The role of vitrectomy must be defined and compared with intravitreal triamcinolone and laser treatment, but vitrectomy may provide a more permanent solution for some eyes
"We know from 13 years of published data that vitrectomy and peeling of the posterior hyaloid membrane, with or without internal limiting membrane (ILM) peeling, can lead to visual improvement in eyes with diffuse clinically significant DME that were previously thought to be refractory to treatment," said Hassan, who is co-director, vitreoretinal program, Associated Retinal Consultants, and assistant professor of biomedical sciences at Oakland University, Michigan, USA. Such eyes typically do not respond as well to macular laser treatment as eyes with DME from focally leaking microaneurysms, and may not be responsive to intravitreal triamcinolone injection either.
"Based on these studies, we know that vitrectomy leads to successful anatomic and visual outcomes in many eyes with diffuse macular oedema, but we still don't entirely know the mechanism, the role of the ILM, the role of enzyme-assisted vitrectomy, or how vitrectomy compares with other treatment modalities," Hassan said.
Unravelling the mechanism mystery
There are questions about how vitrectomy works in these eyes, though it is likely that several mechanisms play a role. Evidence suggests that vitrectomy relieves the anteroposterior vitreomacular traction by creating a posterior vitreous detachment (PVD), he explained, and this results in a reduction of DME. In 1988, Nasrallah and colleagues reported that in eyes with a PVD there was less macular oedema compared with eyes without one. Hikichi and associates in 1997 reported spontaneous resolution of DME in many more eyes that developed PVDs than those that did not when followed over time. In addition, it is known that vitreoschisis occurs often; Schwartz and associates reported in 1996 that vitreoschisis was present in 81% of 179 eyes with proliferative diabetic retinopathy and tractional retinal detachment, Hassan recounted. "Vitreoschisis exists and is likely underdiagnosed in these eyes with a similar mechanism of traction of the posterior hyaloid," he emphasized.
The ILM is likely to play an important role and its removal seems to improve visual and anatomic outcomes, facilitate faster resolution of DME, and lower the recurrence rate of DME, as reported by Gandorfer in 2000. However, results from a 2001 study by Yamamoto and colleagues did not concur with that previous study, Hassan pointed out.
Removal of the ILM helps because it ensures the elimination of all posterior hyaloidal traction, particularly in cases with vitreoschisis, where the ILM strongly adheres to the posterior hyaloid. Removal of the ILM also decreases the recurrence of clinically significant DME after vitrectomy because of epiretinal membrane formation; about 10% of patients have a recurrence of DME when the ILM is not peeled.