CILIARY BODY

Question 1

Which of the following locations best corresponds with the posterior termination of the ciliary body?

Answer 1

Ora serrata

Question 2

The ora bays of the pars plana are directly adjacent to which of the following structures?

Answer 2

Dentate processes of the retina

Question 3

The anterior myoepithelium of the iris is directly continuous with which of the following tissue layers?

Answer 3

Pigmented epithelium of the ciliary body

IRIS CB RETINA
ant myo epi-> pigmented epi->RPE
post pigment epi->nonpig epi-> sensory

The bases of the pigmented epithelial cells face the ciliary body stroma. *** The basement membrane of the pigmented epithelium of the ciliary body is directly continuous with the basement membrane of the RPE cells (a layer in Bruch’s membrane/layer of the choroid)

Question 4

The major arterial circle of the iris supplies which 2 of the following structures?

Answer 4

MACOTI
location: CB stroma
supplies: (1) iris (2) CB processes
blood source: LPCA
*involved in aqueous production

IMCOTCB
location: CB muscle
supplies: CB muscle
blood source: anterior ciliaries

Question 5

Which of the following ciliary body vessels are involved in aqueous humor production?

Answer 5

Marginal capillaries

Question 6

Which of the following ciliary body muscle fibers extend the furthest posteriorly?

Answer 6

Longitudinal

Question 7

The radial ciliary body muscle fibers attach anteriorly to which of the following structures?

Answer 7

Scleral spur

Question 8

Which 2 of the following statements best describes accommodation?

Answer 8

The longitudinal ciliary body muscle fibers shorten

The circular ciliary body muscle fibers shorten

Question 9

When considering sympathetic innervation of the ciliary body, the central neuron cell bodies are located in which of the following structures?

Answer 9

Hypothalamus

Question 10

SENSORY INNERVATION OF CILIARY BODY

Answer 10

Pain due to inflammation of the ciliary body is carried to the nasociliary nerve (branch of ophthalmic division of CNV) via the following two major nerves:
SPCN and LPCN
the cell bodies of these sensory neurons lie in the trigeminal ganglion

Question 11

Distinguish pars plicata and pars plana in terms of width and how much CB muscle each contains.

Answer 11

PARS PLICATA
Width: ~ 2.0 mm
Amount of CB muscle: major portion of the ciliary body muscle (smooth muscle) lies within pars plicata
* iris root inserts into the anterior surface of pars plicata of the CB

PARS PLANA
Width: 4.0 - 4.9 mm
Amount of CB muscle: thinner and less vascular than pars plicata
* smooth, flat posterior part of the ciliary body; extends from pars plicata to ora serrata

Question 12

Where is the CB wider: nasally or temporally?

Answer 12

It is slightly wider temporally (~ 6.9 mm wide) than nasally

Question 13

What is an ora bay? What is a dentate process?

Answer 13

The ora serrata is the anterior termination of the retina

• It is named this because the retina is serrated (scalloped) and the retina forms long, thin dentate processes that interdigitate with ciliary body’s pars plana
• The rounded areas between the dentate processes are the ora bays of pars plana .

Question 14

What is the unpigmented epithelium of the CB directly continuous with:
anteriorly?
posteriorly? (you could do the same for pigmented epithelium of CB and the same for basement membrane of pigmented and unpigmented CB epithelium posteriorly).

Answer 14

Anteriorly, the two epithelial layers of the CB are directly continuous with the two epithelial layers on the surface of the iris:
> non-pigmented CB epithelium is directly continuous with the posterior pigmented epithelium of the iris
> pigmented CB epithelium is directly continuous with the anterior myoepithelium of the iris
*The CB stroma blends with the iris stroma

Posteriorly, the two epithelial layers of the ciliary body are directly continuous with the retina
> The non-pigmented epithelium (NPE) of the ciliary body is a direct continuation of the 9 inner (sensory) layers of the retina (and internal limiting membrane)
> The pigmented epithelium (PE) of the ciliary body is a direct continuation of the retinal pigmented epithelium (RPE)
– RPE = outermost layer of retina (simple cuboidal epithelium)

*Zonular fibers originate from the basement membrane of the unpigmented epithelium of pars plana near the ora serrata

Question 15

Where are the following cell junctions located in the CB epithelium and what cells do they interconnect?

