The orbicularis oculi muscles are often examined in patients with facial paralysis. The orbicularis oculi is a muscle in the face that closes the eyelids. Since it pulls the eyebrows upward, it is the antagonist of the orbicularis oculi. However, the bulbus oculi is not completely spherical. Normally, the bulbus oculi is bulb-like structure. It may be of 5 types, depending on the location on the eyeball ("bulbus oculi"). Below the oculi are lunettes with images of statues in feigned monochromic marble. Concentric carved lines on stone balls appear to be stylised oculi. The apsidal western end has a central wheel window with smaller oculi in each face. Through the perforations in the lantern, sunlight illuminates the dome through an oculi. The galleries make heavy use of natural light through clerestories, oculi, and skylights. Here he painted an arbor pierced by oculi opening to glimpses of playful cherubs. There are 167 windows, including rose windows, round oculi, and tall, pointed lancet windows. Above each panel is a pair of circular oculi windows. In Early Christian and Byzantine architecture, there are examples of the use of circular oculi.