We now know the process of how we can perceive light at a molecular level. But how is the image formed?
Light from our surroundings enters our eye through the dioptric media --- cornea, lens, aqueous humour and vitreous body. Among these, the anterior part of the cornea accounts for providing nearly 2/3 of the refractive power, because it has a highly curved surface and high refractive index.
Light stimulates the photoreceptors on our retina to produce nerve impulses, which will travel along the optic nerve to the visual cortex of our brain. The image formed on the retina is real, inverted and smaller. However, on interpretation by the brain, the images will be upright. This is an inborn ability. Some people put it in this way: we 'see' with our brain, not our eyes.
You may have heard of some people who deliberately invert themselves (stand upside down). After some days, the brain will let them see upright images again.
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