Discrepancy Between Normal Tension Glaucoma and Primary Open Angle Glaucoma with Confocal Microscopy Examination of Corneal Nerves

Abstract

Background To investigate the morphological features of corneal subbasal nerve plexus (CSNP) and Langerhans cells (LCs) in normal tension glaucoma (NTG) and primary open angle glaucoma (POAG) Methods Ten eyes with NTG (8 untreated), 23 eyes with POAG (9 untreated) and 31 eyes of healthy subjects were recruited. CSNP and LCs were assessed by corneal confocal microscopy (CCM) and peripapillary retinal nerve fiber layer (RNFL) was measured with optical coherence tomography (OCT). CCM parameters including nerve fiber length (FL), branch number (BN), nerve width (NW), nerve reflectivity (NR), total and local nerve tortuosity (NT) as well as type 1 and type 2 LCs were compared across all groups, as well as between the topical medication treated and the nontreated patients. Results The NTG had the longest FL(3494.60 ± 523.01), most BN(19.78 ± 5.56), thinnest NW(2.96 ± 1.20), lowest reflectivity (143.03 ± 14.01) and most tortuosity (1.09 ± 0.07) compared with POAG and the normal. The POAG had similar CSNP to the normal. Same results were also found in untreated NTG and untreated POAG. Untreated NTG (3/8), untreated POAG(3/9) and treated POAG (7/14) had significantly more type 2 LCs than the normal (3/31). The treated POAG had longer FL (3240.71 ± 627.81), more BN(19.04 ± 4.58), NW(3.66 ± 0.54), NR(154.65 ± 13.95), more NT(1.07 ± 0.03) than the nontreated but with no significant difference. BN had significant correlations with RNFL thickness in both NTG and POAG groups. Conclusions The NTG had characteristic CSNP quite different from that in the POAG and the normal, while the latter two shared more morphological features. The CCM parameters had associations with the RNFL thickness. Untreated glaucoma patients had obvious immature LCs indicating their relationship to ocular surface inflammation.