Almost immediately after the development of the ophthalmoscope by by Helmholtz in 1851, atlases of the fundus of the eye began to appear. Great excitement reigned because one could at last see arteries and arterioles without the distortions of fixation and staining. It was quickly apparent that these vessels and their accompanying venules varied from patient to patient and that the site of crossing of an arteriole and a venule was particularly prone to alteration in patients with vascular disease. These "crossing phenomena" became the basis for many classifications of vascular disease and indeed even for the definitive diagnosis of specific illnesses. Gradually it became evident that the variety of responses that the retina could make to disease processes was limited and retinal vascular patterns became more a prognostic than a diagnostic tool.
Alas, even this illusion has now been taken from us. Our dearest ophthalmoscopic landmark, the A-V crossing,