Abstract: Tear film is measured without contacting the eye by comparing reflectance from the eye when the tear film is undisturbed with reflectance from the eye when the when the tear film is disturbed. If the reflectance levels differ somewhat, it is an indication that a healthy tear film exhibiting good specular reflection was present initially and was disturbed by the air pulse. However, if the reflectance levels are close to one another, it is an indication that a less-than-normal tear film was present initially (dry eye). In a described embodiment, tear film is disturbed by an air pulse directed at the eye, and a photosensitive detector is positioned to receive light from an illumination beam after the beam is reflected by the eye to generate a reflectance signal. The reflectance signal is evaluated to calculate a tear film index.

Abstract: A method and apparatus for measuring corneal resistance to deformation use an empirically derived function wherein an inward applanation pressure P1 and an outward applanation pressure P2 obtained during a corneal deformation cycle caused by a fluid pulse are separately weighted so as to minimize dependence of the calculated corneal resistance factor (CRF) on intraocular pressure. In one embodiment, the function is optimized, at least in part, to maximize statistical correlation between the calculated corneal resistance factor (CRF) and central corneal thickness.

Abstract: A method and apparatus for measuring intraocular pressure of an eye use an empirically derived function wherein an inward applanation pressure P1 and an outward applanation pressure P2 obtained during a corneal deformation cycle caused by a fluid pulse are separately weighted so as to minimize cornea-related influence on the intraocular pressure value calculated by the function. In one embodiment, the function is optimized, at least in part, to minimize change in calculated IOP between measurements made before surgical alteration of the cornea and measurements made after surgical alteration of the cornea.

Abstract: A method for measuring a biomechanical characteristic of corneal tissue of a cornea comprises the steps of measuring a geometric parameter of the cornea, measuring hysteresis associated with deformation of the cornea, and evaluating the measured geometric parameter and hysteresis. In an ophthalmic system for practicing the method, a pachometer is used to measure corneal thickness and a tonometer is used to measure hysteresis, and the measurement data is supplied to a computer for evaluation. A related method for prequalifying LASIK patients comprises the steps of establishing a multi-dimensional space wherein a first dimension is a geometric corneal parameter and a second dimension is hysteresis associated with corneal deformation, measuring the geometric corneal parameter and hysteresis of the patient's cornea, registering the geometric corneal parameter and corneal hysteresis in a data point in the multi-dimensional space, and evaluating a location of the data point in the multi-dimensional space.

Abstract: A dual mode non-contact tonometer allows selection between a standard measurement mode for patient comfort and an alternate measurement mode wherein pressure-time characteristics of the fluid pulse are varied to allow additional observation of corneal hysteresis associated with the dynamic measurement process. In the alternate measurement mode, measured intraocular pressure corresponding to inward applanation of the cornea and corneal hysteresis derived from a pressure differential associated with inward and outward applanation events in the same measurement pulse allows comparison with a predetermined population normality function to avoid corneal effects so that the actual status of intraocular pressure can be ascertained.

Abstract: A novel tonometry method wherein measured intraocular pressure corresponding to inward applanation of the cornea and corneal hysteresis derived from a pressure differential associated with inward and outward applanation events in the same measurement pulse allows comparison with a predetermined population normality function to avoid corneal effects so that the actual status of intraocular pressure can be ascertained. A dual mode non-contact tonometer allows selection between a standard measurement mode for patient comfort and an alternate measurement mode wherein pressure-time characteristics of the fluid pulse are varied to allow additional observation of corneal hysteresis associated with the dynamic measurement process for carrying out the novel tonometry method. Corresponding tonometry method embodiments include a method adapted for a contact tonometer and a method based on a pair of non-contact tonometer measurements taken using different air pulse pressure ramp rates.

Abstract: A method for measuring a biomechanical characteristic of corneal tissue of a cornea comprises the steps of measuring a geometric parameter of the cornea, measuring hysteresis associated with deformation of the cornea, and evaluating the measured geometric parameter and hysteresis. In an ophthalmic system for practicing the method, a pachometer is used to measure corneal thickness and a tonometer is used to measure hysteresis, and the measurement data is supplied to a computer for evaluation. A related method for prequalifying LASIK patients comprises the steps of establishing a multi-dimensional space wherein a first dimension is a geometric corneal parameter and a second dimension is hysteresis associated with corneal deformation, measuring the geometric corneal parameter and hysteresis of the patient's cornea, registering the geometric corneal parameter and corneal hysteresis in a data point in the multi-dimensional space, and evaluating a location of the data point in the multi-dimensional space.

Abstract: A non-contact tonometer of a type having a cylinder, a piston received by the cylinder for axially directed movement relative to the cylinder, and a driven member for causing the piston to move relative to the cylinder in a compression stroke to generate a fluid pulse for transfiguring a cornea is improved by decoupling the piston from the driven member to eliminate the need for critical alignment between the driven member and piston and allow the piston to be self-aligning with respect to the cylinder.

