The Biomechanical E-Staging: In Vivo Biomechanics in Keratoconus

Abstract

Belinʼs ABCD keratoconus classification system allows keratoconus staging based on the criteria of anterior (A) and posterior (B) corneal curvature, thinnest corneal thickness (C), and best spectacle-corrected visual acuity (D). These parameters also provide a progression assessment, but do not take corneal biomechanics into account. The analysis of corneal biomechanics by the Corvis ST (Oculus, Wetzlar, Germany) allows for separation of healthy and keratoconus corneas, based on the Corvis Biomechanical Index (CBI) and the Tomographic Biomechanical Index (TBI). As Corvis ST measurements are highly reliable and are independent of keratoconus severity, a biomechanical parameter was developed for keratoconus corneas based on the linear term of the CBI. This provides biomechanical keratoconus staging. The Corvis Biomechanical Factor (CBiF) is the basis for the introduction of the biomechanical E-staging, which augments the ABCD classification to the ABCDE classification, thus including the cornerstone of corneal biomechanics. This article highlights strengths and limitations of the ABCDE classification. “Unilateral keratoconus” supposedly turns out to be mostly a snapshot of a highly asymmetric keratectasia. Regular astigmatism is sometimes an important differential diagnosis to keratectasia and may be difficult to differentiate from it. Furthermore, the use of the biomechanical E-staging in daily practice for progression assessment of keratoconus and after its treatment by corneal cross-linking or implantation of intracorneal ring segments will be demonstrated and discussed.

Key words

keratoconus - ABCDE classification - E-staging - biomechanics - Corvis biomechanical factor CBiF

