Commentary: Glaucoma Complicating Vitreoretinal Surgery!

Patients undergoing vitreoretinal surgeries are prone to develop other vision-threatening problems such as cataracts, glaucoma, squint, and corneal decompensation. While it is impossible to predict and prevent such events, adequate care to mitigate these would go a long way in preserving the patient’s vision. The need to update one’s knowledge and skills to this end cannot be understated. The occurrence of ocular hypertension and glaucoma is a crucial postoperative issue in patients undergoing vitreoretinal surgeries. The incidence of open-angle glaucoma was found to be 7.8% and 4.8% in vitrectomized and nonvitrectomized eyes, respectively, with a meta-analytic odds ratio of 1.67.[1] Various causes and mechanisms of the development of secondary glaucoma have been elucidated in the current review.[2] The pathogenesis of glaucoma after vitreoretinal surgeries is still not clear. Independent of the procedure, some eyes are predisposed to glaucoma (e.g., family history of glaucoma, post-trauma, high myopia, uveitis, and neovascularization), possibly due to a suboptimal outflow facility. Apart from this, simple vitrectomy has been proposed as a risk factor for the development of glaucoma.[3] Vitreous is a significant reservoir of ascorbate, an anti-oxidant. Removal of vitreous leads to loss of this anti-oxidative mechanism leading to gradual damage to the trabecular meshwork and glaucoma, which can develop even years after uncomplicated vitrectomy. Removal of the lens altogether increases the risk further.[4] The diagnosis of glaucoma remains a challenge in eyes that have undergone vitreoretinal surgeries. Vitreoretinal procedures with or without scleral explants and the various tamponading agents used can alter the ocular biomechanical properties and lead to variations in IOP measurements.[5] Though Goldmann applanation tonometry (GAT) remains the gold standard for IOP measurement, data are scarce on the standardization of IOP measurement with compensation to these biomechanical changes after vitreoretinal surgeries. It was found that in eyes with silicone oil tamponade, noncontact tonometry gives lower IOP than GAT or corneal visualization Scheimpflug technology (Corvis ST); however, Corvis ST was highly consistent with GAT. Thus, Corvis ST can be an optional noncontact method for measuring postoperative IOP in silicone oil-filled eyes.[6] More studies need to be done comparing various methods of IOP measurement in eyes undergoing vitreoretinal surgeries with various tamponades and scleral explants. It has also been observed that additional procedures performed during membrane peeling or staining during vitrectomy can lead to alterations in the optic nerve morphology and nerve fiber layer thickness, producing glaucomatous-like damage.[4] Thus, conventional glaucoma diagnostic methods may not always be helpful in these patients. Hence, appropriately documenting the disc details preoperatively (wherever possible) and the morphological changes at follow-up visits are necessary for initiating appropriate treatment at the first sign of progression. Another critical aspect is that many of these patients may develop a reduction in peripapillary retinal nerve fiber layer (RNFL) thickness after vitrectomy.[7] This makes the optic nerve head and RNFL more susceptible to damage with even minor increases in intraocular pressure (IOP). Hence, their target IOP must be kept low to prevent further damage. As mentioned in this review, treatment of post-vitreoretinal surgery glaucoma is fraught with several difficulties.[2] Given the occurrence of glaucoma in many of these patients, it is imperative to have a thorough workup in patients undergoing vitreoretinal surgeries to look for glaucoma-related risk factors such as a family history of glaucoma, angle recession, compromised angles, and neovascularization. In such patients, the occurrence of postoperative glaucoma should be anticipated. Medical management may be insufficient, and many patients need surgical interventions to control IOP. Conjunctival scarring poses a significant challenge to conventional trabeculectomy’s success, and many need glaucoma drainage devices (GDD) for refractory glaucoma.[8] To this end, minimally invasive minor gauge vitrectomy that does not require conjunctival dissection can be planned, particularly in patients at high risk of glaucoma. Other surgical precautions such as preserving the crystalline lens or posterior capsule to minimize the migration of silicone oil or gas, avoiding over-fill of tamponading agents, prophylactic peripheral iridectomy, and intraoperative assessment of IOP may be helpful measures. In addition, scleral explants can be preferably avoided in these patients, preserving conjunctiva for possible filtration procedures. Scleral explants can be a challenge for even placing GDDs in these patients. However, as discussed earlier, any patient may develop secondary glaucoma even after an uncomplicated vitrectomy.[3] Thus, care should be taken to look for glaucomatous changes at each visit to the retina specialist, and an active early collaboration of glaucoma specialists should be sought when necessary.