Which part of the eye is primarily evaluated during an electroretinogram (ERG)?

An electroretinogram (ERG) primarily evaluates the function of the retina, specifically the photoreceptor cells known as rods and cones. These cells are critical for converting light into electrical signals, allowing the brain to perceive visual images.

When performing an ERG, electrodes are placed on the surface of the eye to measure the electrical responses generated by the rods and cones when they are stimulated by a light source. This test can provide valuable insights into the health and functionality of the retinal photoreceptors, particularly in diagnosing conditions such as retinitis pigmentosa or other retinal diseases.

The other parts of the eye listed—pupil, iris, and lens—are not the focus of this test because they do not directly contribute to the conversion of light into electrical signals. Instead, they play different roles in the overall function of vision, such as regulating light entry and focusing. Thus, the emphasis during an ERG is specifically on the rods and cones, making this answer correct.