Microfluidics in the eye: a review of glaucoma implants from an engineering perspective

Abstract

We review the natural pathways and glaucoma implant-based artificial pathways of aqueous humour in the eye from a microfluidic perspective.

Droplet Laplace valve‐enabled glaucoma implant for intraocular pressure management

“…The DLV‐incorporated glaucoma implant is designed for accurate aqueous shunting and reliable IOP stabilization. Figure 1e shows an equivalent fluidic circuit model representing the aqueous circulation after the implantation of the DLV 5,8,9 . In a healthy human eye, the aqueous humor is continually secreted by the ciliary body at the posterior chamber (Figure 1b) of the eye at a flow rate of $${Q}_{\text{AH}}$$.…”

“…The secondary route is the uveoscleral drainage (at a rate of $${Q}_{{\rm{U}}}$$), which is independent of the IOP and accounts for approximately 10%–50% of the total drainage 32 . In the fluidic model in Figure 1e, the contribution of the uveoscleral pathway has been subtracted from the secretion rate, namely, $${Q}_{\text{AH}}^{* }={Q}_{\text{AH}}-{Q}_{{\rm{U}}}$$, to simplify the fluidic model 5 . The Goldmann equation formulates the correlation of the IOP with relevant governing parameters, that is, $${IOP}={Q}_{\text{AH}}^{* }\times {\unicode{x0200A}R}_{\text{TM}}+{P}_{{\rm{E}}}$$.…”

“…Medication therapy and noninvasive laser treatment carry a low risk, but provide relatively modest pressure‐lowering effects. In contrast, surgical procedures offer substantial IOP reduction, and they are widely adopted when medication or laser treatment fails to achieve the target IOP range or results in severe complications 5,6 . In recent years, implant surgeries offering precise control of artificial aqueous humor drainage have become the preferred option for refractory glaucoma.…”

“…Glaucoma implants typically reduce the IOP by enhancing the natural pathways or creating a bypassing artificial pathway of aqueous humor 5,7–9 . The artificial subconjunctival space‐targeting glaucoma implants are currently predominant 5,6,10,11 .…”

“…Glaucoma implants typically reduce the IOP by enhancing the natural pathways or creating a bypassing artificial pathway of aqueous humor. 5,[7][8][9] The artificial subconjunctival space-targeting glaucoma implants are currently predominant. 5,6,10,11 Among them, passively valved subconjunctival implants remain the most accepted aqueous shunting devices, mainly due to their superior pressure management performance in reducing complications like hypotony (i.e., low IOP) when compared to the nonvalved implants, 12 in addition to the structural simplicity and higher patient compliance compared to the actively valved counterparts.…”