• zonula occludens
• gap junctions
• desmosomes

Answer 15

ZONULA OCCLUDENS
Zonula occludens (ZO) occlude the lateral surfaces of non-pigmented epithelial cells (NPE) near their apices and are impermeable to the diffusion of macromolecules through the intercellular (extracellular) space between the non-pigmented epithelial cells
* allows non-pigmented epithelial cells (NPE) to selectively transport ions & molecules into the posterior chamber
** part of a junctional complex that includes 3 junctions: zonula occludens, zonula adherens and a desmosomes

GAP JUNCTIONS

• between pigmented (PE) and non-pigmented (NPE) CB epithelium
• couple the epithelial cells of the CB to coordinate the secretory activity of the ciliary body epithelium and lie:
  1. between the apices of the pigmented (PE) & non-pigmented epithelial cells (NPE), 2. along the lateral walls of adjacent pigmented epithelial cells (PE), 3. along lateral walls of adjacent non-pigmented epithelial cells (NPE)

DESMOSOMES

• commonly found between the lateral surfaces of the non-pigmented epithelial cells (NPE)
• less frequently found between the lateral surfaces of the pigmented epithelial cells and at the interface between the pigmented and non- pigmented epithelial cells
• Intercellular adhering junctions (the most plentiful being desmosomes) join adjacent non- pigmented epithelial cells at intervals along the entire length of the cleft and thus ensure the cleft volume does not expand too much

Question 16

What parts of the eye are supplied by the major arterial circle of the iris? Be specific.
What is its location? Be specific.
Which blood vessel predominantly supplies the major arterial circle?

Answer 16

The major arterial circle of the iris (MAC) is located in the ciliary body stroma anterior to the circular fibers of CB muscle, near the iris root

• supplies blood to the iris and ciliary body processes
• branches in the ciliary body processes are involved in aqueous humor production
• LPCA contribute predominantly to the major arterial circle of the iris (MAC)

The intramuscular circle of the ciliary body is located in pars plicata, in the middle of the CB muscle
- it supplies blood to the ciliary body muscle
- the anterior ciliary arteries contribute predominantly to the intramuscular circle of the
ciliary body

Question 17

What vessel do the anterior and posterior arterioles originate from? Which capillaries do the anterior arterioles lead into? Compare the capillaries that receive blood from the anterior and posterior arterioles in terms of location, histology, function and what the capillaries drain into

Answer 17

Each ciliary body process is supplied by branches of the major arterial circle of the iris called the anterior arterioles and posterior arterioles

> Anterior arterioles lead into large dilated “marginal capillaries”, which then drain into choroidal veins

• large, highly permeable marginal capillaries lie in the ciliary body stroma near the epithelium of the ciliary processes
• target = CB epithelium (contribute to aqueous production)

> Posterior arterioles lead into capillaries of smaller caliber, which then drain into the choroidal veins
– These smaller capillaries are located at the base of the ciliary processes and they are NOT fenestrated and do not leak plasma proteins under normal conditions (so they do NOT contribute to aqueous production)

Question 18

Where is the blood aqueous barrier located in the CB and iris, and what forms it?

Answer 18

Blood–aqueous barrier: the ciliary epithelium and capillaries of the iris.

Blood-aqueous barrier is formed by nonpigmented ciliary epithelial cells of the ciliary body and endothelial cells of blood vessels in the iris.

Question 19

Where do ions for aqueous humor production come from? And how do they enter the pigmented epithelium? Be specific.

• How do the ions for aqueous humor production enter the non-pigmented epithelial cells? Be specific.
• Where do the bicarbonate ions come from that end up in the aqueous humor? And how are they ions formed?
• Where are the ions deposited first as they exit the NPE cells? Where does the water component come from and how/why?
• What is the role of the desmosomes interconnecting adjacent NPE cells in the aqueous humor production?

Answer 19

> Where do ions for aqueous humor production come from?
“From the ciliary body stroma”

> How do they enter the pigmented epithelium?
“Na+/H+ and Cl-/HCO3- antiports (that exchange Na+ for H+ and Cl- for HCO3-) and the Na+/ K+/ 2 CI- symport located at the base of the cells”

> How do the ions for aqueous humor production enter the non-pigmented epithelial cells?
“Then the pigmented CB epithelial cells convey the ions to the non-pigmented CB epithelial cells via the gap junctions interconnecting the two epithelial layers and water flows into the non-pigmented cells by diffusion.”