Publikationsverlauf

Eingereicht: 30. November 2022

Angenommen: 14. April 2023

Artikel online veröffentlicht:
22. Juni 2023

• References/Literatur

• 1 Eppig T, Spira-Eppig C, Goebels S. et al. Asymmetry between Left and Right Eyes in Keratoconus Patients Increases with the Severity of the Worse Eye. Curr Eye Res 2018; 43: 848-855 DOI: 10.1080/02713683.2018.1451545.
• 2 Hashemi H, Heydarian S, Hooshmand E. et al. The Prevalence and Risk Factors for Keratoconus: A Systematic Review and Meta-Analysis. Cornea 2020; 39: 263-270 DOI: 10.1097/ICO.0000000000002150.
• 3 de Sanctis U, Loiacono C, Richiardi L. et al. Sensitivity and Specificity of Posterior Corneal Elevation Measured by Pentacam in Discriminating Keratoconus/Subclinical Keratoconus. Ophthalmology 2008; 115: 1534-1539 DOI: 10.1016/j.ophtha.2008.02.020.
• 4 Randleman JB, Dupps WJ, Santhiago MR. et al. Screening for Keratoconus and Related Ectatic Corneal Disorders. Cornea 2015; 34: e20-e22 DOI: 10.1097/ICO.0000000000000500.
• 5 Muftuoglu O, Ayar O, Ozulken K. et al. Posterior corneal elevation and back difference corneal elevation in diagnosing forme fruste keratoconus in the fellow eyes of unilateral keratoconus patients. J Cataract Refract Surg 2013; 39: 1348-1357 DOI: 10.1016/j.jcrs.2013.03.023.
• 6 Golan O, Hwang ES, Lang P. et al. Differences in Posterior Corneal Features Between Normal Corneas and Subclinical Keratoconus. J Refract Surg 2018; 34: 664-670 DOI: 10.3928/1081597X-20180823-02.
• 7 Smadja D, Santhiago MR, Mello GR. et al. Influence of the reference surface shape for discriminating between normal corneas, subclinical keratoconus, and keratoconus. J Refract Surg 2013; 29: 274-281 DOI: 10.3928/1081597X-20130318-07.
• 8 Ambrósio R, Randleman JB. Screening for Ectasia Risk: What Are We Screening For and How Should We Screen For It?. J Refract Surg 2013; 29: 230-232 DOI: 10.3928/1081597X-20130318-01.
• 9 Elkitkat RS, Gharieb HM, Othman IS. Accuracy of the posterior corneal elevation values of Pentacam HR from different reference surfaces in early ectasia diagnosis. Int Ophthalmol 2021; 41: 629-638 DOI: 10.1007/s10792-020-01618-8.
• 10 Flockerzi E, Xanthopoulou K, Goebels SC. et al. Keratoconus staging by decades: a baseline ABCD classification of 1000 patients in the Homburg Keratoconus Center. Br J Ophthalmol 2021; 105: 1069-1075 DOI: 10.1136/bjophthalmol-2020-316789.
• 11 Belin MW, Duncan JK. Keratoconus: The ABCD Grading System. Klin Monbl Augenheilkd 2016; 233: 701-707 DOI: 10.1055/s-0042-100626.
• 12 Belin MW, Meyer JJ, Duncan JK. et al. Assessing Progression of Keratoconus and Cross-linking Efficacy: The Belin ABCD Progression Display. Int J Kerat Ect Cor Dis 2017; 6: 1-10 DOI: 10.5005/jp-journals-10025-1135.
• 13 Flockerzi E, Elzer B, Daas L. et al. The Reliability of Successive Scheimpflug Imaging and Anterior Segment Optical Coherence Tomography Measurements Decreases With Increasing Keratoconus Severity. Cornea 2021; 40: 1433-1439 DOI: 10.1097/ICO.0000000000002657.
• 14 Herber R, Lenk J, Pillunat LE. et al. Comparison of corneal tomography using a novel swept-source optical coherence tomographer and rotating Scheimpflug system in normal and keratoconus eyes: repeatability and agreement analysis. Eye Vis (Lond) 2022; 9: 19 DOI: 10.1186/s40662-022-00290-6.
• 15 Gustafsson I, Faxén T, Vicente A. et al. An inter-day assessment of the ABC parameters in the evaluation of progressive keratoconus. Sci Rep 2021; 11: 16037 DOI: 10.1038/s41598-021-95503-8.
• 16 Elham R, Jafarzadehpur E, Hashemi H. et al. Keratoconus diagnosis using Corvis ST measured biomechanical parameters. J Curr Ophthalmol 2017; 29: 175-181 DOI: 10.1016/j.joco.2017.05.002.
• 17 Tian L, Ko MWL, Wang L. et al. Assessment of ocular biomechanics using dynamic ultra high-speed Scheimpflug imaging in keratoconic and normal eyes. J Refract Surg 2014; 30: 785-791 DOI: 10.3928/1081597X-20140930-01.
• 18 Peña-García P, Peris-Martínez C, Abbouda A. et al. Detection of subclinical keratoconus through non-contact tonometry and the use of discriminant biomechanical functions. J Biomech 2016; 49: 353-363 DOI: 10.1016/j.jbiomech.2015.12.031.
• 19 Ambrósio R, Correia FF, Lopes B. et al. Corneal Biomechanics in Ectatic Diseases: Refractive Surgery Implications. Open Ophthalmol J 2017; 11: 176-193 DOI: 10.2174/1874364101711010176.
• 20 Vinciguerra R, Ambrósio R, Elsheikh A. et al. Detection of Keratoconus With a New Biomechanical Index. J Refract Surg 2016; 32: 803-810 DOI: 10.3928/1081597X-20160629-01.
• 21 Reisdorf S. [Artificial Intelligence for the Development of Screening Parameters in the Field of Corneal Biomechanics]. Klin Monbl Augenheilkd 2019; 236: 1423-1427 DOI: 10.1055/a-1032-8559.
• 22 Langenbucher A, Häfner L, Eppig T. et al. Keratoconus detection and classification from parameters of the Corvis^® ST: A study based on algorithms of machine learning. Ophthalmologe 2021; 118: 697-706 DOI: 10.1007/s00347-020-01231-1.
