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DIT Primer > Primer 23 - The Eye > Flashcards

Primer 23 - The Eye Flashcards

1
Q

From which primary germ cell layer does the lens plate develop?

A

Surface ectoderm thickens to form a Lens Plate.

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2
Q

What are the three main layers of the adult eye ball?

A

Retina, choroid and sclera (from deep to superficial).

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3
Q

How many layers are in the retina and where do they come from?

A

The epithelial outer pigment layer formed from the outer layer of the optic cup. The rest of the nine neural layers of the retina come from the inner layer of the optic cup.

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4
Q

What is the origin of the choroid?

A

Network of capillaries that encircle the optic cup.

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5
Q

What is the origin of the sclera?

A

Condensation of mesenchyme outside the optic cup?

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6
Q

What is the outer sheath of the optic nerve?

A

Dura mater and arachnoid mater.

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7
Q

What primarily accounts for the varied opacity of the sclera and cornea?

A

Differences in the arrangement of and types of collagen; there seems to be a higher content of glycosaminoglycan in the cornea, which results in a greater degree of hydration, and thus wider spaces between the collagen fibers. Also the cornea is avascular.

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8
Q

What is the name of the site where the cornea and sclera meet?

A

The limbus or sclerocorneal junction; site where the blood vessels running in the sclera stop and form capillary beds.

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9
Q

What is the uvea?

A

It a term that encompasses the choroid, ciliary body and iris.

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10
Q

Where do arteries of the choroid come from?

A

Posterior ciliary arteries.

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11
Q

State all the arteries that branch into the eye ball.

A

Internal carotid artery to opthalmic artery to the short posterior ciliary arteries and central artery of retina.

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12
Q

What are the sources of blood supply to the retina and what portion does each supply?

A

The choroid arteries are responsible for 3/4th of the blood supply to the retina and the rest is supplied by the central artery of the retina.

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13
Q

What is the iris and what does it do?

A

It is a pigmented diaphragm with an adjustable central apparature, the pupil, allowing the transmission of light. The iris has a dense anterior layer and a diffuse stromal layer in the center that both consists of fibroblasts, blood vessels, nerves and melanocytes.

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14
Q

Which muscle contracts in order to enlarge the pupil?

A

Dilator pupillae muscle.

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15
Q

What muscle contracts to shrink the size of the pupil?

A

Sphincter pupillae muscle.

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16
Q

How is the ciliary body divided?

A

Into Pars plicata and Pars planum. Both portions are covered in two layers of epithelium (superficial is nonpigmented and the deeper layer is pigmented).

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17
Q

What is the Pars Plicata?

A

It is a division of the ciliary body that faces the lens, it is a series of ridges on inner surface called (ciliary process). Peaks of the ciliary processes are connected to the lens by suspensory ligaments called (zonules).

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18
Q

What is the Pars Planum?

A

A division of the ciliary body that is posterior the lens, it is thin and flat.

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19
Q

Which part of the eye is composed of epithelial cells filled with crystallins and has the ability to change shape?

A

The lens. It is a stacked epithelial cells that have lost their nuclei.

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20
Q

What happens to the lens when the ciliary muscles relax?

A

The tension on the suspensory ligaments increases, which stretches the lens flat, enabling to focus light from far away objects, onto the retina.

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21
Q

What are the boundaries of the anterior chamber of the eye?

A

Cornea and the iris.

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22
Q

What are the boundaries of the posterior chamber of the eye?

A

Iris and the lens.

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23
Q

How is aqueous humor manufactured and what does it do?

A

It is made by the epithelium tips of the ciliary processes from the plasma in the posterior chamber. It nourishes the avascular tissues of the eye.

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24
Q

What is the flow of the aqueous humor?

A

Manufactured by the ciliary process from the posterior chamber and flows into the anterior chamber by flowing between the angle formed by the lens and iris, where it is then drained into the Canal of Schlemm at the irideocorneal angle into the venous system.

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25
Q

What disease process results from the blockage of the aqueous humor pathway?

A

Glaucoma: increase in intraocular pressure that can damage the optic nerve.

26
Q

What is the vitreous body and what does it do?

A

The Vitreous chamber is posterior to the lens and is filled with vitreous body (or humor) which is a gelatinous, translucent mass that helps the eyeball maintain its shape, helps keep the retina in place, and helps support the lens.

27
Q

What is the difference between open angle glaucoma and closed angle glaucoma?

A

Open angle glaucoma is when the angle between the iris and the lens is open but their is blockage in the canal of Schlemm. It is painless and almost always bilateral and insidious.

Closed angle glaucoma is when the angle between the iris and the lens is narrowed or closed. It is painful and abrupt, causing rock hard eye and headache, (red teary eye, hazy cornea, and fixed mid-dilated pupil, which is not reactive to light). It is an emergency.

28
Q

What is the drug to avoid in someone with a closed angle glaucoma and why?

A

Epinephrine because it causes mydriasis, exacerbating the situation.

29
Q

What is the cause of primary glaucoma?

A

A type of juvenile glaucoma, it is caused by angle malformations (trabeculodysgenesis).

30
Q

What is the cause of secondary glaucoma?

A

A type of juvenile glaucoma, it can be acquired or an underlined abnormality, which can present at any age.

31
Q

What does glaucoma cause to the optic disk?

A

It causes cupping of the optic disk: there is a dark circle in the optic disk on examination.

