L4 uveal tract

Question 1

What is the Uvea?

Answer 1

• consists of:
  1. Iris
  2. Ciliary body
  3. Choroid
• is vascular and pigmented
• is a continuous structure with 2 openings
• > pupil anteriorly
• > optic nerve canal posteriorly

Question 2

What are the functions of the uveal tract?

Answer 2

1. Regulates the amount of light entering The Eye (by the iris)
2. Produces and secretes aqueous humour (by ciliary body)
3. Responsible for accomodation (ciliary body)
4. Provides nutrients to outer retina (choroid)

Question 3

What is the iris?

Answer 3

• The anterior most part of the uveal tract
• contains melanocytes that gives colour to the eye
• regulates the size of the pupil by the action of sphincter and dilator muscles
• 2 zones (pupillary and ciliary) seperated by the colarette

Question 4

what are the 3 layers of the iris?

Answer 4

1. anterior border layer
   - contains melanocytes which give the iris colour
2. stroma
   - contains the connective tissues, pigments, blood vessels and sphincter muscle (constricts the pupil)
3. pigment epithelium
   - double layered
   - both pigmented
   - dilator muscles

order from anterior to posterior:
anterior border layer, iris stroma, iris sphincter muscle, iris dilator muscle, iris pigment epithelium

Question 5

describe the anterior border layer

Answer 5

• anterior-most iris layer

- provides colour to the iris

Question 6

describe the iris stroma

Answer 6

contains connective tissue, blood vessels and pigment cells

Question 7

describe the sphincter muscle

Answer 7

• lies in the pupillary zone in the iris stroma
• encircles the pupil
• constricts the pupil
• parasympathetic innervation

Question 8

describe the dilator muscle

Answer 8

• lies in the ciliary zone in the anterior epithelial region
• radially arranged
• dilates the pupil
• sympathetic innervation

Question 9

describe the iris epithelium

Answer 9

• posterior-most iris layer
• double-layered
• both pigmented

Question 10

describe dilator vs sphincter briefly

Answer 10

• dilator muscle is weaker

- sphincter and dilator muscles work in opposite directions, they are antagonistic to each other

Question 11

what is the blood supply of the iris?

Answer 11

the major arterial circle (MAC) is formed from:

• two long ciliary arteries
• seven short anterior ciliary arteries

-> the MAC is located in the iris stroma towards the ciliary stroma

Question 12

what is the nerve supply of the iris?

Answer 12

1. trigeminal nerve (cranial nerve 5/v)

2. oculomotor nerve (cranial nerve 3/ lll) for pupillary actions

Question 13

what is the ciliary body?

Answer 13

has 2 regions:

• pars plicata (ciliary processes)
• pars plana

from anterior to posterior/outer to inner, the layers are: 
1. ciliary muscle 
2. stroma 
3 epithelium 
3a. outer pigmented epithelium 
3b. inner non-pigmented epithelium

Question 14

describe the 3 layers of the ciliary body

Answer 14

1. ciliary muscles (outermost layer)
   - is responsible for the changes of lens shape for accommodation
2. stroma
   - contains blood vessels, connective tissue, pigments
3. epithelium
   - double-layered (outer pigmented and inner non-pigmented epithelium)
   - the inner non-pigmented epithelium in the ciliary processes (pars plicata region) produces aqueous humour

Question 15

describe the pars plicata

Answer 15

• has 3 layers (muscles, stroma and epithelium)
• anterior region of the ciliary body
• contains 70 radially arranged folds known as ciliary processes
• is closer to the iris
• aqueous humour is only produced in the ciliary processes (pars plicata region)
• inner-non pigmented epithelium in the pars plicata region is the site of aqueous production

Question 16

describe the pars plana

Answer 16

• 3 layers (muscle, stroma and epithelium)
• posterior region of the ciliary body
• is the flatter region (extends from the posterior of the pars plicata to the ora serrata)
• located nearer to the choroid
• does NOT contain ciliary processes

Question 17

describe the ora serrata

Answer 17

it is the transition between the ciliary body and the choroid

Question 18

what is the blood supply of the ciliary body?

Answer 18

major arterial circle (MAC), it consists of:

• 2 long posterior ciliary arteries
• 7 short anterior ciliary arteries
• > it is located near the ciliary stroma (near the iris root)

Question 19

what is the nerve supply of the ciliary body?

Answer 19

• trigeminal nerve (cranial nerve 5/ v)

- oculomotor nerve for accommodation (cranial nerve 3/lll)

Question 20

describe the choroid

Answer 20

• it is the posterior-most uveal structure
• vascular and pigmented
• supplies nutrition to the outer retina

- has 4 layers 
(anterior to posterior) 
1. suprachoroid
- contains connective tissue, blood vessels and nerves 
- separates sclera and choroid 

2. stroma
   - contains blood vessels and pigments
3. choriocapillaries (smaller blood vessels)
   - supplies nutrition to the macula (outer retina)
4. Bruch’s membrane
   - aids in the passage of nutrients to the retina

Question 21

what is the choroid’s blood supply?

Answer 21

it is supplied by the posterior ciliary artery and anterior ciliary artery

Question 22

what is the choroid’s nerve supply?

Answer 22

trigeminal nerve ( cranial nerve 5/v)