The use of Medpor-coated tear drainage tube in conjunctivodacryocystorhinostomy

Fan et al's paper¹ on the use of Medpor-coated tear drainage tubes raises some important points regarding conjunctivodacryocystorhinostomy surgery. Jones in his original paper² describes how the tubes allow an epithelial-lined channel to form, connecting the conjunctiva to the nasal mucosa, and in effect keeping the tube outside the body. Porous polyethylene coating of the tube may allow fibrovascular ingrowth, but it simultaneously prevents a continuous epithelium forming, and therefore violates the basic surgical principle of implantable material being beneath a continuous epithelium to prevent infection. The high rates of conjunctival and nasal mucosal overgrowth found with these tubes, largely pyogenic granuloma formation, are the anticipated response to persistent inflammation and low-grade infection. The situation is analogous to pegging of porous orbital implants to increase prosthesis motility, rarely performed now due to the risk of infection and implant extrusion.

Jones² in the same study went further in suggesting that with time many patients would be able to dispense with their tube altogether. In practice, this is rarely the case, and most surgeons aim to retain the tube long term. As described by Rose and Welham ,³ in what is probably the largest series (326 eyes) and longest follow-up (up to 23 years) of conventional Jones tube placements, problems with the tubes are common. At the mean time from tube placement of 1.3 years in Fan et al's¹ paper, the lower replacement rate of Medpor-coated compared to convention tubes(3.8 vs 26%) is seen to be at the expense of increased conjunctival overgrowth (23 vs 5.7%), and the overall rate of complications is therefore in fact comparable with conventional tubes. Medpor-coated tubes fail even to meet two of the key features of an ideal tube proposed by the authors (easy to insert and removable for cleaning if necessary). They appear to have little to recommend them.