External filtration and glaucoma

External filtration develops with a small hole in the wall of the filtration cushion, which leads to leakage of intraocular fluid with a direct communication between the outer surface and the internal cavity of the pillow. The risk factor for the development of external filtration is the intraoperative use of antimetabolic drugs.

The mechanism of development of external filtration: the ischemic filtration pad is stretched and surrounded by a massive scar tissue, which limits the flow of watery moisture beyond its limits. The filtration pad is locally expanded. When the tissue is stretched, exceeding the maximum possible threshold, a traction hole is formed.

The best external filtration is determined by applying fluorescein to its surface and when viewed under a slit lamp with a blue cobalt filter. Positive sample Seidel (Seidel) is manifested by changing the color of the dye to green-yellow when the intraocular fluid flows out of the hole. Sometimes external filtration can be detected only by gently pressing on the eyeball.

External filtration increases the risk of infectious complications and endophthalmitis, therefore, early detection and treatment of this condition should be carried out. To reduce the risk of developing outdoor filtration during surgery, the accuracy of surgery is very important. Particular attention should be paid to the technique of trabeculectomy, conjunctiva stitching. Time, area of application and washing out of antimetabolites, and also to be careful with laser lysis of the joints.

[1], [2], [3], [4], [5], [6], [7]

Treatment of external filtration

Conservative treatment

The advantage of techniques that improve reparative processes is the protection of the patient from surgical intervention. Their disadvantages include the possibility of re-occurrence of filtering when they are ineffective. These methods of treatment are not operations, but each of them has its own risk factors.

• Use of 18 mm soft contact lenses for 2 weeks.
• Use of butyrylmetal-glue glue and silicone disc.
• Introduction of autologous blood into the filtration pad.
• Compression joint application.

Surgery

The following options are possible.

• Conjunctival movement. It is proved that this is a highly effective technique. In patients with late-developed external filtration, who received treatment with the movement of the conjunctiva. There were better overall results, and severe intraocular infections were observed less frequently than in patients receiving more conservative treatment.
• A separate conjunctival transplant. Transplantation of a free conjunctival autologous transplant is a safe and effective technique for reducing the filtration pad and restoring its function.

Patients should be aware that after a revision in the postoperative period, medication or surgical intervention may be required to control intraocular pressure. Amniotic membrane. Transplantation of the amniotic membrane is an alternative treatment if the surgeon believes that the available conjunctival tissue is limited (for example, as a result of her thinning or scarring) or there is already a small ptosis. The technique described below is somewhat different from that of Baden (Budenz) et al. According to this technique, the graft is folded, the main layer is left outside, and the stromal layer is inside.

Technique of sewing the amniotic membrane.

• Separate the conjunctiva surrounding the ischemic filtration pad.
• Remove the old ischemic filtration pad.
• Take the donor amniotic membrane and fold.
• The anterior edges of the transplant are hemmed at the corners to the cornea of the 9-0-0 nylon.
• The posterior margin of the amniotic membrane is located under the free, cut off front part of the conjunctiva.
• The graft is firmly hemmed to the anterior edge of the patient's free conjunctiva by a continuous vikril seam 8-0.
• In the limb zone, a compression nylon suture 9-0 is applied to the front edge of the graft.
• The whole area is checked for external filtration with fluorescein.
• The front compression stitch can be removed after 1 month.

Variations of this technique can be used in the transplantation of the free conjunctiva, add only steps to remove tissue from the selected site and do not fold a free graft. Baden et al. In the study of amniotic membrane transplantation do not offer an effective alternative to conjunctival transplantation for the correction of filtration pads in glaucoma. Accumulated data on the engraftment time of the amniotic membrane transplant were 81% for 6 months, 74% for 1 year and 46% for 2 years. During the entire period of observation, the overall level of engraftment of the displaced conjunctiva was 100%. Baden et al. In their study revealed that the transplantation of the amniotic membrane is less effective than the standard conjunctival transplant. However, the results of their study showed that the use of the amniotic membrane can be successful in certain situations, which indicates the existence of an alternative treatment for external filtration in specific circumstances. In addition, if the graft of the amniotic membrane does not take root, there is always the possibility of a conjunctival transplant. Even modifications of surgical techniques are possible, which affects the final results. The latter statement requires evidence from a randomized clinical trial to compare with the findings of Baden et al. And, of course, time checks.