I read with interest the article by Quek and associates regarding the long-term progression of primary angle-closure glaucoma in Chinese patients. For some time there has been a need for long-term studies of the progression in primary angle-closure glaucoma in the Asian population, where primary angle-closure glaucoma accounts for more than 50% of all cases of glaucoma. This study assumes greater importance in trying to identify risk factors for progression in primary angle-closure glaucoma.
It indeed was interesting that those with visual field deterioration had higher mean overall intraocular pressure (IOP) and higher prevalence of previous acute angle closure. It was surprising that the mean IOP or the range of IOP were not significant risk factors for progression, which is in contrast to earlier randomized controlled trials. A careful re-examination of the results and the methodology give us answers to these observations.
Mean overall IOP was calculated by summation of all IOP recorded, divided by the number of measurements obtained, up to the point of visual field progression. The authors noted the history of previous angle closure attacks in more than 50% of eyes that progressed, compared with 21% of stable eyes. Given this information, it should not be surprising that the mean overall IOP in eyes with prior attacks of angle closure causing intermittent IOP spikes was found to be higher.
The significance of the mean overall IOP decreases, despite nonoverlapping 95% confidence intervals (16.7 to 18.6 mm Hg vs 15.2 to 16.3 mm Hg), unless the intervisit IOP fluctuations and range of IOP after resolution of the attack are taken into account. The confirmation of the above comes from the observation in this study that overall mean IOP was not a risk factor in eyes without previous acute angle closure attacks. It would have been interesting if further subanalysis were carried out to compare progressed eyes with or without prior acute angle closure.
Interestingly, 81% of eyes that progressed had undergone surgery, compared with 68% in stable eyes. This explains a similar IOP range between the 2 groups, with the former requiring aggressive treatment or early surgery. Yet, this would mean more visits, which would imply a lower overall mean IOP, with the same range of IOP between progressing and stable eyes.
Despite the inherent limitations of a retrospective study, this study does open up the need for further prospective studies to confirm the results.