32
Q

How do we diagnose glaucoma?

A

A disk to cup ratio. If the disk to cup ratio is 1:2, then there is glaucoma. Or tonometry but it is not sensitive or specific.

33
Q

What are the classic symptoms of glaucoma?

A

Halos or rainbows seen around lights. Loss of peripheral vision.

34
Q

What are the 3 main types of glaucoma?

A
  1. Open angle glaucoma (most common).
  2. Closed angle glaucoma.
  3. Congenital/juvenile glaucoma.
35
Q

What is the pathophysiology of Macular degeneration?

A

Any degeneration of the elements of the macula (age related, common in diabetics).

36
Q

What is the pathophysiology of Retinal detachment?

A

Separation of the nervous layer of the retina from the pigmented epithelial layer of the retina.

37
Q

What is the pathophysiology of Cataracts?

A

Opacities or clouding of the lens that can result in visual loss or blindness.

38
Q

What type of nervous stimulation, stimulates the dilator pupillae muscle?

A

Sympathetic fibers that synapse at the superior cervical ganglia and follow the internal carotid and opthalmic arteries into the orbit.

39
Q

What type of nervous stimulation, stimulates the constrictor pupillae muscle and ciliary body and muscle?

A

Parasympathetic fibers carried by the occulomotor nerve that arise from the Edinger-Westphal nucleus.

40
Q

Where do the parasympathetic fibers carried in the oculomotor nerve that innervate the constrictor pupillae muscle and ciliary muscle arise?

A

Edinger-Westphal nucleus.

41
Q

What are the 9 Retina sublayers?

A

In the order that light enters:
1. Internal limiting membrane, 2. Nerve fiber layer, 3. Layer of ganglion cell bodies, 4. Inner plexiform layer, 5. Inner nuclear layer, 6. Outer plexiform layer, 7. Outer nuclear layer, 8. external limiting membrane. 9. Bacillary layer.

42
Q

What do rods do? What do cones do?

A

Rods detect light. Cones detect color. Rods outnumber cones by 20x.

43
Q

When and where do the eyes come from?

A

In the third and fourth weeks, a pair of optic vesicles bud laterally from the forebrain portion of the neural tube.

44
Q

Where new rods and cones manufactured?

A

In the epithelial layer of the retina.

45
Q

What nerve cells do cones and rods synapse to?

A

Bipolar cells.

46
Q

What comes in and out of the optic disk?

A

The nerves of the optic nerve exit the optic disk and the arteries of the central artery of the retina enter.

47
Q

What is the “Blind spot” of the retina?

A

The Optic Disc.

48
Q

What is the Macula and what does it do?

A

It is the a place in the retina that gives the clearest, sharpest vision due to the highest concentration of cones.

49
Q

What is the Fovea Centralis?

A

It is the central area of the macula which has the highest concentration of cones in the macula, and is the central area of visual field. There are no rods in the Fovea Centralis.

50
Q

How does the Macula receive it’s blood supply?

A

Branches of the central artery of the retina branch toward the macula but do not touch it. The macula receives it’s blood supply from the overlying choroid.

51
Q

Which side of the optic tract crosses (decussation) to the contralateral side?

A

The optic tract of the medial side cross at the optic chiasm to the contralateral side. The optic tract of the lateral side do not.

52
Q

Which reflex allows the constriction of both pupils when light is only shined into one eye?

A

Pupillary light reflex.

53
Q

What is the entire route of light that enters the eyeball?

A

Goes from retina, to optic tract, and only the medial optic tracts cross over to the other side in the optic chiasm. The fibers then run into the lateral geniculate body, then to the optic radiation and finally to the visual cortex of occipital lobe.

54
Q

What is the name given to the area of the eye responsible for the most acute vision, and where is this area found?

A

It is the fovea centralis, found in the macula.

55
Q

What is the name of the blind spot of the eye? Why is it that there are no photoreceptors located in this area?

A

It is the optic disk. There are no photoreceptors because optic nerves exit and central artery of the retina enters.

56
Q

What is the pathogenesis of open-angle glaucoma?

A

Blocked Canal of Schlemm, increasing the intraocular pressure due to the buildup of aqueous humor, damaging the optic nerves.

57
Q

From where does the ciliary ganglion receive information, and to where does it send information?

A

It receives preganglionic parasympathetics from the oculomotor nerve and sends postganglionic parasympathetics to constrictor pupillae and ciliary muscles.

58
Q

What are the functions of the sphincter and ciliary muscles?

A

Sphincter muscles cause constriction of pupil and ciliary muscle cause accommodation (changing the shape of the lens to focus).

59
Q

Explain the process by which you are able to focus on an object far away?

A

Relaxation of the ciliary muscles cause a flattening of lens, which causes less refraction and greater ability to focus on far away objects.

60
Q

What muscle is responsible for dilating the pupil?

A

Dilator Pupillae Muscle (Innervated by sympathetics).

61
Q

When looking at a patient’s eye, you notice that the pupil remains dilated. What nerve supply to the eye is damaged?

A

Parasympathetic nerve supply (CNIII, and ciliary ganglion). Can also be caused by optic nerve damage or any kind of blindness.

62
Q

Of the cornea and the lens, which has the greatest refractive power, and which has the ability to change shape?

A

Cornea has the greatest refractive power and lens has the ability to change shape.

DIT Primer (30 decks)

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