YAG laser peripheral iridotomy not tied to significant corneal endothelial damage: RCT
Primary angle closure glaucoma (PACG) accounts for nearly a half of global blindness caused by glaucoma. Laser peripheral iridotomy (LPI) is the conventional first-line treatment for individuals with primary angle closure. While LPI is generally felt to be safe, there have been reports of corneal complications including oedema and decompensation after argon laser iridotomies.
The short-term safety of Nd:YAG LPI has been established, but long-term evaluation is limited. The cell count and corneal cell morphology is relevant to corneal endothelial function and decompensation. Limited studies have reported the effect of Nd:YAG laser on endothelial hexagonality.
Liao C, et al performed an analysis to evaluate the influence of Nd:YAG LPI on corneal endothelial cell density (ECD) and morphology in PACS patients over 72 months which was published in British Open Ophthalmology Journal.
"Over 72 months of observation after YAG LPI, corneal ECD declined and morphology changed in both treated and fellow eyes of PACS patients. Although the difference in ECD between treated and fellow eyes was not statistically significant before 54 months, it became statistically significant at 72 months after LPI. That said, the difference was small (<1%).
The study found no association between ECD loss and laser energy required to complete the LPI, suggesting the energy used to create the LPI was not the primary cause of the longterm effect and was minimally invasive to endothelial cells. It is possible that endothelial cell damage could result from environmental changes at the level of the endothelium after iridotomy owing to alterations in aqueous dynamics, breakdown of the blood-aqueous barrier and suspended debris in the aqueous humour."
Ageing is another important factor accounting for the ECD decline in eyes with or without YAG LPI. One explanation can be eyes with shallower anterior chambers are more predisposed to endothelial cell loss due to the increased possibility of irido-trabecular contact. The ECD changes over time among the untreated eyes is primarily driven by ageing effects instead of narrow angles.
The randomised controlled trial design, large sample size, high follow-up rate, long duration of observation and mixed model analysis allowing for inclusion of a time effect are the major advantages of this study.
The study concluded, "a significant decline in ECD was observed in both YAG LPI-treated eyes and control eyes, which was primarily attributed to the ageing effect. The difference between them was not statistically significant until 72 months after the procedure, with a smaller difference of 0.74% (95% CI −1.23% to −0.24%) and minimum clinical significance.Mean cell areas increased significantly over time in both treated and fellow eyes (p<0.01), , but no longitudinal change was observed for hexagonality. In LPI-treated eyes, no significant correlation was found between age, gender, ocular biometrics, intraocular pressure and laser settings with endothelium change, except for time effect (p<0.01)."
Further investigation of the peripheral cornea would help to understand better the long-term safety of YAG LPI.
Source: : Liao C, Zhang J, Jiang Y, et al. Br J Ophthalmol 2021;105:348–353.