A two centre study of the dose-response relation for transscleral diode laser cyclophotocoagulation in refractory glaucoma

Abstract

Background/aims: Transscleral diode laser cyclophotocoagulation ("cyclodiode") is widely used to treat refractory glaucoma. The main aims of this study were to investigate the dose-response relation of cyclodiode and to evaluate possible predictive factors that would help establish optimum treatment parameters.

Methods: A retrospective analysis of the case notes of 263 eyes of 238 consecutive patients who underwent transscleral diode laser cyclophotocoagulation at two centres was undertaken.

Results: Mean intraocular pressure (IOP) decreased significantly from 40.7 mm Hg (SD 13.7) before cyclodiode therapy to 17.7 mm Hg (SD 10.9) post-treatment, a reduction of 52.6% (p = 0.0001). Following cyclodiode, 89% of patients achieved an IOP of less than 22 mm Hg or a greater than 30% drop in IOP. Hypotony occurred in 9.5% of patients, 76% of whom had neovascular glaucoma. A linear dose relation response was found for the 122 eyes with neovascular glaucoma (p = 0.001) but not for the group as a whole. Treatment failure was associated with male sex (multivariate regression analysis, p = 0.008) and low mean energy per treatment session (univariate analysis alone, p = 0.016). High pretreatment IOP (p = 0.031) and high mean energy per treatment episode (p = 0.001) appeared to be associated with the occurrence of hypotony, although multivariate analysis did not support this finding.

Conclusion: Cyclodiode therapy is highly effective but there is a significant risk of hypotony, which may be reduced by applying lower energy in cases of very high pretreatment IOP and in neovascular glaucoma. The dose-response association remains unpredictable, although a linear relation was found for neovascular glaucoma.

Figures

Figure 1

Scatter plot showing the change in IOP following cyclodiode therapy. All points below the diagonal line represent eyes in which there was a fall in IOP.

Figure 2

Dose-response for the whole group (A) and for neovascular glaucoma (B). In neovascular glaucoma there was a linear relation between the total energy applied and the percentage change in IOP following cyclodiode therapy (p = 0.001). NS = not significant.

Figure 3

Response rate for cyclodiode therapy. (A) shows the percentage of patients achieving an adequate response (IOP30%) following each additional treatment episode—that is, the cumulative response rate. (B) shows the response rate for each individual treatment episode.