Ultrastructural changes to corneal stromal cells due to ophthalmic preservatives

Normal and keratectomised rabbit corneas received drops containing preservatives over a two day period. All preservatives investigated caused some change in the morphology of the stromal keratocytes, particularly in the absence of the anterior epithelial barrier. Thimerosal (0.004%) or disodium ethylenediaminetetraacetate (0.1% Na2EDTA) produced only minimum change. Chlorbutanol (0.5%) applied to intact corneas resulted in swelling of the cytoplasm and occasionally breaks in the external cell membrane, whilst in the keratectomised corneas some mitochondria showed swelling and distortion of cristae. In the normal cornea, benzalkonium chloride (0.02% or 0.01% with 0.1% Na2EDTA) resulted in intra and extracellular oedema and contraction of keratocytes. On removal of the superficial layers, there was extensive disruption of mitochondria, other organelles and outer cell membranes resulting in total destruction of some cells. Benzalkonium chloride should not be used on corneas with abnormalities of the epithelium.