Histology of the Eye

Question 1

What are the 3 chambers of the eye

Answer 1

Anterior, posterior, vitreous + chamber

Question 2

What are the 3 layers (tunics) of the eye?

Answer 2

• Fibrous tunic
• Vascular tunic (UVEA)
• Neuroepithelial tunic

Question 3

What structures are included in each of the tunics?

Answer 3

• Fibrous tunic: Sclera &
  cornea.
• Vascular tunic (uvea):
  Choroid, ciliary body &
  iris.
• Neuroepithelial tunic:
  Retina

Question 4

What CT is the sclera composed of?

Answer 4

Dense irregular

Question 5

What is the Lamina fusca sclerae?

Answer 5

The Lamina fusca sclerae is a thin, pigmented layer of the sclera that serves as a transitional layer between the sclera and other structures of the eye, including the choroid, iris, and ciliary body (vascular tunic).

It contains elastic fibres, fibroblasts and melanocytes.

Question 6

What is the Area cribosa?

Answer 6

The sclera forms a sieve-like
structure which subdivides
the optic nerve into
bundles of fibres.

Question 7

What are the 5 layers of the cornea?

Answer 7

1. Corneal
   (anterior) epithelium.
2. Subepithelial
   basement membrane - domestic animals
   OR
   Anterior limiting lamina (primates, birds)
3. Substantia propria
   (stroma).
4. Posterior limiting
   lamina
   (Descemet’s membrane).
5. Posterior epithelium
   (corneal endothelium).

Question 8

What are the 5 layers of the Choroid?

Answer 8

• Suprachoroid layer
• Vascular layer
• Tapetum lucidum
• Choriocapillary layer
• Basal complex (Bruch’s
  membrane)

Question 9

What is the ciliary body composed of?

Answer 9

• Ciliary epithelium
• Vascular layer
• Ciliary muscle

Question 10

What is the iris composed of?

Answer 10

• Stroma (connective
  tissue).
• Two muscles (sphincter
  & dilator).
• Posterior epithelium.

Question 11

What determines eye colour?

Answer 11

the amount of melanin present in the melanocytes of the
stroma.

Question 12

What are the two muscles that regulate the aperture of the pupil?

Answer 12

• Sphincter muscle
• Muscle is located at the pupillary margin.
• Dilator muscle
• Radially arranged muscle.

Question 13

What determines the shape of the pupil in different species?

Answer 13

The orientation of the sphincter muscle

Question 14

How is the sphincter muscle oriented in the different species?

Answer 14

• Circularly around pupil: dog, pig, primates.
• Dorsoventrally around pupil: cat.
• Horizontally around
  pupil: ruminants and
  horse.

Question 15

What causes Glaucoma?

Answer 15

Inadequate drainage of aqueous humor out of the anterior chamber via the spaces of Fontana between the pectinate ligament causes increased intraocular pressure.

Question 16

What two portions make up the retina?

Answer 16

Sensory portion:
* pars optica retinae.

Non-sensory portion:

• pars ciliaris retinae
  (lines ciliary body)
• pars iridica retinae
  (lines iris).

Question 17

What are the 10 layers of the retina?

Answer 17

1. Retinal pigment epithelium
2. Photosensory layer
3. External limiting membrane
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion cell layer
9. Optic nerve layer
10. Internal limiting membrane

Question 18

What are considered refractile media?

Answer 18

• Lens and zonular fibres
• Aqueous humor
• Vitreous body

Question 19

What structures make up the lens?

Answer 19

• Capsule
• Epithelium
• Fibres

Question 20

What is the 3rd eyelid?

Answer 20

• It is a fold of conjunctiva that contains:
• Hyaline cartilage (dog,
  ruminants).
• Elastic cartilage (horse,
  pig, cat).

Question 21

In what species is the deep gland of the 3rd eyelid present?

Answer 21

pigs and ruminants