Which of the following does not consist of hair cells? 

Sensory hair cells are absent in the iris and fovea centralis. The iris contains smooth muscle fibers, and the fovea centralis contains a high density of cone photoreceptor cells for sharp vision.

Sensory hair cells are specialised cells found in certain sensory organs, such as the inner ear (cochlea) for hearing and the vestibular system (semi-circular canals, saccule and utricle) for balance.