Characteristics of corneal biomechanical responses detected by a non‐contact scheimpflug‐based tonometer in eyes with glaucoma

• Published in: Acta ophthalmologica (Oxford, England) Vol. 95; no. 7; pp. e556 - e563
• Main Authors: Jung, Younhea, Park, Hae‐Young L., Yang, Hee Jung, Park, Chan Kee
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01-11-2017
• Subjects: Biomechanical Phenomena; Biomechanics; Cornea; Cornea - diagnostic imaging; Cornea - physiopathology; Corneal Pachymetry; corvis ST; Deformation; deformation amplitude; Deformation mechanisms; Equipment Design; Female; Glaucoma; Glaucoma, Open-Angle - diagnosis; Glaucoma, Open-Angle - physiopathology; Humans; Intraocular Pressure; Male; Mechanical properties; Middle Aged; Prospective Studies; Statistical analysis; Stiffening; Tonometry, Ocular - instrumentation; Viscoelasticity; Visual field; Visual fields; Visual Fields - physiology; glaucoma; deformation amplitude; corvis ST
• ISSN: 1755-375X; 1755-3768
• DOI: 10.1111/aos.13466

Purpose
To determine the corneal biomechanical properties in eyes with glaucoma using a non‐contact Scheimpflug‐based tonometer.
Methods
Corneal biomechanical responses were examined using a non‐contact Scheimpflug‐based tonometer. The tonometer parameters of the normal control group (n = 75) were compared with those of the glaucoma group (n = 136), including an analysis of glaucoma subgroups categorized by visual field loss.
Results
After adjusting for potential confounding factors, including the intraocular pressure (IOP), central corneal thickness (CCT), age and axial length, the deformation amplitude was smaller in the glaucoma group (1.09 ± 0.02 mm) than in the normal control group (1.12 ± 0.02 mm; p value = 0.031). The deformation amplitude and the deflection amplitude of the severe glaucoma group (1.12 ± 0.02 mm and 0.92 ± 0.01 mm) were significantly greater than that of the early glaucoma group (1.07 ± 0.01 mm and 0.88 ± 0.11 mm, p = 0.006 and p = 0.031), whereas that of the moderate glaucoma group (1.09 ± 0.02 mm and 0.90 ± 0.02 mm) was greater than that of the early glaucoma group, but this difference was not statistically significant. The deformation amplitude showed a negative correlation with the CCT in the normal control group (r = −0.235), with a weaker negative relationship observed in the early glaucoma group (r = −0.099). However, in the moderate and severe glaucoma groups, the deformation amplitude showed a positive relationship with the CCT, showing an inverse relationship. The duration and number of antiglaucomatous eyedrops used had negative correlations with the CCT in eyes with moderate and severe glaucoma.
Conclusion
Overall, the glaucoma group showed significantly less deformable corneas than did the normal controls, even after adjusting for the IOP, CCT, age and axial length. However, there were also differences according to the severity of glaucoma, where the corneal deformation amplitude was greater in the severe glaucoma group compared to the early glaucoma group. The combined effects of stiffening due to glaucoma and increased viscoelastic properties caused by the chronic use of antiglaucomatous eyedrops may have resulted in the present findings.