This paper reports on the results of short-term intraocular pressure (IOP)changes in the fellow eye of glaucoma patients after mitomycin C‐augmented trabeculectomy, PreserFloTM microshunt implantation (PMI), and filtering canaloplasty (FCP) (a modified canaloplasty that provides a three-way outflow for the aqueous humor: Schlemm's canal, suprachoroidal outflow enhancement, and subconjunctival filtration).1
The existence of a 'Consensual Ophthalmotonic Reaction' (COR; the consensual ophthalmotonic reaction describes the phenomenon whereby alteration of the IOP in one eye is accompanied by a corresponding pressure change in the contralateral eye) has been widely investigated in the past without reaching actual conclusions due to difficulties in assessing the IOP in same conditions (before and after surgeries) in operated and fellow eyes. The presence of COR in healthy non-glaucomatous eyes has been recently investigated by Voykov et al.;2 they found the presence of COR in healthy individuals undergone cataract surgery, supporting the existence of the COR. Significant IOP elevation in one eye resulted in IOP reduction in the fellow eye. Interestingly, this phenomenon did not exist vice versa. In glaucoma patients, COR has not been unequivocally confirmed, even if several retrospective studies have speculated on its existence and mechanisms of induction. 3-4
The paper of Aghayeva and colleagues is interesting from a clinical point of view. As a matter of fact, mitomycin C-augmented trabeculectomy (TE) induced a significant decrease of the IOP in the operated, and at one week after TE, the median IOP change in the treated eyes was -12 (-18 to -7) mmHg and in the fellow eyes -3 (-6 to 0) mmHg. The higher the IOP reduction was in the surgical eye, the larger was the IOP reduction in the fellow eye (p = 0.001). Interestingly, IOP elevation occurred in 33% and 22% of fellow eyes on the first postoperative day and at one week after TE, respectively.
PMI, determined a significant decrease of the IOP in the operated eyes and an IOP elevation in 35% of fellow eyes both on the first day and at one week after PMI; in 9% of fellow eyes, this IOP rise was more than 50% from baseline on the first day after surgery. The results of FCP were: IOP elevation in 16% and 32% of fellow eyes on the first postoperative day and at one week after FCP, respectively. (FCP is a surgery that is performed in few German Academic Centers, and not widely known and applied elsewhere by other glaucoma specialists).
I congratulate Dr. Aghayeva and his coauthors on their valuable contribution. Nevertheless, due to: IOP variability in different conditions of medical therapy (in the operated and in the fellow eye), carry-over phenomenon of glaucoma drugs, and 'stimulated' adherence to the therapy, as also stated by the authors, the question of inter-eye relationship of IOP changes after unilateral surgery remains unanswered.
This result, if confirmed in larger prospective studies could help us to make more comprehensive surgical choices for each single patient, also considering the clinical condition of the fellow eye.
As general rule, I always warn patients in my clinical practice of possible changes of the IOP in the contralateral eye after laser treatments or surgery (even if it is not my experience of clinically relevant changes following these procedures in the fellow eye), and I never forget to measure the IOP in the fellow unoperated eye, even in the early post-operative periods.