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We are delighted that there is agreement that subconjunctival drainage is an important component of non-penetrating filtering surgery. Blebs, albeit diffuse, are clearly visible both in cases of deep sclerectomy, and in many cases of viscocanalostomy. However, although Ravinet and Mermoud and ourselves are certain that this is an important component for drainage in non-penetrating filtration surgery, it is important to clarify this point. Although we are certain of the importance, there is still controversy over the relative importance of subconjunctival drainage versus other routes such as trans-scleral or via Schlemm's canal in the case of viscocanalostomy.
On the second point, although Mermoud and Ravinet use antimetabolites before cutting into the sclera, they do not apply antimetabolites including mitomycin into the deep scleral bed. Again, although they do not do this, we know that deep application has been used in other centres. Clearly, the risk of intraocular entry is higher in these situations, and that was the reason for making this comment in the editorial, to warn people of the possible dangers of applying mitomycin after a deep scleral dissection.
Regarding the question of additional hypotony after macroperforation, clearly the team are very experienced in doing this surgery. However, from canvassing personal opinion from individuals who are doing this surgery, who are less experienced than them (like the majority of surgeons doing non-penetrating surgery), and also from reports in the literature including randomised prospective trials, macroperforation is associated with early hypotony.3,4 This may well be exacerbated if intraoperative antimetabolites, particularly mitomycin, have been used.
With regard to the comments on the paper by O'Brart et al, we have forwarded the contents of the letter on to the authors and they have replied separately to the comments.
In conclusion, we are pleased that the article and editorial have led to further healthy discussion. Mermoud and his colleagues are to be commended for the work they continue to do in non-penetrating filtration surgery. However, as we said in our editorial, current studies do reveal that none of the current operations for glaucoma are totally ideal yet, and further research, particularly on surgical methods and wound healing control, is needed so that optimal long term pressure control can be achieved for all our patients with a minimum of complications.