GLAUCOMA AND KPRO

Because glaucoma is the most significant vision-threatening complication following Boston Keratoprosthesis Type 1 (B-KPro) surgery, it requires careful preoperative evaluation and postoperative follow-up, said Elena Arrondo MD at the 5th EuCornea Congress in London, UK.

Data from various series show glaucoma is present in as many as 75 per cent of patients who present for B-KPro implantation, and glaucoma can also develop or worsen after the keratoprosthesis surgery through a variety of mechanisms.

All patients should be evaluated for ocular hypertension or glaucoma prior to B-KPro surgery, and only those with an open angle and normal intraocular pressure (IOP) off medication should proceed to B-KPro placement alone, advised Dr Arrondo, glaucoma specialist, Institute of Ocular Microsurgery, Barcelona, Spain.

“Otherwise, glaucoma surgical intervention with a glaucoma drainage device (GDD) or cyclophotocoagulation is indicated and should be performed before or simultaneously with the B-KPro procedure,” she advised.

Low threshold

Dr Arrondo observed there is a low threshold for performing glaucoma surgery in patients with a B-KPro due to the severity of glaucoma in this population, the challenge of obtaining reliable IOP measurements, and considering that response to topical medications tends to be poor.

“IOP control can be achieved in most patients with our current surgical options. Although there is no consensus about what type of procedure is better, a GDD is usually the first choice for most surgeons,” she said.

In GDD procedures, pars plana tube insertion into the posterior chamber is preferred over anterior chamber placement, as it decreases risks of tube exposure, tube kinking and vitreous incarceration. In combination procedures, vitrectomy must be complete so that no vitreous can enter and occlude the tube.

Fascia lata, donant sclera or cornea are used to cover the tube since reabsorption of pericardium occurs over time and can result in tube exposure.

“Tube exposure has also been reported with use of Hoffman elbows or pars plana clips. We never use those techniques and have never had exposure of a posterior chamber inserted tube,” Dr Arrondo said.

She noted that tube placement in the anterior chamber has been done in some eyes, but then the tube is inserted through a sclera tunnel at least 3.5mm from the limbus to avoid mechanical trauma from a bandage contact lens that can lead to tube exposure.

Dr Arrondo reported that in a series of 15 valve procedures performed at her institution in patients with B-KPro, they encountered endophthalmitis with secondary plate exposure in two patients who subsequently underwent valve removal. Complications reported by other groups include hypotony and choroidal detachment.

“Glaucoma progression has also been reported despite normal IOP, and so the target IOP should be very low in patients with B-KPro,” Dr Arrondo said.

CPC (endocyclophotocoagulation or diode laser transscleral CPC) may particularly be chosen instead of a GDD in patients with very low vision, and it also provides very good IOP control after GDD failure.

“CPC avoids concerns about endophthalmitis and tube exposure, but it is difficult to calculate the number of impacts and determine the location of the ciliary processes,” Dr Arrondo said.

Monitoring for glaucoma development and progression in patients with a B-KPro is done using digital pressure to estimate IOP, visual field testing, and optic nerve evaluation.

Visual field testing is done with Goldmann or static perimetry and using a stimulus size based on the patient's visual acuity.

Dr Arrondo noted that optic nerve visualisation in patients with the KPro is similar to visualisation in patients with non-dilated pupils, and that non-mydriatic cameras are a better option for fundus photography.

She added that evaluation of the retinal nerve fibre layer using optical coherence tomography or retinal tomography can also be performed in eyes with a B-KPro, and she presented a case in which clinical assessment of the optic nerve and structural imaging revealed glaucoma progression much earlier than visual field testing.

Elena Arrondo: arrondo@imo.es