> Where do the bicarbonate ions come from that end up in the aqueous humor? And how are they ions formed?
In addition, bicarbonate ions (HC03-) will be actively transported into the intercellular clefts via Cl-/HCO3- antiports and Cl- will be released into the clefts via Cl- channels.

> Where are the ions deposited first as they exit the NPE cells?
“The non-pigmented CB epithelial cells actively transport Na+ from their cytoplasm into the intercellular clefts between the non-pigmented CB epithelial (NPE) cells via a Na+/K+ exchange pump that is driven by the enzyme Na+/K+ ATPase”

> Where does the water component come from and how/why?
“Water flows into the pigmented epithelial cells by diffusion (or water channels?) from the CB stroma…The ionic concentration in the intercellular cleft produces an osmotic gradient that causes diffusion of water out of the NPE cells and into the cleft.”

> What is the role of the desmosomes interconnecting adjacent NPE cells in the aqueous humor production?
“Intercellular adhering junctions (the most plentiful being desmosomes) join adjacent non- pigmented epithelial cells at intervals along the entire length of the cleft and thus ensure the cleft volume does not expand too much”

Question 20

What is the mechanism by which CAIs decrease IOP in the treatment of glaucoma?

Answer 20

The mechanism of action of the CAI’s is the inhibition of the enzyme carbonic anhydrase, so that HC03- + H+are not formed in both the pigmented & non-pigmented CB epithelial cells
– the entry of bicarbonate ions into the posterior chamber is greatly reduced, decreasing the amount of aqueous produced.

Question 21

What is the origin of the zonules?

Answer 21

Zonular fibers originate from the basement membrane of the unpigmented epithelium of pars plana near the ora serrata.
- inner surface of pars plana is covered by zonules
- some zonules originate posterior to the ora serrata,
inserting onto the surface of the peripheral retina.

When they reach the posterior edge of pars plicata the zonules run in the valleys between the adjacent ciliary processes, leaving only the tips of each process exposed
to the posterior chamber.

Question 22

What do the sympathetic fibers innervate in the CB?

Answer 22

Only about 1-2% of the neurons terminating on the ciliary body muscle are sympathetic fibers & they are going to blood vessels of the ciliary body

Question 23

Most of the neurons whose cell bodies lie in the ciliary ganglion innervate

Answer 23

97% of the neurons whose cell bodies lie in the ciliary ganglion innervate the ciliary body

3% of the neurons whose cell bodies lie in the ciliary ganglion innervate the iris sphincter

Question 24

Which CB muscle fibers attach to the choroid (and inner surface of the sclera)?

Answer 24

Longitudinal

Contraction of longitudinal fibers pulls the choroid forward & pushes the ciliary body in towards the lens. As the fibers shorten during contraction, the cross-sectional diameter of the CB is increased so the inner portion of the CB moves closer to the lens

Question 25

What do the longitudinal CB muscle fibers attach to anteriorly?

Answer 25

Anteriorly they attach by tendons to the posterior surface of the scleral spur & to the trabecular meshwork

Question 26

When the CB muscle contracts what happens to the:

• zonules
• anterior surface of the lens
• posterior surface of the lens

Answer 26

When the ciliary body muscle contracts, the ciliary processes move forward & inward, to be closer to the lens. This movement relieves tension on the zonules, allowing the elastic recoil of the capsule to reshape the lens so it can assume it’s more natural convex shape
(i.e. the force is redirected inward at the equator and outward across the anterior & posterior surface of the lens so the lens decreases in circumference and increases in thickness)

• curvature of the posterior lens surface only increases slightly
• curvature of the anterior surface increases more than the posterior surface though the final curvature of the anterior surface does NOT become greater than that of the posterior surface.

Question 27

Where is a junctional complex located in the ciliary body epithelium? What junctions are in the junctional complex?

Answer 27

ZO junctions form a tight barrier (blood- aqueous barrier) that allows non-pigmented epithelial cells (NPE) to selectively transport ions & molecules into the posterior chamber to form the aqueous humor. The ZO junctions of the NPE are part of a junctional complex that includes 3 junctions: zonula occludens, zonula adherens and a desmosome.

