When do rats open their eyes? - briefly
Laboratory rats generally open their eyes between post‑natal day 13 and day 15. Visual acuity reaches near‑adult levels by about day 18.
When do rats open their eyes? - in detail
Rats are born with their eyelids sealed. The eyelid membranes typically rupture during the second week after birth. In laboratory strains of Rattus norvegicus, the majority of pups open their eyes between post‑natal day 13 and day 15, with the median at day 14. Some individuals may begin as early as day 12 or as late as day 16, depending on genetic background and rearing conditions.
Key variables that can shift this timing include:
- Strain differences – albino versus pigmented lines show slight variations in closure duration.
- Litter size and maternal care – larger litters and reduced grooming can delay opening.
- Ambient temperature – cooler environments tend to prolong the sealed‑eyelid period.
- Nutritional status – inadequate milk intake may postpone development.
Eye opening coincides with other sensory milestones: whisker tactile sensitivity becomes functional around day 10, and auditory thresholds improve by day 12. After the membranes rupture, pup visual acuity remains low; functional vision develops progressively over the next two weeks, reaching adult‑like performance near weaning (day 21).
Researchers monitor the exact day of eyelid rupture as a standard developmental marker. Precise recording involves daily visual inspection of each pup from day 10 onward, noting the first sign of a clear cornea. This data assists in aligning experimental timelines across studies of neurodevelopment, pharmacology, and genetics.