This condition is observed frequently in pigmentary glaucoma but I have not encountered any clear explanation on its mechanism
Hi John,
I know this is very late answer, but I was searching for a reverse pupillary block mechanism myself, and came across your question.
The best description I found is from a Medscape article, author Jim C Wang.
https://emedicine.medscape.com/article/1205833-overview#showall
Dr Wang describes the mechanism as follows:
"Reverse pupillary block has been termed to explain the concave iris configuration in eyes with PDS and pigmentary glaucoma. During an eye blink, a small aliquot of aqueous is burped from the posterior chamber to the anterior chamber, resulting in increased pressure in the anterior chamber. This pressure gradient produces posterior bowing of the iris and increases iridolenticular contact. The increased area of iris-lens contact creates a flap-valve effect, maintaining the pressure differential and the posteriorly concave iris configuration. This process is similar to the change in iris and angle configuration that occurs during indentation gonioscopy."
So the flap created by the iris lying against the anterior lens surface, which usually allows fluid to flow between the posterior and anterior chamber, is now shut off and traps aqueous in the anterior chamber.
The question that still remains is: why does this preferentially occur in patients with pigment dispersion syndrome? After all, (almost) everybody blinks right? My thinking on this is that PDS patients are predisposed to an increased area of iridolenticular contact and resultant flap-valve effect, due to iris and angle anatomy (e.g. posterior iris insertion).
I hope this is somewhat helpful.
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