Question

On entering a dark room (dark adaptation), which of the following physiological changes occur in the eye? (Select all that apply)

• A. Conversion of all-trans retinol towards regeneration of rhodopsin photopigment
• B. Mydriasis (pupillary dilatation)
• C. Photopsin and retinal recombine to form rhodopsin (not the reverse)
• D. Increased sensitivity of the retina to light

Hint:

Dark = pupil dilates, rhodopsin regenerates, sensitivity rises; bleaching to opsin happens in light.

Answer 1

The Correct Option is A, B, D

Step 1: Understand dark adaptation.
When a person moves from bright light into a dark room, the retina gradually becomes more sensitive over ~20-30 minutes. This is mediated by regeneration of visual pigments (rhodopsin in rods) and pupillary dilatation.

Step 2: Analyse each statement.
• Mydriasis - correct. In darkness the pupil dilates to allow more light onto the retina. This is an early, rapid component of dark adaptation.
• Increased sensitivity to light - correct. Regenerated rhodopsin and the shift to rod-dominated (scotopic) vision markedly increase retinal sensitivity.
• Retinol channelled to regenerate rhodopsin - correct. In the visual cycle, 11-cis retinal (derived from vitamin A / retinol) recombines with opsin to re-form rhodopsin. So vitamin A metabolism feeds pigment regeneration in the dark.
• Rhodopsin/opsin to photopsin conversion - INCORRECT as written. Bleaching of rhodopsin into opsin + all-trans retinal happens in LIGHT, not in the dark. In darkness the reverse occurs (rhodopsin is re-formed). “Photopsin” refers to cone opsins, not the rod bleaching product, so option 3 is the wrong/false statement.

Step 3: Key fact.
Dark adaptation = pupillary dilatation + regeneration of rhodopsin (using vitamin A) + heightened retinal sensitivity. Bleaching of pigment is a light-phase event, so option 3 is false.