Baerveldt Glaucoma Drainage Device: A postoperative story

Glaucoma, a neurodegenerative disease of the optic nerve, poses a significant public health concern as it is the leading cause of irreversible visual impairment and blindness. Placing a Baerveldt glaucoma drainage device (BGI) in the orbit outside of the eye is a commonly used surgical procedure, when medication and/or (selective) laser trabeculoplasty are not effective, to lower the intraocular pressure (IOP) and slow down, or halt, the progression of the disease. However, trabeculectomy (TE) remains the golden standard.

In chapter 1 and 2, we compared the 2 above-mentioned glaucoma surgical procedures i.e., BGI and TE. We found that both procedures were equally effective as primary procedure in lowering the IOP until 5 years postoperatively. Also, additional surgery due to failure did not differ significantly between the TE and BGI group. However, when considering other factors such as complications and the need for additional medication, primary TE showed better results than BGI surgery (86% versus 30% of the patients were free of medication use, respectively). More diplopia (double vision) cases (28% of the BGI patients versus 3% of the TE patients, 1 year after surgery) were found in the BGI group than in the TE group.

Next, we investigated 2 serious complications, diplopia and endothelium cell density (ECD) loss, specifically after BGI surgery. In chapter 3, we quantified the various forms of surgically induced diplopia in BGI patients and concluded that they were more common than expected. Each type of diplopia was caused by a different mechanism. Diplopia in gaze directions (i.e., in eccentric gaze) was caused by ocular movement restrictions, while diplopia in the primary position turned out to be the result of a deviation in the ocular alignment, outside the patient’s fusion range.

In chapter 4, we explored the efficacy of a possible solution for BGI patients with diplopia. Patients received a BGI with a new surgical technique, called the free plate technique, and were compared with patients who were operated with the conventional, sutured technique. By not suturing the plate to the globe i.e., placing the plate ‘freely’, the plate was assumed to settle in a position in which it and its encompassing bleb would minimally restrict normal eye movements, leading to a reduced risk of developing diplopia. Unfortunately, it turned out that the two groups had approximately the same diplopia incidence (both 28%).

Following these findings, a new question arose: what causes these ocular movement restrictions and deviations after surgery? A subgroup of patients was selected from the previous studies some of which had diplopia while others did not experience diplopia (chapter 5). By using magnetic resonance imaging
(MRI), we found that an excessively large bleb was associated with the diplopia in approximately 1 out of 3 diplopia patients, whereas in the remaining cases no clear explanation could be found.

In a randomised clinical trial, we prospectively explored the ECD loss after BGI implantation (chapter 6). We investigated the incidence and severity, but also possible causes of this complication, up to 2 years after surgery. Our results showed that proximity of the tube to the cornea had a negative impact on the
corneal endothelium. The closer the tube is to the corneal endothelium, the greater the ECD loss, which suggests that placing the tube as far away as possible from the endothelium may reduce the corneal damage. The damage was more pronounced peripherally, close to the tube, than at the centre of the
cornea (an ECD loss of 14.9% peripherally versus a loss of 5.9% centrally at 2 years after surgery).

In addition, we retrospectively investigated a small group of patients that had undergone BGI surgery or TE 5 to 11 years earlier; the ECD loss seemed to continue after 2 years (chapter 7). In addition, the ECD long after BGI surgery was lower than in eyes that had undergone a TE, mainly in the peripheral cornea,
suggesting that the BGI initiates a larger damage to the endothelium in the long-term (approximately 1813 cells/mm2 in BGI patients versus 2285 cells/mm2 in TE patients, 5-11 years after surgery).

Lastly, based on these findings, we formulated some recommendations to improve clinical practice (chapter 8). It may be helpful for patients when considering BGI surgery to have a standardized assessment of their ocular motility as well as of their endothelium, prior to the intervention. When evaluating the ocular motility, attention should be paid to the fusion range in combination with the ocular alignment, the history of strabismus or ocular surgeries and VF loss of the patient. If diplopia develops postoperatively and limits the patient his/her daily activities, prism prescription might be a treatment option for small angle eye deviations in the ocular alignment. Otherwise, the ophthalmologist may investigate if a large bleb is present and, if confirmed, perform additional surgery to empty the large bleb.

Once a cornea with low endothelial cell density is detected in a glaucoma patient in whom glaucoma surgery is considered, one should bear in mind the risk of corneal decompensation and consider potential alternatives before performing the intervention. If BGI surgery is the only option, we suggest leaving the tube long and placing the tube against the iris to limit endothelial cell loss or consider alternative placements. A preoperative ECD count may even be judicious prior to glaucoma surgery of any kind.