Genetics in ophthalmology / Arnold Sorsby.

  • Sorsby, Arnold, 1900-1980.
Date:
1951
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Genetics in ophthalmology / Arnold Sorsby. Source: Wellcome Collection.

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    THE GLOBE AS A WHOLE (ii) A genetic analysis is only possible if the mode of inheritance and the course of the postnatal development of each of the variable components are known. In genetic terms, total refraction presents a problem of continuous variation with its polygenic basis, as opposed to discontinuous variation typically shown by a sharply defined pathological lesion, and usually monofactorial. With these considerable complexities it is hardly surprising that little is known of the inheritance of refractive errors. It is not unlikely that the different components of refraction are inherited not only independently but possibly also in different modes of inheritance and that the resultant total refraction will show the com¬ plexities seen with characters of known polygenic inheritance. Such pedigrees as are available are largely selected because a clear mode of inheritance could be seen. They do not necessarily apply to the general run of cases, though there is little doubt that refraction, like stature, is largely genetically determined. Inheritance of Individual Components of Refraction Little is known as to the inheritance of the individual components of refraction. Corneal refraction There is little direct evidence as to the inheritance of total corneal refraction. Steiger did indeed show that the offspring of individuals with the extremes in corneal refraction tend themselves also to show these extremes. There are a number of pedigrees which show the transmission of astigmatism over several generations, not only as to the amount but also as to the direction of the axis. Whilst it would appear that astigmatism is generally dominant, other modes of inheritance may also occur—recessive, sex-linked—and possibly intermediate inheritance. So little is clearly known that even polygenic inheritance has been suggested. Depth of anterior chamber: refractive power of the lens and axial length Nothing definite is known. Clinical measurement of the depth of the anterior chamber presents some difficulties as regards accurate results, whilst measurement of the refraction of the lens is even more difficult. The development of relatively simple radiological techniques for measuring the axial length and the other diameters of the eye, and also the total refraction of the eye, opens the possibility of obtaining valid data on the inheritance of these components. Inheritance of Total Spherical Refraction Evidence from studies in twins Evidence as to the inheritance of spherical refraction is provided by the extensive studies that have been carried out on twins. In uniovular twins, the range of variation, as calculated by Waardenburg, is 2-75 D. In his own material 119 out of 132 observations (90 per cent) showed differences of 1 D or less, and 98 out of 132 (74 per cent), a difference of 0-5 D or less. (High degrees of myopia were 86