A quarter to a third of keratoprosthesis eyes developed or progressed glaucoma

Design

systematic review and random-effects meta-analysis, GRADE assessed

Population

23 studies, 1,482 eyes after Boston type 1 keratoprosthesis; mean age 54.5 years, mean follow-up 39.4 months

Primary outcome

pooled incidence of postoperative glaucoma events

Effect

any glaucoma event 25.6% (95% CI 18.1-34.8, I² 87.3%); de novo glaucoma 31.1% (20.6-43.9); progression of pre-existing glaucoma 37.7% (17.9-62.6)

Boston type 1 keratoprosthesis is what is left when repeat keratoplasty has failed or was never viable, and it restores sight in eyes that have no other option. This meta-analysis pooled 23 studies and 1,482 eyes with a mean follow-up of 39.4 months to quantify the glaucoma that follows.

Pre-existing glaucoma was present in 45.9% of eyes before surgery. Pooled incidence of any postoperative glaucoma event was 25.6% (95% CI 18.1-34.8), an incidence rate of 0.09 events per eye-year. Among studies reporting it separately, de novo glaucoma occurred in 31.1% (20.6-43.9) and progression of existing glaucoma in 37.7% (17.9-62.6). Ocular hypertension without a confirmed glaucoma diagnosis affected 17.1%. The authors graded the certainty of evidence as very low, and heterogeneity was severe - I² between 70% and 92% - driven by inconsistent definitions of what counts as glaucoma in an eye where intraocular pressure cannot be measured conventionally.

That measurement problem is the whole difficulty. After keratoprosthesis, applanation is not possible and pressure is assessed digitally, so a diagnosis depends on disc and field assessment through a narrow optical cylinder in an eye that often cannot perform reliable perimetry. The clinical conclusion is not that these operations should not be done - the alternative is blindness - but that the glaucoma plan belongs in the preoperative discussion, and that an eye with existing glaucoma may need its drainage surgery considered at the same sitting.

• Assess and document glaucoma status before keratoprosthesis, including disc appearance and any available field
• Plan how intraocular pressure will be monitored postoperatively, given that applanation will not be possible
• Discuss combined or staged glaucoma drainage surgery in eyes with pre-existing disease - nearly 40% progressed
• Use serial disc imaging and, where possible, fields rather than digital pressure assessment alone
• Counsel the patient that glaucoma is a common sequel, not a rare complication

Why it matters

It reframes post-keratoprosthesis glaucoma from a complication to be watched for into a problem to be planned for before the operation.

Don't overread it

Very low certainty evidence with severe heterogeneity from inconsistent glaucoma definitions - the pooled percentages are indicative, not precise.

The statistics, in plain English

The certainty of evidence was graded very low and the I² values of 70% to 92% mean the included studies disagreed profoundly - largely because they defined glaucoma differently. So 25.6% should be read as 'roughly a quarter to a third' rather than as a rate, and the interval for progression of pre-existing glaucoma (17.9-62.6%) is so wide it barely constrains anything. The incidence rate of 0.09 events per eye-year is the more transferable figure, because it accounts for how long each cohort was followed.

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