Abstract: An apparatus for calibrating a non-contact tonometer comprises an electronic eye having a damped pressure sensor for receiving a tonometer air pulse and providing a pressure signal in response to the air pulse, and an applanation simulator connected to the pressure sensor for providing a pseudo-applanation event when the pressure signal reaches a predetermined level corresponding to a known IOP measurement standard. A method for calibrating a non-contact tonometer using the inventive calibration apparatus is also described.

Abstract: A dual mode non-contact tonometer allows selection between a standard measurement mode for patient comfort and an alternate measurement mode wherein pressure-time characteristics of the fluid pulse are varied to allow additional observation of corneal hysteresis associated with the dynamic measurement process. In the alternate measurement mode, measured intraocular pressure corresponding to inward applanation of the cornea and corneal hysteresis derived from a pressure differential associated with inward and outward applanation events in the same measurement pulse allows comparison with a predetermined population normality function to avoid corneal effects so that the actual status of intraocular pressure can be ascertained.

Abstract: A novel tonometry method wherein measured intraocular pressure corresponding to inward applanation of the cornea and corneal hysteresis derived from a pressure differential associated with inward and outward applanation events in the same measurement pulse allows comparison with a predetermined population normality function to avoid corneal effects so that the actual status of intraocular pressure can be ascertained. A dual mode non-contact tonometer allows selection between a standard measurement mode for patient comfort and an alternate measurement mode wherein pressure-time characteristics of the fluid pulse are varied to allow additional observation of corneal hysteresis associated with the dynamic measurement process for carrying out the novel tonometry method. Corresponding tonometry method embodiments include a method adapted for a contact tonometer and a method based on a pair of non-contact tonometer measurements taken using different air pulse pressure ramp rates.

Abstract: An apparatus for calibrating a non-contact tonometer comprises an electronic eye having a damped pressure sensor for receiving a tonometer air pulse and providing a pressure signal in response to the air pulse, and applanation simulation means connected to the pressure sensor for providing a pseudo-applanation event when the pressure signal reaches a predetermined level corresponding to a known IOP measurement standard. A method for calibrating a non-contact tonometer using the inventive calibration apparatus is also described.

Abstract: A non contact tonometer of a type having a fluid pump in flow communication with a fluid discharge tube for directing a fluid pulse at an eye of a patient to observably transfigure the cornea is improved by providing the fluid discharge tube with a flared inlet portion for reducing inlet losses. In a preferred embodiment, the flared inlet portion is defined by a circumferential internal radius.

Abstract: A non-contact tonometer of a type having a cylinder, a piston received by the cylinder for axially directed movement relative to the cylinder, and a driven member for causing the piston to move relative to the cylinder in a compression stroke to generate a fluid pulse for transfiguring a cornea is improved by decoupling the piston from the driven member to eliminate the need for critical alignment between the driven member and piston and allow the piston to be self-aligning with respect to the cylinder.

Abstract: A hand-held non-contact tonometer comprises a housing having a handle portion for enclosing a rechargeable D.C. power source and an upper head portion for enclosing alignment and tonometric measurement systems of the tonometer. An operator can directly view the patient's eye along an optical axis extending through the head portion of the housing, and an instructional display image is superimposed with the directly viewed image of the eye to guide the operator in X-Y-Z alignment based on data supplied by an afocal position detection system. A transceiver for wireless data exchange and a recharging support stand are also provided.

Abstract: A fluid pump system of a non-contact tonometer is numerically simulated through its compression stroke by a simulation software program. System dynamic behavior is modeled for a variety of piston diameters, whereby an optimal piston diameter or range of piston diameters is selected in view of stoke length limitations and target applanation pressure requirements.

Abstract: A non-contact tonometer comprises a fluid pump system having a linear proportional solenoid for driving a piston of the fluid pump system to generate a fluid pulse in a predetermined and controlled manner. The energizing current to the linear proportional solenoid is dictated by data stored in a digital look-up table.

Abstract: A non-contact tonometer comprises a fluid pump system configured and mounted to dissipate vibration energy to reduce the effect of vibrations on measurement components caused by the stroke of a piston with respect to a cylinder in the fuid pump system. In a preferred embodiment, a compression chamber receiving a piston and plenum chamber containing a pressure sensing device are spaced apart from one another and connected by a flow tube formed of a vibration damping material, and at least one vibration damping element is provided between the cylinder and a support frame of the non-contact tonometer.

Abstract: A fluid pump system of a non-contact tonometer is numerically simulated through its compression stroke by a simulation software program. System dynamic behavior is modeled for a variety of piston diameters, whereby an optimal piston diameter or range of piston diameters is selected in view of stoke length limitations and target applanation pressure requirements.

Abstract: A hand-held non-contact tonometer comprises a housing having a handle portion for enclosing a rechargeable D.C. power source and an upper head portion for enclosing alignment and tonometric measurement systems of the tonometer. An operator can directly view the patient's eye along an optical axis extending through the head portion of the housing, and an instructional display image is superimposed with the directly viewed image of the eye to guide the operator in X-Y-Z alignment based on data supplied by an afocal position detection system. A transceiver for wireless data exchange and a recharging support stand are also provided.