Modified Trabeculectomy: Follow-up Study

DD Pandit, SB Unercat, SS Navelkar

Objective: To describe a modified trabeculectomy in which a small perpendicular strip of sclera is removed in addition to ablation of the trabecular meshwork.

Patients and Methods: Modified trabeculectomy was performed in 50 eyes. Follow-up was 5 years.

Results: Intraocular pressure was controlled below 20 mm Hg for 90% of eyes. Vision was maintained for all eyes. The bleb formed was diffuse in 45 eyes (90%).

Conclusion: The major advantage of this modified procedure is that the intraocular pressure remains controlled as the scleral canal continuously drains aqueous. Tenonectomy reduces postoperative fibrosis, thereby reducing bleb failure.

Key Words: Anterior chamber, Modified trabeculectomy, Scleral canal

Asian J Ophthalmol 2003;5(1):3-7.

Introduction


The goal of glaucoma filtering surgery is to establish a permanent flow of aqueous from the anterior chamber to the subconjunctival space, thereby lowering intraocular pressure (IOP). However, the procedures tend to fail over time because of fibroblastic proliferation and subconjuctival fibrosis that occurs during normal healing.¹ Adjunctive use of antifibrotic agents with glaucoma surgery significantly reduces the risk of bleb failure, although their use has been associated with a number of complications. Various modifications to trabeculectomy have been tried over the years. This study is of a new modification for trabeculectomy and its long-term follow-up.

Patients and Methods


All patients were examined preoperatively for IOP, visual acuity, gonioscopy, and visual field. Patients included in the study were receiving medical therapy for established glaucoma but were not controlled with 1 or 2 drugs. The types of glaucoma are shown in Table 1. Postoperatively, patients were evaluated in the first week for anterior chamber formation. Thereafter, patients were followed up every 3 months for 2 years and annually for a further 3 years. Visual acuity, IOP, anterior chamber, and bleb were observed at every visit for the first 2 years, and visual fields were repeated after 1 and 2 years. Further, IOP, visual acuity and visual fields were done annually until 5 years after surgery.

Table 1. Distribution of type of glaucoma.

The modified trabeculectomy was performed as follows:

• peribulbar block was performed with 2% xylocain plus sensorcaine/adrenalin/hyalase
• the conjunctival flap was dissected towards the limbus from 7 mm to 8 mm away
• the first limbal-based scleral flap of one-third thickness, measuring 4 mm perpendicular to and 6 mm parallel to the limbus, was dissected until the surgical limbus was seen (Figure 1 and 2)
  
  

  Figure 1. First limbal-based scleral flap markings.	Figure 2. First scleral flap of one-third thickness being dissected.

  
  
• a second scleral flap was marked out with a Bard Parker knife in the centre of the area left after the first flap, leaving 2 mm on either side - dissection started 1 mm above the upper margin of the first flap (Figure 3)
• on reaching the surgical limbus the second scleral flap was lifted and the anterior chamber was entered with an anterior chamber puncture blade (Figure 4)
  
• the trabecular meshwork was cut to 2 mm x 1 mm with Vanas scissors along with the second scleral flap (Figure 5)
  
  

  Figure 3. Second sleral flap is being dissected.	Figure 4. Second seleral flap lifted at the surgical limbus.

  
  

  Figure 5 a, b, c.. Trabecular meshwork being cut along with the second scleral flap.

  
  
• peripheral iridectomy was performed (Figures 6 and 7)
• the first scleral flap was sutured with 8-0 ethicon at the corners (Figure 8)
• Tenon's membrane was dissected from the conjunctival flap and tenonectomy was performed (Figures 9 and 10)
• the conjuctival flap was sutured with a continuous suture of 8-0 ethicon (Figure 11).
  
  The surgical procedure was consistent regardless of the type of glaucoma or the IOP.
  
  

  Figure 6. Peripheral iridectomy.	Figure 7. Window after cutting the trabecular meshwork.

  
  

  Figure 8. First scleral flap sutured back at the corners.	Figure 9. Tenon's membrane dissected from the conjunctival flap.

  
  

  Figure 10. Tenonectomy performed.	Figure 11. Conjunctival flap sutured back with continuous suture.

Results

In this series of 50 eyes, the IOP was well controlled below 20 mm Hg in 45 (90%) for 5 years follow-up after accomplishment of the modified bleb. The results for the IOP are summarised in Table 2 and 3.

Table 2. Comparison of preoperative and postoperative intraocular pressure (IOP).

Of 30 eyes with a preoperative IOP of 20 to 30 mm Hg, only 2 (6.84%) had a postoperative IOP of less than 10 mm Hg. Fifty percent of eyes had a decrease in IOP between 11 and 15 mm Hg, and 43.26% had an IOP between 16 and 20 mm Hg. The average preoperative IOP was 24 mm Hg for this group and this was controlled at an average of 14 mm Hg after surgery.

