146 VITAMINS A AND CAROTENES 



sible for the greyish-yellow discoloration especially apparent grossly in the 

 conjunctivae of the fornices and semilunar fold; there may also be migration 

 of chromatophores from the limbal pigment ring, giving rise to a smoky 

 discoloration of the bulbar conjunctiva. 



Bitot's spots represent one of the most characteristic features of well- 

 established xerophthalmia. They consist of sharply defined, rounded, tri- 

 angular (with base toward the corneal limbus), or striated and band-like, 

 whitish, foam-like patches located on the sclera of the temporal (usually) 

 palpebral fissure. FasaP^ provides a good picture of these spots. These areas 

 are not wetted by tears, and consist of accumulations of epithelial debris, 

 sebum from Meibomian glands, fatty globules, and masses of xerosis bacilli 

 and other organisms. They detach readily and are rarely seen in histologic 

 sections of the eyeball. ^^ When scraped away they reform rapidly. Patchy 

 islands of xerosis resembling Bitot's spots, often coalescing into much larger 

 placques, may occur on the more protected surfaces of the sclera, in more 

 advanced stages. ^^ It is worthy of note that a chronic type of Bitot's spot, 

 not associated with low vitamin A blood levels or other evidence of the 

 deficiency state and not responding to vitamin A therapy, has been re- 

 ported from Java^^ and Trinidad.-^ 



The cornea shows increasing opaqueness and thickening; patchy areas 

 of xerosis, resembling Bitot's spots, sometimes occur. ^^ This is followed by 

 exfoliation of the epithelial surface, bacterial invasion, thickening and 

 edema of the stroma, infiltration of lymphoid cells and leucocytes, ingrowth 

 of blood vessels and focal necrosis leading to ulceration, perforation, and 

 other ocular pathology such as is observed after various tj'^pes of corneal 

 injury. A thickening of nerve fibers distributed to the cornea, ^^ and pro- 

 nounced loss of sensibility of corneal and scleral surfaces, ^^' -^ have led to 

 suggestions that the ocular lesions, and alterations of epithelia elsewhere, 

 might be secondary to degenerative changes in sensory nerves and indicate 

 a neurotrophic function of vitamin A. This concept has not been supported 

 by careful experimental studies on rabbits,'-^' -^ in which the ocular changes 

 occurring in vitamin A deficiency and during therapeutic repair are quite 

 comparable to those observed in man. 



The histopathology of the lacrimal gland, palpebral conjunctiva, and 

 glands of the eyelids has not been explored. On the basis of gross observa- 

 tions of the ocular apparatus, and pathologic changes observed in other 

 epithelia, it would seem that the palpebral conjunctiva suffers no more 



22 P. Fasal, Arch. Dermalol. and Syphilol. 50, 160 (1944). 



23 Sie-Boen-Lian, Albrecht von Graefe's Arch. Ophthalmol. 139, 17 (1938). 



24 V. M. Metivicr, Am. J. Ophthalmol. 24, 1029 (1941). 



25 I. John, Arch. Ophthalmol. (Chicago) 5, 374 (1931). 



26 M. V. Radhakrishna Rao, Indian J. Med. Research 24, 439 (1936). 



27 I. A. Mann, A. Pirie, K. Tansley, and C. Wood, Am. J. Ophthalmol. 29, 801 (1946). 



