Post-Trabeculectomy Densitometry Shows Corneal Health

Scheimpflug corneal densitometry is a sensitive, objective method to evaluate the health and structural integrity of the cornea and demonstrated a return to near-normal corneal metrics 6 months after undergoing trabeculectomy, a report published in Cornea found. 

In the current prospective study (NCT02959242), researchers set out to investigate changes in corneal transparency and backscatter measured via rotating Scheimpflug imaging 6 months following uncomplicated trabeculectomy with mitomycin C (MMC). Researchers also examined the clinical and demographic features associated with possible changes. 

The cohort included 42 eyes (17 right, 25 left) from 42 patients (mean age, 68±9; 52% men) with primary open-angle glaucoma who underwent first time MMC-augmented trabeculectomy and 22 healthy controls (66±8 years old), matched for age and central corneal thickness (525.1±29.4 µm vs 531.2±13.1 µm, respectively). 

At baseline, 78.6% of patients had high intraocular pressure (IOP) and 21.4% had normal pressure open-angle glaucoma treated with topical IOP-lowering medications (mean treatment duration, 14.3±10 years). A mean of 3.7±1 medications, in different combinations and application frequencies, prior to surgery, were used, including prostaglandins, beta blockers, α-agonists, carboanhydrase inhibitors, and pilocarpine. 

Both IOP and the need for IOP-lowering medications were statistically significantly reduced postoperatively (19±7.7 mm Hg to 11.1±7.7 mm Hg and 3.7±1.0 to 01.1±0.5 medications). 

Six months after trabeculectomy, corneal backscatter was reduced in the entire cornea from 25.5±5.7 to 23.1±5.8 GSUs, with emphasis in the anterior layer. Densitometry values for both the AL and the entire cornea returned close to normal at 6 months postoperative and were not statistically significantly different vs age-matched healthy controls (23.1±5.8 vs 22.8±3.4 GSU). Patients with glaucoma demonstrated significantly higher preoperative corneal backscatter within the optically significant 0 mm to 2 mm and 2 mm to 6 mm annular zone of the AL; this difference was not statistically significant following trabeculectomy. 

Across the entire cornea, preoperative densitometry was higher vs healthy controls. 

Across 3 radial zones of the anterior layer, investigators evaluated preoperative IOP, central corneal thickness, disease duration, sex, number of medications, applications and amount of BAC per day, and postoperative topical steroid use to identify potential correlations. No significant associations were found for any of these parameters. 

Best spectacle corrected visual acuity with Snellen high-contrast visual acuity remained stable, changing insignificantly from 0.21±0.37 to 0.23±0.33 LogMAR in the 6 months post trabeculectomy. Lens status did not change during follow-up, and PNS remained stable in 88% of patients. Mean PNS change was 0.9±0.7 to 0.9±0.7. 

Study limitations include a lack of low-contrast visual acuity testing, which may have identified small changes in visual acuity, no assessment of vision quality (blurring, contrast sensitivity, or glare), and no assessment of endothelial cell counts in all patients. 

“Assessing Scheimpflug corneal density or transparency and its changes might be a sensitive and objective method to evaluate overall ‘health’ or structural integrity of the cornea,” researchers conclude. “[Results] indicate, on one hand, that corneal changes caused by higher IOP and glaucoma medication and its preservatives are probably reversible. On the other hand, the results give evidence of the benefit of earlier glaucoma surgery in the course of the disease.” 

Reference

Pillunat KR, Orphal J, Haase M, Pillunat LE, Herber R. Scheimpflug corneal densitometry changes after trabeculectomy. Cornea. 2020;40(4):408-414. doi:10.1097/ICO.0000000000002439