Ординатура / Офтальмология / Английские материалы / Step by Step Minimally Invasive Glaucoma Surgery_Garg, Melamed, Bovet, Pajic, Carassa, Dada_2006

122 Step by Step Minimally Invasive Glaucoma Surgery

Fig. 8.7: Healon GV was evacuated from the anterior chamber with bimanual irrigation/aspiration

for statistical evaluation of parametric data. The unit of significance was set at a critical p value of <0.05, including Bonferroni correlation for repetitive use of data sets.

Results

Mean preoperative IOP in the study population of 53 patients with primary open-angle glaucoma was 25.6 ± 2.3 mmHg (range18 to 48 mmHg). Average IOP was 17.6 ± 2.7 mmHg (range 2 to 36 mmHg) after a follow-up period of 1 day, 14.9 ± 2.4 mmHg (range 2 to 30 mmHg) after 2 days, 15.7 ± 2.4 mmHg (range 4 to 28 mmHg) after 3 days, 16.0 ± 2.6 mmHg (range 4 to 36 mmHg) after 4 days, 19.0 ± 2.6 mmHg (range 12 to 39 mmHg) after 7 days, 16.9 ± 2.5 mmHg (range 9 to 44 mmHg) after 1 month, 15.1 ± 1.8

Sclerothalamotomy ab Interno a Minimally Invasive 125

Fig. 8.10: Preoperative and postoperative level of

IOP 36 months of follow-up

Average visual acuity after treatment was 0.69 ± 0.31 (range 0.05 to 1.0). In 6 eyes (11.3%) moderate cataract development after surgery which was without influence of visual acuity. Another 3 eyes (5.7%) developed cataract with decreased visual acuity of one Snellen line.

There is no significant difference regarding the cup/ disc ratio at baseline with 0.65±0.18 and at 36 months with 0.66±0.19 (p=0.11) (Figs 8.12A and B).

Sclerothalamotomy ab Interno a Minimally Invasive 127

Fig. 8.12B: Cup/disc ratio at 36 months

There is no significant changes comparing the visual field at baseline with mean defect MD 9.45±2.32, loss variance LV 30.0±5.11 and at 36 months with MD 9.29±2.59, LV 31.4±5.66 (p=0.78 for MD, p=0.96 for LV) (Fig. 8.13).

Temporary IOP elevation higher than 21 mmHg was observed in 12 of 53 eyes (22.6%). These patients responded well to pressure-reducing treatment with one agent and medication could gradually be withdrawn in all of these patients. A single case of hypotension (1.9%) that lasted for 3 days after surgery was observed. Hyphema was present in 6 cases (11.4%) which disappeared within the first 2 weeks after surgery. One eye (1.9%) exhibited transient fibrin formation at pupillary level. Fibrin was cleared within one day after frequent application of topical Dexamethason (Fig. 8.14).

Sclerothalamotomy ab Interno a Minimally Invasive 129

In a pilot study 5 patients with therapy-resistant juvenile glaucoma were treated. We observed an IOP reduction from 41 ± 6.4 mmHg prior to surgery to 12 ± 2.6 mmHg after surgery, a result that has remained stable without any additional pressure-reducing therapy for 24 months.

DISCUSSION

This study reports long-term results of a new surgical technique for treating open angle glaucoma. The STT ab interno method intends the creation of a direct channel between the anterior chamber and the Schlemm canal. Persistence of the sclerotomy can be investigated with a 3- mirror Lens (Goldmann 903). The STT ab interno tip creates a deep sclerotomy with subsequent access of aqueous to the scleral layer. Both aspects may facilitate a bypass effect of aqueous outflow. In light of the fact that about 85 percent of the aqueous humour drains (in physiological terms) trans-trabecularly, we suspect an additional route for aqueous humour absorption in the case of elevated IOP. There is evidence in literature that such bypass effects may be present after surgical intervention which do not lead to the formation of filtering blebs. In a previous study,20 it was ascertained that eyes without filter bleb exhibited very stable long-term IOP regulation postoperatively. In addition to the bypassing of trabecular outflow resistance caused by STT ab interno treatment, outflow resistance may be further reduced by scleral thinning at the base of the thalamus. In addition to that aqueous humour could perhaps be absorbed by the ciliary body.20,27 After early postoperative reduction, the average IOP continued to decline gradually over a period of 6 months before reaching a relatively a constant level. It can be speculated that newly

