Morphological study of the pathogenesis of retinal cotton wool spot.

To investigate the true structural changes in retinal cotton wool spots, serial sections of several blocks of retinal corresponding to cotton wool spots obtained from two hypertensive cases were studied by light and electron microscopy. Occlusion of the feeder arteriole and capillaries, and numerous vacuoles of various sizes in the inner retinal layer were the constant histological features in cotton wool spots. Cytoid body was another change in these areas but it was not a constant feature. Increase of membranous structure resembling endoplasmic reticulum was thought to be incorporated in the formation of the pseudonucleus in the cytoid body. Phagocytosis by macrophages led to the disappearance of the cytoid body. It was concluded that the true feature of the cotton wool spot is nothing but vacuolation, an edematous change of the inner retinal layers due to ischemia following occlusion of the feeder arteriole, and that the cytoid body is only a nonspecific and transient alteration of nerve fibers in the early stage of the ischemic lesion in the retina.