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To the Editor.
—Dr. Stacy has focused upon an area that deserves a great deal of study and thought (ie, how to detect small amounts of corneal epithelial edema, and how to quantify epithelial edema).The method I chose to use (that of sclerotic scatter in a totally darkened room, without the use of the microscope) has been brought into question in rather firm terms.Both the method of sclerotic scatter and indirect retroillumination are based on the principle that an area of optical incongruity in the cornea (an area of different refractive index) will scatter more light than that of a normal cornea. Both methods ultimately depend upon the observer's ability to discriminate subtle changes in a transparent structure. Sclerotic scatter forces the observer to discriminate a fine patch of grey on light background, whereas indirect retroillumination requires the observer to discriminate a pattern of fine circles against a
Miller D. REPLY TO DR. STACY. Arch Ophthalmol. 1968;80(6):813. doi:10.1001/archopht.1968.00980050815027