After the lens, light passes through the vitreous humor of the posterior chamber and is projected onto the layers of the retina (eFig. 9.73). The retina is composed of a non-neural layer and several layers of neural cells with synaptic connections. To reduce the amount of light reflected in the eye, the choroid layer lining the inner surface of the sclera (eFig. 9.72), along with the pigment epithelium layer (non-neural) of the retina, absorb and refract some of the light stimulus (eFig. 9.73). Interdigitating between the pigment epithelial cells, the photoreceptors transduce the light stimulus into an electrical signal in a process called phototransduction. Images formed on the retina are inverted in both vertical and lateral dimensions (eFig. 9.74). Because of this, the visual field is defined as having four quadrants: left/right and upper/lower.