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.

Lower energy levels adequate for effective transcleral diode laser cyclophotocoagulation in Asian eyes with refractory glaucoma

“…Murphy et al, 19 in their study on Caucasian eyes reported results similar to our study, but with higher energy levels. The mean laser energy delivered was 104.1737.5 J per session.…”

“…Reported success rates vary from 66 to 80% in Caucasians 15,18,19 to 92% in Indian eyes. 20 Taking a mean reported success rate of 70% and a difference of at least 20% to be significant, a study with 80% power and 5% significance would require a minimum of 63 patients, by the following formula:…”

“…28 Most clinical studies 15,19 have considered 4-6 weeks as the time frame for the response of DLCP, after which the eyes are re-treated. We waited for 6 weeks before re-treating our patients.…”

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] The chief drawback of these procedures as a group is a narrow therapeutic window, which implies that there is a very small safety zone in which it is effective without causing significant complications. Currently, transcleral laser cyclophotocoagulation (TSCPC) procedures appear to provide the best combination of effectiveness, portability, expense, and ease of use.…”

“…10 The most frequently used lasers for this modality of treatment are the 1064 nm Nd:Yag lasers [8][9][10][11] and 810 nm semiconductor diode. [12][13][14][15][16][17][18][19][20][21][22][23][24] Both wavelengths can produce thermal tissue damage, and there is evidence that the semiconductor diode laser with 810 nm wavelength exhibits less scleral transmission and considerably greater absorption by melanin compared to the 1064 nm Nd:Yag laser. 25 The clinically significant effect is that the energy needed to produce comparable lesions is less with the diode laser compared to that required by the Nd:YAG laser.…”