General

Birds have excellent vision and - in relation to the size of the skull - large eyes. The shape of the eyes varies enormously, ranging from flattened (short anteroposterior axis; most birds) to globular (short anteroposterior axis with a cone shaped intermediate region; diurnal birds of prey) and tubular (long anteroposterior axis, nocturnal birds of prey).

Most prominent characteristics of a birds’ eye are the presence of scleral ossicules  (ossiculae sclerae) (the scleral plate) at the corneal –scleral junction , a cartilage layer in the sclera , the presence of striated muscles in the iris and ciliated body, an avascular retina with specialized double cones and the presence of a pecten oculi that projects from the optic disc in the vitreous body.