The Eye Flashcards
1
Q
What are the 4 sources that the eyes are derived from?
A
Neuroectoderm, Surface ectoderm, Mesoderm, & Neural Crest Cells
2
Q
What 3 things does neuroectoderm differentiate into?
A
“RIO”
Retina, Iris, & Optic Nerve
3
Q
What 2 things does surface ectoderm form?
A
lens and EPIthelium of the cornea
4
Q
What does mesoderm give rise to?
A
The fibrous and vascular coats of the eye.
5
Q
What do neural crest cells differentiate into?
A
choroid, sclera, & ENDOthelium of the cornea
6
Q
Are both the endothelium and epithelium of the cornea derived from the same source?
A
NO!
Endothelium = neural crest cells
Epithelium = surface ectoderm
7
Q
At what day do the eyes appear?
A
Day 22
8
Q
Where do the eyes originate?
A
On the sides of the forebrain.
9
Q
How is the lens placode formed?
A
Formed by changes of the optic vesicles which are induced by contact with surface ectoderm.
10
Q
Where do retinal fissures develop?
A
On the ventral surfaces of the optic cups and along the optic stalks.
11
Q
What gives rise to the hyaloid vessels?
A
Vascular Mesenchyme from the retinal fissures
12
Q
Formational order for the primordia of the eyes?
A
Shallow grooves (form)-> optic vesicles (form) -> lens placode, optic cups, and optic stalks.
13
Q
What does the retina develop from?
A
walls of the optic cups
14
Q
layers of the optic cups & what they form in the retina
A
- outer thinner layer forms the pigmented layer of the retina
- inner thicker layer forms the neural layer of the retina
15
Q
What do the cells of the neural layer of the retina differentiate into?
Hint: Neural layer is the posterior part of the retina.
A
- cones & rods (photoreceptors)
2. bipolar and ganglion cells (cell bodies of neurons)
16
Q
What 3 layers does the mantle layer of the retina give rise to?
A
- outer nuclear layer
- inner nuclear layer
- ganglion cell layer
17
Q
What forms the optic nerve aka cranial nerve 2?
A
The optic stalk together with the ganglion cells.
18
Q
Besides the optic nerve, what else does the optic stalk and ganglion cells form?
A
optic chiasm and optic tract
19
Q
What part of the brain is the optic nerve a tract of?
A
Diencephalon
20
Q
When is the optic nerve completed myelinated?
A
10 weeks (3 months) after birth by oligodendrocytes due to exposure to light
21
Q
What are the most common eye anomalies a result of?
A
Defects in closure of the retinal fissures
22
Q
What is a retinal coloboma and why does it occur?
A
A local gap in the retina which results from defective closure of the retinal fissure.
Extra: It is bilateral & located inferior to the optic disc in most cases.
23
Q
What is a coloboma of the iris and what causes it?
A
It is a defect in the inferior sector of the iris or a notch in the pupillary margin. It results from failure of closure of the retinal fissure during week 6 of development.
Extra: It may involve only the iris or extend deeper into the ciliary body and retina.
24
Q
What causes Congenital Detachment of the Retina?
A
This defect occurs when the inner and outer layers of the optic cup fail to fuse during the fetal period to form the retina and obliterate the intraretinal space.
25
What tests can you perform to diagnose a congenital detachment of the retina?
Fundoscopic Exam & Optical Coherence Tomography
26
What other disorders does congenital detachment of the retina occur in conjunction with?
It occurs in conjunction with other syndromes such as Down syndrome and Marfan syndrome.
27
In detachment of the retina, how are the neural and pigmented layers separated?
They may be separated partially or completely.
28
What causes Retinal Detachment in general?
Retinal detachment may result from unequal rates of growth of the two retinal layers; as a result, the layers of the optic cup are not in perfect apposition. Sometimes the layers of the optic cup appear to have fused and separated later; such secondary detachments usually occur in association with other defects of the eye and head or trauma.
29
What is cyclopia?
In this rare anomaly, the eyes are partially or completely fused, forming a single median eye enclosed in a single orbit.
30
What is associated with cyclopia? And is it compatible with life?
Cyclopia (single midline eye) and synophthalmia (fusion of eyes) represent a spectrum of ocular defects. These severe eye defects are associated with other craniocerebral defects that are incompatible with life.
31
What structure forms superior to a cyclopia?
There is usually a tubular nose (proboscis) superior to the eye.
32
What causes cyclopia?
Cyclopia appears to result from holoprosencephaly which is severe suppression of midline cerebral structures. — these structures develop from the cranial part of the neural plate.
33
Microphtalmia
The eye may be very small with other ocular defects or it may be a normal appearing rudimentary eye. The affected side of the face is underdeveloped and the orbit is small. It may be associated with other congenital anomalies.
