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Perfluoropropane (C3F8), which is frequently used in retinal surgery, is an inert, relatively non-toxic gas which expands and remains in situ for several weeks after intravitreal injection. Subconjunctival retention of C3F8 gas after trabeculectomy has been found to be effective and safe in increasing the success rate of trabeculectomy in young patients with glaucoma.1 The main aim of this study was to evaluate the clinical effectiveness and safety of subconjunctival retention of C3F8 gas after trabeculectomy.
Patients and Methods
Between May 1994 and June 1996, 32 patients (32 eyes) were enrolled in the study. To be eligible for the study, patients were aged between 18 and 35 years, had a diagnosis of primary open angle glaucoma or steroid-induced glaucoma, had no history of prior ocular surgery or laser therapy, and had an intraocular pressure (IOP) that was uncontrolled below 21 mm Hg after maximum medical therapy. Patients were excluded if they had autoimmune diseases with ocular involvement, or if close follow-up was not possible. Only one eye of each patient was included in the study. The patients were randomised into 2 study groups for trabeculectomy. Patients in group A (n = 16) received trabeculectomy only and patients in group B (n = 16) received trabeculectomy and subconjunctival retention of C3F8 0.5 mL. Since the morphologies of filtering blebs of the 2 groups were totally different after surgery, the study was designed in a randomised but unmasked manner.
Trabeculectomy was performed in a standard manner, with a limbus-based conjunctival flap and a mid-thickness triangular scleral flap. The surgical techniques were identical in each group, except that patients in group B received additional pure C3F8 0.5 mL injected subconjunctivally with a 27-gauge needle after the operation. Postoperatively, all patients received topical antibiotics for 2 weeks; topical atropine for 2 to 4 weeks, and topical fluorometholone for 3 weeks. All patients were examined at 2 and 4 weeks and 3, 6, 9 and 12 months postoperatively. Successful IOP control was defined as follows:
- complete success IOP of 21 mm Hg or lower without medication
- qualified success IOP range of 22 to 25 mm Hg without medication or IOP lower than 21 mm Hg with medication.
Failure of surgery was defined as IOP greater than 25 mm Hg without medi-cation or IOP greater than 21 mm Hg with medication, or when further glaucoma surgery was indicated.
 
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Results
Typical characteristics of a C3F8-asso-ciated filtering bleb are an extensive bulging conjunctival cyst in the early postoperative period followed by gradual flattening and diffusion. The average duration for the presence of C3F8 gas within the conjunctival cyst was 28 ± 6 days (range, 12 to 35 days). Mean post-operative IOP measurements at different time intervals are shown in table 1.
| Table 1. Intraocular pressure at different postoperative intervals. |
Time
postoperatively |
Group A
(mm Hg)
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Group B
(mm Hg)
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p value
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Baseline
2 weeks
4 weeks
3 months
6 months
9 months
12 months
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31.2 ± 4.1 (n=16)
13.2 ± 2.9 (n=16)
15.6 ± 3.1 (n=16)
16.8 ± 5.5 (n=16)
17.8 ± 6.2 (n=16)
21.3 ± 7.7 (n=15)
24.2 ± 9.2 (n=13)
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29.3 ± 5.1 (n=16)
12.3 ± 2.1 (n=16)
16.2 ± 3.5 (n=16)
13.7 ± 4.2 (n=16)
14.6 ± 5.7 (n=16)
14.8 ± 6.2 (n=16)
16.4 ± 5.5 (n=15)
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0.25
0.32
0.61
0.08
0.14
0.02
0.02
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Mean IOPs were found to be significantly differ-ent between the 2 groups at months 9 and 12 postoperatively. The total success rate was not significantly different between the 2 groups during the first 9 months. At 12 months postoperatively, the total success rate was 50% in group A and 94% in group B a significant difference (p = 0.016, Fisher's exact test) [table 2]. In addition, none of the patients in group B developed a shallow anterior chamber, while 2 patients in group A did. The incidence of Tenon's cyst in group A was also higher than that in group B (p = 0.083). Visual acuity results were not significantly different between the 2 groups. Both groups had 2 patients who lost 2 or more lines, but most patients experienced no change.
In Summary
The normal wound healing process after trabeculectomy often leads to external fibrosis and eventual closure of a surgical scleral fistula, which results in failure of the surgery. The failure rate is even higher when trabeculectomy is performed in young people. In this study, C3F8, an inert but long-lasting gas, was found to augment the formation of a filtering bleb when retained subconjunctivally after trabeculectomy. The total success rate for patients receiving trabeculectomy and C3F8 subconjunctival retention is significantly higher than that for patients receiving trabeculectomy alone. In addition, the incidence of encapsulated Tenon's cyst was lower in the group receiving C3F8. The mechanism for such results is still not clear, but decreased contact between the conjunctiva and sclera in the early postoperative period may be an important factor. It was also noted that due to the air tamponade effect of C3F8 on the scleral flap, the frequency of postoperative shallow chamber also decreased.
Reference
1. Lu DW, Tai MC, Chiang CH. Subcon-junctival retention of perfluoropropane (C3F8) gas increased the success rates of trabeculectomy in young people. J Ocul Pharmacol Ther 1997;13;235-242.
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