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Med Neuro Block 2 > 7 - Visual System: 1 > Flashcards

7 - Visual System: 1 Flashcards

1
Q

What are some other names for the optic disk? What is papilladema? What is Peripapillary?

A

Optic nerve head
Disk
Papilla

Papilladema: Swollen nerve head.

Peripapillary: near or around the nerve head

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2
Q

What layers make up the cornea from outside to inside? Describe each layer?

A

Epithelium: regenerative; stratified squamous cells

Bowman’s membrane: acellular layer of unorganized collagen fibers; barrier to infection

Stroma: type 1 collagen bundles that bind water and maintain corneal clarity

Descement’s membrane: basement membrane for corneal endothelial cells increase thickness with age

Endothelim: simple squamous; pumps water out of the stroma

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3
Q

What is the function of the cornea?

A

MAJOR refractive structure that protects the eye from environment.

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4
Q

What is myopia? What percentage of Americans have this? Describe the lens shape.

A

Nearsightedness

Can be due to a cornea that’s too strong or an eye that’s too long.

25% of Americans have this

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5
Q

What is hyperopia? What can cause this?

A

Farsightedness.

Can be due to a weak cornea or an eye that’s too short.

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6
Q

What are the three parts of the uvea?

A
  1. Choroid
  2. Ciliary body
  3. Iris
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7
Q

What is the choroid of the uvea? What are it’s layers from OUT to IN?

A

The largest component, which has three layers from out to in:
1. Vessel layer with medium sized arteries and veins, loose CT and melanocytes

  1. Choricocapillary layer: capillaries in one plane, fenestrated
  2. Bruch’s membranes: 3-4 micron thick amorphous hyaline membrane that the retinal pigmented epithelia rest on.
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8
Q

What is the ciliary body? What three regions does it come in contact with?

A

Expansion of the stroma of choroid near the lens. Has trabecular meshwork for draining aqueous humor from anterior chamber.

Contacts: vitreous body, sclera, and the posterior chamber/lens.

Has ciliary processes that project towards lens to increase the SA for fluid secretion.

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9
Q

What is the function of the iris?

A

Covers the lens and regulates light reaching the stroma.

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10
Q

What is the structure of the anterior and posterior aspects of the iris?

A

Anterior aspect made of vascular loose CT with melanocytes: number and type determines eye color.

Posterior surface lines with doubel layer of pigmented epithelium to absorb life.

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11
Q

What two muscle masses rest on the pigmented epithelium and regulate iris opening (pupil diameter)?

A

Radially arranged myoepithelial cells from the dialator pupillae between the vascular and pigment layers (contraction = dilation)

Concentric smoother muscle bundles at the pupil margin (inner aspect of iris) form the sphincter pupillae (contraction = constriction)

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12
Q

What is the structure and function of the anterior chamber?

A

Involved in maintaining intraocular pressure.

Avascular, contains aqueous humor; 99% water; produced by non-pigmented epithelium of the ciliary process.

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13
Q

What is the direction of aqueous humor flow?

A

From ciliary processes to posterior chamber to anterior chamber to trabecular meshwork to Schlemm’s canal to veins of the sclera.

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14
Q

What is the prevalence of Glaucoma? What is a risk factor for it?

A

Leading cause of blindness and vision impairment.

Risk factor: increased intraocular pressure caused by angle closure and inability of aqueous humor to drain.

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15
Q

What are clinical signs of glaucoma?

A

Elevated pressure (tonometry): normal is 12-22 mmHg

Increased cupping of optic nerve head. Cup to disc ratio is 0-1 and higher is WORSE.

Visual field defect (perimetry) will reveal a selective peripheral loss of sensitivity

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16
Q

What is the lamina cribrosa? What can alter this?

A

Network of collagen fibers through which the fibers of the optic nerve exit the eye.

May be altered by glaucoma.

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17
Q

What is the structure of the lens?

A

Transparents structure (avascular with little ECM and no organelles) that has a capsule of ECM surrounding the lens, epithelium at the anterior surface, and lens fibers for the body.

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18
Q

What is the function of the lens? How does it do this?

A

Second to cornea in refractive power (~10 D).

Zonule fibers attached to ciliary muscles help control the lens thickness.

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19
Q

What type of vision occurs when the lens is thinner? Thicker?

A

Thinner: when focused on distant objects - relaxed ciliary muscles

Thicker: when focusing on near objects, ciliary muscles contract and relax tension on the zonule fibers to thicken the lens.

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20
Q

Where/when can cataracts occur? What are they?

A

An opacification of the lens that can occur as the lens ages.

By 80 more than half of all americans have either a cataract or have had cataract surgery.

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21
Q

What are the ways to describe a cataract?

A

Nuclear: located in the center of the lens

Cortical: affect the layer of the lens surrounding the nucleus

Posterior capsular: found in the back outer layers of the lens and develop more rapidly (usually)

22
Q

What occurs with cataract surgery?

A

Removal of the lens (phagoemulsification or extracapsular surgery) and implantation of an IOL.

23
Q

What is the structure and function of the vitreous body?

A

Nearly acellular, avascular structure with type 2 collagen and hyaluronic acid.

Transparent structure of ~99% water for nutritive function .

24
Q

What are the two main layers of the retina that develop from the neural ectoderm?

