Sperduto RD, Hiller R, Chew E, Seigel D, Blair N, Burton TC, Farber MD, Gragoudas ES, Haller J, Seddon JM, Yannuzzi LA. Risk factors for hemiretinal vein occlusion: comparison with risk factors for central and branch retinal vein occlusion: the eye disease case-control study. Ophthalmology. 1998 May; 105(5):765-71.