Authors' Reply: Our article is not trying to make claims of the material performance of nerve fibers. We were simply asserting that as a result of the concentrated loading experienced in the crossover nerve fibers, the tubes could “nip” and disrupt signals. “Elastic buckling” is a state in which the material remains within its elastic behavioral zone and, when unloaded, returns to its undamaged state. A good example would be a Bunsen burner tube. We do not know the material properties of the nerve fiber well enough to be definitive. However, if it were elastic, we may expect retransmission of signals once the loading is removed provided the ionic link can be reestablished. Furthermore, it cannot be presumed that nerve fiber malfunction occurs after the point of irreversible distortion/collapse. Indeed, the clinical recovery after chiasmal decompression would suggest that the point of nerve fiber malfunction occurs before irreversible distortion/collapse. With increasing compression, the proportion of the circumference flattened will increase. The area of flattening will change from that in Figure 1 to that in Figure 2. The formula 1/π × p (Fig. 1) dictates that if p = 1/π, then the pressure difference between crossing and non-crossing cylinders is equal (Figs. 2 and 3). We proposed that it seems unlikely that the nerve fibers could adopt the configuration shown in Figures 2 and 3 without further collapse or malfunctioning. It seems quite possible that a nerve fiber that has adopted the shape in Figure 3 could spontaneously and relatively rapidly return to its normal shape.FIG. 1: A comparison of the different deforming actions of compression applied to crossing (perpendicular) and non-crossing (parallel) fibers. D, diameter of axon and length of nerve segment; p, proportion of circumference flattened by pressure (Reprinted from reference 1).FIG. 2: The degree of flattening has progressed to the point at which the area of contact between crossing and non-crossing cylinders is equal (see Figure 3).FIG. 3: Deformation of two cylinders (representing stylized axons) compressed against each other. Before compression starts (A), neither cylinder is deformed. As the cylinders are compressed against each other (B), there is flattening of the interface (shown in blue), which occupies a fraction, p, of the circumference. When the length of the interface reaches the diameter of the circle, p = 1/π (Reprinted from reference 1).Therefore, we see no reason why a physically distorted cylinder such as a nerve fiber should not return to its previous shape and achieve normal function within hours/days of cessation of a compressive force. In addition, there may also be an element of biologic repair. Gawn G. McIlwaine, FRCS, FRCOphth Zia I. Carrim, MB, ChB Christian J. Lueck, PhD, FRCP (UK), FRCP (Ed), FRACP T. Malcolm Chrisp, PhD Western General Hospital, Edinburgh, Scotland, Southern General Hospital, Glasgow, Scotland; The Canberra Hospital and Australian National University, Canberra, Australia, Heriot-Watt University, Edinburgh, Scotland, [email protected]