Development of the Eye Softchalk Flashcards
Name the embryonic tissue layers that form the eye components.
ECTODERM- lens and part of the cornea
NEUROECTODERM- retina, pigmented epithelium of the iris, and the optic nerve
NEURAL CREST CELLS- choroid, sclera, part of the cornea, cilliary and iris muscles.
MESODERM-cornea, angioblasts of the choroid layer
Describe the development of lens placodes, lens pits, lens vesicles and optic cups.
The surface ectoderm adjacent to the optic vesicles thickens to become the lens placodes. The lens placodes then invaginate into the surface ectoderm becoming the lens pits, which will fuse to form spherical lens vesicles.
As lens vesicles are developing, the optic vesicles invaginate to form double-walled optic cups.
Describe the embryological development of the lens. Recognize congenital cataracts and name its most common causes.
Primordia of the lens is the lens placode, eventually the lens vesicle. Mesenchymal cells migrate into the space between the lens vesicle and the optic cup and will eventually form the vitreous body composed of vitreous humor. The tunica vasculosa lentis extends over the lens with the anterior part being the pupillary membrane, both of which degenerate.
Congenital cataracts are opacities of the lens commonly caused by rubella, trisomy 21, galactosemia, and maternal diabetes.
Discuss the embryological development of the choroid, ciliary body and sclera. Recognize congenital glaucoma and its embryological origin.
The mesenchyme surrounding the optic cup differentiates into an inner vascular space, the choroid, and an outer fibrous layer, the sclera (continuous with the cornea).
The ciliary body is a wedge shaped extension of the choroid.
Congenital glaucoma is an abnormal elevation of intraocular pressure in neonates. This is due to an imbalance between the production of aqueous humor and its outflow. It can be caused by rubella.
Discuss the embryological development of the cornea.
Cornea formation is induced by the lens vesicle. The cornea is formed from three sources:
1)The external (anterior) corneal epithelium-derived from surface ectoderm.
2 and 3) Mesoderm and neural crest cells differentiate into the substantia propria of the cornea and the corneal epithelium.
What is the embryological cause of anophtalmia?
Anophtalmia is the absence of the eye. It is caused by the failure of the optic vesicle to form.
What is coloboma? What is its embryological origin?
- Coloboma is a defect in the inferior sector of the iris or a notch in the pupillary margin, giving the pupil a keyhole appearance.
- Cause: Typically due to failure of closure of the retinal fissure during week 6. But can also be caused by environmental factors.
- A simple coloboma is often hereditary as autosomal dominant
Describe the development of the optic grooves, optic vesicle, and optic stalk.
- Optic grooves are the first thing formed in eye development. These grooves form in the future diencephalic region of the brain.
- As neural folds fuse to form the forebrain, the optic grooves evaginate out into adjacent mesenchyme to form Optic vesicles
- As optic vesicles grow, their distal ends expand and their connection with the forebrain constrict to form the hollow Optic stalks
Describe the retinal (choroidal) fissures. Discuss their anatomical role and their embryological development.
- Choroidal fissures are linear grooves that develop on the ventral surface of the optic cups and along the optic stalks.
- Vascular mesenchyme in these fissures will become the hyaloid artery and vein. Distal parts of these vessels will degenerate, but proximal parts persist as the central artery and vein of the retina.
- the stalk lumen gradually obliterates, leaving a hollow optic stalk that will transform into the solid Optic Nerve (CN II)
What is retinal detachment? What is the anatomical particularity that allows this condition to occur?
The two walls of the optic cup–its thick inner wall and thin outer wall–give rise to the two layers of the retina. The two walls of the optic cup are initially separated by a narrow intraretinal space. This space disappears by the 7th week, BUT the layers never fuse firmly. Thus, trauma to the head can cause retinal detachment = mechanical separation of the two layers of the retina.
Describe the embryological development of the retina.
The two walls of the optic cup–its thick inner wall and thin outer wall–give rise to the two layers of the retina.
- thick inner wall becomes the Neural Retina, the light-sensitive region that contains photoreceptors and cell bodies of neurons
- thin outer wall becomes the melanin-containing pigmented epithelium
From what structure does the iris develop? Which layers of the eye are the iris continuous with?
The iris develops from the rim of the optic cup, which thins and grows inward to partially cover the lens. Thus, the iris contains BOTH layers of the optic cup, which means the iris is continuous with both the neural retina (derived from inner wall) and the pigmented epithelium (outer wall of optic cup).
The iris is also continuous with the double-layered epithelium of the ciliary body
What is the embryological origin of connective tissue of the iris? Of the Dilator pupillae and sphincter pupillae muscles of the iris?
Connective tissue of the iris derive from neural crest cells that migrate into the iris.
The dilator and sphincter pupillae mm derive from neuroectoderm of the optic cup.
Describe the embryological formation of the eyelids, conjunctiva, and lacrimal glands.
- Eyelids develop from neural crest cell mesenchyme AND from two cutaneous folds of ectoderm that grow over the cornea.
- The surface ectoderm forms the eyelashes and lacrimal glands in eyelids.
- Eyelids are adhered at first in week 10. When they finally open ~week 27, the bulbar conjunctiva and palpebral conjunctiva are forming.
