Our results show that cold thermoreceptors sensitive to small temperature changes are distributed throughout the entire ocular surface, most frequently in the highly vascularized perilimbal episclera, but also in the posterior segment of the eye. Nerve fibers activated by cold had spotlike receptive fields and responded to temperature reductions with a nerve impulse discharge that started as soon as the local temperature began to decline, and increased monotonically in firing frequency in parallel with the decrease in temperature.
http://www.iovs.org/cgi/content/full/44/2/697