Abstract
Purpose: To evaluate the dependence of biomechanical metrics on intraocular pressure (IOP). Methods: 233 refractive surgery patients were included in this study—all were examined 3 times with the Corvis ST before and after dilation, and the differences (∆) in the main device parameters were assessed. The data collected included the biomechanically corrected IOP (bIOP), the central corneal thickness (CCT), and six dynamic corneal response (DCR) parameters, namely DA, DARatio2mm, IIR, SP-A1, CBI, and SSI. Participants were divided into three groups according to the changes in patients’ bIOP after mydriasis. Results: Intra-operator repeatability was generally high in most of the DCR parameters obtained before and after dilation. The mean changes in bIOP and CCT after dilation were −0.12 ± 1.36 mmHg and 1.95 ± 5.23 μm, respectively. Only ∆DARatio2mm, ∆IIR, and ∆CBI exhibited a statistically significant correlation with ∆CCT (p < 0.05). The changes in all DCR parameters, especially ∆DA and ∆SP-A1 were also correlated with ∆bIOP (p < 0.01)—a 1-mmHg change in bIOP was associated, on average, with 5.612 and −0.037 units of change in SP-A1 and DA, respectively. In contrast, the weakest correlation with ∆bIOP was exhibited by ∆SSI. Conclusion: Most corneal DCR parameters, provided by the Corvis ST, were correlated with IOP, and more weakly with CCT. Changes experienced in CCT and IOP should therefore be considered in studies on corneal biomechanics and how it is affected by disease progression and surgical or medical procedures.
Highlights
To focus light rays on the retina, the cornea needs to remain transparent and maintain a suitable shape that stays stable with the diurnal changes in intraocular pressure (IOP)
The coefficient of variation (CoV) was approximately 6% (5.99% before mydriasis and 6.29% after). 20.2% of subjects showed an increase in biomechanically corrected IOP (bIOP) measurement post-dilation (2.01 ± 1.50 mmHg, 1.00–9.37 mmHg, Group I), 14.2% exhibited a decrease post-dilation (−1.85 ± 0.80 mmHg, −0.97 ∼ −5.4 mmHg, Group D), and the remaining 65.6% had stable bIOP readings (−0.06 ± 0.50 mmHg, −0.93–0.93 mmHg, Group S)
Repeatability of the biomechanical metrics was similar at the pre- and post-dilation stages
Summary
To focus light rays on the retina, the cornea needs to remain transparent and maintain a suitable shape that stays stable with the diurnal changes in intraocular pressure (IOP). Corvis ST provides more information on corneal biomechanical response, based on ultra-high-speed Scheimpflug technology which records the entire process of corneal deformation and provides measurements such as the stiffness parameter at first applanation (SP-A1) and the integrated inverse radius (IIR). While these biomechanical metrics have been shown to have strong correlation with the cornea’s overall stiffness, they are not independent parameters, but influenced by stiffness-unrelated events such as the diurnal variation in the IOP (Bao et al, 2015)
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