Survival analysis for success of Molteno tube implants

Abstract

Aim: To apply survival analysis in assessing the long term outcome of Molteno tube implantation and to identify risk factors for failure.

Methods: A retrospective, 10 year, consecutive case series study of 119 eyes that underwent implantation of a Molteno tube. The main outcome measures considered were intraocular pressure (IOP), visual acuity, and complications.

Results: A 30% or greater reduction in IOP was achieved in 68.9% of cases. However, the overall, "complete success" rate (IOP <22 mm Hg with no medications) after a mean (SD) follow up period of 43 (33) months (range 6-120) was only 33.6% despite a fall in mean (SD) IOP from 38.2 (8.2) mm Hg to 20.1 (11.0) mm Hg. The "qualified success" rate (IOP <22 mm Hg with or without medications) was 60.5%. Failure was most common in the first postoperative year but could occur after several years, the survival curve having an exponential shape. The only statistically significant risk factor for failure identified was pseudophakia, although eyes with neovascular glaucoma tended to fare poorly. Postoperative IOP tended to be lower after double plate than after single plate implantation. There was no significant difference in outcome based on age, sex, race, previous penetrating keratoplasty, or previous conjunctival surgery.

Conclusions: In eyes at high risk of trabeculectomy failure, implantation of an aqueous shunt device should be considered. Pseudophakia should be considered an additional risk factor for failure. Early failure appeared relatively more common but long term follow up of all cases is recommended to ensure adequate management of late failures.

Figure 1

Scatter plot of mean preoperative intraocular pressure (IOP) against final postoperative IOP for all eyes. Some points overlie others and may represent more than one case. The oblique line of no change in IOP is drawn to show that there was a reduction in IOP for the majority of cases.

Figure 2

Kaplan-Meier survival curves for all patients, plotting the cumulative probabilities against time that (i) the intraocular pressure (IOP) remains below 22 mm Hg without additional medical treatment ("complete" success: CS), (ii) the IOP remains below 22 mm Hg with or without additional medical treatment ("qualified" success: QS); and (iii) the IOP remains below the target IOP (set as a 30% reduction from the mean preoperative IOP; -30%R) following tube implantation.

Figure 3

Intraocular pressure (IOP) versus time profile for the whole patient group. The first point represents the highest recorded preoperative IOP levels and the second point the mean of the three most recent preoperative IOP values. The other points represent the mean IOP values for the appropriate postoperative time point.

Figure 4

Kaplan-Meier survival curves based on diagnostic category, plotting the cumulative probabilities against time that intraocular pressure (IOP) remains below the target IOP (set as a 30% reduction from the mean preoperative IOP) following tube implantation. POAG = primary open angle glaucoma.

Figure 5

Kaplan-Meier survival curves based on age group (0-30 years, 31-60 years, 61-91 years), plotting the cumulative probabilities against time that intraocular pressure (IOP) remains below 22 mm Hg without additional medical treatment ("complete" success) following tube implantation.

Figure 6

Kaplan-Meier survival curves based on type of Molteno tube implanted (single v double plate), plotting the cumulative probabilities against time that intraocular pressure (IOP) remains below the target IOP (set as a 30% reduction from the mean preoperative IOP) following tube implantation.

Figure 7

Kaplan-Meier survival curves based on whether or not the eye had undergone previous glaucoma filtration surgery before tube insertion, plotting the cumulative probabilities against time that intraocular pressure (IOP) remains below the target IOP (set as a 30% reduction from the mean preoperative IOP) following tube implantation.

Figure 8

Kaplan-Meier survival curves based on lens status (phakia, pseudophakia, aphakia), plotting the cumulative probabilities against time that intraocular pressure (IOP) remains below 22 mm Hg without additional medical treatment ("complete" success) following tube implantation.