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Rouzbeh Amini, Lucas A Gsellman; Computational Simulation of Intraocular Pressure Changes after Descent and Subsequent Ascent in Patients with Intravitreal Gas Bubbles. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):119.
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© ARVO (1962-2015); The Authors (2016-present)
To study how descent to low altitude and subsequent ascent without exceeding the initial altitude increase the intraocular pressure (IOP) in the presence of intravitreal gas bubbles.
Our previous mathematical model (Retina, 31:1656-1663) was modified to simulate pressure-induced changes in the intravitreal gas during elevation changes. The IOP was calculated using mathematical models for the pressure-included bubble size changes and aqueous humor flow alterations with no hypotony allowed in the model. Four specific cases were modeled based on recent clinical observations (Eye, 28:892-894). The patients 1-4 initially descended from their homes at 790, 790, 395, 240 m, to a low altitude at 0, 20, 25, and -310 m, respectively. All patients then ascended to the clinic where the initial procedure had taken place (790m). A number of additional cases were also modeled in a series of parametric studies to examine the effects of the bubble size, ascent and descent rates, duration spent at low altitude, and aqueous humor regulating medication.
As shown in a typical simulated case in Fig. 1, the model predicted a large IOP reduction when the patient reached the lower altitude. The gas bubble volume was also reduced by ~4% (initially filling 55% of the vitreous cavity). The peak IOP was observed directly following the ascent from low altitude to high altitude (790m). In the case represented in Fig. 1, the peak IOP was calculated to be 36mmHg. The longer time a patient spent at the low altitude, the higher the IOP reached after the ascent. Such phenomenon was due to aqueous humor accumulation in the eye at low altitude, a feedback mechanism to keep the IOP at its normal physiological level. The highest IOP value of 53 mmHg was predicted with a slow descend (10 m/min) and a rapid ascent (80 m/min).
Our model prediction was consistent with the recent clinical observations. Based on our simulation, patients with intravitreal gas bubbles may be at high risk of elevated IOP after a descent and subsequent ascent to high altitude even without ever exceeding the initial altitude. Further, the reduction in gas bubble size at the low altitude may increase the risk of ocular hypotony and post-surgical retinal detachment. Our simulation suggests that IOP regulating medication may help manage the risks.
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