OHD1 intro into the eye 1 (copy)

intro into the eye

diagram of the eye

Anatomical planes

temporal/lateral: away from the body

medial/nasal: towards the body midline 

cranial; top

caudal; bottom 

anterior front posterior back 

proximal and distal 

planes 

sagittal plane is cut through the body into left and right 

coronal is ct into the body front and back 

transverse is middle 

ipsilateral is same side contralateral is opposite 

4 types of tissues

epithelial

connective

muscle

nervous

what is a tissue

defined as a collection of similar cells that are specialised to perfomr a common function

epithelial tissues 

a thin protective layer 

epithelial cells lie on a basement membrane that attaches them to underlying connective tissue 

classified by shapes 

types of epithelial cells

simple squamous

simplecuboidal

simple columnar

stratified squamous

stratified cuboidal

stratified columnar

transitional epithelium

connnective tissues

provide structure and support for other tissue

consists of cells, fibres and extracellular matrix

the fibres found in connective tissue include flexible collagen fibres with high tensile strength that can undergo extensive stretching

muscle tissues 

3 types: cardiac skeletal and smooth 

muscles are either striated or smooth and are either under voluntary or involuntary control

nervous tissue

composed of 2 types of cells

neurons and neuroglia

the eyelids or palpebrae

functions of the eyelids:

they cover the globe for protection

contain structures that prodice the tear film

on opening they spread the tear film over the anterior surface of the eye

on closure they move the tears towards drainage areas

the eyelids

the palpebral fissure is the area between the open eyelids 

the medial canthus is inner cornerof the eye 

lateral canthus is the outer part of the eye 

the upper and lower eyelids meet at the corners of the palpebral fissure 

eyelid 

the upper eyelid extends to the eyebrows and is divided into the tarsaland orbital parts 

the eyelid margi rests againts the globe and contains the eyelashes and the pores of the meibomian glands 

you have around 150 eyelashes (cilia) in the upper lid and around 75 in the lower lid 

the meibomian gland

produces and secretes meibum

plays role in maintaining the health of the eyes tear film and prpeventing dry eye

in picture grade 4 shows no glands visible so likely person suffers from dry eye

The tear film

the tear film:

1. keeps the surface of the eye moist 

2. traps debris 

3. provides oxygen to the cornea 

4. provides a smooth refractive surface 

5. contains antibacterial substances 

6. miantains corneal hydration 

7. contains growth factors to mediate conreal wound healing 

cornea

can be thought of as the front of a sphere in the front of an eye but is actually more oval.

the radius of the curvature changes between the centre and the periphery of the cornea

layers of the cornea

corneal epithelium is around 50 microns thick

bowman layer is 8-19 microns thick

corneal stroma is 450-500 microns thick

descemet membrane is 5-15 microns thick

corneal endothelium is normally 5 microns thick

endothelial mosaic forms a leaky membrane

bowmans layer

dense fibrous sheet of interwoven collagen fibrils randomly aranged in a mucoprotein gorund substance.

provide biochemical rigidity and shape to the cornea

posteriorly, as layer transitions into the stroma, the fibrils adopt a more orderly arrangement and merge into bundles if damaged cant regenrate 

stroma

middle layer of cornea and it is the tickets

composed of collagen fibrils, keratocytes and extracellular ground substance 

the collagen fibrils have a uniform diameter and run parallel to one another , forming flat bundles called llamelae 

corneal stromal lamellae 

a is lamella oriented parallel to the corneal surface 

b is lamella oriented perpendicular or at an angle to the conreal surface 

c is lamella with keratocyte processes indicated by the arrow embedded between collagen fibres 

A is ground substance filling between lamella 

A: view of lamellae cut into 3 planes 

a: upper lamella cut obliquely

b: lamella cut in corss section

c: cut longitudinally

arrow shows lamellae split into 2

keratocytes 

corneal fibroblasts. 

flattenedc cells that lie between and occasionally within the lamellae. cells not distributed randomly; a corkscrew pattern is recognisable from anterior to posterior

have extensive branching joined by gap junctions

maintain the stroma by synthesising collagen and extracellular matric components

descemets membrane

basement membrane od the endothelium

produced ocntinually and therefore thickens throughout life

thickness of descememts membrane changes with increasing age 

descemet membrane consists of 2 laminae. the anterior lamina is 3 micrometeres thic, banded appearance and a latticework of collagen fibrils secreted during embyronic development. posterior is nonbanded and homogenous - its the portion secreted by the endothelim

descemets exhibits elastic properties- if torn it will curl into the anterior chamber . very resistant to trauma

endothelium

innermost layer of cornea/. lies adjacent to the anterior chamber and is composed of a single layer of flattened cells. the basal part of each cell rests on the descemets 

corneal function

has 2 primary functions:

to refract light and to transmit light

factors that affect the refractive power

the curvature of the anterior conreal surface - more curved light refracted stronger. more refraction so shorter focal point.

