There are two major types of eye structures, simple and compound.
The simple eyes are only simple in structure, the term refers to an optical arrangement composed of a single lens and without an elaborate retina. Simple eyes were thought to not be involved in the formation of images, but only as monitors of levels of light intensity. They consist of a single lens and several sensory cells that are used to detect motion.
Compound eyes are a structure characterized by a variable number of small eyes called ommatidia one lens per eye, each optical unit that makes up a compound eye. Each function is an independent photoreception unit, with an optical system consisting of a cornea, lens, and accessory structures.
The differences between compound eyes and simple eyes:
- Compound eyes are made up of clusters of ommatidia, whereas simple eyes are made up of one single eye.
- Compound eyes are found in most arthropods, annelids, and mollusks.
- Compound eyes can cover a wider angle compared to simple eyes.
- The types of simple eyes are more diversified than compound eyes.
- The polarization of sunlight could be understood via compound eyes, but not simple eyes.
The human eye is still considered to be a simple eye structure, because of the single large lens. In a compound eye, the visual acuity is dependent upon the number and size of ommatidia in the eye structure. In the human eye, visual acuity is dependent on the density of photosensitive cells in the retina. The human eye is approximately one hundred times more improved than that of an insect’s compound eye structure.