Each retina has how many rods/cones
6 million cones and 120 million rods
Explain the difference between rods and cones
rods allow us to see in dim light - don’t provide colour vision therefore in dim light we can only see black, white, shades of grey between
brighter light stimulates cones which do produce colour vision
Describe how the retina can be viewed
with an ophthalmoscope, shines light into the eye through the pupil providing a magnified image of the retina and its blood vessels as well as the optic (II) nerve
surface of the retina is the only place in the body where blood vessels can be seen directly and are examine for pathological changes
Where does the optic (II) nerve exit the eyeball and what is also visible in an image of a retina
optic (II) nerve exits at the site of the optic disc
also visible are the macula lutea and fovea centralis
Describe the optic disc
also called the blind spot, contains no rods or cones so can’t see an image striking the blind spot
Describe the macula lutea
is in the exact centre of the posterior portion of the retina
Describe the fovea centralis
a small depression in the macula lutea, no rods present only cones, area of highest visual acuity or resolution (sharpness of vision)
Describe the lens
normally transparent and lacks blood vessels, helps focus images on the retina for clear vision, divides the interior of the eyeball into 2 cavities = anterior cavity and vitreous chamber
Describe the anterior cavity formed by the lens
consists of 2 chambers = anterior and posterior chambers, both filled with a transparent watery fluid known as aqueous humor - its function is to nourish the lens and corns and is completely replaced about every 90 minutes
Describe the posterior vitreous chamber formed by the lens
contains a transparent jellylike substance called the vitreous body, holds the retina flush against the choroid, giving the retina an even surface for the reception of clear images, doesn’t ungergo constant replacement, consists mostly of water, also contains phagocytic cells that remove debris, keeping this part clear for unobstructed vision
Describe intraocular pressure within the eyeball
produced mainly by the aqueous humor and partly by the vitreous body, maintains the shape of the eyeball and prevents it from collapsing
puncture wounds to the eyeball may cause loss of aqueous humor and the vitreous body causing a decrease in intraocular pressure, a detached retina and in some cases blindess
