Reversal of aqueous flow in myopic, vitrectomized eyes with scleral-fixated intraocular lenses: A proposed mechanism underlying reverse pupillary block.

BACKGROUND

Reverse pupillary block (RPB) is an increasingly recognized complication following secondary scleral-fixated intraocular lens (IOL) implantation, particularly in vitrectomized eyes with high axial myopia. Although its clinical manifestations are well described, the underlying hydrodynamic mechanism remains poorly understood. We sought to visualize aqueous humour flow in vivo and determine whether altered intraocular fluid dynamics could explain the development of RPB.

SETTING

Private practice with a single surgeon.

DESIGN

Retrospective chart review and observational study.

METHODS

Patients who underwent IOL exchange with intrascleral haptic fixation (ISHF) by Yamane technique by a single surgeon underwent slit lamp video microscopy postoperatively using a Haag-Streit BQ900 slit lamp with a IM900 imaging system.

RESULTS

Six eyes of six patients (mean axial length 27.26 mm) demonstrated reproducible movement of suspended particles from the anterior chamber into the posterior segment through the iridolenticular channel. All six eyes underwent concurrent pars plana vitrectomy, although two had previously been vitrectomized. All eyes had one or more prophylactic peripheral iridotomies and none demonstrated active reverse pupillary block or elevated intraocular pressure at the time of observation. However, the observed flow pattern provides a physiological explanation for the reverse pupillary block that had occurred previously or was known to occur intermittently in these anatomically susceptible eyes.

CONCLUSION

In vitrectomized eyes with scleral-fixated IOLs, aqueous humour may preferentially flow from the anterior chamber toward the posterior segment. We propose that this reversed pressure gradient is driven by enhanced posterior aqueous outflow through the retinal pigment epithelium pump in eyes lacking the normal lens-zonule-vitreous barrier. This altered fluid dynamics provides a mechanistic explanation for reverse pupillary block and its relief following peripheral iridotomy.