CLSA Eye Witness Spring 2011 - (Page 12)

Kids Korner ’ In the Beginning: Embryonic Eye Development By linda conlin, aBoc, nclec its formation and separates from ou may fit contact lenses for the ectoderm. Meanwhile, neural infants and very young chilcrest cells have separated from the dren. But do you know how neural plate and migrate to form the eye and the cornea, in particuother neuronal and nonneuronal lar, develop? That background can cells. Once separated, they move help you anticipate the challenges into the area between the lens and and outcomes for these tiniest of the corneal epithelium forming the patients. The ability to see is an corneal endothelium and stromal amazing journey from fertilization keratocytes, the primary cells of to after birth. Any interruption or the stroma. To all that activity, add misstep along the way will result in the formation of the orbits and exeye and vision problems. traocular muscles at 4 weeks gesThe human eye begins to tation. Depending on eye growth develop during the 17th day of after birth, however, the orbits may gestation. Mesoderm cells, the not mature until adolescence. middle layer of the embryo, and The lacrimal glands begin ectoderm cells, the outer layer of to form during the 6th week, but the embryo, form the eye fields Figure 1. Cross section of embryonic mouse eye. there are no tears in the glands in the neural area of the embryo. (7 weeks comparable human development.) Orange area is the developing cornea, blue is the lens cavity until the 3rd month. At 8 weeks, Optic vesicles develop in the eye and green is the posterior lens fibers. the eyelids start to form and fuse fields, and in five days, infold to together to protect the other develform the optic cup. At this point, oping eye structures. (Figure 3) The eyelids begin to sepathe retina and crystalline lens begin to develop. In the rate in the 5th month, but it takes 2 months to complete mean time, surface ectoderm cells are becoming thicker. The lens forms from these thickened cells. By the 32nd day, the process. While the eyelids are fused, the corneal epithelium decreases back to 2 cells in thickness and enlarges you can actually identify the lens, and during the next 3 to 3-1/2 weeks the lens will grow to the size it will be at birth. and matures. The maturing, highly hydrated cornea does not become transparent until the 7th month when the eye (Figure 1) becomes functional. Bowman’s membrane develops durThe critical connection between the developing eye ing month 5 as the cornea becomes inervated. Descemet’s and the brain occurs at 36 days when the optic stalk, the membrane matures just prior to the eyelids opening. precursor to the optic nerve, connects to the forebrain. At 7 weeks the sclera develops from embryonic tissue, Between 30 and 35 days, you can see the start of the iris. which allows the formation of blood vessels. The cornea In 2 more weeks, it is fully developed. connects to the sclera which is nourished by blood. Then Eye development during the first trimester of pregwhy are there no blood vessels in the cornea? The answer nancy is like watching the Grand Finale of Fourth of July is that the cornea develops from ectoderm rather than fireworks. Cells and tissue develop quickly, and simultaembryonic tissue. This critical difference not only provides neously form various eye structures. For example, as the a clear medium for light, but the lack of blood minimizes lens is developing, the cornea forms from ectoderm cells covering the lens. At about 5 weeks of pregnancy this tissue tissue rejection in corneal transplants. During this time the retina is still evolving. It is 2 cells thick. What occurs over the next 2 weeks is amaztakes 6 months for the retinal layers to grow from ing. The 2 cells will nearly double, creating the corneal epithelium. (Figure 2) At this point, the lens has completed the neural ectoderm. The macula needs 4 or 5 12 w w w. c l s a . i n f o | c o n ta c t l e n s s o c i e t y o f a m e r i c a | EyEWitnEss spring 2011 Y http://www.clsa.info http://WWW.CLSA.INFO

Table of Contents for the Digital Edition of CLSA Eye Witness Spring 2011

CLSA Eye Witness Spring 2011

CLSA Eye Witness Spring 2011 - (Page Cover1)
CLSA Eye Witness Spring 2011 - (Page Cover2)
CLSA Eye Witness Spring 2011 - (Page 1)
CLSA Eye Witness Spring 2011 - (Page 2)
CLSA Eye Witness Spring 2011 - (Page 3)
CLSA Eye Witness Spring 2011 - (Page 4)
CLSA Eye Witness Spring 2011 - (Page 5)
CLSA Eye Witness Spring 2011 - (Page 6)
CLSA Eye Witness Spring 2011 - (Page 7)
CLSA Eye Witness Spring 2011 - (Page 8)
CLSA Eye Witness Spring 2011 - (Page 9)
CLSA Eye Witness Spring 2011 - (Page 10)
CLSA Eye Witness Spring 2011 - (Page 11)
CLSA Eye Witness Spring 2011 - (Page 12)
CLSA Eye Witness Spring 2011 - (Page 13)
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CLSA Eye Witness Spring 2011 - (Page 29)
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CLSA Eye Witness Spring 2011 - (Page 31)
CLSA Eye Witness Spring 2011 - (Page 32)
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CLSA Eye Witness Spring 2011 - (Page 35)
CLSA Eye Witness Spring 2011 - (Page 36)
CLSA Eye Witness Spring 2011 - (Page Cover3)
CLSA Eye Witness Spring 2011 - (Page Cover4)
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