34
What does severe microphthalmia result from?
Severe microphthalmia results from arrested development of the eye before the optic vesicle has formed in the fourth week.
35
What does simple microphthalmia result from?
Some cases of microphthalmos are inherited. Most cases of simple microphthalmia are caused by infectious agents such as rubella virus, Toxoplasma Gondii, and herpes simplex virus. (All cross the placental membrane during the late embryonic and early fetal periods.)
36
Anophthalmia
Congenital absence of the eye. The eyelids form, but no eyeballs develop. Usually comes with other severe craniocerebral anomalies.
37
What causes primary anophthalmos?
Early in the fourth week there is a failure in the eye vesicle to form.
38
What causes secondary anophthalmos?
This occurs when development of the forebrain is suppressed and absence of the eye or eyes is one of several anomalies.
39
What is the ciliary body an extension of?
It is an extension of the choroid.
40
What does the ciliary muscle develop from? And what is it's function?
It develops from mesenchyme. The ciliary muscle is responsible for focusing the lens.
41
What forms ciliary processes?
Medial surface of ciliary body that projects towards the lens.
42
What produces aqueous humor?
Ciliary Processes
43
Ciliary processes give rise to what fibers of the lens?
The ciliary processes give rise to the suspensory fibers of the lens (ciliary zonule) which attach to and suspend the lens.
44
Describe the circulation/drainage of aqueous humor.
Aqueous humor circulates through the posterior and anterior chambers and drains into the venous circulation via the trabecular meshwork and the canal of Schlemm.
45
What is the choroid?
It is an inner vascular layer.
46
What is the sclera?
Is it an outer fibrous layer.
47
What are the sclera and choroid differentiated from?
retinal pigment epithelium
48
What does the Iris develop from?
The iris develops from the rim of the optic cup which grows inward and partially covers the lens.
49
What is the epithelium of the Iris continuous with?
The epithelium of the ciliary body, retinal pigment epithelium, and neural retina.
50
What is the stroma of the Iris derived from?
neural crest cells
51
What are the 2 muscles of the Iris? What are they derived from?
The dilator pupillae and sphincter pupillae muscles of the iris are derived from neuroectoderm of the optic cup.
52
What is the color of the iris of most newborns?
light blue grey
53
When does the Iris acquire it's definitive color?
The iris acquires its definitive color after birth as pigmentation occurs during the first 6 to 10 months.
54
What are pigment containing cells called?
chromatophores
55
What determines eye color?
The concentration and distribution of chromatophores in the loose vascular connective tissue of the iris.
56
What color is the eye if the melanin pigment is in the pigmented epithelium on the posterior surface of the iris?
BLUE
57
What color is the eye if the melanin pigment is distributed throughout the stroma of the iris?
BROWN
58
What is congenital aniridia?
In this rare anomaly, there is a lack of iris tissue or almost complete absence of the iris.
59
What causes congenital aniridia?
It results from failure in the development at the rim of the optic cup at week 8. It may be associated with glaucoma. As well as mutation of the Pax6 gene.
60
Mutation of what gene leads to congenital aniridia?
Pax6
61
What does the lens develop from?
From the lens vesicle, which is a derivative of the surface ectoderm.
62
What forms the lens epithelium?
Anterior wall of the lens vesicle.
Extra: posterior wall of the lens vesicle forms primary lens fibers at the end of week 7.
63
Hyaloid Artery (distal part)
Distal part supplies the developing lens but becomes avascular and degenerates in fetal life.
64
What does the lens depend on?
Diffusion from the aqueous humor, in the anterior chamber of the eye, and the vitreous humor.
65
What is the hyaloid canal? Where is it located?
The former site of the hyaloid artery. Located in the vitreous body.
Extra: It is usually invisible in the living eye
66
What is the vitreous body?
The vitreous body forms within the cavity of the optic cup and is composed of vitreous humor.
67
What is primary vitreous humor derived from?
neural crest origin
68
Does primary vitreous humor increase?
It does not increase, but is surrounded by a gelatinous secondary vitreous humor.
69
PERSISTENT PUPILLARY MEMBRANE
Remnants of the pupillary membrane which may persist as web-like strands of connective tissue or vascular arcades over the pupil in neonates, especially in premature infants.
70
What is the treatment for persistent pupillary membrane?
This tissue seldom interferes with vision and tends to atrophy.
71
Function of the pupillary membrane?
Covers the anterior surface of the lens during the embryonic period and most of the fetal period.
72
What happens when the entire pupillary membrane persists?
Very rarely the entire pupillary membrane persists, giving rise to congenital atresia of the pupil (absence of opening of the pupil)
73
What is the treatment for congenital atresia of the pupil?
