Horizontally elongated optic nerve heads

Lindsay A. Kuester et al. (Veterinary Ophthalmology, V. 7, no. 3, 169–173, 2004) note that ‘The squirrel is the only mammal, to our knowledge, with a dramatically horizontally elongated ONH.’ We wish to expand upon that knowledge by noting that we have observed a similarly shaped optic nerve head (ONH) in various members of the deer family including the white-tailed deer ( Odocoileus virginianus ; Fig. 1a); 1 the fallow deer ( Cervus dama ; Fig. 1b); 1 red brocket deer ( Mazama americana ; Fig. 1c); 2 Pere David’s deer ( Elaphurus davidianus ; Fig. 1d); 2 and red deer ( Cervus elaphus ). 3 We concur with Kuester et al . that the ‘why’ relating to this shape is not readily discernible; especially in that deer would most likely have a rod-dominant retina vs. the conedominant squirrel.