ICO Exam

Question 1

Innervation of the conjunctiva

Answer 1

Ophthalmic division of CN V

Question 2

Blood supply of the conjunctiva + where is the vascular watershed between the anterior and posterior territories

Answer 2

• Anterior ciliary arteries supply blood to the bulbar conjunctiva.
• The tarsal conjunctiva is supplied by branches of the marginal arcades of the lids.
• The proximal arcade, running along the upper border of the lid, sends branches proximally to supply the fornical and then the bulbar conjunctiva as the posterior conjunctival arteries.
• The Iimbal blood supply derives from the ciliary arteries through the anterior conjunctival arteries.

vascular watershed between the anterior and posterior territories lies approximately 3 or 4 mOl from the limbus

Question 3

Precorneal tear film layers + expression

Answer 3

• superficial oily layer produced predominantly by the meibomian glands
• middle aqueous layer produced by the main and accessory lacrimal glands
• deep mucin layer derived from the conjunctival goblet cells.

The surface cells of the cornea and conjunctiva also express a mucinous glycocalyx.

Question 4

Corneal epithelium basal cells width and density

Answer 4

12 µm, 6000 cells/mm2

Question 5

Wing cells cornea

Answer 5

Overlying the basal cell layer in the corneal epithelium, 2 or 3 layers, polygonal

Microplicae and microvilli make the apical surfaces of the wing cells highly irregular; however, the
precorneal tear film renders the surfaces optically smooth

Question 6

Superficial corneal epithelial cells thickness

Answer 6

30 µm

Question 7

What nonepothelial cells can appear within the corneal epithelium?

Answer 7

• Wandering histiocytes
• macrophages
• lymphocytes
• pigmented melanocytes
  are usually components of the peripheral cornea.
• Antigen-presenting Langerhans cells are found peripherally and move centrally with age or in response to keratitis.

Question 8

Bowman layer thickness

Answer 8

8-12 µm

Question 9

The stroma’s collagen types

Answer 9

I, III, V, VI

Question 10

What type of collagen forms the anchoring fibril ofthe epithelium?

Answer 10

VII

Question 11

How many keratocytes does the cornea have? %?

Answer 11

~ 2.4 million, ~ 5% of the stromal volume

Question 12

Keratocyte density in the cornea

Answer 12

anteriorly 1058 cells/mm2

posteriorly 771 cells/mm2

Question 13

Macroperiodicy of the fibrils in the corneal stroma

Answer 13

640 Å

Question 14

Collagen fibril orientation in the cornea

Answer 14

• obliquely oriented lamellae in the anterior third of the stroma (with some interlacing)
• parallel lamellae in the posterior two-thirds

The corneal collagen fibrils extend across the entire diameter of the cornea, finally wind­ing circumferentially around the limbus.

Question 15

What is the corneal stroma composed of?

Answer 15

• collagen-producing keratocytes
• ground substance
• col­lagen lamellae

Question 16

Where are the goblet cells in the conjuctiva?

Answer 16

The goblet cells (unicellular mucous glands) are concentrated in the inferior and medial portion of the conjunctiva, especially in the region of the caruncle and plica semilunaris. They are sparsely distributed throughout the remainder of the conjunctiva and are absent in the limbal region.

Question 17

Ground substance of the cornea?

Answer 17

• consists of proteoglycans that run along and between the collagen fibrils.
• Their glycosaminoglycan components (eg, keratan sulfate) are highly charged and account for the swelling property of the stroma.

Question 18

Where are the keratocytes in the cornea?

Answer 18

In the stroma, they lie between the corneal lamellae

Question 19

Corneal keratocytes ?

Answer 19

• synthesize both collagen and proteoglycans.
• highly active cells rich in mitochondria, rough endoplasmic reticula, and Golgi apparatuse
• have attachment structures, communicate by gap junctions, and have unusual fenestrations in their plasma membranes
• Their flat profile and even distribution in the coronal plane ensure a minimum disturbance of light transmission

Question 20

How many types of corneal keratocytes are there?

Answer 20

Studies with vital dyes suggest that there may be at least 3 different types

Question 21

Descemet membrane thickness

Answer 21

• at birth 3-4 µm
• in adulthood 10-12 µm

Thickness increases with age

Question 22

What is the Descemet membrane composed of?

Answer 22

• anterior banded zone that develops in utero
• and a posterior nonbanded zone that is laid down by the corneal endothelium throughout life

( These zones provide a historical record of the synthetic function of the endothelium. )

Question 23

What type of collagen is in the Descemet membrane?

Answer 23

It is rich in type IV collagen

like other basal laminae

Question 24

What are Hassall-Henle warts?

Answer 24

• Peripheral excrescences of the Descemet membrane

- they are common, especially among elderly people

Question 25

How are the central excrescences of the cornea called?

Answer 25

cornea guttae appear with increasing age?

Question 26

What is the corneal endothelium composed of?

Answer 26

a single layer of mostly hexagonal cells derived from the neural crest

Question 27

Corneal endothelium developmental origin?

Answer 27

neuroectodermal

Question 28

Number and density of corneal endothelial cells?

Answer 28

- ~ 500,000 cells | - ~ 3000/mm2

Question 29

How can the size, shape, and morphology of the endothelial cells be observed?

Answer 29

by specular microscopy at the slit lamp

Question 30

Orientation of the corneal endothelial cells

Answer 30

The apical surfaces of these cells face the anterior chamber; their basal surfaces abut the Descemet membrane

Question 31

Corneal endothelial cells - biology

Answer 31

- Typically, young endothelial cells have large nuclei and abundant mitochondria. - The active transport of ions by these cells leads to the transfer of water from the corneal stroma and the maintenance of stromal deturgescence and transparency - Mitosis of the endothelium is rare in humans, and the overall number of endothelial cells decreases with age

Question 32

How do the adjacent corneal endothelial cells interdigitate?

