To the Editor. —In the article in Archives by Mackool and Holtz (95:459-463, 1977), the authors discuss Descemet's membrane detachment, but they seem to have missed the boat. Descemet's membrane detachments are due to a dull knife at cataract surgery or at any other surgery that involves cutting through this membrane. Let's remember that Descemet's membrane is very, very tough; it is the last to rupture with a corneal ulcer. Mackool and Holtz never mention the cause of detachment of Descemet's membrane. They mentioned that they used a razor-blade knife, but I wonder about the usage of this instrument. I have found that a straight puncture wound is notoriously bad; the tip of the knife does not get through the Descemet's membrane but then the tip may push on into the anterior chamber and rip the Descemet's membrane off. I have found it better to cut into the anterior chamber using