Aptel and Denis report a comparative study of changes in iris volume with mydriasis for fellow eyes (after iridotomy) of persons who had suffered a monocular acute angle-closure crisis and eyes of age- and gender- matched persons with open angles. Fellow eyes had to have at least 180 degrees of angle closure on gonioscopy, and could not have plateau iris or have had subjective symptoms of acute angle closure (although how many were excluded on this basis is not reported). Iris volume was estimated using four cross sectional radial images taken with the anterior segment OCT. Predilation iris volumes were similar between the groups, however, iris volume increased in the fellow eyes and decreased in the openangle eyes after dilation with either phenylephrine or tropicamide.
The findings of this study are striking and add to a growing literature supporting the influence of dynamic factors in the development of angle closure. Fellow eyes of persons with an acute angle closure attack not only have shallower anterior chamber depth and more closed angles to begin with, but they respond to stimuli differently as well. A previous report found that even at similar angle opening distance as measured by UBM, angle closure eyes close more in the dark and open less to pilocarpine than open angle eyes. The current report definitively shows that, on average,dilation leads to an increase in iris volume in angle closure eyes, while iris volume decreases in those with open angles. An additional intriguing finding is that brown iris color was independently associated with an increase in iris volume, indicating that the mechanism of angle closure in blue-eyed patients may in fact differ from those with brown irides.
The mechanism of angle closure in blue-eyed patients may in fact differ from those with brown irides
This seminal paper not only offers insight into the fundamental mechanisms of angle closure, it opens the door for additional research to determine the predictive value of iris volume testing on the long-term outcomes of angle closure patients.