Age-related changes of the refractive index of the crystalline lens

In his criticism of our paper, Dr Schachar states that precise comparisons of the isoindical maps of crystalline lenses . . . require that the lenses must be oriented so that their geometric centers and all of their geometric axes coincide , but he gives no justification for this assertion. In fact this is not the case. In order to compare the refractive index distributions for different lenses using our technique it is only necessary for the plane of the image slice to contain the optical axis in each case. The refractive index distributions along either the optical axis or an equatorial radius can then be determined and compared once these images have been converted to refractive index distributions as described in our paper. Such distributions are displayed in Figs. 6 and 7. One advantage of the MRI method is the freedom to select any image plane. In the paper we state Initial scout images were acquired in different planes to ensure the final image plane included the optical (symmetry) axis of the lens . We do not attribute the decline in refractive index of the lens nucleus to the formation of insoluble protein aggregates. We suggest only that a decrease in soluble crystallins may be one possible explanation for the observed decline in nuclear refractive index. There may well be other causes of the refractive changes, but this does not provide a basis for questioning the validity of our conclusions. A decline in nuclear refractive index with age does not necessarily imply a tendency to hyperopia since other changes––for example in lens size and shape––are known to occur simultaneously. The power of the lens depends on the detailed form of the refractive index gradient through the lens, as well as its shape.