Ruby laser transmission and the lens.

The earliest recorded study of the transmission of light by the ocular *media is attributed to Aschkinass (1895), but according to Meyer-Schwickerath (I960) his method was grossly inaccurate. Luckiesh (I92 I) calculated the transmissivity of the ocular media on the basis that it equalled that of a layer of water 2-28 cm. thick. Shoji (1923) and Bucklers (I926) both made measurements of transmission but the wavelengths used were all below 400 m,u. In a classic paper, Ludvigh and McCarthy (I938) estimated the transmission of light of wavelengths from 400 to 820 mg to be 50 per cent. This paper is much quoted in the subsequent literature, and Davson (I963) quotes only the figure of 50 per cent. In fact Ludvigh and McCarthy based their estimate on experiments on only four eyes, all of which had been enucleated because they contained malignant melanomas. It can be reasonably argued that the ocular media may well have undergone pathological change while remaining clear to the naked eye. The results of Ludvigh and McCarthy (1938) appear to have been accepted until 1951, when they were seriously questioned by Wald (I 95 I). At that time Meyer-Schwickerath (I95I), in developing his light-coagulator, became interested in the transmission of light by the ocular media; he repeated the experiments of Ludvigh and McCarthy (I938) and arrived at the same value of 50 per cent. However, he had no hesitation in discarding the results because the specimens used showed signs of post mortem change when examined critically. Weale (I953), discussing the nature of light reaching the retinal elements after its passage through the ocular media, stated that "as far as the human eye is concerned, such knowledge is very inadequate in the case of the enucleated eye and non-existent in that of the eye in situ". Meyer-Schwickerath (I954) carried out further studies and calculated absorption values on the assumption that they were the same as that of 2 28 cm. water, quoting Goldmann, Konig, and Mader (I950) to justify this assumption. Such calculations showed that, at a wavelength of 694-3 mg, transmission via the ocular media was about 95 per cent. Wiesinger, Schmidt, Williams, Tiller, Ruffin, Guerry, and Ham (1956) studied the transmission of light via the ocular media of nine freshly-enucleated rabbit eyes, using a spectrophotometer operating from 380 to I,400 mg±. Their results also showed that, in the 694-3 mg range, transmission is of the order of 95 per cent. The technique appears to be free of major sources of error but, again, all the ocular media were grouped together in this study. There seems to be no work recorded in the literature in which the transmission of non-coherent light through the individual ocular media has been measured. Ham, Williams, Geeraets, Ruffin, and Mueller (I963) and Geeraets and Berry (I968) confirmed the figure of 95 per cent., again using non-coherent light. It may be concluded that the