Corneal button from a penetrating keratoplasty was prepared for histological examination. (A) This image is in the same area as the image in Figure 2 and indicates the deposition of Ig composed of kappa light chains by the immunoperoxidase reaction (brown stain). (B) Transmission electron microscopy uncovered electron-dense extracellular deposits in the same area that exhibited a honeycomb pattern or parallel linear structures with a periodicity of 10–11 nm (original magnification ×27,000). (Used from reference ⁷ with permission of Archives of Ophthalmology.)