title: Corneal Biomechanical Parameters and Asymmetric Visual Field Damage in Patients with Untreated Normal Tension Glaucoma.
abstract: BACKGROUND
  High intraocular pressure (IOP) and low central corneal thickness (CCT) are important validated risk factors for glaucoma, and some studies also have suggested that eyes with more deformable corneas may be in higher risk of the development and worsening of glaucoma. In the present study, we aimed to evaluate the association between corneal biomechanical parameters and asymmetric visual field (VF) damage using a Corvis-ST device in patients with untreated normal tension glaucoma (NTG).
  
  
  METHODS
  In this observational, cross-sectional study, 44 newly diagnosed NTG patients were enrolled. Of these, 31 had asymmetric VF damage, which was defined as a 5-point difference between the eyes according to the Advanced Glaucoma Intervention Study scoring system. Corneal biomechanical parameters were obtained using a Corvis-ST device, such as time from start until the first and second applanation is reached (time A1 and time A2, respectively), cord length of the first and second applanation (length A1 and length A2, respectively), corneal speed during the first and second applanation (velocity A1 and velocity A2, respectively), time from start until highest concavity is reached (time HC), maximum amplitude at the apex of highest concavity (def ampl HC), distance between the two peaks at highest concavity (peak dist HC), and central concave curvature at its highest concavity (radius HC).
  
  
  RESULTS
  Time A1 (7.19 ± 0.28 vs. 7.37 ± 0.41 ms, P = 0.010), length A1 (1.73 [1.70-1.76] vs. 1.78 [1.76-1.79] mm, P = 0.007), length A2 (1.58 [1.46-1.70] vs. 1.84 [1.76-1.92] mm, P< 0.001), peak dist HC (3.53 [3.08-4.00] vs. 4.33 [3.92-4.74] mm, P = 0.010), and radius HC (6.20 ± 0.69 vs. 6.59 ± 1.18 mm, P = 0.032) were significantly lower in the worse eyes than in the better eyes, whereas velocity A1 and def ampl HC were significantly higher (0.156 [0.149-0.163] vs. 0.145 [0.138-0.152] m/s, P = 0.002 and 1.19 ± 0.13 vs. 1.15 ± 0.13 mm, P = 0.005, respectively). There was no significant difference in time A2, velocity A2, and time HC between the two groups. In addition, no difference was observed in IOP, CCT, and axial length. In the univariate and multivariate analyses, some of the Corvis-ST parameters, including time A1 and def ampl HC, were correlated with known risk factors for glaucoma, and there was also a significant positive correlation between def ampl HC and age.
  
  
  CONCLUSIONS
  There were differences in dynamic corneal response parameters but not IOP or CCT between the paired eyes of NTG patients with asymmetric VF damage. We suggest that the shape of the cornea is more easily altered in the worse eyes of asymmetric NTG patients.
authors.affiliation: Department of Ophthalmology, Peking University First Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100034, China.
authors.forename: Bai-Bing
authors.initials: BB
authors.lastname: Li
authors.affiliation: Department of Ophthalmology, Peking University First Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100034, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Cai
authors.affiliation: Department of Ophthalmology, Peking University First Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100034, China.
authors.forename: Ying-Zi
authors.initials: YZ
authors.lastname: Pan
authors.affiliation: Department of Ophthalmology, Peking University First Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100034, China.
authors.forename: Mei
authors.initials: M
authors.lastname: Li
authors.affiliation: Department of Ophthalmology, Beijing Tsinghua Changgung Hospital, Beijing 102218, China.
authors.forename: Rong-Hua
authors.initials: RH
authors.lastname: Qiao
authors.affiliation: Department of Ophthalmology, Peking University First Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100034, China.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Fang
authors.affiliation: Department of Ophthalmology, Peking University First Hospital, Key Laboratory of Vision Loss and Restoration, Ministry of Education, Beijing 100034, China.
authors.forename: Tian
authors.initials: T
authors.lastname: Tian
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D003315:Cornea / Q000378:metabolism* / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D005901:Glaucoma / Q000378:metabolism* / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D057066:Low Tension Glaucoma / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011446:Prospective Studies; D014794:Visual Fields / Q000502:physiology*