Clinical Implications of Specific Features of the New Susanna Glaucoma Drainage Device

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In Reply:
We congratulate Dr Susanna for sharing his thoughts and suggestions about our recently published article.1 As there are scant data regarding the results of the new Susanna Glaucoma Drainage Device, we believe that all information is valuable at this time, especially coming from the inventor of the device.
We would like to separately address the main points raised by Dr Susanna regarding our article. On the author’s first comment it is stated that there is no relationship between the internal diameter of the tube and hypotony risk. Even though previous laboratory studies about tube resistance and aqueous flow have investigated such relationship,2 to the present moment we are unaware of any published laboratory data regarding the new Susanna implant specifically. While dealing (during the surgeries) with a tube with a smaller lumen, our clinical impression was that such characteristic could imply in a lower risk of hypotony. In fact, looking at our hypotony rates (3/58 eyes had early hypotony),1 one can note a relatively low incidence when compared with previous studies.3,4 We would like to emphasize that the design of our study did not include specific resistance/flow tests, and that tube restriction suture was used (and must be used) in all cases, as described in the Methods session of the manuscript.1
Another point raised by Dr Susanna was that the smaller internal diameter of the implant was designed to reduce the likelihood of tube exposure. Although such statement makes sense from a theoretical point of view, once again the authors are unaware of previous articles with this implant investigating such correlation. As an objective metric, we had 2 cases of conjunctival erosion that had required surgical management (average study follow-up was 7 mo).1 Even though this number may seem high at a first sight, we consider this incidence clinically acceptable, as we included only refractory cases in our study. We are certain that a later analysis with longer follow-up will provide more relevant data on this issue.
In conclusion, our short-term results support the new Susanna Glaucoma Drainage Device as an effective and safe alternative for the management of refractory glaucomas. These findings certainly encourage future research about the implant. We believe much still needs to be investigated, especially regarding long-term results and direct comparisons with other commercially available drainage devices. We thank Dr Susanna for sharing his expertise and bringing up important points for discussion.
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