Review Article, Int J Ophthalmic Pathol Vol: 10 Issue: 0

Corneal Hysteresis and its Association with Optic Nerve and Visual Field Damage in Glaucoma

Flora Olsen*

Department of Medicine, University Health Network, Toronto, Canada.

*Corresponding Author: Flora Olsen
Department of Medicine, University Health Network
Toronto, Canada
E-mail: flum@aao.org

Received: November 02, 2021 Accepted: November 16, 2021 Published: November 23, 2021

Citation: Olsen F (2021) Corneal Hysteresis and its Association with Optic Nerve and Visual Field Damage in Glaucoma. Int J Ophthalmic Pathol S5.

Abstract

Keywords: Cornea, Glaucoma, Optic Nerve

Introduction

The cornea can be characterized by its actual aspects, like its thickness, or actual conduct, for instance, biomechanics. At first, the biomechanical properties of the cornea were of interest fundamentally to refractive specialists attempting to get keratoconus or hazard factors for post-laser-aided situ keratomileusis ectasia. Early work on this subject looked to recognize Young’s modulus of the cornea in an assortment of models. The turn of events and commercialization of the corneal hysteresis estimation, be that as it may, made conceivable by the Reichert visual reaction analyzer (ORA), sped up research and clinical involvement with this field for the field of glaucoma.

The ORA depends on noncontact tonometer innovation, which utilizes an air fly to apply power to the cornea and an electrooptical framework to decide applanation [1]. This machine was at first evolved to give a Goldmann applanation tonometry (GAT)- like intraocular pressure (IOP) estimation without sedation or visual contact; in any case, later David Luce, PhD, found that extra corneal data was likewise present in the estimation signal, a further developed ORA was dispatched in 2005 (D. Luce, individual correspondence).

The Corvis ST, delivered by Oculus (Wetzlar, Germany), has likewise been created for biomechanical appraisal of the eye. It utilizes an air stream tonometer to quantify pressure and a rapid Scheimpflug camera to all the while screen corneal development. It can compute different boundaries; notwithstanding, there is restricted distributed writing and the gadget isn’t yet endorsed by the Food and Drug Administration for estimating biomechanical properties.

The Cornea Is Viscoelastic: The cornea, as most organic materials, is ‘viscoelastic’, implying that it contains qualities of both versatile and thick materials. A viscoelastic framework can be represented by an auto suspension swagger. At the point when a heap is applied to the swagger, the reaction is reliant upon both the flexible properties of the part of the curl spring and the consistency of the oil in the safeguard. Viscoelastic materials and frameworks are regularly described by hysteresis. Hysteresis isn’t really a characteristic or steady property, however an estimation portraying how a material or framework reacts to the stacking and dumping of an applied power. Corneal hysteresis mirrors the capacity of corneal tissue to retain and disperse energy during a bidirectional applanation process (where energy is lost as hotness during the fast stacking/dumping of the cornea) [2-3].

Activity Of The Ocular Response Analyzer: As the cornea moves internal and outward because of the expanding and diminishing speed of the air fly, its distortion is followed by an electrooptical framework. The internal and outward applanation occasions are distinguished by the pinnacle sufficiency of the mirrored light hitting the photodetector. Pressure esteems are recorded at the internal (P1) and outward (P2) applanation states. P1 and P2 are a component of the real IOP, the static obstruction of the cornea, and the dynamic (gooey) opposition of the cornea. The normal of P1 and P2 gives a Goldmann-corresponded IOP esteem alluded to as IOPg. The contrast somewhere in the range of P1 and P2 is named corneal hysteresis, given in mmHg.

Corneal Biomechanics And The Measurement Of Intraocular Pressure: The IOPg estimation given by the ORA is expected to assess GAT. In examinations including in excess of 200 patients with glaucoma, both Broman et al.[11] and Ehrlich et al.[15] exhibited that GAT and ORA IOPg show great understanding, with Ehrlich et al. finding a mean GAT–IOPg contrast of 0.1 mmHg (±0.3). Lam et al.[4] showed that IOPg had a mean distinction of 0.33 contrasted and GAT in an investigation of 125 ordinary Chinese eyes.

Corneal Hysteresis In Normal Eyes: Shah announced a normal corneal hysteresis of 10.7 in 207 typical eyes (normal age = 62.1 years) and Carbonaro revealed a mean corneal hysteresis of 10.24 in a huge twin review. Different investigations have detailed comparative estimations. A few examinations have additionally shown that, in typical eyes, corneal hysteresis doesn’t shift altogether for the duration of the day.

References

1. Leung CK, Ye C, Weinreb RN (2013). An ultra-high-speed Scheimpflug camera for evaluation of corneal deformation response and its impact on IOP measurement. Invest Ophthalmol Vis Sci 54:2885–2892.
2. Luce DA (2005). Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J Cataract Refract Surg 31:156–162.
3. Dupps WJ Jr (2007). Hysteresis: new mechanospeak for the ophthalmologist. J Cataract Refract Surg 33:1499–1501.
4. Laiquzzaman M, Bhojwani R, Cunliffe I, Shah S (2006). Diurnal variation of ocular hysteresis in normal subjects: relevance in clinical context. Clin Experiment Ophthalmol 2006; 34:114–118.

References

1. Leung CK, Ye C, Weinreb RN (2013). An ultra-high-speed Scheimpflug camera for evaluation of corneal deformation response and its impact on IOP measurement. Invest Ophthalmol Vis Sci 54:2885–2892.
2. Luce DA (2005). Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J Cataract Refract Surg 31:156–162.
3. Dupps WJ Jr (2007). Hysteresis: new mechanospeak for the ophthalmologist. J Cataract Refract Surg 33:1499–1501.
4. Laiquzzaman M, Bhojwani R, Cunliffe I, Shah S (2006). Diurnal variation of ocular hysteresis in normal subjects: relevance in clinical context. Clin Experiment Ophthalmol 2006; 34:114–118.