476 PROE. B. C. A. WIlvrDLE ON TEBA.TOLOQ-ICA.L EVIDElfCE 



Absence of Iris. — Page* has recorded a case where this con- 

 dition, combined with microphthalmus and nystagmus, existed 

 in a mother, two daughters, and a grand-daughter, two sons and 

 a daughter having escaped. Sedgwick t quotes another where 

 absence of iris ran through three generations. There can be no 

 doubt that this is a blastogenic condition. 



Colohoma. — A failure to close completely on the part of the 

 choroidal fissure, doubtless blastogenic in its nature, though 

 whether due to defect of material or to a nervous cause is not 

 certain. It is hereditary, and Darwin $ has given a case where 

 it passed through four generations. 



Congenital Dislocation of the Lens. — I give here a table, drawn 

 up by Stanford Morton §, where this curious condition was 

 hereditary. 



M.X 



M.X M.n. M.n. M.n. M.X M.x M.X M.x M.x F.n. E.n. P.n. 

 P. X 



M.X M. M.n. M.n. F.n. F.n. M.x 



I I I I III 



M.X F.n. F.n. F.x M.x F.n F.n. 



This defect "is sometimes associated with coloboma of the 

 choroid or optic disc, sometimes with persistent hyaloid artery ; 

 more frequently it is met with in eyes which appear otherwise 

 healthy. A partial lateral displacement indicates a faulty 

 development of the suspensory ligament, by reason of which the 

 traction upon the lens is unequal at different parts of its circum- 

 ference. The displacement is usually upwards or upwards and 

 outwards, indicating a defect in the lower part of the ligament, 

 analogous to an imperfect closure of the foetal slit. It is usually 

 present in both eyes, and is symmetrical or nearly so in the two. 

 It has frequently been met with in several members of one 

 family and in successive generations " ||. The defect from this 

 appears to be one of deficient development, blastogenic in its 

 nature. 



* Lancet, Aug. 8, 1874. i' Fi-om Aminon's Zeitschr., vol. i. no. 4. 



X Op. cit. vol. i. p. 454. § Oph. Hosp. Eeps. is. 435. 



II P. Smith, in Heath's Diet, of Pract. Surg., Art. " Crystalline Lens. ' 



