Naphthalene is known to cause cataracts (clouding over of the lens of the eye) in rats and rabbits. Therefore experimental animals are treated with naphthalene in order to model and study cataracts of elderly humans. It is thought that naphthalene causes cataracts through oxidative stress. Curcumin is the most active chemical part of turmeric, a spice used in Indian curry dishes. It is an effective antioxidant. These scientists studied whether low amounts of dietary curcumin slowed the formation of the cataracts usually caused by naphthalene in rats. They looked for apoptotic cells in the cells covering the lens by measuring DNA formation. Both treated rats and control rats were given naphalene to produce experimental cataracts. Only 0.005% (w/w) curcumin was added to the diet of the treated rats. The treated rats had significantly less clouding of their lenses as compared to the control rats. They found, for the first time, that cataracts caused by naphthalene involved apoptosis of the cells covering the lens. Apoptosis is a type of programmed, deliberate cell death in which the cell corpses and fragments are safely disposed. They also found that that curcumin reduced the apoptotic effect of naphthalene.