review of ocular structures and functions Flashcards
what are the four tissue types in the body?
.nervous
.muscular(smooth , cardiac and skeletal )
.epithelial (covering and glandular)
.connective (loose and dense)
what are glandular exocrine glands split into?
. unicellular glands (goblet cells)
.multicellular glands which is split
1.simple ( one duct )
2.compound ( several ducts)
what do the upper and lower eyelid contain?
meibomian glands ( simple multicellular glands )
what do meibomian glands secrete?
they secrete the sebaceous part of tear film
what does the conjunctiva cover ?
the posterior surface of the eyelids and the exposed surface of the eye as far as the limbus
what makes up the conjunctiva?
it is a mucous membrane containing mucous secreting goblet cells which makes up the mucous layer of tear film
where is the lacrimal gland positioned?
the lacrimal gland is positioned above the upper eyelid
what type of gland is lacrimal gland?
it is a compound gland producing mainly serous secretions
what does the tear film cover?
the tear film covers the front surface of the eye
what are the 3 components of the tear film?
. mucous layer ( conjunctival goblet cells )
.serous secretions ( lacrimal gland )
.sebaceous secretions ( tarsal glands )
how is the tear volume distributed?
the tear volume is distributed over the eyes exposed surface
how is the tear volume drained?
the tear volume is drained through the puncta into the nasolacrimal duct
what are the two skeletal muscles involved in blinking ?
.the orbicularis oculi
.the levator palpebrae superioris muscle
what is the orbicularis oculi?
one of the facial muscles which runs around the eye
its contraction closes the palpebral aperture
what is the levator palpebrae superioris muscle?
.runs along the top of the eye ball and sends tendons into the eyelid
. its contraction raises the upper lid
what is the outer coat of the eye mostly made of ?
opaque sclera which is modified into transparent cornea at front of eye
what is the corneoscleral junction known as ?
limbus
what is connective tissue made of?
. fibres ( collagen , elastic , reticular )
.cells ( fibroblast , mast cell )
. ground substances
what are connective tissue arrangement?
. loose ( fibres arranged loosely ) adipose and areolar
.dense ( fibres tightly packed ) regular and irregular
what is the human cornea structure?
. epithelium . bowmans layer .stroma . decements membrane .endothelium
what type of connective tissue makes up the corneal stroma?
.dense regular connective tissue
.its made up of tightly packed and regularly arranged collagen
.this makes the corneal stroma transparent
what type of connective tissue makes up the sclera?
. the collagen in the sclera is irregular
. this makes the sclera opaque
what is the outer corneal layer known as?
corneal epitheluim
what type of tissue makes up the corneal epithelium ?
.stratified squamous epithelium
.it protects from the dirt
what is the inner surface of cornea known as ?
corneal endothelium
what type of tissue makes up the corneal endothelium?
simple squamous epithelium
allows avascular cornea to exchange substance with the aqueous humour
where does the light go after traversing the cornea?
anterior chamber which is filled with aqueous humour
what is the uvea made up of ?
. iris that forms the pupil
.ciliary body
.choroid
what is the choroid?
vascular layer sandwiched between the sclera and retina
what is the main function of the choroid?
supply nutrients to the outer retina
what is bruchs membrane?
separates the choroid and retina
what is the iris?
iris is an offshoot of the ciliary body and forms the pupil
what is the structure of the iris?
its posterior surface is covered by 2 layered epithelium containing melanin.
this ensures that the only light that enters the eye is through the pupil
what types of tissue makes up the stroma?
loose areolar connective tissue , allowing it to change shape as the pupil size changes
what are the two smooth muscles in the iris?
. the iris sphincter - constricts the pupil . it is parasympathetically innervated
.the iris dilator - opens up the pupil . it is sympathetically innervated
what is the ciliary body divided into?
.anterior ridge pars plicata
. posterior , smooth , thinner pars plana
what is the pars plicata made of ?
the pars plicata is made up of a series of ridges known as ciliary processes
what is the ciliary process covered by?
the ciliary process is covered by a 2 layered epithelium
. the pigmented epithelium - part of the eyes black box effect
.the unpigmented epithelium - produces aqueous humour
what is the function of the aqueous humour ?
. the aqueous travels from the ciliary body , past the lens and supplies the avascular lens and cornea with nutrients
how is the aqueous humour drained?
it is drained through the trabecular meshwork into the canal of schlemm at the filtration angle
what is the ciliary body?
the part of the eye that connects the iris to the choroid
what is the bulk of the ciliary body made of?
the bulk of the ciliary body is made of smooth ciliary muscle
how is the lens attached to the ciliary body?
the lens is attached to the ciliary body by suspensory ligaments
what are the 3 layers of the lens?
. an elastic capsule covering the entire surface
. a simple epithelium underneath this
. the bulk of the lens is made of elongated cells (lens fibres )
what is the shape of lens fibres?
lens fibres are long hexagonal cells that run from the front to the back surface of the lens
how are adjacent lens fibres joined?
adjacent lens fibres are joined by gap junctions to allow the flow of nutrients
what is the lens capsule function?
. its elasticity plays an important role in accommodation
. it also plays an important role in cataract surgery
. the capsule also forms a barrier stopping large particulate matter such as inflammatory cells entering the lens , while allowing smaller necessary metabolites through
what happens in cataract surgery?
in cataract surgery the lens stroma is liquefied by an ultra sound probe and sucked out , leaving the capsule behind like an empty bag , which is then filled with an artificial lens
what is the eyes total refractive power?
60 D
this is due to the difference between the refractive index of air and the refractive index of the cornea.
.most of the eyes refractive power is provided by the cornea (45D)
how much refractive power does the lens provide?
the lens provides ( 15D )
what is the main function of the lens?
fine focus the image through the process of accommodation
how is the human eye at rest?
at rest the human eye is emmetropic
parallel light rays from distant objects are focussed on the retina
how are close objects focussed?
close objects are focussed behind the retina
how to bring close objects into focus?
eye must increase its refractive power
this is known as accommodation
how is the lens during un accommodation?
unaccommodated - lens is under tension and pulled flat
how is the lens during accommodation?
accommodated - tension on the lens is released and it takes a rounded shape
what is presbyopia?
loss of accommodative ability with age
where is the retina?
.the retina lines the back of the eye , terminating at the ora serrata
how many layers are on the retina?
it is a 10 layered structure made up of various types of neurons and glial cells
what is the outer layer of the retina composed of ?
. photoreceptors
. cones (c) - sensitive at high light ( photopic) levels
. rods (r) - subserve low light (scotopic) vision
what is the function of photoreceptors?
converts the optical image into nervous potential (phototransduction)
what are the 5 main types of neurons that make up the retina?
. photoreceptors . horizontal cells . amacrine cells . bipolar cells . ganglion cells
how does light reach the photoreceptors?
light traverses the inner retinal neurons before reaching the photoreceptors
how do electrical signals leave the retina?
the electrical signals leave via ganglion cell axons , which make up the optic nerve
how is the fovea characterised?
the fovea is characterised by a dip in an avascular dip in the retina
what is the function of the fovea?
the fovea subserve the highest acuity vision .
we move our eyes to image in high lightt levels to image objects of interest on this region
what is the structure of the optic nerve?
out of the optic nerve comes branches of the central retinal artery , that supply the inner retina
what is the macula region?
the centre which is the fovea
what are the 6 striated extra ocular responsible for the movement of the eye?
. superior rectus . inferior rectus . superior oblique . inferior oblique . lateral rectus . medial rectus
