Most eye tests performed in 8 hours

While at the eye doctor yesterday for a routine check-up, I noticed a plaque on the wall of the lobby. It was the word 'Guinness' that happened to catch my eye, and looking closer I realized it was a certificate from Guinness World Records recognizing the ophthalmology department I was in for performing the most eye tests in an 8-hour period: a total of 1,109 tests!

I hadn't known that speed eye testing was a thing.

However, some googling reveals that their record has subsequently been shattered. The Guinness website lists the current record holder as "V Senthilbalaji" of Karur, India, which performed 25,355 eye tests in 8 hours on April 4, 2015. (I'm assuming V Senthilbalaji must be the name of a hospital).

But what are the rules for gaining this record? Is there no limit on how many doctors can participate? In which case, speed isn't as important as just collecting a whole bunch of eye doctors in one place. And what exactly counts as an 'eye test'?

(My apologies for the lousy quality of the picture below. I'm blaming it on my phone's lousy camera. Or maybe I just need my eyes checked...)