The image which is formed on the retina through the lens of the eye is very similar to a pin-hole camera, the image is reversed both horizontally and vertically. The lens of the eye is purely used to focus this images.
2006-06-28 00:48:58
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answer #1
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answered by danparker_58 2
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In adult humans the entire retina is 72% of a sphere about 22 mm in diameter. At the center of the retina is the optic disc, sometimes known as "the blind spot" because it lacks photoreceptors. It appears as an oval white area of 3 mm2. Temporal (in the direction of the temples) to this disc is the macula. At its center is the fovea, a pit that is most sensitive to light and is responsible for our sharp central vision. Human and non-human primates possess one fovea as opposed to certain bird species such as the hawk who actually are bifoviate and dogs and cats which possess no fovea but a central band known as the visual streak. Around the fovea extends the central retina for about 6 mm and then the peripheral retina. The edge of the retina is defined by the ora serrata. The length from one ora to the other (or macula), the most sensitive area along the horizontal meridian is about 3.2 mm.
In section the retina is no more than 0.5 mm thick. It has three layers of nerve cells and two of synapses. The optic nerve carries the ganglion cell axons to the brain and the blood vessels that open into the retina. As a byproduct of evolution, the ganglion cells lie innermost in the retina while the photoreceptive cells lie outermost. Because of this arrangement, light must first pass through the thickness of the retina before reaching the rods and cones. However it does not pass through the epithelium or the choroid (both of which are opaque).
The white blood cells in the capillaries in front of the photoreceptors can be perceived as tiny bright moving dots when looking into blue light. This is known as the blue field entoptic phenomenon (or Scheerer's phenomenon).
Between the ganglion cell layer and the rods and cones there are two layers of neuropils where synaptic contacts are made. The neuropil layers are the outer plexiform layer and the inner plexiform layer. In the outer the rod and cones connect to the vertically running bipolar cells and the horizontally oriented horizontal cells connect to ganglion cells.
The central retina is cone-dominated and the peripheral retina is rod-dominated. In total there are about six million cones and a hundred and twenty-five million rods. At the centre of the macula is the foveal pit where the cones are smallest and in a hexagonal mosaic, the most efficient and highest density. Below the pit the other retina layers are displaced, before building up along the foveal slope until the rim of the fovea or parafovea which is the thickest portion of the retina. The macula has a yellow pigmentation from screening pigments and is known as the macula lutea.
2006-06-28 01:01:02
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answer #2
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answered by Anonymous
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That is a great THINK ABOUT IT. Another one is the newest research into the Heart/Brain connection. There is a great Bible Scripture that says, "In the latter days that men's hearts will fail them for looking after the things that are coming upon the earth." When a person feels stress, feels overwhelmed,anxious, uncertain and fear, the heart is sending chaotic and incoherent signals to the brain/mind, triggering stressful responses. The higher cortical functions are inhibited, meaning the heart and brain are out of alignment. When the heart and brain are aligned one feels more wholeness and solutions to problems are more apparent. Evidently the heart is more important than the brain because it forms in the body and starts beating before the brain is formed. Scripture tells us in Proverbs 4 to "Guard your heart with all dilligence, because out of it flows the issues of life." The heart receives from nerve endings and from blood and "life is in the blood " as said in Scripure. Very interesting!
2016-03-27 06:44:15
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answer #3
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answered by Anonymous
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The image is
inverted
diminished
real
2006-06-28 02:45:25
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answer #4
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answered by utkarsh 3
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an inverted,real image of the object on the retina.
2014-04-03 16:56:06
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answer #5
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answered by shaz 2
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the image that the retina forms is inverted.
2006-06-28 01:15:33
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answer #6
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answered by JaSmiNE 2
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real and inverted
2015-04-03 03:05:51
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answer #7
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answered by n 1
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its upside down
2006-06-28 00:45:57
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answer #8
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answered by blueblast66 1
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