Glaucoma filtering surgery usually takes about 35 minutes and you should try and lie flat and still for this period. The operation can still be performed if you can’t extend your neck fully because of arthritis. A small amount of iodine is placed on the eye to clean it and drapes placed over the lids and forehead. The drape is tented up from the nose downwards so your nose and mouth are open directly to air so there are no problems breathing.

The aim of surgery is to create a small opening in the eye, guarded by a flap valve (the scleral flap), which lets a controlled amount of fluid out of the eye under the conjunctiva. 3 fine sutures are placed in the flap, which can be removed in the out patient clinic, up to 3 weeks after the operation, if the pressure in the eye remains high. Because the body tries to heal a wound, we use Mitomycin-C in small doses to treat the conjunctiva to prevent the surgically induced opening from closing. At the end of the operation, the eye is covered by a pad and shield.

The flap is created by dissecting a plane of the sclera after the conjunctiva has been recessed. A guillotine-cutting instrument is used to punch a hole in the underlying cornea to allow fluid out of the eye, through the flap-valve and under the conjunctiva, where it is drained by blood vessels supplying the conjunctiva.

The following diagram illustrates the placement of the sutures in the scleral flap:-

Early after the operation, the scleral flap will look like this:-

Compare the above picture with the diagram. Some time after the operation, you should be off all drops and have a small raised area of conjunctiva under the upper lid. This is where the fluid from inside the is draining into:-