Device for use in the eye

Details Device for use in the eye Device for use in the eye

1999-08-16

2001-02-13

Manuel, George (Department: 3737)

Surgery

Means for introducing or removing material from body for...

Material introduced into and removed from body through...

Reexamination Certificate

active

06186974

ABSTRACT:

The present invention relates to a device for insertion in the eye, specifically to a drainage implant for a glaucoma patient, and to a method for using such a device.
BACKGROUND OF THE INVENTION
Glaucoma is a common cause of blindness or visual impairment throughout the world, affecting about 1 person in 40 at some point in their life to a varying degree. In glaucoma, the fluid drainage pathways from the eye become restricted or damaged. As a result, fluid pressure within the eye (the intra-ocular fluid pressure, IOP) rises and the optic nerve is damaged by the raised fluid pressure.
Medical treatment, typically by the application of eye drops containing drugs which either decrease intraocular fluid production or increase outflow, requires lifelong compliance which is only infrequently attained in practice. Medical treatment is often only partially successful in retarding disease progression, with continued optic nerve damage and visual field loss.
The alternative is glaucoma drainage or filtration surgery (GFS), in which a drainage channel (the GFS channel or fistula) is created through the wall of the sclerocorneal junction by a laser beam or other means to connect the anterior chamber (the fluid space within the eyeball in front of the pupil) directly with the subconjunctival space (the space beneath the membrane covering the white of the eye). The GFS channel thus provides a route through which fluid can drain from the interior of the eye to the subconjunctival space. Successful GFS has been shown to provide better quality IOP control and better protection from disease progression than medical treatment in glaucoma.
However, problems arise in controlling drainage of fluid after GFS. Excessive drainage leading to hypotony (IOP less than a safe minimum level, which is about 5 mmHg) can result in a number of sight threatening complications including suprachoroidal haemorrhage and hypotony maculopathy. On the other hand, inadequate drainage with an insufficient IOP reduction (more than 15 mmHg) increases the risk of continued optic nerve damage. The IOP should ideally stay within the safe range (ie 5-15 mmHg) after GFS avoiding both early hypotony and later inadequate drainage. No current GFS technique achieves this goal consistently and complications after GFS remain common.
After GFS, limited subconjunctival scarring tends to form a partial seal around the area of the surgical drainage outlet (bleb formation). This process adds an additional flow resistance element (bleb resistance) and results in an increase in IOP from the initial postoperative level, which continues until postoperative inflammation subsides and the wound healing response is complete. This postoperative wound healing response varies considerably between individuals and is often modulated with anti-scarring treatments such as 5-fluorouracil and mitomycin C. IOP thus stabilises at a variable final level. To achieve the lowest safe final IOP level safely, current GFS techniques attempt to build a resistance element into the GFS channel (guarding, or fistular resistance) to protect from early overdrainage which can ideally be retained if bleb resistance is low, or abolished if bleb resistance is adequate to prevent late hypotony.
Currently preferred surgical practice, trabeculectomy with releasable sutures, uses a partial thickness scleral flap secured by one or more sutures tied in a slip knot to provide a trap-door type covering over the drainage passage through the wall of the eye. Guarding provided by this scleral flap, and hence the initial postoperative IOP level, is inconsistent. Also, early suture release often results in hypotony, whereas scarring beneath the scleral flap tends to make later suture release ineffective in abolishing fistular resistance.
SUMMARY OF PRIOR ART
In another form of GFS, a glaucoma filtration implant (GFI) is inserted into the GFS channel. Current GFIs are commonly associated with excessive drainage and early postoperative hypotony. This results from either poor control over flow through the GFI, uncontrolled external leakage of fluid between the GFI and the walls of the GFS channel into which it is inserted, or both poor internal flow control and external leakage.
A variety of GFIs are in clinical use. The first device to be made clinically available, and which is probably the device preferred by most ophthalmic surgeons, is the Molteno implant. This consists of a flexible silicone rubber drainage tube, one end of which is introduced into the anterior chamber and the other end of which opens onto a plate shaped explant formed of moulded polypropylene, which is secured to the sclera 5-6 mm supertemporal from the limbus through a fornix-based conjunctival flap. The open side of the plate faces outwards. The original Molteno implant had no internal mechanism which created flow resistance. The long term flow resistance is created by the bleb which forms by wound healing mechanisms over the explant. In order to avoid postoperative hypotony, it was necessary either to install the implant in two stages (the tube being inserted in the second stage) or with the tube temporarily ligated, for instance using a biodegradable or laser ablatable suture.
The flow rate following implantation to the original Molteno device depends primarily upon the rate at which the fluid can drain from the plate explant, which in turn depends upon the wound healing reaction. Whilst some control is available by providing implants having different plate areas, this is inadequate in many circumstances. Improvements in the design include the Molteno dual ridge device which has a v-shaped ridge on the plate adjacent to the tube plate junction dividing the available spacing in the concave side of the plate into a small anti-chamber (having a volume of approximately 15 microliters) and a larger main chamber. In use aqueous humour must percolate between the overlying Tenon capsule and the ridge to fill the larger main chamber, from which it can filter. Whilst this provides some improvement to control of flow resistance, this is still inadequate in some circumstances.
Another variation on the original Molteno device is the Baerveldt device. This again consists of a plate shaped explant and a tube opening onto the concave side of the plate, but is implanted in apposition to the sclera rather than the conjunctiva (as for the Molteno implant).
One problem with both the original and dual ridge Molteno devices and the Baerveldt device is that the flow resistance is very dependent upon suture tension. For all of the devices the eventual IOP can be too low for safety and all are subject to progressive fibrous obliteration by continued subconjunctival wound healing processes after surgery, which may result in eventual filtration failure. All of the above devices depend upon bleb resistance for flow resistance and require implantation by two stages or use of removable or biodegradable ligatures.
Devices are available which incorporate valves in the flow passage to avoid immediate postoperative hypotony and the need for a two stage surgical procedure or the use of ligatures. Two such devices are in clinical use, the Krupin device which uses a slit valve and the Ahmed device which uses a venturi type valve. One problem with at least the Krupin device is that of hysteresis, that is that the valve closes at a lower pressure than it opens. In addition both devices have been shown not to open and close as claimed in vivo (Prata et al, Ophthalmology (1995) 102, 894-904). For both these devices therefore the “valves” behave only as flow restriction devices, with the main contribution to resistance to flow being bleb formation. Both these devices are subject to eventual fibrous obliteration and filtration failure.
In WO-A-91/12046 a plate type device has an elongated tube having an elliptical external section. This is said to reduce leakage of aqueous humour by providing a closer fit between individual lamellae in the sclerotic layer, between which the tube is implanted. The diameter of the internal lumen through the tube is select

Affiliated with

Also associated with

Rating

Device for use in the eye does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Device for use in the eye, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device for use in the eye will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2613159