Effect of Molteno Implant Tube on the Corneal Endothelium

Abstract

Corneal complications, secondary to corneal endothelial compromise, have been associated with glaucoma drainage devices (GDD) since their introduction. Such complications can adversely affect patients’ visual outcomes and subsequently lead to failure of treatment. The exact mechanism of how the drainage devices affect the corneal endothelium is not very well understood. The literature lacks evidence, specifically, for the effect of Molteno® glaucoma implants (Molteno Ophthalmic Limited, Dunedin, New Zealand) on the corneal endothelium. With the development of non-invasive, office-based instruments such as the specular microscope and anterior segment optical coherence tomography (AS-OCT), one can visualise the tube of GDD and quantitatively and qualitatively examine the corneal endothelium.

This study was conducted to describe the relationship between Molteno implant tube positioning in the anterior chamber, and corneal endothelial parameters, over time. Twenty-six patients attending the Eye Department at Dunedin Public Hospital with previous Molteno implant surgery were enrolled over 6-month period in 2014. Their contralateral glaucomatous eyes were used as controls if those eyes did not have Molteno implants. All enrolled Molteno implant eyes (cases) and controls underwent non-contact specular microscopy examination of their endothelia at central and peripheral corneal locations. These measures were repeated at three monthly intervals for one year. Molteno implant eyes further underwent AS-OCT examination to measure the geometric positioning of the tube in the anterior chamber in relation to the posterior surface of the cornea. At the final visit, a significant difference in corneal endothelial densities (ECD) was observed between cases and controls in central and peripheral corneal locations. In cases eyes, central ECD loss over 6 months was estimated around 7.2%, which was higher than the control group. Tube length and tube-cornea angle were associated with localised peripheral ECD loss in the vicinity of the Molteno tube. Corneal endothelial assessment prior to Molteno implant insertion and post-operative imaging of the tube, can be informative regarding the potential of risk corneal complications.