Further comment on ‘The mechanical properties of the rabbit and human cornea’

Abstract

In offering our comments on the paper by Jue and Maurice, it was our hope that the errors and oversights contained therein could be corrected, and that perhaps the original data could be carefully re-examined, since we feel that it is important. Our initial comments on this paper addressed the importance of tissue thickness to the resulting stress-strain relations in the cornea. While we feel that the authors have not properly addressed these issues, we bear no malicious intent, and our respect for David Maurice is great. However, there are several important issues which require further discussion and clarification for proper interpretation of the authors’ experimental results. Jue and Maurice presented Fig. 7 to clarify the presentation of their results; only here are the experimental results presented on the same axes. Our arguments are not to discredit the data presented, but rather to question the conclusions drawn, as portrayed in Fig. 7. Figures 3a, b, c and 4a, b and c depict, respectively, the intact cornea, the isolated stroma and Descemet’s membrane, each on axes that are scaled differently. Furthermore, it is pressure and not stress that has been plotted along the Y axis, and the authors refer to intraocular pressure synonymously with stress, when they are in fact not synonymous quantities. We have succinctly outlined below the specific issues appearing in the paper that, in our opinion, require clarification and/or correction. (1) Figure 3 is problematic because: (i) The intact rabbit cornea (Fig. 3a) experiences greater deformation than the isolated rabbit stroma (Fig. 3b) for the same value of intraocular pressure. This is physically impossible. Removal of tissue cannot result in a decrease in extensibility; by extensibility we mean deformation at a given pressure. (ii) Descemet’s membrane (Fig. 3c) behaves very similarly to the intact cornea, even though it is much thinner. The question arises: was tissue thickness taken into account here? (iii) Changes made to scaling along the X axes in these figures causes confusion in their interpretation. (2) Paragraph 1 on p. 851 states: ‘In contrast, when Descemet’s membrane and some posterior stromal layers were removed, the tissue became almost non-extensible.’ This statement makes no sense quantitatively, as thickness of the F = Applied Force