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The optic disc or optic nerve head is the point of exit for ganglion cell axons leaving the eye. Because there are no rods or cones overlying the optic disc, it corresponds to a small physiological blind spot in each eye. The ganglion cell axons form the optic nerve after they leave the eye. The optic disc represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together. The optic disc is also the entry point for the major blood vessels that supply the retina.〔blind spot. (2011). In Encyclopædia Britannica. Retrieved from http://www.britannica.com/EBchecked/topic/69390/blind-spot〕 The optic disc in a normal human eye carries from 1 to 1.2 million neurons from the eye towards the brain. ==Anatomy== The optic disc is placed 3 to 4 mm to the nasal side of the fovea. It is a vertical oval, with average dimensions of 1.76mm horizontally by 1.92mm vertically.〔Duane's Ophthalmology (2006). Ch. 4 Anatomy of the Visual Sensory System〕 There is a central depression, of variable size, called the optic cup. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「optic disc」の詳細全文を読む スポンサード リンク
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