Patients with chronic CRVO who are receiving monthly injections of Bevacizumab treatment for at least 12 months will be recruited. Upon recruitment each patient will undergo a screening Ophthalmologic examination including visual acuity, refraction and OCT. This will be followed by a series of 40 daily hyperbaric chamber treatments. A repeated ophthalmic examination will be done after 20 and 40 hyperbaric sessions.