Dark adaptation is the physical and chemical adjustments of the eye that make vision possible in relative darkness. Which option best describes this process?

• A. Physical and chemical adjustments of the eye that make vision possible in relative darkness.
• B. A process by which the eye adapts to bright daylight.
• C. The pupil's response to light intensity.
• D. A temporary loss of night vision.

Answer: (A)

Dark adaptation involves both a quick physical change and slower chemical changes in the retina that together make vision possible in low light. The quick part is the pupil dilating to let in more light. Over a longer period, the photoreceptors undergo chemical adjustments—primarily the regeneration of rhodopsin in the rods—so they become more sensitive to faint light. This combination lowers the threshold for detecting light and improves vision as it gets darker.

The other options miss how the eye actually adapts. Adapting to bright daylight describes light adaptation, not dark adaptation. The pupil’s response to light is only part of the process and doesn’t capture the chemical changes in the retina. A temporary loss of night vision describes impairment, not the normal adaptation that enhances vision in darkness.