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Transverse section of head of chick embryo of forty-eight hours’ incubation Transverse section of head of chick embryo of fifty-two hours’ incubation, showing the lens and the optic cup. Eye formation in the human embryo begins at approximately three weeks into embryonic development and continues through the tenth week. [1]
The eyes begin to develop as a pair of diverticula (pouches) from the lateral aspects of the forebrain.These diverticula make their appearance before the closure of the anterior end of the neural tube; [1] [2] after the closure of the tube around the 4th week of development, they are known as the optic vesicles.
Pax6 is a transcription factor that is essential to the development of the lens placode. More specifically, it is needed for the surface ectoderm to fully develop. Pax6 has been identified as a necessary transcription factor for the thickness of the lens placode. [3] SOX2 is a transcription factor that works alongside Pax6 to develop the lens ...
During embryonic development of the eye, the outer wall of the bulb of the optic vesicles becomes thickened and invaginated, and the bulb is thus converted into a cup, the optic cup (or ophthalmic cup), consisting of two strata of cells.
Closure of the choroidal fissure in the optic stalk occurs during the seventh week of development. The former optic stalk is then called the optic nerve . [ 3 ] In short, the optic stalks are the structures that precede the optic nerves embryologically .
The human eye, showing the iris and pupil. In 1802, philosopher William Paley called it a miracle of "design."In 1859, Charles Darwin himself wrote in his Origin of Species, that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree". [3]
The ectoderm generates the outer layer of the embryo, and it forms from the embryo's epiblast. [13] The ectoderm develops into the surface ectoderm, neural crest, and the neural tube. [14] The surface ectoderm develops into: epidermis, hair, nails, lens of the eye, sebaceous glands, cornea, tooth enamel, the epithelium of the mouth and nose.
Human embryonic development covers the first eight weeks of development, which have 23 stages, called Carnegie stages. At the beginning of the ninth week, the embryo is termed a fetus (spelled "foetus" in British English). In comparison to the embryo, the fetus has more recognizable external features and a more complete set of developing organs.