Eye-pod

Eye-pods were the eyes of the Cybermen, which granted them vision. Matching the original humanoid form, the eye-pods numbered two on the faceplate of the Cyber-helmet. (PROSE: Earthshock, The Tenth Planet et al.) A feature of the eye-pod in several but not all Cyber-subspecies was the presence of "tear drop" etchings. (AUDIO: The Early Cybermen, TV: The Wheel in Space et al.)

Variants
The CyberMondasians had eye-pods with no tear drops. In certain cases at least, their organic eyes still remained and were visible behind the eye-pod. (TV: The Tenth Planet, World Enough and Time)

The CyberTelosians had eye-pods with no tear drops. (TV: The Moonbase et al.)

The Cybermen of the early CyberFaction had eye-pods with tear drops. (TV: The Invasion et al.) These were retained by the later CyberFaction. In addition, the mouth slit sported a similar drop shape. (TV: The Wheel in Space)

Cybermen of Pete's World were able to establish a visual link, transmitting the vision of their eye-pods to other devices. During the Battle of Canary Wharf, Cyber-Units Ten-Six-Five and Ten-Six-Six opened a visual link connected to a laptop computer within Torchwood Tower, allowing Cyber-Leader One to witness the disastrous confrontation with Dalek Thay and make visual contact with Dalek Sec, meeting the Cult of Skaro's communications barrier. (TV: Doomsday)

The eye-pods of the Cyberdrones, who appeared as disembodied Cyber-heads, gave a blue glow of light as they served as both a means of vision, providing a heads-up-display to pinpoint targets, and an energy weapon, firing blue pulses. (TV: Ascension of the Cybermen)

Individual cases
Turning against the Cybermen following her upgrade to Cyber-form at Canary Wharf, Yvonne Hartman was seen to shed what appeared to be a tear of oil from her left eye-pod. (TV: Doomsday)

Following her conversion into a Mondasian Cyberman aboard the Mondasian colony ship, Bill Potts appeared to shed a tear, which the Twelfth Doctor found to be a real tear. As it turned out, the tears had been left to Bill by Heather, in the form of the sentient oil. (TV: The Doctor Falls)

Having undergone a partial cyber-conversion, Ashad's human body was housed in an incomplete, weathered Cyber-suit resembling those associated with the Cyberiad, (TV: Nightmare in Silver) but with an unique Cyber-helmet with an incomplete faceplate that exposed the left side of his face including his eye. (TV: The Haunting of Villa Diodati, Ascension of the Cybermen)

Behind the scenes
Ascension of the Cybermen featured a smooth transition from the "cold opening" into the title sequence, with the scene going through the eye-pod of a Cyber-helmet.