Question 28

Sensory innervation to the ciliary body is carried in which nerves?
Cell bodies of these sensory neurons are located here:

Answer 28

Pain due to inflammation of the ciliary body is carried to the nasociliary nerve (branch of ophthalmic division of CNV) via the following two major nerves: SPCN and LPCN. The cell bodies of these sensory neurons lie in the trigeminal ganglion.

Question 29

(CO) 1. Describe the specific position/location of the ciliary body inside the eyeball and on the
outside of the eyeball. Know approximate anterior - posterior extents (i.e. width) and
differences nasally vs. temporally

Answer 29

see previous question

Width = (around 6mm wide entire) the ciliary body extends from a point 1.5 mm posterior to the comeal limbus to a point ~ 7.0 -9.2 mm posterior to the limbus (i.e. temporally it ends ~ 8.4 mm posterior to the limbus while nasally it ends ~ 7.0 mm posterior to the limbus)

Question 30

(CO) 2. Name & describe the two components of the ciliary body: pars plana and pars plicata. Know
which part is wider (anterior -posterior), anatomical relationships to zonules, iris root and retina where applicable and the unique characteristics of the ciliary body”s two parts.
- Know the specific origin of the zonules
- Define dentate process and ora bays

Answer 30

PARS PLANA

• around 4mm wide, thinner and less vascular
• close to retina, terminating at ora serrata
• contains dentate processes/ora bays
• zonular fibers originate from unpigmented epithelium of pars plana (basement epithelium) near ora serrata

PARS PLICATA

• around 2mm wide; iris root inserts into anterior surface
• inner surface has 70-80 ridges called “ciliary processes” (valleys of Kuhnt); ciliary processes close to lens equator

Question 31

(CO) 3. Name the three main components of the ciliary body.

Answer 31

1. Ciliary Body Epithelium (two epithelial layers; the apex of the cells face each other, like the epithelium of the iris)
2. Ciliary Body Stroma (loose CT)
3. Ciliary Body Muscle (smooth muscle)

Question 32

(CO) 4. Name & describe the two layers of the ciliary body epithelium. Be sure to include:

• Epithelial type, which are pigmented and which are not, position of apex and base and anatomical relationships, what the epithelial layers and their basement membranes are continuous with anteriorly and posteriorly
• types of junctions and the location of the zonula occludens junctions; location of the blood-aqueous barrier and what forms it.

Answer 32

> Inner, non-pigmented epithelial cell layer (NPE)
– cells are simple columnar epithelial cells located adjacent to the lens and vitreous
Outer, pigmented epithelial cell layer (PE)
– cells are simple cuboidal epithelial cells located adjacent to the ciliary body stroma

Question 33

(CO) 5. Discuss aqueous humor production in detail. Be sure to include:
- which cells produce the aqueous humor
- how the ions and water get from the marginal capillaries to the posterior chamber
(include cells the ions pass through, junctions, pumps & symports used and their locations, etc.)
- which cells contain carbonic anhydrase and what it is used for
- where the non-pigmented epithelial cells transport the ions and water
- mechanism of action of CAl glaucoma medications in reducing intraocular pressure

Answer 33

> Aqueous humor produced by ciliary body epithelium (epithelial cells at the tips of the CB processes) into the posterior chamber
Ions are actively transported across the CB epithelium, creating an osmotic gradient leading to water flow (blood vessels in CB stroma-> stroma-> epithelium-> posterior chamber
See page 17 for the process
carbonic anhydrase in the pigmented CB epithelial (PE) cells increases the turnover of the two antiports both by converting CO2 (that diffused into the cells) & H2O to H+ and HCO3- and by directly stimulating both exchangers to create more aqueous
Water flows into the pigmented epithelial cells by diffusion (or water channels?) from
the CB stroma

Question 34

(CO) 6. Name and describe the vasculature of the ciliary body, the processes and the ciliary body muscle. Be sure to include:
Locations of major blood vessels like major arterial circle of iris and intramuscular
circle, their origin and their branches
– what specific part of the eye they supply
– what blood vessel is the main contributor to forming the major arterial circle of iris
and the intramuscular circle
– origin of the anterior & posterior arterioles
– characteristics of the marginal capillaries

Answer 34

see previous question

Question 35

(CO) 7. Differences between the anterior arterioles and posterior arterioles in terms of location, types and size of capillaries they lead into, how much they contribute to aqueous humor production

Answer 35

see previous question

*only anterior contributes to aqueous production

Question 36

(CO) 8. Describe the types of capillaries found in the ciliary body stroma, ciliary body muscle and iris stroma (i.e. which are continuous capillaries, which are fenestrated with diaphragms, etc.)