Surgery or laser treatment is needed in some cases to provide an adequate pupil.
74
Persistence of the Hyaloid Artery
It persists as a freely moving, nonfunctional vessel or as a wormlike structure projecting from the optic disc. Or it may form a cyst. in most cases the eye is microphthalmic.
75
What 3 sources form the cornea?
1. surface ectoderm
2. mesenchyme
3. neural crest cells
76
What part of the cornea does surface ectoderm form?
external corneal epithelium
77
What are the characteristics of the mesenchyme that forms the cornea?
It is derived from mesoderm and it is continuous with the sclera.
78
What part of the cornea do neural crest cells differentiate into? Where do they come from?
corneal endothelium; And migrate from lip of optic cup.
79
What are the 2 optic chambers?
1. anterior chamber of the eye
| 2. posterior chamber of the eye
80
How do the anterior and posterior chambers of the eye communicate?
Through the scleral venous sinus
81
What does the anterior chamber develop from?
Develops from a space of mesenchyme located in between the developing lens and cornea.
82
What does the posterior chamber develop from?
Develops from a space of mesenchyme that is posterior to the developing iris and the anterior to the developing lens.
83
What is congenital glaucoma?
Abnormal elevation of intraocular pressure in newborn infants that results from abnormal development of the drainage mechanism of the aqueous humor during the fetal period.
84
What may cause congenital glaucoma?
It may result from rubella infection during early pregnancy.
85
What do congenital cataracts look like?
The lens is opaque and appears grayish white.
86
Treatment for congenital cataracts?
Treatment requires surgery at a very early age. Without treatment blindness will occur.
87
What may cause congenital cataracts?
May be caused by teratogenic agents like rubella virus.
88
What do eyelids develop from?
The eyelids develop during the 6th week from mesenchyme derived from neural crest cells, and from ectoderm that grows over the cornea.
89
How long are the eyelids adherent?
By week 10th the eyelids adhere to one another and remain adherent until week 28th.
90
When and where does a conjunctival sac occur?
While the eyelids are closed there is a closed conjunctival sac anterior to the cornea.
91
What happens as the eyelids open?
As the eyelids open, the bulbar conjunctiva covers the anterior part of the sclera, and the palpebral conjunctiva lines the inner surface of the eyelids.
92
What is congenital aphakia?
Absence of the lens is extremely rare and results from failure of the lens placode to form during the fourth week. Aphakia may also result from failure of lens induction by the optic vesicle.
93
What causes edema of the Optic Disc?
An increase in CSF pressure (often resulting from increased intracranial pressure) slows venous return from the retina, causing papilledema (fluid accumulation) of the optic disc. This occurs because the retinal vessels are covered by pia mater and lie in the extension of the subarachnoid space that surrounds the optic nerve.
94
What is a drooping eyelid called?
A drooping eyelid is called ptosis or blepharoptosis.
Extra: Drooping of the superior (upper) eyelids at birth is common.
95
Why might Ptosis (blepharoptosis) occur?
From failure of normal development of the levator muscle of the eyelid.
OR
From prenatal injury or dystrophy of the oculomotor nerve (CN III).
96
What may ptosis be associated with?
Ptosis may be associated with the inability to move the eyeball superiorly. This would also mean there is also poor eyeball development.
Extra: Congenital ptosis is present in several syndromes.
97
Coloboma of the Eyelid
Large defects of the eyelid (palpebral colobomas) are uncommon. A coloboma is usually characterized by a small notch in the superior eyelid, but the defect may involve almost the entire lid.
A coloboma of the inferior eyelid is rare.
98
What causes Palpebral colobomas?
Palpebral colobomas may result from local developmental disturbances in the formation and growth of the eyelids.
99
What is Cryptophthalmos?
results from congenital absence of the eyelids; as a result skin covers the eye. The eyeball is small and defective, and the cornea and conjunctiva do not develop. The defect means absence of the palpebral fissure, with no development of eyelashes and eyebrows and other eye defects.
100
Retrolental fibroplasia
(Retinopathy of Prematurity) is an oxygen-induced retinopathy seen in premature infants.
101
What causes Retinitis Pigmentosa (RP)?
Hereditary degeneration and atrophy of the retina. RP may be transmitted as an autosomal recessive, autosomal dominant, or X- linked trait.
102
What are characteristics of RP?
Characterized by degeneration of rods, night blindness (nyctalopia), and "gun barrel vision.
103
What syndrome may RP be associated with & what is the treatment?
RP may also be due to abetalipoproteinemia (Bassen-Kornzweig syndrome), which may be stopped with massive doses of vitamin A.
