Vocabulary List, Eyesight
Fovea: a small area on the retina constituting the area of most distinct vision. Hawks, falcons, and other fast-flying birds have 2 fovea – a central one and a temporal one, allowing them to focus on two distinct images simultaneously Nictitating Membrane: a third eyelid found in birds, reptiles, and some fish; this eyelid comes across the eye from the side, often when a raptor is diving after prey, in order to protect the eyeball from debris and keep it moistOptic nerve: a bundle of nerve fibers connecting the retina of the eye with the brain Scleral ring: the bony ring which holds a raptor’s eyeball in place in the skull Rods: light-sensitive cells lining the retina of the eye; they are particularly good at detecting low light levels, but not in differentiating color Cones: cells lining the retina that are responsible for visual acuity and sensing color information. Birds typically have more cones in their eyes than do humans, allowing them to see more than 3 primary colors. Oil droplets are also present in these cells, functioning like filters which alter color in the same way pink or yellow sunglasses do. UV light: light wavelengths of 3000-4000 angstroms (300-400 nanometers), invisible to humans, but visible to most other species Cornea: the transparent layer of the eye, found anterior, and whose curvature effects focusing capabilities, or ‘accommodation’ Lens: structure in the eye responsible for focusing. The curvature of the lens changes when the attached ciliary muscles contract and relax. Accommodation: focusing adjustments made by the lens and cornea of the eye
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