General Differences
In general, feline eyesight works exactly the same as human eyesight. However, there are some differences. For example, felines have a larger cornea which allows more light to enter the eye. The feline pupil can also be shaped differently: vertical slit when constricted and a round shape when dilated. The slit shaped pupil allows more light to enter the eye in dimmer conditions (Malmstrom et al., 2006). There are also some more subtle differences such as the iris being paler than that of the human. The main goal of these differences is to help protect the eye as well as to allow more light to enter so that a feline can see easier when there is no light.

Image courtesy of www.sailblogs.com

Third Eyelid
There is one major difference between the human and feline eyes: the presence of the third eyelid. Felines have upper and lower eyelids, like humans, in order to help sheathe the eyeballs. However, for further protection, all felines have an opaque, white third eyelid, between the lower lid and inside corner of each eye. This layer helps moisten the eye and clear dust from the surface of the cornea (Nuyttens et al., 1994). This third eyelid cannot be easily seen. However, it being visible is a sign of poor condition or ill health for the feline eye. Therefore, feline eyes are often used for medical studies because of this obvious symptom. For example, studies are being done on optical neuritis. When a feline develops optical neuritis the third eyelid become easily visible. Thus research is being done on felines in hopes for finding medical solutions for optical neuritis in humans (Nell, 2008). Due to the third eyelid, felines make very god test subjects.

Picture of third eyelid protruding from a feline's eye (Image courtesy of www.vetmed.wsu.edu)

Questions or Comments? Please e-mail me at mirogers@davidson.edu