Chronic venous insufficiency is a term used to describe the changes that can take place in the tissues of the leg, due to longstanding high pressure in the veins. There are many patients with typical changes of chronic venous insufficiency, but no obvious problem with their superficial veins. Credit to The Australian and NZ Vascular Surgeons who have extensive information on their website.
For additional reading here is a link to the Jobst US website
Note: when asked to provide treatment to clients with CVI, a GP or specialist approval / signoff will be sought.