In a retrospective (2010-2013) cohort study, Zheng et al. evaluated a 5% random sample of medicare beneficiaries aged 65 years or above and reported on risk of glaucoma surgery within one year of corneal transplant surgery (CTS) from 3098 patient files (1310 had baseline Glaucoma - 42%). This included 1919 endothelial keratoplasties (EK), 1012 penetrating keratoplasties (PK) and less than 50 lamellar keratoplasties (ALK) and Keratoprosthesis (KPro) procedures. Rates of glaucoma surgery within one year of any CTS ranged from 6.1% to 9.4% in the corneal transplant groups, without statistically significant differences among groups. However, 10.0% of patients with pre-existing glaucoma required glaucoma surgery following any transplant surgery, compared with 5.3% of patients without preexisting glaucoma. This included 12.4% of PK patients with pre-existing glaucoma compared with 2.8% of PK patients without pre-existing glaucoma.
The three major conclusions from the paper were that (I) the rates of glaucoma surgery are significantly higher in patients undergoing CTS as compared to those who do not; (II) there were no significant difference in one year rates of glaucoma surgery between different types of cornea transplant procedures; and (III) pre-existing glaucoma overall increased the chances of glaucoma surgery by two-fold after any CTS and especially after penetrating keraptoplasty (2.8% vs 12.4%, p < 0.01) in patients aged more than 65 years.
Although the study reports no difference in rates of glaucoma surgery in eyes undergoing PK/ EK versus LK and KPro, the data set for the latter two is quite small and may not be an accurate estimation. One would expect a higher incidence of glaucoma in eyes with KPro, however, eyes which underwent a combined tube with KPro were not included in the analysis. Another issue is that the incidence of glaucoma increases over time and the results are only reported for glaucoma surgery within 12 months of the corneal procedure. A major limitation of the study was that due to problems in coding with ICD9, it was not possible to ascertain that glaucoma surgery was performed in the eye with corneal transplant or the fellow eye. There was also no information on eyes undergoing diode laser/endo-cytophotocoagulation which are often performed in eyes with poor visual potential after corneal transplant procedures.
Despite these limitations, the study provides important information on the rates of glaucoma surgery after corneal transplant procedures, and highlights the importance of pre-existing glaucoma as a risk factor for post keratoplasty glaucoma, as well as the need for long-term follow-up with IOP checks and optic disc evaluation in all eyes undergoing any form of corneal transplant surgery.