and the fovea is the area of the eye with the highest sensitivity to fine details. Cones in the central fovea express opsins that are sensitive to green and red light. These cones are the 'midget' pathways that also underpin high acuity functions of the fovea. The fovea is employed for accurate vision in the direction where it is pointed. It comprises less than 1% of retinal size but takes up over 50% of the visual cortex in the brain. The fovea sees only the central two degrees of the visual field, (approximately twice the width of your thumbnail at arm's length). If an object is large and thus covers a large angle, the eyes must constantly shift their gaze to subsequently bring different portions of the image into the fovea (as in reading). Foveal fixation is also considered as a overt form of attention which allows to focus sensory processing resources on the most relevant sources of information. Also, foveated vision may allow speeding up learning of specific visual tasks by disregarding not relevant context and focusing on the relevant information only with lower dimensionality. Since the fovea does not have rods, it is not sensitive to dim lighting. Hence, in order to observe dim stars, astronomers use averted vision, looking out of the side of their eyes where the density of rods is greater, and hence dim objects are more easily visible. The fovea has a high concentration of the yellow carotenoid pigments lutein and zeaxanthin. They are concentrated in the Henle fiber layer (photoreceptor axons that go radially outward from the fovea) and to a lesser extent in the cones. They are believed to play a protective role against the effects of high intensities of blue light which can damage the sensitive cones. The pigments also enhance the acuity of the fovea by reducing the sensitivity of the fovea to short wavelengths and counteracting the effect of chromatic aberration. This is also accompanied by a lower density of blue cones at the center of the fovea. The maximum density of blue cones occurs in a ring about the fovea. Consequently, the maximum acuity for blue light is lower than that of other colours and occurs approximately 1° off center. Angular size of foveal cones On average, each square millimeter (mm) of the fovea contains approximately 147,000 cone cells, or cones per millimeter. The average focal length of