L23 - Vascular Layer

Question 1

What are the three main structures of the uveal tract?

Answer 1

Choroid, ciliary body, iris.

Question 2

What is the iris?

Answer 2

A thin, pigmented, contractile circular structure that is the anterior extension of the uveal tract, forming the pupil.

Question 3

Where does the iris extend from and to?

Answer 3

From the iris root to the iris margin that forms the pupil.

Question 4

What is the central aperture of the iris called?

Answer 4

The pupil.

Question 5

What lies on the anterior lens surface and is surrounded by aqueous humour?

Answer 5

The iris.

Question 6

What is the function of the iris/pupil in terms of retinal illumination?

Answer 6

Controls retinal illumination and maintains constant retinal illumination in response to changes in lighting.

Question 7

How does the iris/pupil facilitate adaptation to light?

Answer 7

Provides immediate facilitation of light or dark adaptation with abrupt changes in lighting.

Question 8

How does the iris/pupil affect depth of focus?

Answer 8

Miosis during near effort produces a pinhole effect, reducing refractive error and increasing depth of focus.

Question 9

How does the iris/pupil reduce optical aberration?

Answer 9

Minimizes optical aberrations in the lens by limiting the light rays entering the eye.

Question 10

When do glare and aberrations commonly occur?

Answer 10

With a large pupil in darkness or after mydriasis.

Question 11

What are the two main zones of the iris topography?

Answer 11

Pupillary zone and ciliary zone.

Question 12

What is the collarette of the iris?

Answer 12

A feature separating the pupillary zone from the ciliary zone.

Question 13

What is the pupillary ruff?

Answer 13

The anterior termination of the iris pigmented epithelium at the margin of the pupil.

Question 14

What are Fuchs crypts?

Answer 14

Deep radial slits or ridges in the pupillary zone due to the radial arrangement of vessels and connective tissue.

Question 15

How is the ciliary zone of the iris divided?

Answer 15

Into inner smooth area, middle furrowed area (contraction), and marginal cribriform area (visible only in gonioscopy).

Question 16

What are the four distinct layers of the iris microstructure?

Answer 16

Anterior border layer, stroma, anterior epithelium, posterior epithelium.

Question 17

What is the anterior border layer of the iris composed of?

Answer 17

Thin, discontinuous condensed anterior stroma, collagen fibrils, fibroblasts, and melanocytes.

Question 18

What determines iris color?

Answer 18

Character of melanin and amount of pigmentation, not the number of melanocytes.

Question 19

What is an iris naevus?

Answer 19

Benign proliferation of uveal melanocytic cells.

Question 20

What can malignant transformation of an iris naevus lead to?

Answer 20

Iris melanoma.

Question 21

What is the stroma of the iris composed of?

Answer 21

Loose, pigmented, highly vascular connective tissue with pigmented (melanocytes, clump cells) and non-pigmented (fibroblast, lymphocyte, macrophage, mast cells) cells, muscles, collagen fibrils, and ground substance.

Question 22

What are the two types of iris muscles?

Answer 22

Sphincter muscle (pupillary zone) and dilator muscle (ciliary zone).

Question 23

What is the function and innervation of the sphincter pupillae?

Answer 23

Contracts to decrease pupil size (miosis); supplied by parasympathetic nerve.

Question 24

What is the function and innervation of the dilator pupillae?

Answer 24

Contracts to increase pupil size (mydriasis); supplied by sympathetic nerve.

Question 25

What is dual innervation of the iris?

Answer 25

Both parasympathetic and sympathetic systems control pupil size.

Question 26

What is the direct light reflex?

Answer 26

Shining light in one eye causes pupillary constriction in the same eye.

Question 27

What is the consensual light reflex?

Answer 27

Shining light in one eye causes pupillary constriction in the other eye.

Question 28

What is the major arterial circle of the iris?

Answer 28

An arterial ring around the external circumference of the iris formed by the long posterior ciliary arteries.

Question 29

What is the minor arterial circle of the iris?

Answer 29

A circle proximal to the pupil.

Question 30

What are the main parts of the ciliary body?

Answer 30

Pars plicata (anterior vascular part) and pars plana (posterior flat avascular part).

Question 31

What are the main functions of the ciliary body?

Answer 31

Aqueous humor production, lens accommodation, facilitates aqueous drainage.

Question 32

What are ciliary processes?

Answer 32

70-80 finger-like projections with vascular core radiating from pars plicata, increasing surface area for secretion and serving as attachment for lens zonulas.

Question 33

What are the main layers of the ciliary body microstructure?

Answer 33

Ciliary epithelium (non-pigmented and pigmented), stroma (vascular layer), muscular layer (ciliary muscle), and supraciliaris.

Question 34

What is the supraciliaris?

Answer 34

Outermost layer of loose connective tissue adjacent to the sclera, allowing the ciliary body to slide against the sclera.

Question 35

What are the two layers of ciliary epithelium?

Answer 35

Pigmented epithelium (outer, next to stroma) and non-pigmented epithelium (inner, faces posterior chamber).

Question 36

What is the function of the non-pigmented ciliary epithelium?

Answer 36

Produces aqueous humor and glycoprotein of vitreous; forms part of the blood-aqueous barrier.

Question 37

What is the ciliary stroma composed of?

Answer 37

Loose bundles of collagen, ciliary vessels, capillaries in ciliary processes, and ciliary veins.

Question 38

What are the three groups of ciliary muscle fibers?

Answer 38

Longitudinal (meridional), radial (oblique), and circular (sphincteric).

Question 39

What is the function of the ciliary muscle?

Answer 39

Accommodation (lens shape change) and facilitation of aqueous filtration.

Question 40

What is the choroid?

Answer 40

A highly pigmented, vascular loose connective tissue layer between the sclera and retina, rich in melanocytes.

Question 41

What are the functions of the choroid?

Answer 41

Nourishment for adjacent retina, blocks light entering through sclera, retains light entering through pupil.

Question 42

What are the three layers of the choroid?

Answer 42

Inner Bruch’s membrane, middle stroma/vascular layer, suprachoroid.

Question 43

What is Bruch’s membrane?

Answer 43

A thin connective tissue membrane between the choriocapillaris (choroid) and RPE (retina), preventing choroid vessels from penetrating the retina but allowing nutrients and proteins.

Question 44

What are the five microscopic layers of Bruch’s membrane?

Answer 44

Basement membrane of RPE, inner collagenous layer, elastic tissue layer, outer collagenous layer, basement membrane of choriocapillaris.

Question 45

What percentage of ocular blood flow does the choroidal circulation account for?

Answer 45

85%.

Question 46

What supplies the choroid with blood?

Answer 46

Branches of the ophthalmic artery via anterior and posterior arterial systems.