Glaucoma DS group include rates of 61 %14 and 52 %,15 which are better than those
of Lüke et al.’s VC group (following which they observed a bleb), who had 12-month success rates of 30 %. In trabeculectomy, establishing subconjunctival flow of aqueous is essential to bleb survival. Speculatively, by creating two routes for the aqueous to drain, (i.e., through Schlemm’s canal and subconjunctivally in the case of those who perform VC with loose scleral flap suturing), both routes may work suboptimally: if flow through Schlemm’s canal diverts flow away from the subconjunctival bleb, this may affect bleb survival, with a reciprocal effect on Schlemm’s canal.
These are slightly better than O’Brart et al.’s VCMMC group (following which they observed a bleb) 12-month results of 60 %.27
By applying a similar logic to VCMMC and DSMMC, the expectation is that the VCMMC group would fare less well than the DSMMC group. Twelve-month success results from the DSMMC group include 78 %17 and 67 %.18
VC with tight suturing of the sclera appears effective at lowering IOP in the medium term. Loose suturing of the scleral flap may be detrimental to the success rates of VC surgery.
Combined Cataract Extraction and Viscocanalostomy Tanito et al.29
would expect PhacoDS results to be better than the DS group. Anand and Anand32
published two-year success rates of 60 % (n=48, success
<19 mmHg) with PhacoDS. Seventy-one percent required GP; 21 % required needle revisions with either 5-FU or MMC. This compares favorably with the success rates of Khairy et al.14
of 37 % at 24
months (n=43, success <22 mmHg) with DS. This contrasts with phacotrabeculectomy, where IOP reduction rate and progressive follow-up results seem better when trabeculectomy is performed alone.33–36
Perhaps excessive inflammation generated during phacotrabeculectomy leads to increased probability of surgical failure.
Concomitant cataract extraction with DS may improve short-term success rates of DS surgery.
Cataract Extraction + Deep Sclerectomy + Mitomycin C (PhacoDSMMC) Anand and Anand32
published two-year success rates of 76 % with
PhacoDS + MMC (PhacoDSMMC), comparing favorably with 60 % in the PhacoDS group (n=48, success <19 mmHg). In the PhacoDS group, 71 % required GP and 21 % required needle revisions with either 5-FU or MMC. In the PhacoDSMMC group, 62 % required GP and 18 % required needle revisions with either 5-FU or MMC. Guedes et al.18
published published 12-month data with success rates of 95 % (n=18,
success <21 mmHg, separate-site cataract surgery) with combined cataract extraction and VC (phacoemulsification + VC [PhacoVC]). Park et al.30
published 24-month success rates of 61 % (n=84, success
commented on lower GP rates in PhacoVC. As Wishart’s cataract surgery is achieved through the same site as VC, could the cataract wound contribute to IOP control post-operatively, at least for a short time? This might explain the lower rates of post-operative GP in this group. If the same-site keratotomy wound (used for phacoemulsification) does remain patent post-operatively, thereby acting as an ab interno goniotrabeculotomy, then separate-site PhacoVC might be expected to have poorer success rates than same-site PhacoVC. Indeed, Park et al.’s results30 Dagres’s28
<21 mmHg, separate site cataract surgery). Wishart and Dagres28 published three-year success rates of 89 % (n=80, success ≤21 mmHg, same-site cataract surgery). Wishart and Dagres’s results are better than those of the VC group, which featured multiple scleral flap sutures,9,25 where three-year results were 59 % and 76 %, respectively. Wishart and Dagres28
are not as good as Wishart and at equivalent time-points: Wishart and Dagres’s 24-month
success rate was 92 % (n=131, success ≤21 mmHg). Park et al.’s patients were Japanese and Wishart and Dagres’s were Caucasian.
Concomitant cataract surgery through same-site incision may improve short-to-medium-term success rates of VC surgery.
Combined Cataract Extraction and Deep Sclerectomy
Unlike PhacoVC, combined cataract extraction and DS (PhacoDS) through the same site would likely increase the risks of hypotony and flat anterior chambers, as there would no longer be a ‘guarding’ effect from an intact TDW. Hence, surgical techniques in the literature describe separate-site surgery for this technique. As cataract surgery alone has been shown to reduce IOP in open-angle glaucoma,31
one 30
three-year success rates of 56 % in PhacoDSMMC (n=41, success <21 mmHg); 12 % required GP.
Concomitant use of MMC may improve the short-to-medium-term success rates of DS.
Viscocanalostomy + Canaloplasty (VCc) In VC + canaloplasty (VCc), once Schlemm’s canal has been de-roofed, it is viscodissected and circumferentially cannulated with a microcatheter. Once Schlemm’s canal has been cannulated, the microcatheter is withdrawn with a 10/0 polypropylene suture attached to the distal end. Having been pulled back through the entire length of the Schlemm’s canal with the withdrawal of the microcatheter, this suture is then locked under tension on a hypotonous eye. The rest of the procedure is as per VC. Grieshaber et al.37
published 12-month success
rates of 94 % (n=25, success ≤21 mmHg); GP was required in six eyes. Lewis et al.38
published three-year success rates of 40 % (n=89, success
≤21 mmHg), while their 12-month success rate was 57 % (n=91, success ≤21 mmHg). They also published a three-year success rate of 78 % (n=27, success ≤21 mmHg) when combined with cataract surgery.
VCc can achieve excellent success rates in the short term. Excellent medium-term success rates can be obtained with concomitant cataract extraction. Whether these results are better than VC and PhacoVC remains to be determined.
Who Should Undergo Deep Sclerectomy or Viscocanalostomy?
What is a surgeon’s motivation not to perform a trabeculectomy? Is it early hypotony or flat anterior chambers? Is it late bleb leaks or late endophthalmitis and a wish to avoid using MMC? (And if so, can the patient afford collagen/hyaluronic acid implants?) Is it to minimize post-operative care? The answers to these questions will determine which alternative to trabeculectomy may be optimal.
US OPHTHALMIC REVIEW
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