CORNEA 



77 



this case the optical properties of the scar are such as to give rise 

 to a pictorial reproduction of its image at the posterior corneal 

 face of the block of light. It can be understood how an observer, 

 studying only the posterior face within a restricted field under a 

 high magnification of, say, X 35 or more, could misinterpret such 

 an optical effect as being a pathological condition at the posterior 

 face ; this mistake is particularly apt to be made by the beginner 

 when the false appearance is caused by minute bullae of the epithe- 

 lium of the anterior face whose shadows may make ring-like mark- 

 ings at the posterior face (see Fig. 46, C). This deeper optical 



B 



Fig. 45. — A, Scar of the anterior corneal face following 

 injury. B, Scar of the posterior corneal face following 

 surgical penetration. {Drawn by Theodore Ilamblin, Ltd.) 



modification of the corneal beam by surface features sometimes 

 makes it difficult to distinguish the exact depth to which a per- 

 forating injury, or its resulting scar, extends. Accidental per- 

 forations of the cornea nearly always leave for the rest of life 

 a scar detectable by slit-lamp examination. Clean deliberate 

 minute surgical penetrations often leave little or no evidence of 

 their course through the epithelium and the substance of the 

 cornea, whose cells regenerate to bridge the gap ; but every 

 surgical penetration which is complete and goes through the 

 posterior face leaves a permanent indication at this face, because 

 the hyaline material which is afterwards secreted by the endothelial 

 cells to fill the gap in Descemet's membrane is never in regular 



