5: ciliary body , aq humour & IOP(copy)

ciliary body

when viewed from the nterior eye, the ciliary body is a ring shaped structure

posterior area of ciliary body which terminates at the ora serrata, appears flat but anterior has lots of foolds that extends into the posterior chamber

sagittal section of ciliary body

ciliary body has triangular shap 

one corner lies at the scleral supr, the iris root extends from centre of base 

outer side of triangle lies against the sclera and inner side lines the posterior chamber ad a small part of vitreous 

apex located at ora serrata 

ciliary body is the light blue part

traingular as looking at one slice of it

it makes the aqueous humour that keeps the eye round and gives nourishment

passageway of aqueous humour

produced by non pigmented ciliary epithelium of ciliary processes

comes from posterior chamber to the pupil

pupil to theanterior chamber and the aqueous circulates:

warm iris → cool cornea → sets up convective current

then from anterior chamber angle it passes through trabecular meshwork and enters the schlemms canal

enters the episcleral veins or uveoscleral outlfow to to the supachoroidal space

posterior view of ciliary body  

pars plana is flatter 

plicata are the ciliry processes that allow constricion of eye 

what is the ciliary body divided into

pars plicata

pars plana

pars plicata 

wider , anterior portion containing ciliary processes 

cilliary processes extend into posterior chamber and the regions between them are called valleys of kuhnt 

pars plana

flatter region of the ciliary body, extends from the posterior [art of the pars plicata to the ora serrata, which is the transition between ciliary body and choroid

ora serrata has serrated pattern,called teeth, and rounded portions that lie between teeth are oral bays

dentate processes

elongations of retinal tissue into the region of the pars plana

what fibres course from the cilary body

zonule fibres course from ciliary body to the lens. some of these fibres instert into the internal limiting membrane of pars plana region and travel forward through valleys between ciliary processes

what is ciliary body attached to

vitreous base, which extends forward over the posterior pars plana

ciliary muscles 

light section on picture on right is stroma 

black outline is pigmented epithelium 

shaded area around black line is non pigmented epithelium 

layers of the ciliary body

1.supraciliary layer - outermost

2.ciliary muscle

3.stroma

4.epithelial layers: outer basement membrane, pigmented epithelium, non pigmented epithelium, inner basement membrane

supraciliaris layer of ciliary body 

outermost layer of ciliary body adjacent to sclera. 

loose connective tissue arranged in ribbonlike layers containing pigmented melanocytes, fibroblasts and collagen bands 

arrangement allows ciliary boody to slide against the sclera without detaching from or stretching the tissue 

arrangement also allows accumulation of fluid within its spaces which may cause displacement of ciliary body from sclera. 

damage to this laye caused by trauma may result in ciliary body detachment

ciliary muscle

smooth muscle tissue

function is controlling accomodation

long radial and circular directions

longitudinal muscle fibres lie adjacent to supraciliaris and parallel to sclera

radial fibres form wider shorter Vsthat originate at the scleral spur and insert into connective tissue near base of ciliary proceses

innermost region of ciliary muscle , annular muscle is formed of cicular muscle bundles with a sphincter type of action. located near major circle of iris .

what is ciliary muscle innervated by

autonomic nervous system. parasympathetic stimulation activates muscle for contraction whereas sympatheic innervation has inhibitory effect that is a function of level of parasymp activity 

ciliary stroma

connective loose tissue

function is supporting framework for muscle and blood vessels

lies between muscle and epithelial layers and forms the core of each of the ciliary processes

separated bundles of ciliary muscle

stroma thins in pars plana where it continues as choroidal stroma

major arterial circle of iris

located in the ciliary stroma to ciliary muscle and near the iris root

ciliary epithelium 

2 layers of epitheliumpositioned apex to apex , cover the ciliary bpdy and line psterior chamger and part of vitreous chamber 

intercellular junctions, desmosomes and tight junctions connect the two layers 

gap junctions between apical surfaces provide a mans of cellular communication between the layers and are important in formatin of aqueous 

both layers involved in secretion

outer layer of the ciliary epithelium

pigmented and cuboidal and simple 

function is light absorption in posterior cavity

cells joined by desmosomes and gap junctions 

anteriorly, its continous with ant iris epithelium

posteriorly, its continours with retil pigment epithelium to stroma 

basement membrane attaches pigment epithelium to the stroma 

unpigmented simple epithelium of ciliary

composed of columnar cells in the pars plana and cuboidal in the pars plicata

lateral walls of the cells contain extensive interdigitations and are joined, near their apices by desmosomes , gap junctions and zonula occludens whcih form one sitte of blood aqueous barrier

function is secretion of aq humour,and serve as a barrier between blood and aqueous