• 23 Ambrósio R, Lopes BT, Faria-Correia F. et al. Integration of Scheimpflug-Based Corneal Tomography and Biomechanical Assessments for Enhancing Ectasia Detection. J Refract Surg 2017; 33: 434-443 DOI: 10.3928/1081597X-20170426-02.
• 24 Shen Y, Han T, Jhanji V. et al. Correlation Between Corneal Topographic, Densitometry, and Biomechanical Parameters in Keratoconus Eyes. Trans Vis Sci Tech 2019; 8: 12 DOI: 10.1167/tvst.8.3.12.
• 25 Koh S, Inoue R, Ambrósio R. et al. Correlation Between Corneal Biomechanical Indices and the Severity of Keratoconus. Cornea 2020; 39: 215-221 DOI: 10.1097/ICO.0000000000002129.
• 26 Herber R, Pillunat LE, Raiskup F. Development of a classification system based on corneal biomechanical properties using artificial intelligence predicting keratoconus severity. Eye Vis (Lond) 2021; 8: 21 DOI: 10.1186/s40662-021-00244-4.
• 27 Shetty R, Nuijts RM, Srivatsa P. et al. Understanding the Correlation between Tomographic and Biomechanical Severity of Keratoconic Corneas. Biomed Res Int 2015; 2015: 294197 DOI: 10.1155/2015/294197.
• 28 Flockerzi E, Vinciguerra R, Belin MW. et al. Correlation of the Corvis Biomechanical Factor CBiF with tomographic parameters in keratoconus. J Cataract Refract Surg 2022; 48: 215-221 DOI: 10.1097/j.jcrs.0000000000000740.
• 29 Flockerzi E, Vinciguerra R, Belin MW. et al. Combined biomechanical and tomographic keratoconus staging: Adding a biomechanical parameter to the ABCD keratoconus staging system. Acta Ophthalmol 2022; 100: e1135-e1142 DOI: 10.1111/aos.15044.
• 30 Flockerzi E, Häfner L, Xanthopoulou K. et al. Reliability analysis of successive Corneal Visualization Scheimpflug Technology measurements in different keratoconus stages. Acta Ophthalmol 2022; 100: e83-e90 DOI: 10.1111/aos.14857.
• 31 Eliasy A, Chen KJ, Vinciguerra R. et al. Determination of Corneal Biomechanical Behavior in-vivo for Healthy Eyes Using CorVis ST Tonometry: Stress-Strain Index. Front Bioeng Biotechnol 2019; 7: 105 DOI: 10.3389/fbioe.2019.00105.
• 32 Gomes JAP, Tan D, Rapuano CJ. et al. Global consensus on keratoconus and ectatic diseases. Cornea 2015; 34: 359-369 DOI: 10.1097/ICO.0000000000000408.
• 33 Amsler M. The “forme fruste” of keratoconus. Wien Klin Wochenschr 1961; 73: 842-843
• 34 Salomão MQ, Höffling-Lima AL, Esporcatte LPG, Faria Correia F, Lopes BT, Sena N, Machado AP, Ambrósio R. Redefining Forme Fruste Keratoconus. In: Almodin E, Nassaralla BA, Sandes J. eds. Keratoconus. Cham: Springer International Publishing; 2022: 853-867
• 35 Vinciguerra R, Ambrósio R, Roberts CJ. et al. Biomechanical Characterization of Subclinical Keratoconus Without Topographic or Tomographic Abnormalities. J Refract Surg 2017; 33: 399-407 DOI: 10.3928/1081597X-20170213-01.
• 36 Herber R, Hasanli A, Lenk J. et al. Evaluation of Corneal Biomechanical Indices in Distinguishing Between Normal, Very Asymmetric, and Bilateral Keratoconic Eyes. J Refract Surg 2022; 38: 364-372 DOI: 10.3928/1081597X-20220601-01.
• 37 Flockerzi E, Xanthopoulou K, Daas L. et al. Evaluation of Dynamic Corneal Response Parameters and the Biomechanical E-Staging After Accelerated Corneal Cross-Linking in Keratoconus. Asia Pac J Ophthalmol (Phila) 2022; 11: 514-520 DOI: 10.1097/APO.0000000000000580.
• 38 Xanthopoulou K, Milioti G, Daas L. et al. Accelerated corneal crosslinking causes pseudoprogression in keratoconus within the first 6 weeks without affecting posterior corneal curvature. Eur J Ophthalmol 2022; 32: 2565-2576 DOI: 10.1177/11206721221099257.
• 39 Caporossi A, Mazzotta C, Baiocchi S. et al. Long-term Results of Riboflavin Ultraviolet A Corneal Collagen Cross-linking for Keratoconus in Italy: The Siena Eye Cross Study. Am J Ophthalmol 2010; 149: 585-593 DOI: 10.1016/j.ajo.2009.10.021.
• 40 Greenstein SA, Shah VP, Fry KL. et al. Corneal thickness changes after corneal collagen crosslinking for keratoconus and corneal ectasia: one-year results. J Cataract Refract Surg 2011; 37: 691-700 DOI: 10.1016/j.jcrs.2010.10.052.
• 41 Herber R, Francis M, Spoerl E. et al. Evaluation of Biomechanical Changes After Accelerated Cross-Linking in Progressive Keratoconus: A Prospective Follow-Up Study. Cornea 2023; DOI: 10.1097/ICO.0000000000003219.
• 42 Herber R, Vinciguerra R, Tredici C. et al. Repeatability of corneal deformation response parameters by dynamic ultra-high speed Scheimpflug imaging before and after corneal cross-linking. J Cataract Refract Surg 2023; DOI: 10.1097/j.jcrs.0000000000001136.
• 43 Zare M, Mehrjardi H, Afarideh M. et al. Visual, keratometric and corneal biomechanical changes after Intacs SK implantation for moderate to severe keratoconus. J Ophthalmic Vis Res 2016; 11: 17 DOI: 10.4103/2008-322X.180698.
• 44 Matar C, Daas L, Suffo S. et al. Reliability of corneal tomography after implantation of intracorneal ring segments for keratoconus. Ophthalmologe 2020; 117: 1092-1099 DOI: 10.1007/s00347-020-01074-w.
• 45 Kang MJ, Byun YS, Yoo YS. et al. Long-term outcome of intrastromal corneal ring segments in keratoconus: Five-year follow up. Sci Rep 2019; 9: 315 DOI: 10.1038/s41598-018-36668-7.