Electroretinography is the study of retinal cell function. There are several types of electroretinograms (full-field, pattern, multifocal). Each type of test targets different types of cells in the retina.
The full-field ERG records a single response to a flash (or series of flashes) of light. The flash ERG is comprised of four basic parts, split into two sections.
A healthy eye has two types of photoreceptors - rods and cones, both named for their general shape. Cone cells are sensitive to color and are primarily responsible for daytime (photopic) vision, and rods are more sensitive to dim light, making them suited towards night-time (scotopic) vision. To test both rods and cones, the full-field ERG has a photopic (light adapted) section that tests primarily cone cell function, and a scotopic (dark-adapted) section that tests primarily rod cell function.
The light-adapted section of the ERG has two halves, a single flash response and a response to a rapidly flickering light.
The dark-adapted section of the ERG has three parts, a dim flash, a bright flash, and a very bright flash.