Answer 32

- in a complex way and form a variety of adherent junctions, but desmosomes are never observed between normal cells - In cross section, pinocytotic vesicles and a terminal web (a meshwork of fine fibrils that increases the density of the cytoplasm) can be observed toward the apical surface of the cells. - Junctional complexes are present at the overlapping apicolateral boundaries of contiguous cells. - They form a significant but lesser barrier to ion and water flow than do the tight junctions of the epithelium.

Question 33

What does corneal endothelial dysfunction and loss cause?

Answer 33

It may cause endothelial decompensation, stromal edema, and vision failure In humans, endothelial mitosis is limited, and destruction of cells causes cell density to decrease and residual cells to spread and enlarge.

Question 34

Causes of corneal endothelial dysfunction and loss

Answer 34

- surgical injury, - inflammation, - inherited disease (eg, Fuchs endothelial dystrophy

Question 35

How are the superficial corneal epithelial cells attached to eachother?

Answer 35

occlusion of the zonular fibers (sometimes referred to as zonules). These zonular fibers confer the properties of a semipermeable membrane to the epithelium

Question 36

How are the deeper corneal epithelial cells attached to eachother?

Answer 36

desmosomes

Question 37

How do the corneal keratocytes communicate?

Answer 37

by gap juctions

Question 38

How much of the globe does the sclera cover?

Answer 38

posterior 4/5

Question 39

Where do the tendons of the rectus muscles insert?

Answer 39

superficial scleral collagen

Question 40

Sclera thickness

Answer 40

- thinnest (0.3 mm) just behind the insertions of the rectus muscles - thickest (1.0 mm) at the posterior pole around the optic nerve head. - 0.4-0.5 mm thick at the equator - 0.6 mm thick anterior to the muscle insertions

Question 41

Where can scleral rupture occur following a blunt trauma?

Answer 41

- in a circumferential arc parallel to the corneal limbus opposite the site of impact - at the insertion of the rectus muscles - at the equator of the globe The most common site is the superonasal quadrant near the limbus

Question 42

Scleral vessels

Answer 42

the sclera is essentially avascular except for the superficial vessels of the episclera and the intrascleral vascular plexus located just posterior to the limbus.

Question 43

What are emissaria (sclera)?

Answer 43

Numerous channels that penetrate the sclera, allowing for the passage of arteries, veins, and nerves. Extraocular extension of malignant melanoma of the choroid often occurs by way of the emissaria.

Question 44

What are Axenfeld loops?

Answer 44

Branches of the ciliary nerves that supply the cornea sometimes leave the sclera to form loops posterior to the nasal and temporal limbus. They are sometimes pigmented and, consequently, have been mistaken for uveal tissue or malignant melanoma. They are typically found a constant distance from the corneoscleral junction, usually within 3-4 (?) mm of the limbus. ``` DD: Nevi Malignant Melanoma Cysts Scleral Foreign Bodies ```

Question 45

What does the episclera consist of?

Answer 45

A dense vascular connective tissue that merges deeply with the superficial sclera and superficially with the Tenon capsule and the conjunctiva.

Question 46

What does the scleral stroma consist of?

Answer 46

- bundles of collagen - fibroblasts - a moderate amount of ground substance

Question 47

Diameter of the scleral collagen fibers

Answer 47

- outer scleral collagen fibers 1600 Å | - inner collagen fibers 1000 Å

Question 48

What do the bundles of scleral collagen fibers contain?

Answer 48

- electron-dense bodies - fibroblasts - melanocytes

Question 49

Why is the sclera not transparent like the cornea?

Answer 49

- greater variation in fibril separation and diameter - the greater degree of fibril interweaving in the sclera In addition, the lack of vascular elements, such as the scleral emissaria, contributes to corneal clarity.

Question 50

Collagen fibrils of the sclera - orientation, buildup

Answer 50

- vary in size and shape and taper at their ends, indicating that they are not continuous fibers as in the cornea - The inner layer of the sclera (lamina fusca) blends imperceptibly with the suprachoroidal and supraciliary lamellae of the uveal tract. The collagen fibers in this portion of the sclera branch and intermingle with the outer ciliary body and choroid.

Question 51

Limbal structures

Answer 51

l. conjunctiva and limbal palisades 2. Tenon capsule 3. episclera 4. corneoscleral stroma 5. aqueous outflow apparatus

Question 52

What is the Schwalbe line?

Answer 52

termination of the Descemet membrane

Question 53

Zones of the surgical limbus

Answer 53

2 equal zones: (1) an anterior bluish-gray zone overlying the clear cornea and extending from the Bowman layer to the Schwalbe line and (2) a posterior white zone overlying the trabecular meshwork and extending from the Schwalbe line to the scleral spur, or iris root.

Question 54

What is the limbus histologically?

Answer 54

- The transition from opaque sclera to clear cornea occurs gradually over 1.0-1.5 mm and is difficult to define histologically. - The corneoscleral junction begins centrally in a plane connecting the end of the Bowman layer and the Schwalbe line - Internally, its posterior limit is the anterior tip of the scleral spur - Pathologists consider the posterior limit of the limbus to be formed by another plane perpendicular to the surface of the eye, approximately 1.5 mm posterior to the termination of the Bowman layer in the horizontal meridian and 2.0 mm posterior in the vertical meridian, where there is greater scleral overlap