metabolically active, have large number of mitochondria than pigmented cellls and thus a higher degree fof metabolic activity

baswment membrane of non pigmented epithelium

line posterior chamber and extends into invaginations and is continous wih internal limiting membrane of reitna

what is the attachment site for zonular fibres fibres 

the internal limiting membrane also the attachment for fibres of the vitrous base 

structure in the pars plana

looking at the left eye

ciliary muscle organisation

blood vessels of the anterior eye 

major circle of iris supplies blood to the iris

then the capillaires go into the ciliary body

those then secrete liquids into the pigmented and non pigmnted epithelium

then secrete through pupil, and anterior chamber it exits out canal of schlemm

canall connected to anterior ciliary artery os goes through here

exits out the anterior ciliary vein

ciliary body- structure of the ciliary processes

ciliary processes are lined by 2 layers of epithelium: outer pigmented and inner pigmented

lots of folds to increase surface area

outer surface will have un pigmented cells

what are ciliary processes

folds or ridges on the inner surface of ciliary body, arranged in crcular pattern behind the iris

inside posterior chamber

each process has a core of connective tissue and capillaries covered by 2 layers of epithelium; pigmentated and no pigmented

produces aq humour

how is aqueous humour produced 

produced from blood in the capillaries of the ciliary processes and transported to anterior chamber via the ciliary epithelium

flow of aqueous humour 

aq is formed in ciliary processes, moves out around the crystalline lens and through pupil, and flows out of anterior chamber through trabecular meshwork into the schlemms canal and then to episcleral veins

what is trabecular meshwork

encircles the circumference of anterior chamber occupying most of the inner aspect of the internal scleral sulcus. cross section- has a triangular shape 

flattened perforated sheets 

open latticework with branches interlacing 

canal of schlemm

circular vessel and a venous channel

contains aq humor rather than blood

tight junctions of the inner wall restrict blood flow into the canal between the lateral walls of the cells

what is the unconventional outflow of aqueous

an an=venue by which aqueuous exits the anterior chamber

passes through spaces within the uveal meshwork

fluid then passes into the connective tissue spaces surrounding ciliary muscle bundles , moves into suprachoroidal space and absorbed into and through the sclera

where does remainder of aq follow: conventional outflow pathway 

moves through the meshwork and into the narrower pores of the corneascleral meshwork and through the juxtacanicular tissue and the endothelial lining into schlemms canal 

internal wall of schlemms canal

contains number of evaginatinos or blind pouches that extend into the juxtacanicular tissue toward the meshwork

these internal collector channels can be long and branching, and serve to increase surface area of canal

endothelial cells lining external wall of schelmms canal 

the endothelial cells lining wall are joined by zonula occludens and contain no vacuoles 

external collector channels re distributed around outer wall of schlemms canal and branch from it to empty into either deep scleral plexus or intrascelral plexus ov veins . which in turn drain into episcleral veins

what 3 mechanims contriute to production and secretion of aqueous humor

diffusion, ultrafilteration and active secretion

diffusion

passive

movement from high to low concentration

small molecules like h20, 02 and c02 can diffuse across membrane 

lipid soluble substances ie cell membrane 

ultrafilteration

passive

movement from high to low pressure

involves hydrostatic pressure

secretion

active

high energy bod (ATP) and diffusing it into ADP, and producing energy

energy used to secrete something

non depenent on the concentration gradient

what is aqueous humor 

a clear fluid in anterior and posterior chamber of eye 

produced by eptihelial cells of ciliary body 

provifed nutrition to cornea and lens 

removes excretory products from both structures 

conributes to maintenance of the intraocular pressure of the eye 

structure of cell membrane

lipids form most of surface area and about 425 i wieght. generally hydrophobic 

proteins account for 55% of weight, many functions like anchoring and transport of substances by channel or carrier activity 

carbohydrates account for 3% of weight - functions include lubrication and protection, anchoring and locomotion 

hydrophobic tails and hydrophillic heads - lipid bilayer

cholesterol moelcules in cell membrane

found in the central fatty acid portion decrease the membranes permeability to water soluble molecules

lysosomes in cell membrane

digestiive systems containing enzymes take up bacteria and break down into molecules that are reused or reabsorbed into the cytoplasm to be transported to cell membrane and out of the cell

channel proteins 

create water filled passages linking the intracellular and extracellular spaces 

facillitate ion movement across lipid bilayer and move ions 

carrier proteins in facillitated diffusion

carrier proteins bind to substrates that they carry across the membrane , molecule slike glucose and amino acids move through this way

osmosis 

aqueous humor is mostly water so most of water moves across ciliary eptihelium via osmosis 

