Portable device for the measurement of refractive error in the eye

Abstract

A portable device for the measurement of refractive error in the eye is disclosed. The device generally includes a liquid lens that the patient looks through, a projective array of static lenses, an electronic display, a system of electronics, and software that controls the potential applied to the liquid lens, controls the display, and runs the algorithm that processes patient feedback in order to determine the correct corrective lens powers. Housed in a singular body that can be held and positioned in front of the patient's eye, the device allows direct feedback and interaction by a patient using a remote control. Altogether, the device is automatically determines a voltage of the liquid lens that provides the patient with the clearest vision, which can be used to calculate the prescription corrective lens power.

Claims

1. A portable device for the measurement of refractive error in the eye, comprising: an optical assembly that is made of a liquid lens that the patient looks through followed by a projective array of static lenses, an electronic display that the patient looks through the optical assembly at, a system of electronics (accompanied by a battery or batteries), and software that runs on the electronics system.

2. The portable device for the measurement of refractive error in the eye of claim 1, wherein the components are housed in a manufactured or machined housing.

3. The portable device for the measurement of refractive error in the eye of claim 1, wherein the projective array of static lenses in the optical assembly contains lenses positioned relative to each other and overall is positioned relative to the display to project the image of the display to a virtual distance.

4. The portable device for the measurement of refractive error in the eye of claim 1, wherein the liquid lens in the optical assembly is electronically controllable by the electronics system.

5. The portable device for the measurement of refractive error in the eye of claim 1, wherein the display can show the reference graphic for a patient to compare the clarity of liquid lens voltages.

6. The portable device for the measurement of refractive error in the eye of claim 1, wherein the display can show the voltage and calculated prescription power that provides the patient with the clearest vision.

7. The portable device for the measurement of refractive error in the eye of claim 1, wherein the electronics system controls the potential applied to the liquid lens.

8. The portable device for the measurement of refractive error in the eye of claim 1, wherein the electronics system controls the electronics display.

9. The portable device for the measurement of refractive error in the eye of claim 1, wherein the electronics system runs the algorithm that processes patient feedback in order to determine the liquid lens voltage that provides the clearest vision.

10. The portable device for the measurement of refractive error in the eye of claim 9, wherein the algorithm can be calibrated to calculate a corrective lens prescription power for an eye based on the liquid lens voltage that provides the clearest vision.

11. The portable device for the measurement of refractive error in the eye of claim 10, wherein the algorithm can utilize the calibration data to provide a prescription lens power for the eyes of a patient.

12. The portable device for the measurement of refractive error in the eye of claim 1, wherein a patient can position the device in front of their eye.

13. The portable device for the measurement of refractive error in the eye of claim 1, wherein a patient can provide feedback about the clarity of the lens voltage.

14. The portable device for the measurement of refractive error in the eye of claim 13, wherein the patient's feedback can be entered into the device by either the patient or another person assisting in the operation of the device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is an isometric view of a housing for an embodiment of the present invention.

[0028] FIG. 2 is an isometric view of an optical assembly for an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A. Overview

[0029] The device contains an optical assembly that the patient looks through to view a display. The display and liquid lens are controlled by the electronics system, which directs the lens driving component of the system to apply certain desired voltages onto the lens, directs the display controlling component of the system to display certain graphics and information, and runs the power determination algorithm. As seen in FIG. 1, other optional modifications to the housing such as a cable passthrough 7 and an inlet for the patient to fit their nose 3.

B. Optical Assembly

[0030] The optical assembly shown in FIG. 2 present in the invention contains a set of at least one static lens, arranged in a specific sequence at calculated distances away from the screen. The lenses are placed into precisely located spots, such as in 9. The purpose of the array of lenses is to project the image of the display to a virtual distance that is much further away from the patient's eyes than in physical reality. Embodiments of the invention may use one of a wide range of distances (with typical virtual distances being fifteen and twenty feet). With the image virtually projected to a distance that simulates the distance between the patient and the screen displaying the test chart in a typical optometrist's or ophthalmologist's office, the light rays emanating from any point of the display will leave the projective array being almost entirely parallel to each other. This serves to relax the accommodation reflex in the eye, such that the ciliary muscles are entirely relaxed so the far vision prescription is accurate.

