A model for designing intraocular pressure-regulating glaucoma implants

Abstract

Glaucoma is a group of eye conditions that damage the optic nerve, the health of which is vital for vision. The key risk factor for the development and progression of this disease is increased intraocular pressure (IOP). Implantable glaucoma drainage devices have been developed to divert aqueous humor from the glaucomatous eye as a means of reducing IOP. The artificial drainage pathway created by these devices drives the fluid into a filtering bleb. The long-term success of filtration surgery is dictated by the proper functioning of the bleb and overlying Tenon’s and conjunctival tissue. To better understand the influence of the health condition of these tissues on IOP, we have developed a mathematical model of fluid production in the eye, its removal from the anterior chamber by a particular glaucoma implant–the PRESERFLO® MicroShunt–, drainage into the bleb and absorption by the subconjunctival vasculature. The mathematical model was numerically solved by commercial FEM package COMSOL. Our numerical results of IOP for different postoperative conditions are consistent with the available evidence on IOP outcomes after the implantation of this device. To obtain insight into the adjustments in the implant’s hydrodynamic resistance that are required for IOP control when hypotony or bleb scarring due to tissue fibrosis take place, we have simulated the flow through a microshunt with an adjustable lumen diameter. Our findings show that increasing the hydrodynamic resistance of the microshunt by reducing the lumen diameter, can effectively help to prevent hypotony. However, decreasing the hydrodynamic resistance of the implant will not sufficiently decrease the IOP to acceptable levels when the bleb is encapsulated due to tissue fibrosis. Therefore, to effectively reduce IOP, the adjustable glaucoma implant should be combined with a means of reducing fibrosis. The results reported herein may provide guidelines to support the design of future glaucoma implants with adjustable hydrodynamic resistances.

Magnetically actuated glaucoma drainage device for regulating intraocular pressure after implantation

“…To simulate this condition, the outlet of the devices was connected to a column of water mimicking the pressure in the bleb when hypotony is most likely to occur (~1.38 mmHg, or 1.88 cmH 2 O). This pressure was calculated in our previous work 17 .

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“…During bleb maturation, the balanced production and degradation of the extracellular matrix and collagen produce a tissue-strengthening effect, which limits the filtration of aqueous humor from the bleb into the subconjunctival tissue 16 . Until this phase is reached, which might take up to a few months, there may be overfiltration of aqueous humor, resulting in hypotony 17 . This vision-threatening condition may lead to vision loss in up to 20% of patients, and it can be accompanied by a shallow anterior chamber and other complications, such as choroidal effusions and suprachoroidal hemorrhage 18 .…”

“…The dimensions of this channel were predetermined to achieve a desired minimum pressure in the case of hypotony when the device was in the low-flow mode. According to our previously described numerical model 17 , to obtain a healthy IOP of 10 mmHg, the bypass channel must have a cross-sectional area of 50 × 50 µm (width × height). However, this optimal pressure can only be attained if the micropencil totally stops the flow through the main outlet channel.…”

Systematic Preserflo MicroShunt Intraluminal Stenting for Hypotony Prevention in Highly Myopic Patients: A Comparative Study

“…Although the effect of the 10.0 nylon stent for outflow restriction as a treatment for postoperative prolonged hypotony was previously described [ 23 ], this is the first study to investigate the efficacy of PMS flow restriction in high-risk myopic eyes and its preventive effect on the early hypotony rate. In vitro studies proved that the PMS does not offer hydraulic resistance to outflow similarly to other non-valved shunts, for example, Molteno and Baerveldt [ 24 , 25 , 26 ]; therefore, the only opposition to excessive outflow is the filtration bleb pressure, which, in the early postoperative period, is minimal due to the absence of conjunctival and Tenon fibrosis [ 25 ]. It follows that a major problem of non-valved, bleb-forming, shunt implantation is the early outflow control [ 8 , 9 , 10 , 11 , 24 , 27 , 28 ], and early hypotony is a relatively frequent complication compared to late hypotony, which occurs more rarely.…”

Eficiencia antiinflamatoria de dexametasona 1.0 mg/ml vs bromfenaco 0.9 mg/ml administrados previo a la facotrabeculectomía en pacientes con Glaucoma

“…Consiste en la creación de un drenaje externo hacia el espacio subconjuntival, que da lugar a la formación de una elevación conjuntival denominada ampolla filtrante. (Pereira et al, 2022;Saeed et al, 2023). La ampolla filtrante es un área sobre elevada de la conjuntiva situada sobre la zona de drenaje del humor acuoso.…”