Aqueous Shunts
Neil T. Choplin, Carlo E. Traverso in Atlas of Glaucoma, 2014
The restriction of flow of aqueous humor from the eye is important in the prevention of immediate postoperative hypotony and its attendant complications. Implants that do not have such a mechanism, the Molteno, Baerveldt, and Schocket band implants, are usually inserted in either a two-stage procedure, in which encapsulation of the bleb is allowed to occur before a second surgery to actually insert the tube into the eye, or a one-stage procedure, in which the flow of aqueous is restricted by a suture ligature around the tube or an internal stent. Several aqueous shunts, specifically the Krupin Valve implant, Joseph implant, White pump-shunt, OptiMed Glaucoma Pressure Regulator, and Ahmed Glaucoma Valve implant, have pressure-sensitive valves or internal mechanisms to restrict the flow of aqueous from the eye with the goal being to prevent ocular hypotony in the immediate postoperative period. Prata and co-authors reported that the Ahmed and Krupin implants function as flow-restricting devices at flow rates of 2–25 μ1/min.3 Through in vitro tests with human plasma, they showed that the Ahmed and Krupin implants had greater resistance (change in pressure/change in flow) than partially ligated Baerveldt implants.3
Management of endophthalmitis
A Peyman MD Gholam, A Meffert MD Stephen, D Conway MD FACS Mandi, Chiasson Trisha in Vitreoretinal Surgical Techniques, 2019
Because blebitis may progress to endophthalmitis, aggressive antimicrobial therapy is warranted and may include oral quinolones. Moreover, diligent follow-up to detect extension into the vitreous cavity for prompt intravitreal treatment is important. Busbee et al59 analyzed outcomes in 68 consecutive bleb-associated endophthalmitis cases, and reported that prompt pars plana vitrectomy (PPV) with vitreous biopsy and intravitreal antibiotics achieved better visual outcomes in this dreadful clinical situation. One-third of eyes that underwent PPV had visual acuity (VA) of 20/100 or better. Overall, the incidence of no light perception (NLP) 12 months after bleb-associated endophthalmitis was 35%. Culture-positive vitreous isolates were associated with a higher incidence of NLP vision. Streptococcal species were isolated in 32% of positive cultures, S. epidermidis in 26%, and Enterococcus spp. and Serratia spp. in 12% each. Endophthalmitis associated with the Ahmed glaucoma valve implantation has been reported in 1.7% of eyes and appears to be five times more common in children. In both adults and children, endophthalmitis was associated with conjunctival dehiscence over the glaucoma drainage device as the major risk factor. Common organisms isolated from the vitreous included Haemophilus influenzae and streptococci.60 Bayraktar et al61 reported delayed-onset Streptococcus pyogenes endophthalmitis in a child’s eye with an Ahmed valve where the conjunctiva and Tenon’s capsule over the valve plate had been penetrated by one of the polypropylene fixation sutures one year after placement. It should also be noted that Propioni-bacterium acnes can be sequestered in glaucoma drainage devices. P. acnes was diagnosed by polymerase chain reaction (PCR), Southern blot, and electron microscopy as the cause of anterior nongranulomatous uveitis 4 months following cataract surgery in the eye of a 7-year-old child with preexisting congenital glaucoma and a pre-existing Molteno drainage implant. Extraction of the glaucoma drainage device was required to control chronic inflammation. This case report illustrates the higher risk of the younger age group and the need for sophisticated molecular diagnosis to detect pathogens in these difficult eyes.62
Improving glaucoma management for the Boston keratoprosthesis type 1: tubes versus lasers
Published in Expert Review of Ophthalmology, 2020
Dominique Geoffrion, Mona Harissi-Dagher
Aqueous tube shunts are preferred over trabeculectomy in general for pseudophakic eyes, previous failed trabeculectomy, and glaucoma due to complex ocular surgery. Tube shunts also have less risks of inflamed conjunctiva, infection, and bleb dysesthesia in comparison to trabeculectomy. Valved and nonvalved GDD are both used in KPro eyes to shunt aqueous humor to the subconjunctival space away from the limbus. Valved devices have a flow restrictor while nonvalved do not. Valved devices can be used in mild to moderate glaucoma and have less frequent hypotony, while nonvalved devices can be used for more advanced glaucoma where a lower IOP is the target. The most commonly used valved device is the Ahmed glaucoma valve (AGV; New World Medical, Inc, Rancho Cucamonga, CA). One of the most frequently used nonvalved devices is the Baerveldt glaucoma implant (Abbott Medical Optics, Santa Ana, CA). Tube shunts can be placed in the anterior chamber, the ciliary sulcus, or through the pars plana into the vitreous cavity.
XEN Gel Implant: a new surgical approach in glaucoma
Published in Expert Review of Medical Devices, 2018
Ankita Chaudhary, Lauriane Salinas, Jacopo Guidotti, André Mermoud, Kaweh Mansouri
This study clearly demonstrates the effectiveness and good safety profile of XEN Gel Implant in refractory glaucoma. Baerveldt glaucoma implant (Johnson & Johnson, New Brunswick, NJ, USA) and Ahmed glaucoma valve (New World Medical, Rancho Cucamonga, CA, USA) have already been studied in refractory glaucoma [53–57]. The XEN Gel Implant also effectively lowers IOP and medication use with a favorable safety profile. Complications like endophthalmitis, loss of light perception, retinal detachment, or tube obstruction at 1 year reported for Baerveldt implant and Ahmed valve [53,56] were not observed with XEN Gel Implant. The failure rates for the XEN Gel Implant were also in line with those observed in the ahmed baerveldt comparison study [56], and the Baerveldt glaucoma implant in the AVB study, and better than those reported for the Ahmed glaucoma valve in the AVB [53] study.
Corneal transplantation in children - when and how?
Published in Expert Review of Ophthalmology, 2023
Abha Gour, Aastha Garg, Shailja Tibrewal, Julie Pegu, Sonal Gupta, Umang Mathur, Virender Sangwan
In case of extensive conjunctival scarring, glaucoma drainage devices like Ahmed glaucoma valve or non-valved implants like Baerveldt or Aurolab aqueous drainage implants can be used to control IOP. Complications are not uncommon with these valved procedures like hypertensive phase, tube or plate exposure, tube shortening, or tube cornea touch. The best placement of the tube in a phakic child is in the anterior chamber (AC), and in pseudophakic or aphakic eyes, sulcus placement is a safer option as the tube is placed away from the cornea. Micromovements of the tube occur with every blink or eye rubbing and may lead to tube cornea touch. Aqueous shunts may also cause changes in the protein content of aqueous humor in selective endothelial keratoplasty that may cause further endothelial cell loss. Transscleral cyclophotocoagulation (TSCPC) is commonly reserved for eyes when the vision potential is guarded or in eyes with highly dysgenetic/disorganized anterior segment structures. The challenges are many, but a careful and systematic evaluation with the choice of the most appropriate management can salvage the vision in most of these children.
Related Knowledge Centers
- Eye
- Glaucoma
- Intraocular Pressure
- Trabecular Meshwork
- Uveitis
- Shunt
- Aqueous Humour
- Bleb
- Trabeculectomy
- Primary Juvenile Glaucoma