They do cataract surgery in a trailer so eye exams should be dead easy!
Seriously; if the equipment is inadequate then just walk away; it’s your professional livelihood that’s on the line here. I’ve spent 15+ years locuming in everything from upmarket independent to scummy retail bucket shop & I’ve done days that I really should have walked away from. I’m slowly learning to look after myself a bit better.
If it was booked through an agency then tell the agency why you refused to work; as long as your concerns are reasonable then it should cause you no problems.