Inside a Damselfly Eye

What am I looking at?

This is a coronal section (a slice from top to bottom) through a single eye of the common blue damselfly (Enallagma cyathigerum). The cells’ nuclei are labeled in red (1) and show the location of the cell bodies of photoreceptors and other supporting cells. You can see the arrangement of these cell bodies even better in the second image. The actin protein is labeled in blue (2) and outlines the supporting structure of the individual rod-shaped segments of the eye.

Biology in the background

Insects’ eyes are very different from humans’ camera-like eyes. However, each type of eye has a lens, cells called photoreceptors that detect light, and other cells that support the photoreceptors and help process visual information.

Insect eyes are classified as compound eyes because they have multiple units within the eye that can detect light. In contrast, mammals have a single continuous unit (called the retina) that detects light. Compound eyes are made of rod-like, cylindrical units called ommatidia, each of which is equipped with a corneal lens that focuses light onto the photoreceptor cells. These units are separated from their neighbors by a barrier of pigment cells. Within the ommatidia, eight photoreceptor cells are aligned along the length of each ommatidium, forming a structure called the rhabdom.

This image is about 1 millimeter across, or roughly 13 times larger than the width of a human hair.

Technique

This image was created using confocal microscopy.