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Glaucoma Dialogue IGR 12-3

Response

Comment by Stephen Vernon & Rotchfold & Anthony King on:

26370 Transscleral diode laser cycloablation in patients with good vision, Rotchford AP; Jayasawal R; Madhusudhan S et al., British Journal of Ophthalmology, 2010; 94: 1180-1183

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We thank the reviewers for their considered responses to our paper outlining the results of a standardized cyclodiode protocol on eyes with good vision in refractory glaucoma, and the general agreement that this modality of treatment deserves further consideration in complex cases where other modalities are unavailable or impractical. Our paper was written to address the lack of literature on this subject. We were able to identify only a single, small report specifically addressing the visual acuity outcome of cyclodiode in patients with refractory glaucoma who do not already have visual impairment.¹ Papers using diode or its less efficient predecessor Nd:YAG laser are legion in patients with poor acuity. However, these are clearly a group with different underlying pathology and clinical needs and extrapolating to those with good acuity is not intuitively justifiable. In our study we consistently applied a standard, relatively conservative treatment protocol. Post-treatment hypotony is associated with visual loss after cycloablation² and its incidence appears to be consistently related to the dose of laser energy delivered in a treatment session. Notably, protocols employing < 60J per session are free of this sight-threatening complication in the literature.³ For this reason, our protocol uses a relatively low dose (56J) and we accept that retreatment will be necessary in a proportion of patients (37% in this study) which more safely allows us to titrate the treatment dose. Overall, there can be little doubt regarding the effectiveness of this treatment protocol as 80% of eyes had an IOP ≤ 21 mmHg with at least a 20% reduction in IOP without further surgical intervention or acetazolamide after a mean of five years follow up.

Our results justify the treatment of individuals with refractory glaucoma with cyclophotocoagulation when other modalities are considered impractical or excessively risky, provided our protocol is followed

A retrospective study such as this justifiably incurs criticism, particularly with regard to the accuracy of outcome measurement and the lack of universal visual field data. Recruitment into our study was based on a single baseline recording of visual acuity and it is likely that this has introduced bias against good post-laser acuities as a result of regression towards the mean. For this reason, as well as for consistency with the existing glaucoma literature, we elected to use a two line reduction in acuity as our primary outcome measure. The uncontrolled nature of this study also limits the conclusions we can draw. The group was heterogeneous and patients of the type enrolled in this study lose vision over time as a result of the underlying pathology or co-morbidity independently of treatment.² For this reason, as we have stated, a randomised controlled trial would be of value. However, as we have pointed out, in many of our cases alternatives were either rejected by the patient or impracticable due to other ocular or systemic issues. The subjects in this study, collected over a twelve-year period, represent only a small proportion both of the total number of glaucoma procedures performed in our unit during that time. It is neither our practice nor our suggestion that transcleral cyclodiode should replace other forms of surgical intervention in all, or even the majority of cases of refractory glaucoma. That would be to over interpret the results of our study. We would, nevertheless, advocate a RCT in patients with refractory glaucoma whose visual field is not at endstage in order to eradicate the effect of minimal glaucomatous progression on acuity loss.

In the meantime, we believe our results justify the treatment of individuals with refractory glaucoma with cyclophotocoagulation when other modalities are considered impractical or excessively risky, provided our protocol is followed.

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