Clinical Studies:

CVOS Study: early PRP for CVO

Summarized by Prethy Rao, MD MPH (Retina and Vitreous of Texas)

Citations: CVOS Group. A Randomized Clinical Trial of Early Panretinal Photocoagulation for Ischemic Central Retinal Vein Occlusion: The Central Vein Occlusion Study Group N Report. Ophthalmology 1995;102:1434-1444

  • Objective

    To evaluate the efficacy of early prophylactic panretinal photocoagulation (PRP) in the prevention of 2 clock hours of neovascularization of the iris or any angle neovascularization (TC-INV/ANV) in patients with ischemic retinal vein occlusions versus therapeutic PRP after the development of TC-NVI/ANV


    Multicenter, randomized, controlled trial

  • Duration

    3 years


Randomization scheme and interventions:

Randomized 1:1

  1. (a) Early PRP before TC-INV/ANV ("early treatment group")
    • Supplemental fill in PRP was performed when TC-INV/ANV developed in a prophylactically treated eye.
  2. (b)Delayed PRP after TC-INV/ANV ("no early treatment group")
    • PRP was also permitted for eyes that developed retinal neovascularization in the "no early treatment group."

Method of PRP: The settings were the following: spot size 500-100 microns, moderate intensity, 0.2 second duration, 0.5-1 burn width apart. Treatment was applied in all quadrants and avoided over areas of retinal hemorrhages or retinal vessels. Laser was not done less than 2 DD from the fovea or < 500 microns nasal to the disc

Follow up: Patients were followed monthly with serial slit lamp examinations, gonioscopy, and slit lamp photographs for up to 6 months, 8 months after entry, then q 4 months until the end of the study duration. Fluorescein angiograms were obtained at baseline and then annually. Patients that developed TC-INV/ANV were followed monthly until deemed stable (minimum of 6 months of follow up).

Study Duration: 3 years



Study population



Adverse events