Contributors: Richard J. Grostern and Daniel M. Albert
Oxalosis (hyperoxaluria) is a disorder in which there are excessive levels of oxalic acid in the serum and urine. The condition is divided into two main types: primary oxalosis [oxalosis - primary] and secondary oxalosis [oxalosis - secondary]. Excess oxalic acid in the blood combines with calcium to form calcium oxalate crystals which precipitate in tissues. These crystals have been found in the kidney, thyroid gland, walls of blood vessels, myocardium, and the retinal pigment epithelium.Common ocular findings include the clinical appearance of a flecked retina. Flecked retina syndrome has been reported in several cases of oxalosis  in association with methoxyflurane toxicity, both through iatrogenic use and abuse of methoxyflurane. Fine yellow crystalline deposits are seen throughout the fundus. Areas of retinal ischemia may also be found in the form of cotton wool spots, presumably as a result of small vessel occlusion. On histopathologic examination of tissue from one case calcium oxalate crystals were noted at the level of the retinal pigment epithelium and ciliary body pigment epithelium. The examiners of a methoxyflurane abuser noted crystals at the level of the neural retina and the retinal pigment epithelium on clinical examination. In both cases renal failure from secondary oxalosis was present, as proven by biopsy. Serum oxalate levels can be measured. Tissue biopsy can easily reveal the presence of calcium oxalate crystals.