[0031] Embodiments of the invention may opt to use, for the projective array component, the following formula for the effective focal length f of two thin lenses, one with focal lens f.sub.1 and the other with focal length f.sub.2, separated by a distance d:

[00001]$\frac{1}{f}=\frac{1}{f_1}+\frac{1}{f_2}-\frac{d}{f_1.Math.f_2}.$

[0032] In addition, when two thin lenses are placed in sequence, there is a plane known as the real principle plane, which is the virtual location of a single lens with the effective focal length (calculated using the method above) that has the same effect on light rays as the two lenses in sequence. To calculate the distance p between the first lens (the lens through which light passes first) and the real principle plane, the following formula can be used:

[00002]$p=d.Math..Math.\frac{f}{f_1}.$

[0033] Using these equations, any set of lenses can be recursively combined, pair by pair, until it can be effectively treated as a single lens with focal length F, located a distance D from to the front of the array (which can be taken to be the location of the lens closest to the screen) with a certain effective focal length. Once the lens system has been simplified to a single lens using the mathematics described above or some other mathematical treatment of the optical properties of the set of lenses, the following modified version of the thin lens equation may be used to calculate the distance V of the virtual image of the display from the front of the lens assembly, with S being the distance between the display and the front of the projective lens array:

[00003]$\frac{1}{F}=\frac{1}{S+D}-\frac{1}{V+D}.$

[0034] While there are infinitely many combinations of lenses and values of V that yield a virtual image sufficiently far away, a value of fifteen to twenty feet would match the common eye exam office. The methods described above or other methods may be used to calculate the positioning of the lenses relative to the display; however, all will yield the distance between the screen and the real principle plane of the combination to be slightly less than the effective focal length of the system. This yields the result of the light emanating from the display being refracted such that it enters the liquid lens component of the optical assembly virtually parallel.

[0035] The other component of the optical assembly is the liquid lens, which would be inserted in the location 8 on FIG. 2. Liquid lenses are devices that contain two transparent, immiscible liquids of different refractive indices, one a polar liquid and the other a nonpolar liquid. When an electric potential is applied across the two liquids, the curvature of the boundary between the two liquids changes. In a liquid lens, these two liquids and electrodes are enclosed in a cylindrical housing with clear apertures on the front and back, such that light passes through and is refracted at the boundary. By applying different voltages, the light will refract to different degrees, effectively resulting in a lens with variable power.

[0036] A liquid lens would be located in behind the optical assembly, and during use, the patient looks through the liquid lens as the algorithm that is described hereinafter runs. The optical assembly fits into (or is manufactured directly on) the housing at 6.

C. Display

[0037] Located just beyond the optical assembly (from the patient's perspective) at position 1 in FIG. 1 is the display. The display is mounted either within the housing or outside of the housing, with a clear path such that it can be seen through the optical assembly. The display has a number of responsibilities.

[0038] During use, in which an eye test is being conducted on a patient, the display shows a graphic that the patient uses to subjectively determine clarity. The mechanics of an algorithm that may be used in an embodiment of the invention are described hereinafter, but the patient compares at least two lens voltages and provides feedback to the system as to which one makes the graphic appear clearer to them. The graphic may be any image or computer generated graphic; the most common and recommended graphic is a test chart defined by the LogMAR standard, which prescribes rows of optotypes that are logarithmically sized and logarithmically spaced. Each optotype should have strokes that are equal in width, and each letter should be equally legible. It is also recommended that the graphic be frequently switched throughout the test to prevent eye fatigue.

[0039] The display should notify the patient that their selection was recorded successfully with a graphic, such as a checkmark.

[0040] At the end of the test, the display should read out the final lens voltage and the prescription refractive power for that eye.

