[The function-structure impairment pattern of optic nerves in primary open-angle glaucoma and normal-tension glaucoma]

Abstract

Objective: To investigate the characteristics of impairment of the visual field (VF) and retinal nerve fiber layer (RNFL) and the differences of progression pattern of early, middle and late stages of primary open-angle glaucoma (POAG) and normal-tension glaucoma (NTG) , and to analyze the correspondence of structure and function. Methods: Cross-sectional study. POAG patients, NTG patients and healthy volunteers who were enrolled from February 2008 to May 2017 at Department of Ophthalmology, Eye & ENT Hospital of Fudan University, underwent basic ophthalmic examination, Humphrey central 24-2 threshold test and optical coherence tomography. Patients were divided into early, middle and late stages according to the mean defect (MD) index of the VF test. According to the RNFL distributional characteristics, the pattern deviation map and RNFL were divided into 6 sectors. The differences of each sector's MD and RNFL thickness in the healthy group and groups of patients at 3 stages were analyzed using the Kruskal-Wallis test, and the correlation of MD and RNFL thickness of each sector was analyzed using the Pearson coefficient. Results: In the POAG group, there were 84 cases (84 eyes) including 35 eyes of early stage, 20 eyes of middle stage and 29 eyes of late stage, with a male/female ratio of 43∶41, aged (45±15) years. In the NTG group, 69 cases (69 eyes) included 30 eyes of early stage, 20 eyes of middle stage and 19 eyes of late stage, with a male/female ratio of 33∶36, aged (49±13) years. The control group had 23 cases (23 eyes), with a male/female ratio of 16∶17 and an age of (44±10) years. There was no significant difference in male/female ratio, age or best corrected visual acuity among the three groups. (1) In the middle stage of POAG, the VF defects of inferior hemi-fields were more severe than the superior (t=21.62, P=0.000), which was opposite to the late stage of POAG (t=-3.28, P=0.003). In each stage of NTG, there was no significant difference between two hemi-fields. In the control group, the MD values(antilog) of VF in the superior peripheral arch (PEA), superior paracentral arch (PAA), inferior PEA and PAA, temporal and central regions were 0.87 (0.63-1.11)/L, 0.74 (0.61-0.83)/L, 0.72 (0.55-0.97)/L, 0.65 (0.51-0.87)/L, 0.69 (0.57-0.97)/L, and 0.82 (0.54-0.93)/L, respectively. The sectoral MD values in the VF sectors of POAG were significant compared with the control group (P<0.05): superior PAA for early stage [0.61 (0.18-0.92)/L, H=21.58], superior PEA and PAA for middle stage [0.61 (0.15-0.87)/L, 0.21 (0.00-0.78)/L, H=25.99, 34.91], superior PEA and PAA, inferior PEA and PAA for late stage [0.01 (0.00-1.13)/L, 0.00 (0.00-0.76)/L, 0.41 (0.00-1.07)/L, 0.21 (0.00-0.95)/L, H=46.27, 54.19, 25.64, 28.10]. With the aggravation of POAG, superior PAA had the largest reduction percentage of sectoral MD. The sectoral MD values in the VF sectors of NTG were significant compared with the control group (P<0.05): superior PAA for early stage [0.54 (0.19-0.80)/L, H=20.93], superior PAA for middle stage [0.60 (0.02-1.01)/L, H=22.13], superior PEA and PAA, inferior PEA and PAA for late stage [0.33 (0.00-0.90)/L, 0.05 (0.00-0.92)/L, 0.16 (0.01-0.87)/L, 0.64 (0.02-1.10)/L, H=37.66, 42.78, 35.15, 37.15]. With the aggravation of NTG, the largest reduction percentage of sectoral MD was found in superior PAA at the beginning but in inferior PAA at last. (2) The RNFL thickness of the control group in Region 1NI, 2TI, 3NS, 4TS, 5N, and 6T was 112.76 (63.54-150.99) μm, 134.89 (89.44-198.55) μm, 96.52 (57.32-158.79) μm, 120.96 (69.25-148.48) μm, 71.85 (65.03-95.47) μm, and 66.24 (55.44-90.97) μm, respectively. The sectoral thickness in the RNFL sectors of POAG were significant compared with the control group (P<0.05): 2TI for early stage [109.17 (43.77-173.86) μm, H=31.50], 1NI, 2TI and 4TS for middle stage [71.54 (49.92-94.98) μm, 62.92 (42.33-102.73) μm, 84.20 (45.98-120.13) μm, H=38.91, 49.89, 30.60], 1NI, 2TI, 3NS, 4TS, 5N and 6T for late stage [61.76 (39.32-97.99) μm, 59.59 (42.80-108.69) μm, 67.28 (42.56-117.96) μm, 65.16 (41.96-138.02) μm, 59.45 (21.04-78.48) μm, 53.74 (27.88-92.71) μm, H=52.76, 55.06, 35.76, 41.72, 41.32, 29.93]. With the aggravation of POAG, at the beginning 2TI had the largest reduction percentage of RNFL thickness but 4TS had it at last. The sectoral thickness in the RNFL sectors of NTG were significantly different from the control group (P<0.05): 2TI for early stage [78.97 (47.77-131.45) μm, H=28.86], 1NI, 2TI, 3NS and 4TS for middle stage [61.46 (49.69-97.38) μm, 74.51 (40.25-135.16) μm, 86.36 (42.70-105.06) μm, 83.60 (54.75-117.35) μm, H=38.76, 35.64, 22.47, 24.14], 1NI, 2TI, 3NS, 4TS and 6T for late stage [61.45 (49.09-92.64) μm, 54.35 (37.40-102.62) μm, 63.72 (28.68-105.55) μm, 61.00 (44.92-108.49) μm, 50.33 (35.62-82.09) μm, H=42.56, 51.50, 36.11, 47.44, 25.50]. With the aggravation of NTG, the sector with the largest reduction percentage of thickness changed from 2TI to NI and 4TS. (3) The VF superior PAA-RNFL 2TI had the highest Pearson correlation coefficient in POAG (r=0.630, P<0.001), while it was the inferior PAA-4TS in NTG (r=0.645, P<0.001). Conclusions: The impairment patterns of VF and RNFL in each stage of POAG and NTG are distinctly different from certain rules of aggravation. The sector with the strongest correlation of function-structure is the VF superior PAA-RNFL inferior temporal sector in POAG and inferior PAA-superior temporal sector in NTG. (Chin J Ophthalmol, 2018, 54: 811-819).

Keywords: Glaucoma; Glaucoma, open-angle; Intraocular pressure; Nerve fibers; Visual fields.