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Editors Selection IGR 24-1

Response

Comment by Jennifer Burr & Augusto Azuara Blanco on:

70327 Effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE): a randomised controlled trial, Azuara-Blanco A; Burr J; Ramsay C et al., Lancet, 2016; 388: 1389-1397

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We agree with Professor Bourne's observations and gratefully accept his congratulatory remarks.

It would be difficult not to agree with Professor Tham's comments regarding the concept of selecting treatments according to mechanism. Further research focused on better understanding the mechanisms and to evaluate the possibly different relative efficacy of interventions will be valuable. At the moment, patients with PAC/PACG and clear lens have the same initial treatment, i.e., laser iridotomy (regardless of the mechanism). The research question that EAGLE addressed was whether lens extraction for PAC/PACG is superior than current practice. The study was not a mechanistic evaluation of alternative management of PACG. EAGLE was a comparative effectiveness trial designed to inform clinicians, patients and policy makers when faced with treatment choices in the initial management of people presenting with (high IOP) PAC or PACG.

Dr. Xu expresses concerns regarding the definition of clear lens and the balance of refractive errors in the study population. EAGLE was a randomized controlled trial, the characteristics of the study population are balanced between groups. Across all the patient-reported outcome measures, capturing visual impairment and functioning, general health and glaucoma specific symptoms there is a consistent difference between treatments favoring lens extraction at all time points up to 36 months.

Regarding Dr. Xu's questions (Q) some can be answered (A) by reviewing in detail the published paper:

Q — "This brings into question the study's definition of a clear lens, which intuitively should not contribute to any visual impairment. Was it simply 20/20 best corrected visual acuity? Were assessments such as glare testing performed?"

A — We used clinical examination to decide whether a potential participant had cataract (as described in the Methods section). Glare testing was not done. We recognize that participants (without cataract) could have different degrees of lens clarity. Thus, as described in the Statistical Analysis section (page 1392) we did a subgroup analysis and compared the primary outcome between patients with excellent and slightly decreased visual acuity (≥ 85 ETDRS letters vs < 85 ETDRS letters). We did not find a difference in outcomes between these two subgroups.

Q — "The distribution of refractive errors in the study population is also not made clear"

A — Table 2 has median and interquartile range of refractive error.

Q — "When compared to hyperopes, emmetropes and myopes with excellent visual acuity are more likely be unhappy with a sub-optimal refractive outcome and full-time spectacle dependence."

A — We did not plan subgroup analysis according to the type of refractive error.

Q — "The authors briefly discuss the IOP-lowering benefit of clear lens extraction over LPI, but do not conjecture as to why this advantage is so modest."

A — In the Discussion section (pages 1394-1395) we wrote: "Intraocular pressure was better with clear-lens extraction than with standard care, with the mean pressure being around 1 mmHg lower in the clear-lens extraction group at 3 years. Although this difference is small and by itself is unlikely to be clinically relevant, only 21% of participants in the clear-lens extraction group received any further treatment to control intraocular pressure, compared with 61% who received at least one glaucoma drop in the laser peripheral iridotomy group. The study protocol stipulated a target intraocular pressure and allowed clinicians to escalate treatment if and when needed to achieve this. Thus, large differences in mean intraocular pressure were not expected. The superior clinical efficacy of initial clear-lens extraction is supported by the reduced need for further glaucoma surgery in this group than in the standard care group (one vs 24 operations). The resulting reduction in intraocular pressure associated with the glaucoma surgery probably blunted the difference in the efficacy of lowering of intraocular pressure between the two treatment groups."

Q — "The data also does not explicitly mention the number of surgical patients who received goniosynechiolysis, which by itself is a potent IOP-lowering treatment in angle closure patients."

A — In the first paragraph of the Results section (page 1303) we wrote: "18 (9%) participants had synechiolysis associated with the phaco." Finally we would agree with part of Dr. Xu's conclusion: "clear lens extraction is a viable alternative to LPI…"

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