Of 12 eyes with a preoperative IOP between 31 and 40 mm Hg, 25% had a decrease in IOP of 11 to 15 mm Hg, and 67% of eyes had postoperative IOPs of16 to 20 mm Hg, and only 8% of eyes had an IOP of more than 20 mm Hg (21 to 25 mm Hg). The average preoperative IOP for this group was 35 mm Hg and this was controlled to 16 mm Hg preoperatively.

Of 5 eyes with a preoperative IOP of 41 to 50 mm Hg, 80% had a postoperative IOP between 16 and 20 mm Hg, and 20% had postoperative IOPs ranging from 21 to 25 mm Hg. In this group, the average preoperative IOP was 43 mm Hg and this was controlled to a postoperative average of 19 mm Hg.

Of 3 eyes with a preoperative IOP of 51 to 60 mm Hg, 67% of eyes had a postoperative IOP between 21 and 25 mm Hg, and 33% had an IOP of more than 26 mm Hg. The average preoperative IOP was 56 mm Hg and the average postoperative IOP was 24 mm Hg.

Table 4 shows the comparison of preoperative and postoperative visual acuity. The visual acuities remained the same, with no deterioration during follow-up. Bleb formation with the modified procedure was good and diffuse away from the limbus in 90% of eyes and caused minimal postoperative irritation (Table 5, Figures 12 and 13).

Table 4. Comparison of preoperative and postoperative visual acuities.

Table 5. Type of bleb.

Figure 12. Conjunctival bleb in one of the patients after 2 years.	Figure 13. Superior opening of functional scleral tunnel.

Discussion

IOP is the only risk factor for glaucoma that can be manipulated to alter the course of the disease. Considerable effort has been directed towards control of the devastating clinical consequences of increased IOP associated with glaucoma. While great success has been obtained with pharmacological therapy, reliable surgical procedures for ensuring continuous aqueous outflow are still being sought.

The effectiveness of glaucoma surgery is closely related to the degree of scarring. The filtering procedure tends to fail over time because of fibroblastic proliferation and subconjunctival fibrosis, which occurs during the normal process of wound healing.¹ Adjunctive use of antifibrotic agents such as mitomycin C or 5-fluorouracil at the site of surgery has significantly reduced the risk of bleb failure. The use of these agents has been associated with complications, however, and the long-term safety and efficacy of these agents is yet to be established.^2-5

Modified trabeculectomy with tenonectomy, as described in this study, was associated with effective IOP control in the 5-year follow up. These results demonstrate that, irrespective of the type of glaucoma and the preoperative IOP, this procedure effectively lowers the IOP to 14 to 20 mm Hg in 90% of patients. During 5 years of follow-up after surgery there was no deterioration in visual fields, visual acuity, or IOP control. In addition, the optic disc: cup ratio was between 0.5 to 0.8 preoperatively for most of the patients and did not show any further deterioration during the postoperative follow-up.

With this modified approach the intraoperative and postoperative complications are almost nil. The anterior chamber almost invariably forms within the first postoperative week, the bleb is diffuse for 90% of eyes, and is located well away from the limbus, causing minimal irritation to the patient and leaving a good limbal gap for further surgeries to the eye. Of 50 patients operated for glaucoma, 2 patients underwent cataract surgery and maintained their precataract visual acuity and IOP.

The higher success rate achieved with this procedure results from the fact that the removal of the small strip of sclera along with the portion of trabecular meshwork reduces the possibility of bleb failure by providing continuous drainage through the newly formed channel. Tenonectomy also reduces subconjuctival fibrosis at the time of normal wound healing, thus facilitating continuous filtration through the channel.


Conclusion

These patients were followed up for 5 years and only 8% of patients required medication to maintain the IOP below 20 mm Hg. Most of the patients IOPs (92%) remained controlled with surgery. In conclusion, modified trabeculectomy with tenonectomy offers a reliable method of controlling IOP for patients with glaucoma.


References

1. Skuta GL. Wound healing in glaucoma filtering surgery. Surv Ophthlmol 1987; 32:139-170.
   
2. Greenfield DS, Liesmann JM, Jee J, Ritch R. Late onset bleb leaks after glaucoma filtering surgery. Arch Ophthalmol 1998;116:443-447.
3. Singh J, O'Brien C, Chawle HB. Success rates and complications of intra-operative 0.2 mg/ml mitomycin in trabeculectomy surgery. Eye 1995;9: 460-466.
4. Rockwood EJ, Parrish RK II, Heller DN, et al. Glaucoma filtering surgery with 5 FU. Ophthalmology 1987;94:1071-1078.
5. Zachanic PT, Deppermenn SR, Schuman JS. Ocular hypotomy after trabeculectomy with mitomycin C. AJO 1993;116:314-316.
   
   
   

   Address for Correspondence Dr DD Pandit Department of Ophthalmology Mumbai Port Trust Hospital Wadala Mumbai 400 037 India Fax: (91 022) 414 5115 E-mail: