Direct answer first: The comb-like structure you’re asking about on a duck’s eye is called the pecten oculi. It is a specialized, comb-like projection of blood vessels in the choroid layer of the avian eye. It helps nourish the retina and may play a role in reducing light scatter and supporting metabolic needs of avian vision. Background and details
- What it is: The pecten oculi (Latin for “comb of the eye”) is a pigmented, non-sensory structure that projects into the vitreous humor from the region near where the optic nerve enters the eye. It often forms a pleated, accordion-like or comb-like appearance inside the eye, and in some birds can take conical or vaned shapes depending on species.
- Where it sits: It lies posteroventrally within the eye and is attached at its base to the optic disc, with folds extending toward the apex into the vitreous body.
- Function: The pecten oculi is thought to supply nutrients to the avascular retina and may help with metabolic support of retinal cells. It is not a sensory structure like the retina itself but a vascular adaptation related to retinal nutrition in birds.
- Variations among birds: Different species show variations in the pecten’s morphology—conical, pleated (accordion-like), or vaned forms—with multiple folds and a bridge-like region that connects folds at the apex. The exact shape and number of folds can vary by species and individual.
Extra context on related “comb-like” structures
- In birds, another famous comb-like structure is found in the bill, where lamellae line the edges of the beak to aid filtering and strain-water intake; these are keratinous processes rather than vascular structures and serve a different function from the ocular pecten.
- The term “pecten” is used in other contexts in biology to describe similar comb-like structures, including some bill lamellae; however, the pecten oculi specifically refers to the eye’s vascular comb in birds.
If you’d like, I can pull more specific examples for particular duck species (e.g., Baladi duck or dabbling ducks) or compare the pecten oculi to bill lamellae in terms of structure and function.