goes from low to high concentration volume of water 

net diffusion of water 

ultrafilteration- pressure

high to low pressure

net effect is that ultrafilteration plays little part in production of aq humor

pressure in capillaries of ciliary body is offset by oncotic pressure in tissue of ciliary processes which result from protein leakage through fenestrated capillaries

secretion by active transport

done through sodium potassium exchange pump

sodium-potassium activated ATPase is an enzyme in the cell membrane

role is to break down ATP to ADP releasing phosphate which supplies energy for sodium potassium exchange

mechanism exchanges 3 intracellular Na ions in the ciliary epithelium for 2 extracellular K ions

the 3 positive charges leave making inside more negative

net movement of sodium ions to posterior chamber produces a conc gradient which causes water to flow into the chamber by osmosis

water drawn out of cell and into tight junction area that is then released.

what is iop 

intraocular pressure is the fluid pressure inside the eye 

prodcution of aqueous humor

drainage of the fluid through trabecular meshwork

supports refractive structures and intraocular contents

nutrients to avascular structures

IOP relies on what?

Relies on the balance between the secretion of aq humor from ciliary body and the outflow resistance in the trabecular meshwork

angle structures

what is the health range of IOP 

11-21mmHg

the eye requires a constant volume of aqueous to be present in the eye to give a constant pressure

production=outflow

IOP errors 

increased outflow= low IOP : retinal detachment/ odema risk 

normal outflow- rasied IOP= raised IOP : rare cause of glaucoma 

production> outflow- raised IOP : glaucoma

increased outflow of fluid = lower IOP 

means the aqueous humor is draining faster than normal through the eyes drinage pathways

eye is losinf fluid faster than its being produced, reducing the pressure inside the eye

decreases stress on the optic nerve

can cause blurred vison, corneal swelling and retinal problems

decrease in outflow

fluid inside the eye isnt draining properly, whilst aq is still being produced

fluid accumulates which raises IOP

puts stress on optic nerve which can lead to glaucoma

can be due to blocked trabecular meshwork

closure of the angle between cornea and iris

how is IOP measured

measured using tonometry

goldmann machine

or pulsair which is non contact tonometry

what is IOP affected by 

balance of secretion and drainage of aqueous fluid 

produced by ciliary body at 2-3 microlitres per minute 

drains through tabecular meshwokr or via uveoscleral route 

variations of IOP

iop can change every day

its highest in the morning and lowest at night

average ocular pressure barely changes throughout life

important systemic factors of IOP

systolic blood pressure

diabetes

BMI

ethnicity in factors affecting iop 

higher mean in poeple of african descent 

increased age increment 

also have thinner corneas 

lower mean in poeple of east african descent 

iop shown to decrease with age 

family history in factors affecting iop

higher iop with a family history of OHT or glaucoma

artefactual changes affecting iop

depends of pulse

standing lower than reclining; if lying down it increases

after immersing hand in cold water

very high iop 

acute closed angle glaucoma

pupil blocks drainage 

retinal or choroidal detachment 

leakage of ocular fluid after penerating injuries or surgery 

intraocular inflammation

what are iop measuremnts affected by

corneal thickness

curvature

hydration - too much liquid increases pressure; odema

biochemical behaviour

variations

dinural

disease

age

racial background

short term factors affecting iop measurement

breath holding- when doing pulsair can increase pressure

lid sqeezing increases pressure

opening eyes wide- increases iop

ocular pulse can increase or decrease value

accomodation - increases as lens taking up more curvature space

eye movement- increase when moving a lot

tight clothing around the neck +1-3mmHg

recent contact lens removal increases value

eye rubbing - increases when rub then decrease after

medium term effects of measuring iop 

diurnal variation of IOP 3-5 mmHg up to 10mmHg in glaucoma 

posture changes - lying down increases pressure 

repeated iop measurements- reduces pressure of iop -5mmHg 

recent alcohol consumption - decreases value

recent exercise - incrases during, decreases after 

recent consumption of fluids increase 

prescribed or recreational medication - increase or decrease 

long term factors affecting iop measurement

age- increases in caucasian and decrease in east asian

seasons +1-2mmHg in winter

smoking increases iop value

caffeine +2mmHg

diabetes, blood pressure and BMI: increase value of iop

drugs affecting iop

drugs that inhibit production act on the ciliary epithelia, either by interfereing with neural pathways or by inhibiting intracellular enzymes that maintain the ionic transport mechanisms in the formation of aq

beta blockers decrease aq production

certain prostaglandin may increase trabecular meshwork outlfow

aging changes in anterior chamber 

with age the anterior chamber angle width narrows and volume decreases

due to decrease in aq production , a decrease in denisty and size of vacuoles , an accumulation of extracellular matrix plaques in the juxtacanalicular tissue and the inner wall of schlemms canal