▪ This is a case of progressive development of excessive astigmatism in an eye with repeat filtering surgery with MMC for medically uncontrolled uveitic secondary glaucoma. The astigmatism apparently started to develop between 4 and 5 years after the first filtering surgery and from 2 to 3 years after the second filtering surgery.
In trying to systematically approach how to best rehabilitate the vision in the patient's left eye, the following questions must be evaluated: What is the probable cause of the development of the astigmatism? Is the situation/astigmatism stable or developing further? Can the cause be reverted? If not, what can be done?
The most probable cause for the progressive astigmatism is flattening of the nasal superior/temporal inferior meridian (around 150 degrees). The topographies demonstrate very asymmetrical flattening in the 150-degree meridian with extreme flattening in the nasal superior hemimeridian, while the steepening vertical to it is relatively symmetrical and is therefore probably due to coupling. This suggests distention and sliding of the tissue surrounding the first trabeculectomy site as the most probable cause for the progressive development of astigmatism. The most likely reason for this late mechanical weakening is partial scleral necrosis as a late consequence of the MMC application.
From the data given in the description of the case, current stability of the situation cannot be concluded. It is probable the process had not yet come to a standstill.
If one were to causally treat this condition, supposing that the “working hypothesis” given above is correct, major surgery would be involved. In principle, one would have to open the conjunctiva, preferably at the limbus, and expose the first trabeculectomy site. Depending on the findings, any identifiable area of scleral atrophy/thinning would be delineated and reinforced with a donor scleral patch, lamellarly anchored in surrounding healthy sclera, using a technique resembling epikeratophakia. As this site is obviously no longer active in controlling the pressure, the scleral patch would be lamellarly anchored in the peripheral-most portion of the cornea not exhibiting atrophic signs as a consequence of the MMC application. The conjunctiva, preferably with as much of Tenon's as can be mobilized, would be attached over the patch. The fixation of the patch with single sutures (preferably of nonresorbable material) would need to be performed in a manner to ensure massive hypercorrection (ie, steepening of the 150-degree meridian) is achieved. This eye would be left to heal and stabilize over many months. It would probably be well over 1 year before the effect of the surgery could be judged. Once the situation is stable, it would need to be evaluated and further corrective measures contemplated according to the situation.
This solution would have the advantage of the potential for long-term, if not permanent, stabilization. The obvious disadvantage is a long rehabilitation period and poor predictability of the outcome. As this is a relatively young man, this option may be worth the effort but must be thoroughly discussed with the patient.
If this option is not pursued for whatever reason, one would have to wait until relative stability is achieved. This may practically be supposed to occur when 2 successive topographies of at least a 2- to 3-month interval show no further progression. One could then perform phacoemulsification of the existing cataract, which could be expected to progress, and implant a custom toric IOL.
Two other options are implanting the sulcus version of the IOL for potentially easier exchangeability (the optic could still be “buttoned-in” behind the capsulorhexis) or proceeding straightforward with intracapsular implantation. The surgeon would have to chose 1 of these 2 equivalent options based on personal preference and objective findings, such as endothelial cell count and the tissue situation at the superior nasal limbus.
Whatever decision is made, this case shows that MMC application in glaucoma surgery is by no means trivial. Although in this case of uveitic secondary glaucoma the indication for the use of MMC cannot generally be criticized, it may serve as a warning against the sometimes advocated generous, if not generalized use, of this highly toxic substance. It must not be assumed that this case is a singular exception.