1. JP Deva (jennypd@utar.edu.my)
COMPARISON OF PRELIMINARY RESULTS FROM CROSSLINKED KERATOCONUS AND NORMAL CORNEAE USING ORA
JP Deva
Faculty of Medicine and Health Sciences, University Tunku Abdul Rahman, MALAYSIA
Introduction
Crosslinking(CXL) the Keratoconus Cornea has been the means to a effective stabilisation, regularisation and visual rehabilitation for Keratoconus in the last decade. The corneal lamellae have realigned at molecular level as a resul of CXL. Corneal Hysteresis(CH) and Corneal Resistance Factor(CRF) have become important indicators of the improved Biomechanical system of the postCXL Cornea using the Ocular Response Analyzer (ORA).
Results
Figures: 1
Purpose
To evaluate, validate and confirm that after CXL treatment the Keratoconus Cornea is biomechanical ly a stronger and stabilised visco-elastic structure.
Methods
1 2 Crosslinked Keratoconus patients and 12 Normal Controls were analysed using the ORA.. These cases had CXL done 2- 3 years ago.
IOPcc, IOPg, WS, CH, CRF were measured and compared
All Keratoconus patients and controls were in the age group 20-30yrs.
However, while KC subjects were Indian Male, the Controls were Chinese Male.
This may pose a racial bias
Figures: 2a and 2b
Figure: 3
Discussion
Fig. 1 The graphs indicate that IOPg and CH have a similar relationship as in Keratoconus.
Fig.2a The 2 signal peaks indicate good response to CXL.
Fig. 2b The upper graph(RE) shows distorted signals indicating keratoconus is insufficiently treated. Post CXL. The lower graph (LE) shows a normal Ora Signal Analysis.
Fig 3. CH-CRF ratio: In normal cornea CH value is less than or near to CRF
Higher CH value than CRF is present in Keratoconus, even after CXL treatment indicating residual weakness in some advanced KC cases
Though Corneal Hysteresi(CH) does not follow Young’s Modulus of Elasticity, it stil is a visco- elastic structure biomechnically. It is a measure of the difference in the inward and outward pressure in the dynamic bidirectional Applanation process using ORA. . Thus in postCXL cornea, the reduced CH indicates the stronger biomechanics resulting from CXL treatmen.t. and reconfirms that the visual outcome will be improved, the high astigmatism also reduced by the lamellae reallignment.
Further studies and largerstudy population groups will enable these preliminary observations to be substantiated further.
Conclusion
Corneal Hysteresis is reduced in post-CXL keratoconus eyes. This enables KC patient’s cornea to become stabilised and regularise and become a biomechanically stronger structure.
Main References from Ocular Response Analyzer Publication Abstracts
Dianne H Glass, Cynthia J Roberts et al. A Viscoelastic Biomechanical Model of the Cornea Describing the effect of Viscosity and Elasticity on Hysteresis.
.Kamiya K, Hagishima M, Fujimura F, Shimizu. Factors affecting Corneal Hysteresis in Normal eyes.