LXXX BOWMAN LECTURE . 



discoid form, must be due to the influence of the male 

 parent in many cases (e.g. Fig. II). Some fairly large 

 pedigrees have now been collected, and one of them seems 

 to show conclusively that the discoid or " Coppock " form 

 and ordinary lamellar cataract are essentially the same, 

 and not, as we at first thought, independent forms ; so 

 that the two names, discoid and lamellar, should be used 

 only when convenient for descriptive purposes. (In the 

 pedigree furnishing Fig. 12 both forms occurred.) The 

 discoid is probably only the smallest possible form of 

 lamellar, so small that the two layers are united or indis- 

 tinguishable. The position of the disc or flattened lamella 

 at a deeper level than the nucleus of the normal lens, but 

 in front of the posterior capsule, still awaits satisfactory 

 explanation, though perhaps related to displacement of the 

 nucleus backwards from some developmental cause. * 



Opinions have differed for many years as to whether 

 lamellar cataract of ordinary sizes is always congenital, 

 i. e. actually formed before birth, or sometimes post- 

 natal. I think the evidence is conclusive that it may be 

 either one or the other according to the diameter of 

 the opaque s^ell, but that in most of the hereditary cases 

 the process occurs towards the end of foetal life. The 

 diameter of the human lens at the fourth month of foetal 

 life is about 3'3 mm., at the sixth month 4'5 mm., at the 

 seventh month 5 mm., and at birth 5'75 mm.f Between 

 birth and one year old the diameter is about 7'4 mm.J 

 If shrinkage of the nucleus is the first stage in the 

 formation of the opaque peri-nuclear layer the dimensions 

 of the opacity may be a trifle less than the dimensions 

 of the clear cortex from which the opacity was formed; 



* According to Treacher Collins displacement of the nucleus back- 

 wards may occur in the foatal lens as a consequence of faulty backward 

 growth of the lateral lens-fibres. "Developmental Deformities of the 

 Crystalline Lens/' The Ophthalmoscope, 1908. 



f Treacher Collins, Researches into Ihe Anatomy and Pathology of Eye, 

 1896, p. 5. 



t Dub, quoted by Parsons in his Pathology of the Eye, ii, 1905, 

 p. 405. 



