DISORDERS IN RELATION TO THE EYE 763 



or the dark-brown which is usually reckoned as black. There is a marked 

 difference in individual irides in the distribution and arrangement of 

 the pigment granules, some irides appearing of an even tone and others 

 showing a marked speckling, usually of a lighter color than the even back- 

 ground. This too is a fruitful field for study, notably in lower animals 

 and in birds who show the most brilliant and variegated pigmentation of 

 the iris and of the tapetum. 



Pigmentation of the iris, resulting in a brown eye, appears to be a 

 dominant Mendelian characteristic. As this pigmentation associates with 

 a relative vagotonia it gives color to the hypothesis that dominant char- 

 acteristics are vagotonic and in some way connected with the hereditary 

 transmission of pigment and energy. A crossed or double influence is 

 noted in those cases in which we find a blue iris and dark hair as in cer- 

 tain Kelt-Iberians or the less frequent combination of brown eyes with 

 flaxen head-growth (Germanic-Latin mixtures in Swabia and Bavaria). 



The pigment of the lids is that of the common integument in general 

 and shows, both in health and disease, the same reactions, which are largely 

 endocrin. The disturbances in internal secretion which attend menstrua- 

 tion, pregnancy, the menopause, and senility are mirrored in pigment 

 anomalies among which we may cite chloasma and the irregular pig- 

 mentations of gerontoderma, and xanthelasma. Xanthoma diabeticorum 

 has almost a site- of election in the soft skin of the lids, and xeroderma 

 pigmentosum of heredito-specific origin often affects the conjunctiva as 

 well as the lids. Histogenetically, the superficiay epithelium of the cor- 

 nea is related to and must be reckoned with the lid-skin and conjunctiva 

 which it parallels in its clinical manifestations. 



The relation of pigment to hair is notable in the simultaneous oc- 

 currence of heavy brows, often tending to join, with dark irides and long 

 heavy lashes. Pigment changes in ocular disease are most striking in the 

 chorioretinal degenerations noted above, which depend on a specific 

 heredity probably mediated by a developmental or nutritional dyscrinism 

 which is quite analogous to the changes brought about by certain definite 

 vitamin deficiencies. 



Iris pigment may be so altered by chronic or relapsing inflammations 

 as to cause a marked difference in coloring of two originally like eyes 

 (heterochromia iridis) the degenerative nature of which is indicated by 

 the frequent association, with cataractous changes in the lens. Migration 

 of pigment from the iris into the tissues of the iris angle, the ligamentum 

 pectinatum, and the neighborhood of Schlemm's canal have been noted 

 both in glaucoma and in senile, otherwise normal eyes. 



Anomalies of Ocular Pigmentation. Irregular distribution, deficiency 

 or excess of ocular pigment is almost invariably associated with definite 

 forms of visual deterioration and evidence of degenerative, rather than 



