ABSTRACT
Goldmann applanation tonometry is commonly used for measuring intraocular pressure (IOP) to diagnose glaucoma. However, the measured IOP by conventional applanation tonometry is valid only under the assumption that all subjects have the same structural eye stiffness. This paper challenges in vivo measurement of eye stiffness with a noninvasive approach and investigates individual differences of eye stiffness. Eye stiffness is defined by the applied force and displacement of the cornea. The displacement is detected based on captured images by a high resolution camera. The experimental results show that the measured stiffness nicely matches the analytical result that is derived from a simple spherical deformation model with an internal pressure. However, some subjects have different eye stiffness even with the same IOP. IOP with abnormal stiffness may be over/underestimated by conventional applanation tonometry. The proposed eye stiffness measurement can help detect the misestimated eye and it contributes to the early detection of glaucoma.
Subject(s)
Cornea/physiology , Diagnosis, Computer-Assisted/methods , Intraocular Pressure/physiology , Models, Biological , Tonometry, Ocular/methods , Computer Simulation , Elasticity , Humans , Reproducibility of Results , Sensitivity and Specificity , Stress, MechanicalABSTRACT
Goldmann applanation tonometry is commonly used for measuring IOP (IntraOcular Pressure) to diagnose glaucoma. However, the measured IOP by the applanation tonometry is valid only under the assumption that all the subjects have the same structural eye stiffness. Abnormal eye stiffness makes abnormal corneal deformation and thus the current applanation tonometer misestimates the IOP. This study challenges to measure the eye stiffness in vivo with a non-invasive approach for detecting the abnormal deformation. The deformation of the cornea and the contact area between the probe and the cornea are simultaneously captured by cameras during the experiment. Experimental results show that some subjects have different relationship among the force, the displacement and the contact area even with same IOP. The proposed eye stiffness measurement can help detecting the abnormal deformation and the eyes with misestimated IOP.
Subject(s)
Eye/physiopathology , Tonometry, Ocular/methods , Adult , Aged , Aged, 80 and over , Cornea/physiopathology , Glaucoma/physiopathology , Humans , Intraocular Pressure , Middle Aged , Tonometry, Ocular/instrumentationABSTRACT
The internal eye pressure is an important index for judging whether an eye suffers from glaucoma or not. The conventional eye pressure measurement is valid only under the condition that all subjects have the same structural eye stiffness. This paper challenges the practice of measuring the stiffness of a human eye by pressing the cornea with a contact probe. The displacement of the eye is captured by a camera with high resolution. Experimental results suggest that the measured eye stiffness nicely matches with the theoretical estimation. Based on the experimental results, the difference between the eye stiffness measured by the contact method and the non-contact method is discussed.
Subject(s)
Cornea/physiology , Hardness Tests/methods , Intraocular Pressure/physiology , Models, Biological , Physical Stimulation/methods , Tonometry, Ocular/methods , Adult , Computer Simulation , Elasticity , Female , Humans , Male , Reproducibility of Results , Sensitivity and Specificity , Stress, MechanicalABSTRACT
Non-contact tonometers are widely used to measure the internal eye pressure, i.e. the IntraOcular Pressure (IOP), which is an important parameter for the diagnosis and treatment of glaucoma. During the measurement, the eye is deformed by a short air pulse. Commonly the pressure dependent deformation is estimated from the time when the eye becomes flat, which is derived from the monitored reflection of an incident infrared light. We used a high speed camera to capture the complete motion of the eye directly and obtain more data during the pressure measurement. Assuming a simple eye model with non-linear material properties of the cornea, we extend our previous analysis of the motion of the eye, and obtain a similar principle shape of the eye deformation as observed in the experiments.
Subject(s)
Diagnostic Techniques, Ophthalmological , Eye Movements , Eye/pathology , Glaucoma/diagnosis , Glaucoma/pathology , Intraocular Pressure , Tonometry, Ocular/instrumentation , Tonometry, Ocular/methods , Adult , Age Factors , Aged , Equipment Design , Humans , Infrared Rays , Light , Phantoms, Imaging , Time FactorsABSTRACT
This paper presents novel details on the dynamic behavior of human eyes (see Fig.1). A high speed camera is used to capture the movement of the eye surface, which is excited by an air jet. For one group of subjects the dynamic respose of the eyes ends shortly after the air jet stops. For another group of subjects a distinct offset in the displacement remains, which takes a significantly longer time to vanish. The two distinct phases in the eye movement are the result of the dynamic response of the cornea and the total eye, respectively. A deeper understanding of the eye dynamics is important for obtaining a higher reliability of diagnostic tools for glaucoma.
