Comparison of the Ahmed Glaucoma Valve FP7 and FP8 in Pediatric Glaucoma: a Randomized Clinical Trial.

INTRODUCTION

The drainage implants have become an important alternative in the treatment of pediatric glaucoma refractory to angular and filtration surgery or medical therapy (1). Such implants drain the aqueous humor from the anterior chamber of the eye to a plate positioned above the sclera, between the rectus muscles. The aqueous humor goes through the pseudocyst that forms around the plate by passive diffusion and is drained by the venous capillaries and lymphatic system.

The Ahmed drainage implant (New World Medical, Inc., Rancho Cucamonga, CA, USA) is a device with flow restrictors, which decreases the incidence of postoperative complications such as hypotony (2-3). It is made of silicone and comes in two sizes. The FP7 model has a surface of 184 mm2, 13mm wide and 16mm long. The FP8 model presents 96mm2 surface, 9.6 mm wide and 10mm long.

Studies in animals and adult humans suggest that the surface area of the implant plate is directly related to the amount of aqueous fluid drained through the same (4-7). In contrast, a very large implant can result in the extrusion of the same, uncontrolled intraocular pressure, corneal injury by endothelial touch, patient discomfort and ocular motility problems. The use of pediatric size implants in small eyes can avoid such complications. A high rate (34.8%) of anterior plate of the tubes in children under 2 years of age has been reported (8-9). On the other hand, the use of pediatric implante may affect the control of intraocular pressure (IOP) due to reduced drainage area (10), especially in eyes with increasing axial diameter, a result of increased eye pressure that happens in children with glaucoma. However, there is no study in the literature comparing different sizes of drainage implants in pediatric patients.

A study to compare the success rates and complications between FP7 and FP8 models is essential in order to standardize a conduct in choosing the type of implant. Currently, the choice of the drainage implant model to be used in every child lies on the free choice and personal preference of the surgeon. There is no standard procedure, based on scientific evidence for this choice.