Computational simulation of aqueous humour dynamics in the presence of a posterior-chamber versus iris-fixed phakic intraocular lens

Abstract

PurposeTo compare aqueous humour (AH) dynamics in the presence of a precrystalline (Implantable Collamer Lens®; ICL) or iris-fixed (Artiflex®) phakic intraocular lens (PIOL).MethodsBy computational fluid dynamics simulation, AH flow was modelled through a peripheral iridotomy (PI) or central lens hole (both 360 μm) in the presence of an Artiflex or ICL lens, respectively. The impacts of AH flow were then determined in terms of wall shear stress (WSS) produced on the endothelium or crystalline lens. Effects were also modelled for different scenarios of pupil diameter (PD 3.5 or 5.5 mm), ICL vault (100, 350, 800 μm) and number of Artiflex iridotomies (1 or 2) and location (12 or 6 o’clock).ResultsFor a PD of 3.5 mm, AH volumes flowing from the posterior to the anterior chamber were 37.6% of total flow through the lens hole (ICL) and 84.2% through PI (Artiflex). For an enlarged PD (5.5 mm), corresponding values were 10.3% and 81.9% respectively, so PI constitutes a very efficient way of evacuating AH. Central endothelial WSS in Pa was lower for the large vault ICL and the Artiflex (1−03 and 1.1−03 respectively) compared to the PIOL-free eye (1.6−03). Crystalline lens WSS was highest for the lowest vault ICL (1−04).ConclusionsAH flow varied according to the presence of a precrystalline or iris-fixed intraocular lens. Endothelial WSS was lower for an implanted ICL with large vault and Artiflex than in the PIOL-free eye, while highest crystalline WSS was recorded for the lowest vault ICL.

Numerical model to predict and compare the hypotensive efficacy and safety of minimally invasive glaucoma surgery devices

“…Variables included in the simulation were based on standard values for an adult human eye [16,[25][26][27][28][29][30][31][32] (Table 2). The numerical procedure was the same as described by Fernandez-Vigo et al [33] and Agujetas et al [34]. However, our simulations incorporated a new element that was not included in those studies: the flow across both the trabecular meshwork and the implanted device.…”

The Implantable Collamer Lens with a central port: review of the literature

“…In a second study, these authors determined that the flow around the crystalline lens reached a maximum with a hole size of ~0.4 mm, indicating that “the current model, based on a central hole size of 0.36 mm, was close to ideal.”10 Recently, these authors also reported that “laser iridotomy is unnecessary from the viewpoint of theoretical aqueous circulation” in the presence of a central hole 11. Fernández-Vigo et al reported a full three-dimensional study based on computational fluid dynamics and concluded that “the circulation of aqueous humor is influenced by the type of lens implanted, being more physiological in the central hole model than in the one that requires an iridotomy.”12 These authors more recently provided an interesting theoretical paper describing a model of the circulation of aqueous humor in eyes with and without phakic refractive lenses 13…”

A Mathematical Model of Corneal Metabolism in the Presence of an Iris-Fixated Phakic Intraocular Lens

“…Firstly, we neglected the possible presence of an iridotomy, which is often created when a PIOL is implanted. Iridotomy creates an additional passage from the posterior to the anterior chamber, 6,35 thus modifying fluid flow characteristics in the anterior chamber. We note, however, that iridotomies are typically produced in the periphery of the iris.…”

“…We note that in the present work we neglected the presence of an iridotomy, that is, a perforation in the iris, which is typically performed when iris-fixated lenses are implanted and whose role on the fluid dynamics in the anterior chamber in the presence of a PIOL has been investigated by Fernández-Vigo et al 6,28…”

“…Mechanical friction between the endothelium and the PIOL has also been postulated to possibly cause cell detachment in patients with the habit of rubbing their eyes or sleeping face down. Various authors [4][5][6] have investigated through mathematical models the possible role of changes in the wall shear stress on the cornea due to aqueous humor motion on endothelial cell detachment. The authors have found that implantation of a PIOL does not induce a significant increase of the stress on the cornea and thus this is unlikely to cause cell loss.…”