Answer 36

Ciliary body stroma
Much of the open space in the stroma is probably filled with fluid leaking from the capillaries.

Ciliary body muscle
The intramuscular circle of the CB supplies blood to the ciliary body muscle. The capillaries in the CB muscle have a smaller diameter, thicker endothelium &
no fenestrations

“Remember that the major arterial circle of the iris supplies both the CB and iris with different capillary types
- it provides fenestrated capillaries with diaphragms to the ciliary processes – Leaky for aqueous production
- it provides continuous capillaries with zonula occludens to the iris stroma (need the blood aqueous barrier (created by the ZO junctions) to prevent
proteins in the iris capillaries from getting into the aqueous humor in the anterior chamber)”

Question 37

(CO) 10. Describe the innervation of the ciliary body muscle. Be sure to include:
- Location of cell bodies of preganglionic and postganglionic parasympathetic fibers
- Name of postganglionic parasympathetic neuron axons
- How CB muscle innervation compares to sphincter pupillae muscle innervation in terms
of number of fibers
- What the sympathetic fibers innervate in the CB
- What % of fibers to the CB muscle are sympathetic vs. parasympathetic
- Names of nerves providing sensory innervation to the ciliary body and where their cell bodies are located.

Answer 37

PARASYMPATHETIC INNERVATION
Cell bodies of preganglionic parasympathetic fibers are in the Edinger- Westphal nucleus
> The cell bodies lie in midbrain dorsal to the oculomotor nucleus (located at
superior colliculus level)
> their axons travel with CN III and then with the inferior division of CN III and motor root of the ciliary ganglion
> they synapse in the ciliary ganglion

Cell bodies of postganglionic parasympathetic fibers lie in the ciliary ganglion
> their axons form the short posterior ciliary nerves (SPCN)
> their axons pierce the back of the eyeball, pass through the suprachoroidal & supraciliary space to reach the CB muscle and sphincter pupillae muscle
> these neurons directly innervate the ciliary body muscle and sphincter muscle of the pupil
(97% ciliary body, 3% iris sphincter)

Central neuron cell bodies are located in the hypothalamus.
> their axons travel through the brainstem and terminate on cell bodies of preganglionic
neurons in the lateral horn gray C8, Tl, T2 levels of spinal cord (ciliospinal center of
Budge)

Preganglionic neuron cell bodies located in lateral horn gray C8, T1, T2 levels of spinal cord (ciliospinal center of Budge)
> their axons cross apex of lung and terminate in the superior cervical sympathetic
chain ganglion

Postganglionic neuron cell bodies lie in the superior cervical sympathetic ganglion
> Axons are distributed to the iris and ciliary body via the long posterior ciliary nerves (LPCN)
> Only about 1-2% of the neurons terminating on the ciliary body muscle are sympathetic fibers & they are going to blood vessels of the ciliary body

Question 38

(CO) 11. Describe what happens during accommodation to:

• Lens, including thickness change and what part of the lens becomes more convex
• Ciliary body muscle, in general
• Zonules

Answer 38

see previous question

Question 39

(CO) 12. Give a good anatomical reason why:

• IOP may be reduced if someone has uveitis
• protein is in the aqueous humor if someone has uveitiis and what the presence of protein in the aqueous humor is referred to as clinically

Answer 39

Disruption of the zonula occludens junctions at the apicolateral borders of the NPE cells has been shown to occur in experimental anterior uveitis and it leads to increased amounts of proteins in the aqueous humor.

The proteins (“flare”) would have leaked into the ciliary body stroma from the ”leaky” marginal capillaries, diffused between the adjacent pigmented CB epithelial cells and then could freely diffuse into the intercellular cleft between adjacent non-pigmented cells and finally reach the aqueous humor in the posterior chamber!

Based on clinical research, when ciliary body inflammation occurs, as in anterior uveitis (i.e. inflammation of both iris & ciliary body), gap junctions “disappear” in the ciliary body epithelium. This results in decreased secretion of aqueous humor and therefore leads to the decreased IOP that usually accompanies anterior uveitis.