change in the refractive index from air to cornea

corneal thickness

the curvature of the posterior corneal surface

change in the refrcative index from cornea to aqueos humor

corneal metabolism 

the cornea is metablically active and requires a stable supply of oxygen and glucose 

when your eyes are open oxygen is derived primarily from oxygen dissolved in the tear film ( from atmosphere)

glucose and other nutrients and vitamins are absorbed from the aq humor through the leaky endothelium 

aquaporins

small integral membrane proteins residing in the plasma membrane, some are water selective and others transport glycerol.

corneal repai- wound healing

corneal injury initiates lots of mechaniss to repair damaged tissure. directed by various biomolecules such as integrins, cytokines and growth factors. corneal integrins are integral membrane glycoproteins that maintain corneal function

bowmans membrane 

doesnt regenerate if damaged but will be replaced either by stroma-like fibrous tissue or by epithelium

beneath corneal epithelium made from randomly arranged collagen fibres and provides strucural support 

sclera

thick dense connective tissue layer that is continuous with corneal stroma at the limbus.

collagen fibrils are arranged into lamellae but are more irregular than the corneal lamellae

the irregular running of lamellae coupled with the irregular spacing between scleral components induce light scattering which makes the sclera opaque

scleral spur

its a region of circularly orientaated collagen bundles that extends from the inner aspect of the sclera

At the posterior edge its fibres blend with the scleralfibres and in cross section looks like a spur

limbus

located t corneascleral junction that encircles the periphery or cornea.

narrow transitional zone and involved in regeneration and nutrition as contains blood vesssels that supply nutrients

lamina cribosa 

the output of the eyeball is via the optic nerve at the back of the eye 

its passed through the posterior sclera which is bridged by a network of scleral tissue called lamina cribosa

lamina cribosa is the weakest area of the outer connective tissue 

episclera

episclera is a vascularised connective tissue that lies infront of the sclera

episclera is joined to the tenon capsle by stands of connective tissue

tenon capsule: thin fibrous membrane surrounding most of eyeball from optic nerve to the limbus ( the border between the cornea and sclera near front of the eye)

tenon capsule

a thin fibrous sheet of connective tissue that lies in front of the episcleral

contains smooth muscle fibres that regulate the tension of extraocular muscles

conjunctiva 

divided into 3 sections 

1. the bulbar conjunctiva which covers the sclera 

2. the palpebral conjunctiva which lines the eyelids 

3. the conjunctival fornix which is the cul de sac connecting the other 2.

limbus

located at the intersection between cornea and sclera

the external and internal scleral sulci associated with this transtion are clearly visible in cross sections through the limbus

iridectomy 

in some cases of glaucoma an iridectomy is performed to facillitate movement of aqueous from the posterior chamber to the anterior chamber 

iridectomy uses a laser to make an opening in the iris without exciting tissue 

anterior iris epithelium and dilator muscle

the dilator muscle is present from the iris root to a point in the stoma below the midpoint of the sphincter

the dilator muscle causes the pupil to get bigger in low-light conditions (mydriasis)

the anterior iris epithelium continues posteriorly as the pigmented epithelium of the ciliary body

posterior iris epithelium

the second epithelial layer posterior to the stroma is in the posterior iris epithelium a single layer of heavily pigmented columnar cells

the epithelial cells curl around from the posterior iris to the anterior surfave at the pupillary margin forming the pigmented pupillary ruff which encircles the pupil

iris colour

iris colour is determined by a number of factors

the arrangment of connective tissue components in the anterior tissue components in the anterior border layer and stroma, the number of melanocytes and the size and density of melanin granules within the melanocytes

ciliary body

divided into 2 parts: the pars plicata and the pars plana

• pars plicata: wider anterior portion containing the ciliary processes

• pars plana: flatter region of the ciliary body it extends from posterior pars plicata to the ora serrata

histological features of the ciliary body 

the supraciliaris is the outermost layer of the ciliray body adjacent to the sclera 

the ciliary muscle is composed of smooth muscle fibres oriented in three directions- longitudinal, radial and circular 

more histological features of ciliary body

the stroma of the ciliary body is highly vascularisd and lies between the muscleand the epithelial layers

2 layers of epithelium cover ciliary body and line the posterior chamber and part of vitreous chamber

outer layer of epithelium cells are pigmented and cuboidal while inner layer are non pigmented and columnar

functions of ciliary body

accomodation

production of aqueous and vitreous components

regulation of material allowed in the aqueous

choroid 

located between the sclera and the retina 

composed of: suprachoroidal lamina. choroidal stroma, choriocapillaris and bruch membrane 

choroid

the suprachoroidal lamina is a thin pigmented layer of connective tissue that lies between the sclera and choroid

choroidal stroma is highly vascularised loose connective tissue with larger vessels occupying the outer layer

more on choroid

the specialised capillary bed within the choroid is called choriocapillaris

the innermost layer of the choroid is Bruch membrane. fine filaments from the RPE merge with fibrils contributing to the tight adhesion between choroid and retina

function of choroid 

provide oxygen and nutrients to the outer retina 

allow catabolites for the retina to be removed 

thermoregulate the retina and interocular pressure drainage