How Is an Image Formed in the Human Eye?
An image is formed in the human eye when light passes through the pupil, is refracted by the lens and is absorbed by pigment cells in the retina, altering the pigments and triggering neurons to fire. The particular arrangement of the stimulated cells is interpreted by the brain into a separate image for each eye. The two eyes look at images from slightly different angles, allowing the perception of depth.
The human eye is a complex organ capable of perceiving relatively great detail. While other organisms have better vision in low-light conditions or at great distances, the combination of precise color perception, depth perception and general acuity at close distances is very strong in humans. The eyes are capable of adapting to varying distance and light levels.
When light passes through the lens, it is inverted, so light that hits the top of the retina comes from the bottom of the field of view and the light on the left of the retina comes from the right part of the field of view. The brain automatically reorients this information to its proper location. The retina has two different types of sensors, rods and cones, which are responsible for low-light vision and color vision, respectively.