D. Electronics System

[0041] In order to control the display and lens, as well as run the algorithm described below, the invention requires an electronic system. There are a number of necessary components of this electronic system.

[0042] The Liquid Lens Driver is an integrated circuit (IC) capable of controlling the liquid lens. This IC would input the voltage supplied by a direct-current battery in the device (likely a five volt supply) as well as commands from the Liquid Lens Instructor, and outputs a PWM (pulse-width modulation) signal to the liquid lens such that the root-mean-square voltage is in the range of electrical potentials that allows the lens to modulate its optical power throughout the full range of powers.

[0043] The Liquid Lens Controller is a microprocessor-based computing unit that provides the Liquid Lens Driver with commands that correspond to specific desired output voltages. The Liquid Lens Controller, in turn, takes input from the Algorithmic Processing Unit as to exactly what voltages to instruct the Driver to apply to the liquid lens.

[0044] The Algorithmic Processing Unit is a microprocessor-based computing unit that runs the Power Determination Algorithm described hereinafter, instructing the Liquid Lens Controller to command the Driver to apply whatever desired voltage the current stage of the algorithm requires. It also takes input directly from the patient, as described in the details of the algorithm.

[0045] The Display Controller is a microprocessor-based computing unit that controls the display to display both the reference graphics specified earlier and display data produced by the Algorithmic Processing Unit.

[0046] All of these components together serve as the electronics unit of the device. Note that, while they are described as discreet units, they may exist in any combination of the units. For instance, multiple microprocessing units described may be implemented on the same logic board or even within a singular, specialized integrated circuit. Locations for electronics mounting can bee seen in FIG. 1 at positions 4 and 5. They may also share or individually use any set of batteries, which may be located inside the housing or attached to it 2. Portions of the electronics may also be packaged with the display itself, as may be the case in the application of a widescreen mobile phone.

E. Power Determination Algorithm

[0047] As mentioned previously, some component the electronics system must run an algorithm that takes patient feedback in order to, throughout the course of the test, present the patient with lens voltages that provide clearer and clearer vision, until the voltage that provides the subjective clearest vision is found.

[0048] Embodiments of the invention may implement one of many variations of the following algorithm. In each cycle, the algorithm should generate a set of lens voltages. Any two voltage in the set should be separated by a certain coarse increment. The patient, by interacting with a button wired to the electronics system or a remote control connected to the system, should be able to switch between each of the voltages in the set; the electronics system should control the liquid lens to apply that voltage. The patient, once inspecting all voltages in the set, should choose the one that provides the clearest vision. Then, the algorithm should use the selected voltage to generate a new set. If the patient selects a voltage that is more extreme than any prior voltage, the new set should contain voltages more extreme than any prior voltage. If the patient selects a voltage that is less extreme than certain previously displayed voltages, this indicates that the algorithm has found an approximate range of voltages that provides the clearest vision. As such, the algorithm should decrease the size of the voltage increment, making the adjustments finer, and generate a new set to sweep the approximate range.

[0049] This process should continue until a value that provides the clearest vision is found using a voltage increment that is smaller enough than the patient can no longer discern changes. In practice, this will correspond to an increment in prescription power of approximately one-quarter diopter.

[0050] Once this clearest voltage has been determined, it should be used as the input of a calibrated regression which calculates the prescription lens power for that eye of the patient.

F. Calibration

[0051] In order to determine this regression, a number of samples with the embodiment of the invention should be conducted. Patients with a range of refractive error should be tested in both eyes to determine the voltage that provides that eye with that the clearest vision in that specific embodiment of the invention. Patients should also receive prescriptions from a standard phoropter. Then, mathematical regressions can be used on the data, with the independent variable being the voltage and the dependent variable being the prescription power determined by the standard phoropter prescription, which is taken to be the exact value for that patient. The regression will likely be linear, but others fall within the scope of the invention.

[0052] Once this regression has been found, the software algorithm can be updated to automatically calculate the prescription power from the final voltage.