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.

Does the Bursa Pre-Macularis protect the fovea from shear stress? A possible mechanical role.

Purpose of present study is to evaluate whether the Pre-Macular Bursa (PMB) modifies Wall Shear Stress (WSS) at the retinal surface during saccadic movements. We created a mathematical model consisting of 25,000 grid cells and simulated a horizontal saccade spanning 50° in 0.17s, both in absence and in presence of the PMB. Wall Shear Stress SS was computed throughout the retinal surface and the posterior pole was divided into 3 Zones comprising 400 nodes each: Zone 1 (radius 3.5 mm; 0°-17°) corresponding to the PMB area; Zone 2 (concentric annular area 5 mm in radius; 22°) and Zone 3 (concentric annular area 5.5 mm; 28°). The PMB reduced WSS significantly at the macula and increased it in the immediate surroundings. Average WSS in Zone 1 was 1.53 ±â€¯1.01 (max 4.23 Pa) with PMB Vs 6.94 ±â€¯9.23 (max 35.83 Pa) without. Zone 2 WSS was 9.39 ±â€¯10.33 (max 48.36 Pa) with PMB Vs 6.95 ±â€¯9.40 (max 38.60 Pa) without Zone 3 WSS was 8.41 ±â€¯10.03 (max 43.16 Pa) with PMB Vs 6.88 ±â€¯9.42 (max 39.43 Pa) without (p < 0.001 in all cases). The PMB significantly reduces WSS over the retinal surface underlying the bursa region; conversely, WSS slightly increases it in the immediate neighboring areas.

Silicone Oil Tamponade-Retina Contact in Highly Myopic Eyes With and Without Encircling Bands: A Computational Fluid Dynamics Study.

Purpose: To investigate the behavior of silicone oil (SiO) at a steady equilibrium and during saccades in pseudophakic highly myopic eyes with posterior staphyloma with and without an encircling band and compare it to behavior in emmetropic eyes. The SiO-retina contact area and shear stress were calculated by computational fluid dynamics. Methods: A numerical model of an emmetropic eye and a myopic eye with and without scleral band underwent a saccade of 50°/0.137 s. The vitreous chamber surface was divided into superior and inferior 180° sectors: lens, pre-equator, post-equator, and macula. SiO-retina contact was evaluated as a function of fill percentages between 80% and 90% for standing, 45° upward tilt, and supine patients. Maximum and average shear stress were calculated. Results: Overall, SiO-retina contact ranged between 40% and 83%; fill percentage varied between 80% and 95%. Neither the encircling scleral band nor the staphyloma significantly affected the SiO-retina contact area, although the presence of a scleral band proved disadvantageous when gazing 45° upward. The inferior retina-SiO contact remained below 40% despite 95% SiO fill. The SS significantly increased at the scleral band indentation and decreased elsewhere. The staphyloma greatly reduced shear stress at the macula. Conclusions: The presence of a myopic staphyloma reduces shear stress at the macula but does not alter SiO-retina contact significantly. The apposition of a 360° scleral band may reduce SiO-retina contact at least in some postures and increases the SS at the indentation. Translational Relevance: Assessing SiO-retina contact when vitreous chamber geometry changes according to pathologic or iatrogenic modifications allows accurate prediction of real-life tamponade behavior and helps explain surgical outcomes.

Computational Fluid Dynamics of Intraocular Silicone Oil Tamponade.

Purpose: To investigate the behavior of silicone oil (SiO) at the steady equilibrium and during saccades and calculate SiO-retina contact, shear stress (SS), and shear rate (SR). Methods: A 24 mm phakic eye mesh model underwent 50°/0.137s saccade. The vitreous chamber compartment was divided into superior and inferior 180° sectors: lens, pre-equator, postequator, and macula. SiO-retina contact was evaluated as a function of fill percentages between 80% and 90% for a standing patient, 45° upward gaze, and supine. SS and SR for 1000 mPa-s (SiO1000) and 5000 mPa-s (SiO5000) silicon oil were calculated. Results: SiO fill between 80% to 90% allowed 55% to 78% retinal contact. The superior retina always kept better contact with SiO, regardless of the fill percentage (P < 0.01). SiO interface thoroughly contacted the macula only in standing position. SS followed a bimodal behavior and was always significantly higher for SiO5000 compared to SiO1000 (P < 0.01) throughout the saccade. The macula suffered the highest mean SS in standing position, while throughout the saccade the average SS was maximum at the SiO-aqueous interface. SR was significantly higher for SiO1000 compared to SiO5000 (P < 0.001). Conclusions: SS on the retinal surface may instantaneously exceed reported retinal adhesiveness values especially at the SiO-aqueous interface and possibly favor redetachment. Despite 90% SiO fill the inferior retina remains extremely difficult to tamponade. Translational Relevance: Accurate assessment of retina-tamponade interaction may explain recurrent inferior retinal redetachment, silicone oil emulsification, and help to develop better vitreous substitutes.