A fully continuous eye phantom to mimic the intraocular pressure induced-deformation of the human cornea

Abstract

Purpose : To diagnose glaucoma or to check the effectiveness of glaucoma treatment, intraocular pressure(IOP) is measured with a tonometer and the reliability of the measurand of the tonometer is important. In this study, we developed a new type of eye phantom to accurately evaluate the tonometer.

Methods : Former eye phantoms’ cornea is fixed to a rigid part. In this type of eye phantom, deformation occurs only in the cornea due to relatively flexibility when the IOP changes. However, it is different from that of a human eye. In order to solve the problem, we developed a full eye phantom(FEP) which cornea is not fixed and is a continuum using the molding method and the principle of buoynacy. Based on the human data of structural and physical properties, we fabricated FEPs and fixed-cornea eye phantoms(CEP) with 3 different central corneal thickness(CCT)(450, 500 and 550 μm). To confirm that the cornea deformation of the eye phantoms is mimic to that of human eye, comparative experiments between the two types of eye phantoms and in vivo human eyes were conducted. We measured the deformation and IOP of the FEP and CEP using optical coherence tomography and non-contact tonometer, respectively. Also, we measured deformation and IOP from in vivo human subjects with corneal analyzer and non-contact tonometer, respectively.

Results : While the CCT changes were very similar between FEPs and CEPs, the relation between the corneal radius of curvature(CRC) and the IOP was dependent on the type of eye phantom. For the CEP, the CRC drastically decreased as internal pressure increased. However, we found that the changes in the CRC of FEP was dependent on initial CCT(CCT₀). When CCT₀ was less than 450μm, the CRC slightly decreased as IOP increased. Meanwhile, the CRC increased as IOP increased if CCT₀ was 550μm. In vivo human experiments revealed that the relation between the CRC on the IOP is much closer to those observed FEP.

Conclusions : Considering the structural deformation of human cornea, we found that the FEP mimics the human eye more accurately than the CEP. In addition, the tonometry readings of IOP show that the values from the CEP were overestimated, while those from the FEP were not. For these reasons, we expect that the FEP could be suitable for the estimation of true IOP.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Picture and the internal structure for FEP((a)(b)) and CEP((c)(d))

 

IOP-induced deformation in CEP((a)(b)) and FEP((c)(d))