[Magnetic resonance imaging features of tear outflow and structural changes of the lacrimal sac and nasolacrimal duct in normal subjects with eyes closed]

Abstract

Objective: To investigate the static and dynamic features of the normal lacrimal sac (LS)-nasolacrimal duct (NLD), and find out if tear flows while the subject is in supine position with eyes closed. Methods: Cross-sectional study. Healthy volunteers and patients whose head were examined by MRI in Guangdong Provincial Hospital of Integrated Traditional Chinese and Western Medicine with normal LS-NLD were recruited. The normal lacrimal ducts of the candidates were scanned, while candidates remained in supine position, by static or dynamic imaging procedures with a 1.5T MRI system, which adopted the thinnest slice thickness, consecutive sections (no spacing) and two scanning planes (axial and coronal planes of LS-NLD). The static and dynamic imaging procedures were done in June and July 2014 and October 2015, respectively. The static imaging was performed with conventional T(2)WI, contrast-enhanced 3D FIESTA-C, contrast-enhanced T(1)WI and heavy T(2)WI pulse sequences under normal physiological condition, and 104 eyes with normal LS-NLD from 39 patients and 13 healthy volunteers (21 male and 31 female) aged 10 to 75 years were scanned with the static procedure. The dynamic imaging was done with heavy T(2)WI pulse sequence. The coronal dynamic imaging was done only after 0.9% NaCl was instilled in the conjunctival sacs, and 20 eyes with normal LS-NLD of 10 volunteers (6 male and 4 female) aged 23 to 53 years were scanned with the coronal dynamic procedure. The axial dynamic imaging was done under normal physiological condition and after 0.9% NaCl was instilled in the conjunctival sacs respectively, and 20 eyes with normal LS-NLD of 10 volunteers (8 male and 2 female) aged 20 to 40 years were scanned with the axial dynamic procedure. The incidences on the axial dynamic imaging under the two conditions were compared with χ(2) test. Results: A total of 104 eyes with normal LS-NLD (52 candidates) were scanned with the static imaging sequences. In all LS-NLDs, an indentation located at the posterior-lateral side wall of the junction of LS-NLD was discovered, and its depth was variable. In 28.8% (30/104) of LS, 64.4% (67/104) of the junctions and 22.1% (23/104) of NLD, lumens were closed. As for the coronal dynamic imaging (20 eyes with normal LS-NLD in 10 subjects), segmental tear transit was observed in 15/20 of NLD. As for the axial dynamic imaging (20 eyes with normal LS-NLD in 10 subjects), after 0.9% NaCl was instilled, dynamic changing of their lumen size was revealed in 17/20 of LS-NL and the occurrence rate of the lumen size changing (29.3%, 94/321, the number of the axial slices with lumen changes/total number of the axial slices imaged) was higher than that (16.4%,52/317) under normal physiological condition. The difference between the two rates was statistically significant (χ(2)=14.993, P<0.001). LS contained more tear than NLD. Conclusion: While the candidates are in supine position with eyes closed (absolutely no blinking), an indentation is at the posterior-lateral side wall of the junction of LS-NLD, and there are autonomous, segmental lumen open-close actions in normal LS-NLD and tear transit in their lumens. (Chin J Ophthalmol, 2018, 54: 205-211).

Keywords: Magnetic resonance imaging; Nasolacrimal duct; Supine position; Tears.