Specular microscopy in the identification of deep corneal opacities

Specular microscopy provides a level of magnification and differentiation of detail which approaches that of a histological examination, and has the advantage of being a noninvasive procedure. This makes specular microscopy useful not only in examining the corneal endothelium, but also in identifying deep corneal opacities, which fall into two broad groups: 1) exogenous materials deposited in the cornea; and 2) endogenous pathologic corneal changes. Exogenous materials in the cornea have a wide variety of appearances, including the typical appearance of caterpillar hairs, the multifaceted appearance of glass foreign bodies, the regular geometric appearance of cholesterol crystals and cigar-shaped myeloma crystals or the more irregular deposits of chlorpromazine. Endogenous changes include ghost vessels, larger striate corneal nerves, fasciculi of fine parallel lines in keratoconus, criss-cross irregularly running lines in resolved keratitis, and a shagreen or cellophane-like appearance suggesting thickening of Descemet's membrane. While some deep corneal opacities are easily diagnosed clinically, the nature of others may be difficult to determine and specular microscopy is a valuable aid in such cases.