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      Association between corneal biomechanical parameters and myopic refractive errors in young Indian individuals

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          Abstract

          PURPOSE:

          To report corneal biomechanical parameters in young myopic Indian individuals.

          METHODS:

          It is a retrospective study where young myopic individuals aged between 19 and 36 years who have undergone corneal biomechanics assessment using Corvis ST between January 2017 and December 2017 were enrolled. Individuals with central corneal thickness (CCT) <500 microns, intraocular pressure (IOP) >21 mmHg, history of any systemic and ocular disease, any previous ocular surgery, high astigmatism, corneal disease such as keratoconus, poor scans quality, and individuals with any missing data were also excluded. Corneal biomechanical parameters were noted in mild to moderate and high myopia.

          RESULTS:

          We analyzed the 266 eyes of 266 myopic individuals, of which 167 and 99 eyes had mild to moderate and high myopia, respectively. All the individuals were matched for age, IOP, and CCT ( P > 0.05). Twenty-three of 32 parameters were similar in different degrees of myopia whereas 9 parameters were significantly different in high myopes as compared to low to moderate myopes. First applanation (A1) parameters and Vinciguerra screening parameters were similar in both the groups ( P > 0.05). Second applanation (A2) parameters were similar in both the groups ( P > 0.05) except A2 time, A2 deformation, amplitude (DA) ( P < 0.05). Highest concavity (HC) parameters were significantly different in both the groups ( P < 0.05) except HCDA, HC deflection length, and HC delta arc length ( P > 0.05).

          CONCLUSIONS:

          High myopic eyes showed a significantly higher maximum deflection amplitude, lesser A2 time and HC time, less A2DA, smaller HC radius than mild to moderate myopia indicating softer, more deformable corneas. However, better predictor of corneal biomechanics such as Stiffness parameters at A1 (SPA1), DA ratio max, integrated radius, and Corvis Biomechanical Index were similar among both the groups of myopia.

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          Most cited references27

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          Determining in vivo biomechanical properties of the cornea with an ocular response analyzer.

          David Luce (2005)
          To study the results of an ocular response analyzer (ORA) to determine the biomechanical properties of the cornea and their relationship to intraocular pressure (IOP). Reichert Inc., Depew, New York, USA. The ORA (Reichert) makes 2 essentially instantaneous applanation measurements that permit determination of corneal and IOP effects. Measurements of several populations indicate that corneal hysteresis, a biomechanical measure, varied over a dynamic range of 1.8 to 14.6 mm Hg and was only weakly correlated with corneal thickness (r(2)=0.12); this is related to the observation that some subjects with relatively thick corneas have less-than-average corneal hysteresis. Corneal hysteresis changes diurnally, presumably as a result of hydration changes. Keratoconus, Fuchs' dystrophy, and post-LASIK patients demonstrated low corneal hysteresis. The corneal hysteresis biomechanical measure may prove valuable for qualification and predictions of outcomes of refractive surgery and in other cases in which corneal biomechanics are important.
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            Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes.

            Dolores Ortiz, David Piñero, Mohamed Shabayek … (2007)
            To compare the biomechanical properties of normal, post-laser in situ keratomileusis (LASIK), and keratoconic corneas evaluated by corneal hysteresis and the corneal resistance factor measured with the Reichert Ocular Response Analyzer (ORA). Instituto Oftalmológico de Alicante, Vissum, Alicante, Spain. Two hundred fifty eyes were divided into 3 groups: normal (control group), post-LASIK, and keratoconus. The corneal biomechanical properties were measured with the ORA, which uses a dynamic bidirectional applanation process. The main outcome measures were intraocular pressure, corneal hysteresis, and the corneal resistance factor. The control group had 165 eyes; the LASIK group, 65 eyes; and the keratoconus group, 21 eyes. In the control group, the mean corneal hysteresis value was 10.8 mm Hg +/- 1.5 (SD) and the mean corneal resistance factor, 11.0 +/- 1.6 mm Hg. The corneal hysteresis value was lower in older eyes, and the difference between the youngest age group (9 to 14 years) and oldest age group (60 to 80 years) was statistically significant (P = .01, t test). One month after LASIK, corneal hysteresis and the corneal resistance factor decreased significantly, from 10.44 to 9.3 mm Hg and from 10.07 to 8.13 mm Hg, respectively. In the keratoconus group, the mean corneal hysteresis was 7.5 +/- 1.2 mm Hg and the mean corneal resistance factor, 6.2 +/- 1.9 mm Hg. There were statistically significant differences in both biomechanical parameters between keratoconic eyes and post-LASIK eyes (P<.001, t test). The corneal hysteresis and corneal resistance factor values were significantly lower in keratoconic eyes than in post-LASIK eyes. Future work is needed to determine whether these differences are useful in detecting keratoconus when other diagnostic tests are equivocal.
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              Corneal deformation measurement using Scheimpflug noncontact tonometry.

