Eye problems after surgery

A family member a week ago had surgery on his left Bicep after a rupture. He has had his arm in a sling the entire time and will for 6 weeks while it heals. In the past few days he has been complaining of blurry eyesight (he has a cataract but this is much worse than usual), double vision and strain in the opposite eye to his arm. Halfway through today it has been occasionally going cross eyed with that eye. Is it pressure from the sling on his neck? Is there anything we can do?

Gender: Male

Age: 62

Height: 176cm

Weight: 100kg

Medication: Tapentadol SR (current) , Celebrex (Finished)

Smoking: Cannabis