## 3. Results and Discussion
### Model-Experiment Comparison
#### 3.2.3 Optical Power  
Influence of the Geometry  
The optical power variations with pressure are shown in Figure 13 for the models that employed spherical and biconical surfaces.  
The optical power behavior obtained from computational modeling presented significant differences compared with the experimental results (see Figure 3). In the former, an increase in optical power for the pressures took place, which rose to 4.00 kPa, plus lower values for an ulterior pressure increase. In the latter, a decreasing monotone behavior was noted.  
Major differences were observed between the spherical and biconical models, which were around 2 D within the studied pressure range.  
Influence of the Boundary Conditions  
Figure 12: Apical displacements versus applied pressure for the experimental and biomechanical modeling results.  
Figure 13: Optical power versus pressure for the spherical and biconical geometries.  
Figure 14 shows the optical power variation with the pressure for the different employed boundary conditions.  
Similar behavior occurred to that obtained in Figure 13. The maximum optical power value obtained was at 4.67 kPa in the model with a fixed border and 4.00 kPa in the remaining cases. The biggest differences were observed for 4.00 kPa. The models that used the eyeball came closer to one another and presented bigger differences, falling between 3.33 and 4.67 kPa. The fixed border model presented the highest optical power values and the widest variations, which was related to the applied support, and forced the material to undergo more marked deformations. These two deformation types were lesser for the scleral ring model and the eyeball model.  
In these cases, an optical power analysis showed that the differences found among the models led to a much more in-depth study of the real cornea conditions, which was essential if the cornea behavior was to be reproduced. It was also very interesting to see how the used models very accurately reproduced the experimental behavior of some parameters, such as apical displacement and pachymetry, but that of the optical power of the cornea differed. This result indicates that determining the apical displacement or pachymetry is insufficient to verify the quality with which a computational model reproduces the experimental results.  
The optical power variation from computational modeling has only been reported in five of the consulted references [32; 33; 34; 35; 36]. Their authors employed the material and geometrical parameters taken from the experimental results reported by other authors and did not directly determine the curvature radii. According to these results, the change in the optical power monotony versus the pressure curves obtained in our simulations would be the expected result, but the causes of this behavior and the conditions that could influence it were unclear. A more in-depth study into the influence of mathematical modeling is necessary to characterize the material properties and to analyze different boundary conditions. To better understand this tissue behavior, more experimental results are necessary, in which the curvature radii could be measured for each pressure increment.  
Our laboratory lacks an automatic pump with the appropriate characteristics to carry out such tests, which is why we resorted to manual insertion. However, tests were carried out on numerous occasions to establish a robust sensitive protocol with the experiment to be run.  
Figure 14: Optical power behavior versus pressure for the employed boundary conditions.