There is ample evidence about the deleterious effect of cataract surgery on a functioning glaucoma filtering surgery. Less evidence exists, however, on the effect of cataract surgery on patients with a glaucoma drainage device (GDD).
Purohit et al. conducted a retrospective comparative study to evaluate the effect of cataract surgery in patients with trabeculectomies (n = 15) and GDD (n = 23), analysing intraocular pressure (IOP), visual field and retinal nerve fiber layer (RNFL) over 24 months.
The authors found that the increase in IOP over the follow-up period was greater in the GDD group than in the trabeculectomy group. In addition, in the GDD group there was a significant worsening of the mean visual field defect while this difference was not significant in the trabeculectomy group. Regarding the RNFL, the changes were also greater in the GDD group.
These results may have been influenced by some differences between the groups. First of all, in 40% of the trabeculectomy eyes a 5-fluorouracil injection was given at the time of cataract surgery while no antimetabolites were used in the GDD group. Other differences between the groups at baseline were mean age (lower in the GDD group), race (lower percentage of Caucasians in the GDD group) and type of glaucoma (more secondary glaucoma in the GDD group). These differences may have also influenced the results.
The present study therefore shows that cataract surgery can affect the function of a previously implanted GDD. However, the differences at baseline and the different use of antimetabolites make comparison between the two groups difficult.