A
  1. Neural (sensory) retina

2. Retinal pigment epithelium

25
Q

What are the regions of specialization in the neural retina?

A

Fovea: “small pit” region used for high acuity vision

Anterior the number of neural elements in the retina declines and becomes a single later of epithelium (unpigmented) that covers the ciliary body.

26
Q

What are the inner and outer segments of photoreceptors (rods and cones)? What is the connecting cilium?

A

Inner segments: organelles for protein synthesis and energy production

Outer segments: flattened membrane discs with photosensitive visual pigments (opsin)

Connecting cilium: transport of proteins to OS: 10 bil opsin molecules per second.

27
Q

What are the two types of photoreceptors? Describe their shape and function.

A

Rods: long, slender outer segments. Numerous at the fovea and very light sensitive.

Cones: conical outer segments with membrane discs. Less sensitive than rods. Responsible for high acuity and color vision.

28
Q

What anatomical events define fovea specialization?

A

Cone packing increases

Foveal pit develops after a thickening of the retina

Site of incipient fovea is avascular all along.

29
Q

What is the retinal pigment epithelium (RPE) structure?

A

Simple cuboidal melanin containing epithelium between the neural retina and Bruch’s membrane, the ECM separating the REP and the capillary bed of the coroid.

Provides outer blood-retinal barrier.

~40 photoreceptors/RPE cell

30
Q

What are the major functions of the retinal pigment epithelium (RPE)?

A

Transports nutrients and ions between photoreceptors and choricapillaries

Outer segment renewal

Helps absorb light for the retina and has the enzyme that turns all trans retinal back to 11-cis retina

31
Q

When does the retinal pigment epithelium (RPE) recycle outer segments? How much does it recycle?

A

It engulfs, digests, and recycles about 10% mass of each photoreceptor outer segment/day.

This occurs on a daily schedule: peak rod OS disc shedding at dawn and peak cone OS disc shedding at dusk.

32
Q

What is age-related macular degeneration (AMD)? What type of visual defect is common with this?

A

Drusen develop within Bruch’s membrane causing slow vision loss that deteriorate central vision first.

Due to RPD sloughing off OS and making toxic byproducts.

Metamorphosia is common - amsler grid testing.

33
Q

What are the risk factors and treatment of Age-related macular degeneration?

A

Risk: Family Hx, smoking, blue eyes, CFH mutation.

Treatment: focused halting progression from dry to “wet” - anti-VEGF

34
Q

What are the two blood supplies of the inner retina?

A

Inner retina supplied by the superior and inferior temporal arteries (branches of the central retinal artery).

35
Q

Describe the anatomical foveal specialization?

A

Avascular zone

Excavation of inner retinal neurons (foveal pit)

High cone density, absence of robs

36
Q

Impaired foveal specialization is a hallmark of diseases like _____ and _____.

A

Aniridia and albinism.

37
Q

What is albinism?

A

Inherited disorder of melanin biosynthesis associated with absent or reduced melaninpigment in eye, skin, and hair.

1:17,000

38
Q

What are the two types of oculocutaneous albinism (OCA)? How is it inherited?

A

Autosomal recessive.

OCA1A: no pigment anywhere
OCA1B: some pigment due to leaky mutation allowing residual enzyme tyrosinase

39
Q

How is ocular albinism (OA) inherited?

A

X-linked.

Typically normal skin and hair.

40
Q

What are the universal visual symptoms of albinism?

A

Nystagmus (rapid side to side movement) , refractive errors, photophobia, reduced acuity, macular translucency, iris transillumination, altered retinostriate projections, and foveal hypoplasia (arrested foveal development).

41
Q

What are clinical signs of albinism?

A

Iris transillumination

Macular translucency

Altered ipsi/contra impairs stereo vision

Foveal hypoplasia

42
Q

What is the sclera and what does the sclera become anteriorly?

A

Outermost covering over the eye.

From the edges of the iris the sclera becomes the cornea.

43
Q

The optic nerve is _____ in relation to the fovea which is more ______.

A

The optic nerve is more nasal, compared to the fovea which is more temporal.

44
Q

What is the macula?

A

A region surrounding the fovea.

45
Q

Why don’t higher-order aberrations normally impact day to day vision? When can eye aberration effects be noticed?

A

Because we can change our pupil size

In dark conditions you will notice the effects more, or after lasiks.

46
Q

When looking at a VM slide, how would you tell which layer is more external on the retina?

A

The pigmented layers are on the outside of the retina.

47
Q

When looking at a VM slide, how would you know if you’re looking at cells in the periphery (far from fovea) or central (near the fovea)?

A

Peripheral regions will have fewer ganglion cells.

Central regions will have more ganglion cells.

48
Q

Where is there 0 robs and the highest density of cones. Where are there no photoreceptors?

A

At the fovea.

No photoreceptors are the optic disk.

49
Q

What happens to fovea cells as a newborn gets older?

A

They have increased cone packing.

50
Q

Describe the dual blood supply to the retina?

A

Inner retina fed by the renal artery system from the ophthalmic artery (30%).

Everything else (80%) fed by the ophthalmic artery through the ciliary artery system (anterior and posterior ciliary artery).

Med Neuro Block 2 (14 decks)

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