A google search yielded a pixel to millimeter converter that requires you to also input pixel density (dpi). Hope this helps. https://www.pixelto.net/px-to-mm-converter

Our old ASL 501 uses a BRIGHT PUPIL approach. Hence, we constructed an artificial eye (4 mm white disk centered in a black surround) and glued this to a tongue depressor (flat stick). After calibrating the eye tracker, we have the participant close their eyes, lay the artificial eye on top of their closed eye lid and then record the instantaneous pupil diameter (pixels) displayed on the GUI screen. A fresh tongue depressor is prepared for each new participant to preserve good hygiene. Knowing the number of pixels subtended by a 4mm target at the working distance allows us to convert raw diameter in pixels to mm. If the H6 uses a DARK PUPIL just reverse the contrast of your artificial eye (i.e., black pupil with white surround). Hope that helps.

Thank you Anastasia Gorbunova . Unfortunately, I don't have this info at the moment, but I will consider your answer.

Frank Schieber thank you for your reply. The H6 works with the same reflection method (bright pupil). The artificial eye is also instructed by ASL user guide and seems efficient. If the system uses 2D images to discriminate reflected and non-reflected pixels, a cardboard print with known ''pupil'' size should work too, what do you think? It would be easier to lay on, handle and store it, besides the cheap but existing costs.

A cardboard print with a "white" pupil of known diameter should work just fine.

Hello sir,I am also working on Pupillometry. I would like to share one of my published article which yields pupil size and response to light. I hope it will be useful for the same. Find the attachment

Dear Siva, thank you for sharing your work, I really appreciate it. I will take a look on it. I am currently working on various pupil analysis, so it will be of great value.

Best regards,

Gabriel.