              Y Hon, Andrew K C Lam (2012)
              To determine the intraexaminer repeatability and intersession reproducibility of corneal deformation measurement using Scheimpflug noncontact tonometry (Corvis ST) on normal subjects. Thirty-seven adults aged 20 to 48 years were invited to have their corneal deformation and curvature measurements taken using Corvis ST and Pentacam, respectively. Three consecutive measurements were taken for each instrument between 9:00 and 11:00 AM for intraexaminer repeatability analysis. Participants returned between 3:00 and 5:00 PM the same day for intersession reproducibility analysis. The most repeatable corneal parameter measured by Corvis ST was central corneal thickness ([CCT] ICC, 0.96; precision, 10.85 μm; repeatability, 15.34 μm; CV, 1.01%), followed by deformation amplitude ([DA] ICC, 0.80; precision, 0.08 mm; repeatability, 0.13 mm; CV, 4.33%), first applanation time ([1st A-time] ICC, 0.77; precision, 0.22 milliseconds; repeatability, 0.31 milliseconds; CV, 1.42), and intraocular pressure ([IOP] ICC, 0.75; precision, 1.39 mm Hg; repeatability, 1.97 mm Hg; CV, 4.98). Other parameters showed poor repeatability. The DA and 1st A-time showed good intersession reproducibility. The 95% limits of agreement were +0.13 to -0.13 mm for DA and +0.27 to -0.33 milliseconds for 1st A-time. The DA was negatively correlated with central corneal thickness (r = -0.53, p < 0.001) but not with corneal curvatures (flattest curvature, r = 0.13, p = 0.46; steepest curvature, r = 0.05, p = 0.75). Corneal deformation parameters DA and 1st A-time were repeatable and reproducible. A thinner cornea was associated with a higher corneal deformation. Measurement of DA serves as an indicator of corneal biomechanical properties.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Taiwan J Ophthalmol
                Journal ID (iso-abbrev): Taiwan J Ophthalmol
                Journal ID (publisher-id): TJO
                Title: Taiwan Journal of Ophthalmology
                Publisher: Wolters Kluwer - Medknow (India )
                ISSN (Print): 2211-5056
                ISSN (Electronic): 2211-5072
                Publication date Collection: Jan-Mar 2020
                Publication date (Electronic): 04 March 2020
                Volume: 10
                Issue: 1
                Pages: 45-53
                Affiliations
                [1 ] Department of Cornea and Refractive Surgeries, Kenia Eye Hospital, Mumbai, Maharashtra, India
                [2 ] Kenia Foundation, Mumbai, Maharashtra, India
                [3 ] Kenia Medical and Research Foundation, Mumbai, Maharashtra, India
                Author notes
                [* ] Address for correspondence: Prof. Onkar H. Pirdankar, Kenia Medical and Research Foundation, Mumbai, Maharashtra, India. E-mail: pirdankar_onkar@ 123456yahoo.com
                Article
                Publisher ID: TJO-10-45
                DOI: 10.4103/tjo.tjo_15_19
                PMC ID: 7158932
                PubMed ID: 32309124
                SO-VID: 8c93103d-a81a-4a49-b47a-afbde0ccbe49
                Copyright © Copyright: © 2020 Taiwan J Ophthalmol
                License:

                This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.

                History
                Date received : 22 February 2019
                Date accepted : 06 June 2019
                Categories
                Subject: Original Article

                Keywords: corneal biomechanical parameters,corvis st,myopia
                Data availability:
                Keywords: corneal biomechanical parameters, corvis st, myopia

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