272A #1

Question 1

Retina

Answer 1

is the only tissue able to process light

Question 2

Vision

Answer 2

When your brain processes information for your eye.
Vision = Visual perception which is the ability for your to interpret the surrounding environment by processing information that is contained in visible light.

Question 3

Eyes

Answer 3

are the sensors of visual information.

Question 4

Vision perception

Answer 4

is an interpretation so requires integration of information.

Question 5

Vision is a perceptual process that requires three basic parts.

Answer 5

1. The eye
2. The optic connection to the brain.
3. The brain

Question 6

Light is processed by the retina –>

Answer 6

retina –> optic nerve –> LGN (lateral geniculate nucleus of the thalamus which is the first relay station) –> optic radiations –> primary visual cortex.

Question 7

Visual field

Answer 7

All the space an eye can see in any given instance in time.

• Horizontally the visual field extends to 60 degrees nasally and 100 degrees temporally.
• Binocularly there is an overlapping zone of 120 degrees.

Question 8

Image projection the retina

Answer 8

The retinal visual field is upside down and back to front.

Question 9

Optic nerve

Answer 9

Monocular information is transmitted by the optic nerve.. Cross of information at the optic chiasma.

Question 10

Optic Chiasma

Answer 10

The point of visual pathway where information from left and right VF, detected by each eye is sorted to be transferred to one same side of the brain.

Crossing over of information at level of chiasm, allows our brain to process information of where they are in the visual field.

Question 11

Visual pathway

Answer 11

Transmits sensation from the retina to the brain.

Question 12

At the chiasma

Answer 12

Fibres from the temporal part of each eye pass through the LGN of the same side of the brain.
Fibres from the nasal part of the eye cross to the contralateral LGN.
Then optic tracts, LGN, radiations contain nerve fibres from both eyes.

Question 13

Congenital

Answer 13

Present from birth

Question 14

Anatomy of the eye

Answer 14

Most anterior part of the eye is the cornea –> anterior chamber/ aqueous humous –> Iris –> lens –> space called vitreous humour.
Then consecutive layers of retina, choroid and sclera.

Question 15

Embryogenesis

Answer 15

Is the process by which the embryo forms and develops.
Refers to the stages of prenatal development.
- In the 2 weeks after fertilisation the ovum/egg undergoes a series of repeated cell divisions –> 16 cell stage (morula) –> cells differentiate into ICM and trophoblast (blastocysts).
Humans form from the ICM and trophoblasts form the placenta and supporting tissue.
ICM –> zygote –> mitotic divisions with no significant growth –> multicellular embryo
ICM –> epiblast and hypoblast.

Question 16

Key stages in embryogenesis

Answer 16

day 1, fertilised egg –> day 2 8 cell-zygote –> day 4, 16-cell morula –> day 5, blastocyst –> day 6, zone hatching –> day 7, invades the uterine wall –> day 9, cell mass differentiates –> day 12, bilaminar disc forms –> day 14, mesoderm forms –> day 23, amniotic sac grows.

Question 17

Eye forms

Answer 17

about 22-23 days onward. In the first month of development post-fertilisation the CNS is forming which is when the first structures of the eyes appear.

Question 18

Eye development

Answer 18

The eye derives from the most anterior part of the developing neural tube. (From the mesoderm and ectoderm NOT the endoderm).

• Surface ectoderm.
• Neural ectoderm.
• Neural crest cells
• Mesoderm - specifically the mesenchyme.

Eye is an extension of the brain. Projection/outgrowth from the most anterior part of the CNS.

Question 19

Surface ectoderm forms the

Answer 19

cornea, conjunctival epithelium, lens, lacrimal gland.

Question 20

Neural ectoderm forms the

Answer 20

Retina, smooth muscle of the iris, optic nerve.

Question 21

Neural crest cells form the

Answer 21

endothelium cornea, anterior chamber, trabecular meshwork, sclera,

Question 22

Mesenchyme

Answer 22

Sclera, cornea especially the stroma, part of the vitreous, choroid, iris, ciliary muscle.

Question 23

Mechanism - the process of induction.

Answer 23

Eye develops as a process of ‘induction’ of one tissue by another.
Induction - process by which tissues molecularly influence differentiation of other tissues.

Question 24

The 2 main types of molecules involved in induction are the growth factors and the homeobox genes.

Answer 24

Growth factors modulate migration, proliferation and differentiation of cells. E.g. TGF (beta) is involved in the formation of the neural crest cells and the FGF is involved in formation of the mesoderm.

Homeobox genes are genes that code for a protein that regulates how other genes work.
E.g. master regulator - Pax6 gene. A defect in this gene can cause aniridia (no iris).
PAX6 also involved in formation of the retina, iris, lens.

Question 25

Organogenesis

Answer 25

The process of formation of organs.

Question 26

Neurulation

Answer 26

Formation of the CNS = formation of the neural tube.
Process expands day 24-28 of development.
Neural crest cells originate on both side of the neural tube.

Question 27

Cornea

Answer 27

Transparent layer forming the front of the eye.

Question 28

Neural crest cells

Answer 28

The migration of cells after the preliminary tissues are formed.
Arise from the neural ectoderm when the neural tube is formed.
Transient population of cells. After they migrate to different regions of the embryo, differentiation occurs.
The make a major contribution to the CT in the eye and orbit e.g. sclera, cornea.

Question 29

Eyes develop from the anterior part of the neural tube during neurulation.

Answer 29

As an extension of the neural tube.

Question 30

Sequence of tissue differentiation

Answer 30

1. Optic peduncles.
2. Lens Placode
3. Optic vesicle.
4. Lens vesicle.
5. Lens and retina
6. Cornea

Question 31

Hyaloid artery

Answer 31

Only in the embryonic stage.
Contained within the optic stalk and extends to the lens.
Purpose of the hyaloid artery is to supply nutrients and materials to the developing lens.
About 10th week of development the lens grow independent of a blood supply so the hyaloid artery usually regresses.

Question 32

Choroid fissure

Answer 32

is a groove that extends along the ventral part of the optic stalk.
Continuation of the invagination that forms the optic cup.
The blood vessels (hyaloid artery) enters the eye through the choroid fissure.
Eventually sealed during development. Failure to close - coloboma.

Question 33

Coloboma

Answer 33

Condition with absence of part or all the tissue.

Question 34

Iris

Answer 34

is the tissue in front of the lens. By the 2nd month of development, it hasn’t formed yet.

Question 35

Last structure to develop/appear in the eye is the

Answer 35

iris (between the lens and cornea).

Question 36

Uveal tract - ciliary body

Answer 36

Uveal tract is the name given to the anterior structures of the eye = group of tissues in the anterior part of the eye.
- Refers to the cornea, trabecular meshwork and the ciliary body.

Question 37

Iris

Answer 37

is vascularised. The blood vessels develop from the tunica vasculosa retina.
Iris forms last as an outgrowth of the tip of the retina, contains mesenchymal cells and blood vessels.

Question 38

Suture and Zonules of the lens.

Answer 38

Sutures - during embryogenesis the lens fibres meet in three branches, forming a Y shape. (Growing fibres pushing all the old ones to the middle of the lens).
The sutures formed after birth has multiple branches, not Y shaped.
Zonular fibrils = or suspensory ligaments of the lens are a bunch of radially arranged, thread like fibrils that help hold the lens in place.

Question 39

Optic nerve

Answer 39

is the name of the axons from ganglion cells that extend from retina to brain.