Computation of the temperature rise at the corneal endothelium during cataract surgery by modeling of heat generation inside the anterior chamber

Temperature Change of Ophthalmic Viscosurgical Devices in a Bi-Chamber Set-Up at a Flow of 0 and 20mL/min

Purpose

To understand the role of ophthalmic viscosurgical devices (OVDs) in corneal incision contracture (CIC). Specifically, the aim was to evaluate with the tip of the phacoemulsification needle free of OVD, how various OVDs near the tip and sleeve may transmit thermal energy to the incision site.

Methods

A small chamber was filled with balanced saline solution (BSS), and a thin membrane was placed on the surface. OVD was placed atop the membrane. A temperature probe was placed in the OVD, while the handpiece pierced the membrane. The experiment was run both with and without flow and vacuum. Temperature measurements were gathered for each of the OVDs at four separate time points at 0 and 20mL/min flow.

Results

As expected, there was a more pronounced temperature increase in all test groups with no fluid flow. While the temperature increase was not significantly different from BSS for any of the OVDs tested at either 0 or 20mL/min, Viscoat showed the most variable results at both flow settings.

Conclusion

As long as the phaco tip is not in OVD, residual OVD near the incision is not exothermic and so not an additional risk for CIC.

Phacoemulsification and IOL-Implantation without Using Viscoelastics: Combined Modeling of Thermo Fluid Dynamics, Clinical Outcomes, and Endothelial Cell Density

Phacoemulsification is a widely used surgical method in cataract surgery with a high energy ultrasound source. The viscoelastic is considered to be tissue protective. The aim of this study is to investigate during surgery the impact of using viscoelastic versus no viscoelastic on clinical outcomes, potential complications and effect on endothelial cell density. The study group included 64 patients, who were subjected to phacoemulsification using balanced salt solution (BSS). Control group consisted of 62 patients, who underwent phacoemulsification using Hyaloronic acid 1% Healon 1%. Student’s t-test was applied for statistical analysis. The simulations of temperature changes during phacoemulsification were performed by COMSOL Multiphysics software. In the BSS group, a mean endothelial cell loss (ECL) of 4.5% was measured one month postoperatively, while in the Healon group ECL was 5.3%. Data analysis showed no significant difference in ECL between the groups (Student’s t-test, p = 0.8). No significant difference was observed in endothelial cell morphology and IOP between the two groups pre- and postoperatively (all p > 0.05). The modeling of thermo fluid dynamics showed that the heating of the cornea is slightly less when Healon was used as irrigation fluid. The phacoemulsification technique can be performed by an experienced surgeon with viscoelastics or continuous anterior chamber (AC) irrigation on the same level of safety regarding endothelial cell damage, providing equally satisfying clinical outcomes.

Relationship between Corneal Temperature and Intraocular Pressure in Healthy Individuals: A Clinical Thermographic Analysis

Purpose. To study the geographical distribution of corneal temperature (CT) and its influence on the intraocular pressure (IOP) of healthy human volunteers. Materials and Methods. Fifteen subjects (7 M, 8 F), 33.8 ± 17.4 years old, were enrolled in this pilot, cross-sectional study. Measurements of CT were taken after one hour with closed eyelids (CET) or closed eyelids with a cooling mask (cm-CET) and compared to baseline. Results. If compared to baseline, after CET, average CT significantly increased by 0.56°C in the RE and by 0.48°C in the LE (p < 0.001) and IOP concomitantly significantly increased by 1.13 mmHg and 1.46 mmHg, respectively, in each eye (p < 0.001). After cm-CET, average CT significantly decreased by 0.11°C and 0.20°C, respectively, in the RE and LE (RE p = 0.04; LE p = 0.024), followed by a significant IOP decrease of 2.19 mmHg and 1.54 mmHg, respectively, in each eye (RE p < 0.001; LE p = 0.0019). Conclusion. Significant variations of CT occurred after CET and cm-CET and were directly correlated with significant differences of IOP. It can be speculated that both oxidative stress and sympathetic nerve fiber stimulation by temperature oscillations may affect the regulation of AH vortex flow and turnover, thus influencing IOP values.

Experimental and Numerical Determination of the Local Temperature Distribution during Phacoemulsification and Comparison of Different Surgery Situations within Enucleated Porcine Eyes

Phacoemulsification, a common treatment for cataract, is accompanied by cell damage at the corneal endothelium. Thermal exposure during treatment has been considered a reason for this damage, but a thorough experimental and theoretical assessment of the local temperature distribution inside the eye had not yet been conducted. Measurements in porcine eyes and a finite-element simulation enabled such an assessment and localized the highest temperature rise very close to the probe. The results described in this study indicate that a distance of 1 mm between the probe and the endothelium should be maintained during treatment as a safety margin, especially when fluid flow is blocked. The highest measured temperature rise with surgically reasonable system settings and unblocked fluid flow was 1.11°C. The finite-element simulation described here is able to calculate the temperature rise at the endothelium and could serve as a tool for comparing arbitrary surgical situations with respect to thermal exposure of the endothelium.