## 2 Materials and Methods
### Experimental Procedure  
In this study, four experiments were performed to explore three main aspects of this technique for IOP sensing: (1) Feasibility and efficacy of the STM technique (performed in the AC of an ex vivo pig eye) to estimate the collapse time, (2) the relationship between the induced IOP and the first collapse time of the laser-induced cavitation bubbles, and (3) the dependence of the first collapse time on the delivered energy per laser pulse. In all cases, we used the STM technique in the AC of an ex vivo pig eye to estimate the bubble collapse time with a good precision. In the first experiment, we obtained and analyzed the photodiode signal from the STM technique during cavitation for a set of three energy-per-pulse values: 11.2, 12.8, and 13.9 mJ. Figure 3: Setup of the STM technique within the anterior chamber (AC). The cavitation bubbles are generated right below the cornea center 1 mm within the AC. The scattered probe beam is collected by a lens system to send the transmitted light onto a photodiode. Figure 2: Experimental setup for the spatial transmittance modulation (STM) technique and the equivalent target plane (ETP) system in ex vivo pig eyes. During the following experiments, we used and classified two types of pig eyes as functions of their transverse diameters of smaller and greater than 2.6 cm, which were labeled as Small (S) and Medium (M), respectively. In the second experiment, we measured the first collapse time as a function of the externally induced pressure within the 10 to 60 mmHg range (which expands from normal to abnormal IOP). The externally applied pressure was varied in steps of 4 mmHg. The first collapse measurements were performed by doing a statistical averaging over 16 STM traces, i.e., 16 laser shots at a repetition rate of 1 Hz. We used two pump energy values: 13 and 16.4 mJ corresponding to a fluence at the beam waist of (including the incremental factor (1.8\(\times\)) in the beam waist due to refraction, and it was obtained by simulation in WinLens 3D Basic) 7.8 and 9.9 kJ/cm\({}^{2}\). For the third experiment, in which we studied and described the collapse time as a function of the delivered laser energy, we used three eyes of the same dimensions (M); however, for measuring the collapse time dependence with pressure, we used two medium-sized eyes and one small one. In the fourth experiment, we used 3 shots of the pump pulses, such that we were able to analyze the data dispersion for the first collapse time at increasing (3 mmHg steps) pressure within the IOP. The delivered energy per pulse was set between 11 and 14 mJ--both at the same 1 Hz repetition rate and delivering 3-5 shots per either energy or pressure value. The pump energy range was selected such that the delivered fluence was slightly above the threshold for the first collapse time in order to be clearly identified and measured. Figure 4 shows the trend of the collapse time for multiple shots at the same energy per pulse for three pulse energies: 12, 13, and 13.9 mJ; we defined zones I, II, and III to take into account the shot-to-shot energy fluctuations. It is possible to observe the dependence of the collapse time on the delivered laser pulse energy. The larger the delivered energy, the longer the collapse time. In addition, note that the significant dispersion of the collapse time among the three pig eyes for a certain energy value is probably due to an unintentional difference in the initial alignment of the STM setup for each one of the pig eyes, recalling that the collapse time measured from the STM technique is sensitive to the alignment of the pump-probe system. Table 1 summarizes the statistical behavior of Figure 4, analyzing the trends in the standard deviation and the interquartile range (IQR) for each pig eye and energy zone.