The two main types of eyes are the front-facing main eye, called ocelli and secondary eyes. In other arthropods, ocelli only detects the direction of light, but in spiders, these eyes form a true image. The primary eye contains the muscles that move the retina to focus and track the image. Most spiders have poor eyesight, but the ocelli in the jumping spider exceeds the cockroach (the insect with the best vision) and is close to the human spider. Due to their location, ocelli is also known as the pre-media eye or AME. Secondary eyes come from compound eyes, but they have no facets. They are usually smaller than the main eye. These eyes lack muscle and are completely motionless. Most secondary eyes are round, but some are oval or half moon shaped. Identify the eye based on location. The anterior lateral eye (ALE) is the apical eye on the side of the head. The posterior lateral eye (PLE) is the second row of eyes on the side of the head. The posterior median eye (PME) is located in the middle of the head. The secondary eye may face forward, or be on the side, top or back of the spider’s head. Secondary eyes have multiple functions. In some cases, the lateral eye enlarges the range of the dominant eye, making the arthropod a wide-angle image. The secondary eye acts as a motion detector and provides depth perception information to help the spider locate the distance and the direction of the prey or threat. In nighttime species, the eye has a tapetum that reflects light and helps the spider see it in dim light. Spiders with tapetum show a shimmering glow when illuminated at night.