Numerical Study of Aqueous Humor Flow in Human Eyes

The study of intraocular aqueous humor (AH) flow is helpful to understand the mechanism of some eye diseases such as glaucoma. A numerical study of AH flow inside human eyes with the computational fluid dynamics (CFD) were carried out to address the following flow processes: AH secreted in the posterior chamber by the ciliary body entering the anterior chamber through the iris-lens gap of 5 μm and 30 μm respectively, and discharging through the trabecular meshwork (TM). Detailed flow fields in different eye orientations were analyzed. Results show that, in general the intraocular pressure distributions are similar in all cases; the pressure in the posterior chamber is around 30 Pa higher than that in the anterior chamber with the 5 μm iris-lens gap, and they are almost equal with the 30 μm iris-lens gap. The pressure drop in the TM is noticeable. The pressure difference between the anterior and posterior chambers drives AH from the posterior chamber to the anterior chamber, while the temperature difference between cornea and iris surfaces causes the natural convection, which is the dominant flow in the anterior chamber. The pressure difference due to natural convection is in the magnitude of millipascal, and the higher-pressure region forms where warmer AH gathers. For the vertical orientation, warmer fluid rises along the iris surface and then turns downwards as it encounters the higher resistance in the upper TM regions. The flow then descends along the corneal surface toward the lower TM. For the upward-facing position, AH entering the pupil rises along the center line of the anterior chamber, and moves down along the cornea surface leading to 2 large symmetric recirculation zones. For the downward-facing position, the circulation route is opposite to that of the upward-facing position. With no buoyancy, the averaged velocity will be 1 to 2 orders of magnitude smaller than that with buoyancy.