The link says it is a funduscope, meaning she can image her retina with it. It is basically a camera with a very specialized optics package that allows for taking photos through the lens of the eye. See https://en.wikipedia.org/wiki/Ophthalmoscopy for examples of retinal imaging.
Astronaut Serena Auñón-Chancellor, a member of the Expedition 56 crew currently aboard the International Space Station, examined her eye with a Funduscope with remote support from doctors on the ground. (emphasis added)
There seems to be something about spaceflight that impairs vision (https://www.nasa.gov/mission_pages/station/research/experiments/1038.html) and this may be connected to experiments trying to find a cause.
the OIS logo seems to belong to a (defunct?) manufacturer of opthalmography equipment: google "ois winstation"
Hypoperfusion (meaning less blood flow than necessary) is detectable on funduscopy images, especially if they have access to pictures taken before the flight for comparison.
The link i gave above, about the immpaired vision after spaceflights, mentions ocular flattening - a usual funduscope would not be able to give measurements on that, but this one has an unusally long tube, so maybe the optics allow for more measurement modes?
Other pictures with the same instrument cite a 'ocular health' experiment that is ongoing on ISS: https://www.nasa.gov/mission_pages/station/research/experiments/204.html;
It says about funduscopy:
Fundoscopy: Direct fundoscopy is performed on the right and left eye
to obtain images of the retinal surface. Subjects receive this exam as
part of their preflight, in-flight, and postflight ophthalmological
assessment. Since dilation is required for fundoscopy testing,
sessions are scheduled around in-flight piloting, EVA and docking
activities. All in-flight exams are remotely guided. Still images and
short cine clips are recorded. Up to four additional examinations may
be conducted postflight if abnormalities of the fundus persist.
The funduscopy is the only test in the 'ocular health'-experiments that can be done with the instrument held like that.