Imaging Unveils Mechanics of Cystoid Macular Edema Following Anterior Uveitis

Using swept-source optical coherence tomography (SS-OCT), researchers have identified connecting channels between the premacular bursa and Cloquet’s canal, according to a publication in Acta Ophthalmologica. The study suggests that inflammatory cytokines may drain from the anterior chamber through this system of channels and increase the risk of cystoid macular edema (CME), the investigators explain.

Researchers employed both SS-OCT and en face imaging to evaluate the vitreous of patients with anterior uveitis, as well as the relationship between premacular bursa and prepapillary area of Martegiani. 

Between 2018 and 2020, 135 eyes of 135 consecutive patients (mean age, 31.22 years; 59% women) with newly diagnosed anterior uveitis were enrolled in the cross-sectional study. All patients underwent baseline fluorescein angiography to exclude intermediate or posterior uveitis involvement. Patients also underwent a complete optical examination, including best-corrected visual acuity (BCVA), intraocular pressure measurement, and slit-lamp biomicroscopy of the anterior and posterior segments. 

On SS-OCT scan, all eyes showed an optically empty space overlying the macula; this was compatible with the premacular bursa. All eyes also demonstrated a smaller optically empty space “compatible with the termination of the Cloquet’s canal.” SS-OCT scan identification of the premacular bursa and Cloquet’s canal had an interrater reliability of k=0.97 and 0.93, respectively. 

On en face images, the premacular bursa and Cloquet’s canals were visualized as 2 oval lacunas near the vitreoretinal interface. Mean horizontal and vertical diameters of the bursa were measured in all eyes; in all cases, lacunas of the premacular bursa were larger than those of the Cloquet’s canals. 

Forty-five healthy patients were also included in the study (mean age, 33.47 years, 51% women). Researchers also enrolled 90 patients with anterior uveitis (mean age, 30.10 years; 62% women). 

Eyes with anterior uveitis were divided by SUN cell grading into 5 categories. In the anterior uveitis group, mean horizontal and vertical diameters of the premacular bursa and its mean en face area were significantly larger vs the premacular bursa area of healthy eyes. There was no statistically significant difference in Cloquet’s canal diameter. 

In the 90 patients with anterior uveitis, 37 eyes — 27% of the total cohort and 41% of the anterior uveitis group — presented with CME. The mean age of the patients with secondary CME was 28.78 years. No statistical correlation was noted between the degree of anterior chamber inflammation and the presence of CME. 

Premacular bursa diameters were significantly larger in anterior uveitis patients with cystoid macular edema vs the 53 eyes with anterior uveitis only and vs healthy eyes. 

Multiple anterior and superior horizontal and vertical scans showed that a total of 101 eyes had a clear connection between premacular bursa and Cloquet’s canal. 

Within the en face images of these 101 eyes indicated a connection between these vitreous spaces on SS-OCT, corresponding en face images of the premacular bursa demonstrated a structure that was oval in the -500 µm depth slab. This structure became crescent shaped as the scan moved towards the anterior vitreous (-800 µm depth). 

In the remaining 34 eyes, there was no connection identified in the subjective evaluation of the SS-OCT scans; the premacular bursa en face aspect remained as an isolated oval structure even during dynamic assessment. 

A connection between the premacular bursa and the Cloquet’s canal was detected in 51% of healthy eyes via linear SS-OCT scans; in 90 eyes with anterior uveitis, researchers were able to detect this connection in 87% of cases. In 100% of the 37 eyes with both anterior uveitis and cystoid macular edema, presence of the communicating channel between the premacular bursa and the peripapillary gap was identified. 

The likelihood of a connection between the premacular bursa and the Cloquet’s canal was 3.50 times higher in patients with anterior uveitis relative to the control group; cystoid macular edema was positively correlated with the detection of a connection between the premacular bursa and peripapillary gap. 

Study limitations include those inherent to cross-sectional research as well as differences in vitreous architecture that may not be the cause of cystoid macular edema. 

“SS-OCT showed the detailed structure of vitreous chambers and channels in vivo in eyes with [anterior uveitis],” according to the researchers. “The premacular bursa was found to fuse with Cloquet’s canal in 93.1% of eyes with [anterior uveitis], thus creating an anteroposterior connection between the retrolental and premacular spaces that can facilitate CME development in the absence of posterior segment active inflammation.” 

Reference

Pichi F, Neri P, Hay S, Parrulli S, Zicarelli F, Invernizzi A. An en face swept source optical coherence tomography study of the vitreous in eyes with anterior uveitis. Acta Ophthalmol. Published online July 4, 2021. doi:10.1111/aos.14965