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Editor,—I read with considerable interest the paper by Spencer and Vernon1 on the results of a standard protocol for transscleral diode laser cyclophotocoagulation (“cyclodiode”). The particular importance of this paper with regard to more widespread use of this therapy lies in the high percentage (64%) of treated eyes with pretreatment Snellen acuity, and while a third of these eyes lost 2 or more lines of Snellen acuity, it appears this was, in most cases, not directly attributable to the cyclodiode treatment, with particular note being made of the low rate of cystoid macula oedema.1
The authors report success rates in achieving IOP control with a standard protocol, but, as in most other published series, record findings after “repeat as necessary” retreatments (in this study up to five in number). While this is of obvious interest to clinicians, it may be of almost equal utility to know the effect of a single treatment. In an earlier paper, also using a standardised treatment protocol for cyclodiode treatment,2 an attempt was made to elucidate any dose-effect relation from a single cyclodiode treatment session. With a single treatment totalling 90 J through 360°, a mean lowering of IOP of 48% was achieved, but the predictability of outcomes in this series was hampered by the high number of neovascular glaucoma (NVG) cases, which are recognised as having highly variable responses.3 It would seem that Spencer and Vernon are uniquely placed—with their standard protocol and low numbers of NVG cases—to provide data pertaining to any dose-effect relation from a single treatment, information which may be used to enhance the predictability of the procedure for individual patients.
The authors also note that their cohort was largely free of cases having had previous cyclodestructive procedures: that is by definition not true, however, of all the retreatment cases, and the authors appear not only to have been reasonably forthright in their pursuit of an IOP <22 mm Hg, but appear to have applied the same laser dose irrespective of the number of retreatments, with their retreatment plan leaving no untreated quadrant. In the series noted above, using a half standardised single treatment (45 J over 180°) for cases judged clinically to be at risk of hypotony (which included cases having had previous cyclodestructive procedures) a mean IOP reduction of 36% was still achieved.2 It would therefore be of great interest to know whether any cases in Spencer and Vernon's paper were excluded from retreatment, despite inadequate postoperative IOP control, because of a concern about possible hypotony; similarly, it would be useful to know whether “all comers” were treated in the study period, or whether there were specific exclusions from standardised cyclodiode treatment because of this perceived risk.
Editor,—We thank Dr Walland for his interest in our paper and for summarising the results of his study which was published following our paper's submission. It is difficult to quantify the dose-effect from a single treatment in cyclodiode because (a) it would depend on the follow up period as the effect may diminish with time, and (b) one would have to continue all the prelaser antiglaucoma medications (not always desirable) to see the true effect.
However, we can analyse the “single dose effect allowing for a reduction of medications” from our study by examining the results of only those eyes which had one treatment session (32). This subgroup contained seven primary open angle glaucoma, five aphakic, two pseudophakic, seven uveitic, three corneal/PK, four rubeotic, one silicone oil, and three trauma cases, thus representing the whole spectrum of the cohort treated. Although this subgroup, by definition, selects out the “best case scenario”, this was achieved in over 50% of cases treated. With a mean follow up of 19 months, the IOP of this subgroup decreased from a mean of 31.2 mm Hg to a mean of 16.2 mm Hg, with a 45% mean percentage reduction. This was associated with a reduction in numbers of patients taking acetazolamide from 88% to 6% and a mean medication usage from 2.2 to 1.2. None of these results differs significantly from those of the whole cohort.
In our study no eyes were denied treatment or retreatment because of a perceived risk of hypotony, and “all comers” were indeed treated by this modality if enhanced filtering surgery was considered contraindicated. It may be of interest to know that 71% of the cases were referred into our service from other consultants throughout our region (population approximately six million). We cannot state that all eligible cases were treated by us, but we believe our cohort is likely to be representative of cases referred to other glaucoma specialists with a similar population to that found in the East Midlands of England.
We note that, in Walland's study, the mean post-laser IOP at a mean of 10.4 months was 25.8 mm Hg with only 55% <22 mm Hg even when a “full” treatment of 90 J was delivered. Although this may be as a result of the large numbers of patients with neovascular glaucoma in this group, it may also be due to the time and power output settings used (1.5 seconds and 1.5 W). With our settings of 2 seconds and 2 J per shot we were able to control IOP with a 65.7% reduction using a mean of 1.7 treatments in our neovascular subgroup. Reducing the output per shot, as in Walland's study, may result in a reduction in treatment effect overall despite higher total energies delivered. This could be due to transmission attenuation in certain eyes, operator technique variation, probe output differences, and ciliary process uptake/susceptibility factors.
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