Analysis of Fellow Eye Intraocular Pressure Changes After Glaucoma Surgery in 1 Eye

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To the Editor:
We read with great interest the article by Kaushik et al1 “Change in intraocular pressure in the fellow eye after glaucoma surgery in 1 eye.” It is very important to monitor the intraocular pressure (IOP) in the fellow eye postsurgery in 1 eye because frequently the fellow eye is neglected by the patient. The other reasons for an elevated IOP in the fellow eye can be a central mechanism as mentioned in the study or an increase in the prostaglandin level in response to the inflammation in the operated eye. Also, it may be the only seeing eye or better eye of the 2.
The authors analyzed 3 groups of patients who had undergone trabeculectomy, Ahmed glaucoma valve (AGV) implant, and AADI implant for control of IOP and then studied the effect of it on the fellow eye. The result obtained is very interesting. However, we have a few queries regarding the inclusion criteria and methodology and we believe that the authors will clear our doubts.
Although all the 3 surgical procedures reduce IOP, the IOP-lowering effect of AADI, which is a Baerveldt-type implant, starts only after 4 to 6 weeks as the ligated suture starts dissolving.2 Thus, IOP increase in the fellow eye in an early phase cannot be explained by the central mechanism as mentioned by the authors. However, it is possible that the cause of raised IOP in these cases can be the increase in the prostaglandin level. The authors have also analyzed those patients who had medically uncontrolled IOP in the fellow eye when 1 eye was operated. This group of patients in our opinion should have been excluded as the IOP fluctuations in these eyes are not predictable and can be very high. Thus, this phenomenon cannot be attributed to surgery in the other eye only.
The authors have considered an IOP difference of 4 mm Hg as significant. Considering that the value of 6 or 8 mm Hg3 is usually taken as clinically significant for diurnal variation, water-drinking test and prone dark-room test, in our opinion with a minimum difference of 6 mm Hg, would have been more convincing. The rationale behind considering 4 mm Hg as clinically significant is not clear.
The study has excluded any fellow eye with a history of YAG laser iridotomy. However, they included 8 fellow eyes belonging to primary angle-closure glaucoma group. Primary angle-closure glaucoma is known to cause very high IOP fluctuations and YAG PI is essential to relieve the pupillary block and have a better control of IOP. Thus, the IOP fluctuation in fellow eye may be a natural course of the angle-closure glaucoma itself rather than an effect due to other eye surgery.
All eyes with uveitis, diabetic retinopathy, or retinal vein occlusion, which are the commonest causes of neovascular glaucoma (NVG), were excluded in the methodology, but 4 eyes with NVG have been mentioned in the analysis. However, the cause of NVG in these cases is not clear. Also the power of the study has not been mentioned for the sample size considered.
We conducted a similar study at our institute and we would like to share our experience. We enrolled 42 posttrabeculectomy with mitomycin C patients and 20 post-AGV (AGV; New World Medical, Los Ranchos, CA) implantation patients. There were 43 male and 19 female patients. Mean age of the patients was 39.77±17.78 years. Rest of the baseline characteristics are given in Tables 1 and 2.
The 2 cases of NVG included were secondary to ocular ischemic syndrome. Our data being parametric, we used ANOVA with Bonferroni and t test (unpaired) for the analysis.
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