We observe an increase in the number of cases of severe irreversible corneal oedema after laser iridotomy (LI), and the disorder is one of the common reasons for corneal oedema in Japan. In order to study clinical characteristics of the disorder, we analysed data of 98 consecutive eyes with LI-induced corneal oedema that was treated by our hospital between 1995 and 2005. This number represents approximately 3.6% of the total number of corneal transplants, and the incidence seems to be increasing (table 1). The mean duration between LI and first visit was 7.4 years. Prophylactic purpose, especially for the treatment of occludable angle was the leading cause of LI. In 28 eyes in which the laser type was identified, 27 eyes use argon laser (96.4%). The mean number of laser pulses was 421 (range 6–1990), and the mean laser energy was 22.5 J (range 0.9–80.2). At the time of initial examination, corrected visual acuity ranged from light perception to 20/30, with a mean value of 0.029. Eight eyes (8.2%) had pre-existing glaucoma.

All patients received corneal transplantation, associated with cataract surgery in most cases (table 2) With a mean follow-up period of 36.1 months, 91 grafts (92.9%) remained clear, among which, seven eyes received repeated corneal transplantation. Graft rejection was noted in eight eyes (8.2%), and postsurgical glaucoma was noted in 18 eyes (18.4%).

Discussion

Primary angle-closure glaucoma (PACG) is responsible for a large percentage of the glaucoma-blind population, especially in East Asia. In a recent Japanese survey, the prevalence of primary angle closure (PAC) and PACG in those over 40 years was estimated to be 1.3% and 0.6%, respectively.1 LI is the recommended therapy for both PACG and PAC. Although it is considered safer and easier than surgical iridectomy, the present results demonstrate that an irreversible corneal oedema may develop as a late complication. Most of the previous studies reported sporadic case series,2 3 and this report takes into account a large number of cases.

According to a recent national survey conducted in Japan, there were 490 eyes of LI-induced corneal oedema between 1999 and 2001,4 and the incidence is growing.5 Based on a questionnaire sent to facilities from which patients were referred to us, the incidence of LI-induced corneal oedema can be estimated as approximately 1.8% of the LIs. Approximately $0.5 million is spent annually on total healthcare costs, and the occurrence of the disorder further exacerbates the shortage of donor corneas.

There are a number of hypotheses regarding the pathogenesis of LI-induced corneal oedema, including increase in temperature in local aqueous humour, breakdown of the blood–aqueous barrier, delivery of high energy, and continuous jetting of aqueous humour toward the corneal endothelium.6 As many of the LI-induced corneal oedemas developed long after LI, chronic abnormalities appear to be the most likely cause. Indeed, the laser energy applied did not appear to exceed the recommended levels to any great extent in many eyes, although high energy levels were employed in some cases in the present study. While the exact pathogenesis remains unclear, the ophthalmologist should consider other options—for example, surgical excision or LI using YAG laser.

Fortunately, the prognosis for LI-induced corneal oedema seems no worse than that for corneal oedema arising from other causes. Simultaneous cataract surgery was performed in most cases, deepening the anterior chamber, and thus potentially altering the anatomical relationship between the iris and cornea.

As the use of lasers is widespread among Asian ophthalmologists, we may predict an increase in LI-related corneal oedema in the near future. Physicians should be aware of this iatrogenic disorder and the fact that laser treatment is not always safe.

Acknowledgements

We would like to thank J Williams, Tokyo Dental College, for his help with the English in the manuscript.