Physical model for absorption of intraocular gas

DO DAILY ACTIVITIES AFFECT GAS TAMPONADE‒RETINA CONTACT AFTER PARS PLANA VITRECTOMY?: A Computational Fluid Dynamics Study

PURPOSE

To calculate the retinal surface alternatively in contact with gas and aqueous because of fluid sloshing during daily activities such as ocular saccade, turning the head, standing up, and being a passenger of a braking car.

METHODS

Fluid dynamics of aqueous and gas tamponade was reproduced using computational methods using the OpenFOAM open-source library. The double-fluid dynamics was simulated by the volume of fluid method and setting the contact angle at the aqueous-gas-retina interface.

RESULTS

Sloshing increased the retinal surface in contact with aqueous by 13% to 16% regardless of fill rate and standing up determined the largest area of wet retina, followed by car braking, head rotation, and ocular saccade ( P < 0.001). All activities except the ocular saccade determined a significant increase in the surface of retina in contact with the aqueous ( P < 0.005). Car braking induced the highest shear stress (6.06 Pa); standing up determined the highest specific impulse and saccade the lowest.

CONCLUSION

Daily activities instantaneously reduce the amount of retina consistently in contact with gas tamponade and increase shear stress giving aqueous a potential access to the subretinal space regardless of patients' compliance.

GAS-FOVEAL CONTACT: A New Approach to Evaluating Positioning Regimens in Macular Hole Surgery

PURPOSE

To compare gas-foveal contact in face-down positioning (FDP) and nonsupine positioning (NSP), to analyze causes of gas-foveal separation and to determine how gas-foveal contact affects clinical outcome after idiopathic macular hole repair.

METHODS

Single center, randomized controlled study. Participants with an idiopathic macular hole were allocated to either FDP or NSP. Primary outcome was gas-foveal contact, calculated by analyzing positioning in relation to intraocular gas fill. Positioning was measured with an electronic device recording positioning for 72 hours postoperatively.

RESULTS

Positioning data were available for 33/35 in the FDP group and 35/37 in the NSP group, thus results are based on 68 analyzed participants. Median gas-foveal contact was 99.82% (range 73.6-100.0) in the FDP group and 99.57% (range 85.3-100.0) in the NSP group (P = 0.22). In a statistical model, gas fill had a significant relation to gas-foveal contact (P < 0.0001), whereas whether the surgeon prescribed FDP or NSP was not significant (P = 0.20). Of clinical relevance, gas-foveal contact seemed to influence idiopathic macular hole closure (P = 0.02).

CONCLUSION

We found no significant difference in gas-foveal contact between the positioning groups. The role of positioning after idiopathic macular hole surgery seems to be better characterized from examining both patient positioning and gas fill objectively. We propose gas-foveal contact as a new outcome for evaluating positioning regimens.