Eiichiro Sugimoto

Contact-Based Stiffness Sensing of Human Eye

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.

Understanding eye deformation in non-contact tonometry

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

Dynamic sensing of human eye using a high speed camera

The eye pressure is an important index for judging whether an eye suffers from glaucoma or not. Conventional eye pressure measurements provide us with meaningful data only under the assumption that all the subjects have the same eye stiffness. Our former work, however, says that the assumption is not valid. This work is an extended version. By combining both a high speed camera with 5000[fps] and an air puff supply system, the eye surface can be precisely tracked with respect to time. We introduce a new parameter, which is the displacement at a predetermined applied force. We found that the parameter can strongly emphasize the characteristic of the individual eye stiffness and keeps a high correlation with the measured external eye pressure, so called IOP (intraocular pressure).

Measurement and Analysis of Human Eye Excited by an Air Pulse

For the diagnosis and treatment of glaucoma, a reliable and non-invasive measurement method of the internal eye pressure, i.e. the intraocular pressure (IOP), is desired. The IOP resists a deformation of the eye and thus non-contact tonometers, which deform the eye by a short air pulse, are suitable to estimate the IOP. By monitoring the reflection of an incident infrared light, the tonometer measures the time an applied air jet flattens part of the eye. The relationship between flattening time and IOP are provided by calibration. In our work, we used an additional high speed camera to capture the eye deformation directly and obtain more data during the pressure measurement. We show that the principle shape of the deformation can be understood by assuming simple non-linear material properties of the cornea in an eye model. Furthermore, we discuss which sources of error are still needed to be overcome to give a medical meaningful diagnosis for the examined eye by the data from the high speed camera

Dynamic Properties of Human Eyes

This paper presents novel details on the dynamic behavior of human eyes. 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 response 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

Eye Stiffness Measurement by Probe Contact Method

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

Contact Probe Based Stiffness Sensing of Human Eye by Considering Contact Area

The contact tonometer is commonly used for measuring the internal eye pressure to diagnose glaucoma. However, the conventional eye pressure measurement is valid only under the assumption that all subjects have the same structural eye stiffness. This paper challenges to measure the contact area between the probe and the cornea in addition to the corneal deformation for considering the individual differences in the structural eye stiffness. Prior to the experiment, a spherical model of an eye is developed and the analytical eye stiffness is introduced. The experiment is conducted based on the contact method where a contact probe is pressed on an anesthetized cornea. The deformation of the cornea and the contact area are captured by cameras during the experiment. The experimental results show that the measured stiffness nicely matches the analytical solution based on the constructed model. However, some subjects have different relationships between the displacement and the contact area even with similar estimated eye pressures. This suggests that the structural eye stiffness should be considered for more precise diagnoses of glaucoma.