The anatomical basis of the caecocentral scotoma. New observations and a review. It is shown that the 'papillomacular bundle' of optic nerve fibres, although a concept discussed frequently in the clinical literature, lacks a clear anatomical definition. It is suggested that the explanation for this is that the 'bundle' was originally described in autopsy studies of toxic amblyopia, not normal anatomy. The optic nerve fibre projection and vascular architecture of the caecocentral region of the retina is described. These anatomical features are discussed in relation to a number of possible anatomical explanations for the fact that a caecocentral scotoma is the characteristic field defect found in toxic amblyopia. We have been unable to identify a distinct anatomical feature which might explain this vulnerability but suggest that the problem has not as yet been clearly addressed by anatomists. 