The human eye has many different parts that are all needed to help us see, including rods, the optic nerve, and cones. The cones are receptor cells that help us see fine details of things and tend to help us see in situations where there is light or daylight. The majority of cones are in the center of the retina (we have approximately 6 million cones in each eye). When you squint to try to read or see something more clearly, what you are actually doing is focusing the image on this grouping of the cones in order to see the fine details. Cones also help us with color perception.