visual part 1

Question 1

What is the vitreous body

Answer 1

Vitreous body is clear gel like fluid contains hyaluronic acid and type II collagen fibrils that are slowly replaced
. 99% water

Question 2

What is the hyaloid artery and what did it do? What are floaters?

Answer 2

Hyaloid canal is the vestige of hyaloid artery used to nourish embryonic lens.
Blood and cell debris is removed by local phagocytes, but residual pieces of hyaloid artery remain as a type of “floater”

Question 3

How do the sclera and cornea differ?

Answer 3

Sclera is dense, white CT into which
insert the extrinsic muscles of eye

Cornea is continuous with sclera, but
transparent to allow light to project
to retina.
Avascular, it draws its nutrients from aqueous humor by
diffusion

Question 4

How much do the cornea and the lens each contribute to light refraction?

Answer 4

Most refraction is done by the cornea,but is a fixed structure
• 2/3 vs 1/3
The remaining refraction is variably controlled by the lens

Question 5

What is the cellular and CT makeup of the lens and how is it attached within the orbit?

Answer 5

Held in place by suspensory ligaments
–
Zonule fibers extend from ciliary body to the equatorial perimeter of the lens

Capsule is elastic (collagen IV and glycoprotein). Germinal zone produces new cells during life.After migration from germinal zone, cells lose their nuclei and become transparent

Question 6

How does the lens accommodate to near and far vision?

Answer 6

Resting convexity of lens maintained by
outward pull of suspensory ligaments from the ciliary body
•
Inward pull by intrinsic elastic fibers

Increased convexity of the lens focuses the light from a closer source for “near vision,” while decreased convexity focuses the light from a more distant source for “far vision.”

Question 7

What muscles and nerves are involved in lens accomodation?

Answer 7

Convexity of the lens is altered by the ciliary muscle
= Accommodation
•
Ciliary muscles actively relax tension of suspensory ligaments

Parasympathetic neurons travel along the oculomotor nerve (CN III) • Ciliary ganglion is a parasympathetic ganglion. Postganglionic neurons in the ciliary ganglion activate ciliary muscle to contract lens

Question 8

What are cataracts?

Answer 8

Cataracts is the reduction of vision due to

opaqueness of the lens

Question 9

Describe aqueous humor and its circulation. How does it compare to the vitreous body?

Answer 9

Ciliary processes secrete humor into anterior and posterior chambers
•
Schlemm’s canal (scleral venous sinus) absorbs humor into venous system

Question 10

What is glaucoma?

Answer 10

Build up of fluid pressure due to inadequate drainage into Schlemm’s canal

Question 11

Describe the iris in terms of CT, blood vessels, smooth muscles, innervation and pigments

Answer 11

contains pigmented striations of CT, blood vessels & smooth muscle
Stroma:CT with melanocytes; melanin absorbs and refracts different frequencies (colors)
Constrictor & dilator pupillae
Pigment: epithelium- continuous on posterior surface of iris; completelyabsorbs all light restricting incoming
light to within pupil. Melanin amount/ distribution gives color

Question 12

How does the iris affect entry of light into the orbit?

Answer 12

controlling the aperture of the pupil. Sphincter Pupillae: Constricts pupil & reduces
incoming light. Sympathetic activity increases light
entry into the eye. Parasympathetic Dilator Pupillae Opens pupil & increases
incoming light. Smaller pupils increase the range of focus

Question 13

Account for the different colors of the eye.

Answer 13

Genetic trait that involves distribution of melanin pigments
•
Color of eyes is determined by different patterns of light
refraction by melanin.
–> Rayleigh scattering and turbidity of stroma

Question 14

Describe the circuit and action of the consensual pupillary reflex

Answer 14

Light→melanopsin ganglion cells→Pretectal n.→E-W nucleus→Ciliary Ganglion→Pupil

constriction of both pupils in response to light shone in one eye. maintains homeostatic level of light entering the eye

Question 15

What is the Edinger-Westphal nucleus? The ciliary ganglion?

Answer 15

Preganglionic neurons are located within EdingerWestphal nucleus, one of the nuclei of the oculomotor
nerve (CN III) in midbrain

Ciliary ganglion is a parasympathetic ganglion located
near the posterior surface of the eyeball

Postganglionic neurons in the ciliary ganglion activate
sphincter pupillae to constrict pupil,
ciliary muscle to contract lens

Question 16

What is the tarsal muscle and how does it function?

Answer 16

Tarsal muscle to raise upper eyelid, smooth muscle just deep to the levator palpebrae superioris, attaches to the
tarsal plate in the eyelid. Innervated sympathetically

Question 17

Describe the embryonic development of the eye: retina, meninges, lens

Answer 17

eyeball is derived from embryonic brain.
Neural tube is derived & separated from ectoderm. Rostral part forms the cerebral hemispheres including the eyes
Neural tube contacts ectoderm from which lens placode forms (ectoderm!!).
Neural and pigmented retinal layers derived from the optic vesicle.
Sclera and choroid are derived from embryonic meningeal tissues.