130 Step by Step Minimally Invasive Glaucoma Surgery

formed blood vessel and lymph vessel close to the surgical site, may contribute to the decrease of IOP level during follow up.2

In literature the success rate range for trabeculectomy ranges between 57 and 96 percent,1,4,9,12,14-18,21- 23,30,32-35 for deep sclerectomy without collagen device between 57 and 74 percent, and for deep sclerectomy with collagen device between 58 and 90 percent.1,5,15,24 The STT ab interno technique with a complete success rate of 90.6 percent is comparable with other so far published surgery methods.

Advantages of the STT ab interno method, compared with trabeculectomy and perforating and non-perforating deep sclerectomy seem to be a rate of postoperative complications and a constant level of reduced IOP. Hypotension, a frequent finding in trabeculectomy, perforating deep sclerectomy and non-perforating deep sclerectomy, is a relatively rare postoperative complication. The most frequent early complications in trabeculectomy are hyphema (24.6%), shallow anterior chamber (23.9%), hypotony (24.3%), wound leak (17.8%) and choroidale detachment (14.1%). The most frequent late complications are cataract (20.2%), visual loss (18.8%), iris incarceration (5.1%) and encapsulated bleb (3.4%). After STT ab interno cataract development was seen in 17 percent with only 5.7 percent loss of one line of visual acuity after 36 months. Compared with other techniques STT ab interno seems to be a relatively save surgical technique.1,5,6,7,15,16

Transient IOP elevation after STT ab interno may occur in the first 6 weeks and can be effectively brought under control with the use of a topical medication. In most cases, IOP-reducing therapy could be gradually withdrawn after 3 weeks post surgery. It was necessary to continue pressure-reducing therapy in 5 of 53 eyes, in all this cases medication was effective in controlling IOP.

Sclerothalamotomy ab Interno a Minimally Invasive 131

Problems of scarring to the Tenon’s capsule, fibroblast proliferation and secondary occlusion associated with trabeculectomy which are induced by the surgical procedure itself may the reason behind the practice of antimetabolites applications (Mitomycin C at concentration of 0.2-0.4 mg/ml for 1-5 minutes). Although this practice was conceived to modulate wound healing and thus to counteract scar formation, it often resulted in serious complications, such as scleral necrosis and an increased incidence of avascular filter bleb and their late complications.28 The surgical procedure applied in this study avoids stimulation of episcleral and conjunctival proliferations and may therefore be related with less secondary cell invasion at the filtrating bypass.

Preliminary histological investigations of post mortem human eyes following STT ab interno did not indicate signs of indirect necrosis in cell layers adjacent to the thalamus formed by high-frequency diathermy. It is yet unknown, if the inner surface of the thalamus will be covered by endothelial cells of corneal or trabecular origin, and whether the thalamus and its function will remain intact on a much longer time scale.

Avantages to STT ab interno include the comparative simplicity and quickness of the surgical procedure itself.

This study point out, that the performance of 4 thalami has so far proved sufficient, what corresponds to a resorption surface area of 2.4 mm². The number of 4 thalami was defined empirical. Regarding the results of this study the creation of 4 thalami seems to provide a sufficient longterm decrease of IOP as a low rate of postoperative complications. For a further potentiality of IOP decreasing effect we recommend to perform up to 6 thalami.

A randomized multicenter study will be conducted in the future to compare STT ab interno, trabeculectomy, and