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PDFOn the hypothesis that consanguinity in the parents intensifies a tendency toward blindness we should expect to find among the congenitally blind a larger proportion of consanguineous parentage than among those blind from specific causes. In Table XXIII a general classification of the causes of blindness is given together with the consanguinity of parents. Specific causes in which the percentage of consanguinity differs in a marked degree from the average, are given parenthetically.
TABLE XXIII. ------------------------------------------------------------
------------------- | |Consanguinity of | | | Parents | Percentages | |--------------------------------------------- | | | Not | Not | | Not | Not Cause of Blindness. |Total.|Cousins|cousins|stated|Cousins|cousins|stated ------------------------------------------------------------
------------------- Total |64,763| 2,527|53,980 | 8,256| 3.9 | 83.4 | 12.7 ------------------------------------------------------------
------------------- Opacity of the eye |33,930| 1,000|28,797 | 4,133| 2.9 | 84.9 | 12.2 ------------------------------------------------------------
------------------- a. Causes affecting cornea|11,380| 444|10,016 | 920| 3.9 | 88.0 | 8.1 (1) Measles | 1,451| 73| 1,267 | 111| 5.0 | 87.4 | 7.6 (2) Scrofula | 1,165| 71| 1,026 | 68| 6.1 | 88.1 | 5.8 b. Causes affecting iris | 1,307| 33| 1,093 | 181| 2.5 | 83.6 | 13.9 c. Causes affecting lens |11,769| 228| 9,467 | 2,074| 1.9 | 80.4 | 17.7 d. Other causes | 9,474| 235| 8,221 | 1,018| 2.5 | 86.8 | 10.7 ------------------------------------------------------------
------------------- Nervous apparatus affected| 7,944| 276| 6,980 | 688| 3.5 | 87.8 | 8.7 ------------------------------------------------------------
------------------- Unclassified |14,885| 938|12,463 | 1,484| 6.3 | 83.7 | 10.0 ------------------------------------------------------------
------------------- (1) Congenital | 4,728| 632| 3,666 | 430|13.4 | 77.5 | 9.1 (2) Other causes |10,157| 306| 8,797 | 1,054| 3.0 | 86.6 | 10.4 ------------------------------------------------------------
------------------- Unknown | 8,004| 313| 5,740 | 1,951| 3.9 | 71.7 | 24.4 ------------------------------------------------------------
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To quote from the Report:
The only specific causes, other than congenital, to which is due a greater proportion of the total cases of blindness among those whose parents were cousins than among those whose parents were not related, are: Catarrh (parents cousins 28.1, parents not cousins 8.7 per 1,000), scarlet fever (parents cousins 10.7, parents not cousins 10.1 per 1,000), scrofula (parents cousins 28.9, parents not cousins 19 per 1,000), and measles (parents cousins 28.9, parents not cousins 23.5 per 1,000). The difference in these proportions is but slight, and the relative number of cases of blindness attributed to each of the other causes is greater among those whose parents were not related.[77]
[Footnote 77: U.S. Census, 1900, op. cit., p. 17.]
