Computational study of aqueous humor dynamics in two different models of posterior chamber phakic lenses

Abstract

Purpose: To compare the behavior of aqueous humor (AH) and analyze flow differences between V4b and V4c implantable collamer lenses (ICLs)^©.

Methods: We utilized computational fluid dynamics (CFD), which simulates the properties of flow in a given model to compare the AH flow through an iridotomy which is typically performed after implantation of a V4b lens to that of the central hole of a V4c lens. The following simulation conditions were used: laminar flow with a flow rate of 2 microliters/min; temperature: 37°C in the anterior chamber and 34°C in the cornea. The gravitational effect was also computed. For calculation of flow rate, mean resistance time was analyzed. The volume and flow rate in 4 scenarios were compared according to the type of lens and pupillary diameter (PD): 1) V4b implant lens with an iridotomy of 360 microns and a PD of 3 mm; 2) V4b implant lens with an iridotomy of 360 microns and a PD of 4.5 mm; 3) V4c implant lens with a central hole of 360 microns and a PD of 3 mm; 4) V4c implant lens with a central hole of 360 microns and a PD of 4.5 mm.

Results: With a V4b implant and an iridotomy with a PD of 3 mm, the flow through the iridotomy represents 28.35% of the total flow rate with a volume of 0.68 microliters/minute and a velocity of 0.14 mm/sec. Increasing the PD from 3 to 4.5 mm (scenario 2) reduced flow through the iridotomy to 13.27% of total, with a volume of 0.32 microliters/minute and a velocity of 0.06 mm/sec. When using a V4c lens with a 3mm PD (scenario 3), flow through the central hole represents 22.7% of total , with a volume of 0.54 microliters/minute and a velocity of 0.13 mm/sec. Increasing the PD from 3 to 4.5 mm (scenario 4), reduced the flow through the central hole to 9.77% of total, with a volume of 0.23 microliters/minute and a velocity of 0.05 mm/sec.

Conclusions: Aqueous humor flow varies depending on ICL^© implanted. Flow was influenced by the presence of an iridotomy versus the presence of a central hole in the lens. Flow through the iridotomy (V4b) was greater than flow through the central hole (V4c), although V4c lenses seem to better simulate physiologic flow of aqueous humor in the eye. With both lenses, increasing pupillary diameter decreased the rate of aqueous humor through the iridotomy or central hole of the lens.