Patent Application
20230181031
Corrective lenses for visual deficiencies of the refractive power of the eye are commonly used. However, for many people, specifically older adults, these lenses do not fully correct for the experienced deficiencies due to inaccuracies calculating an exact prescription. Problems with night vision and driving an automobile are frequent. This need for improved vision is well established. Additionally, the number of pixels available for electronic display has increased significantly, which presents new opportunities for viewing minute details. To improve the quality of corrective optics, it is necessary to precisely determine the entire wavefront, typically expressed as wavefront deviations or optical path differences, at the exit pupil for a give object point. This description is commonly known as the pupil function. The pupil function can be determined by dividing the pupil into segments, determining the optical power of those individual segments, and then combining those values mathematically. The pupil function can then be used to enable the characterization of the entire image wavefront, from which MTF or any other quality value can be computed. MTF and other subsequent calculations enable the specification of appropriate corrective lenses in an objective manner because it deals purely with calculable measurements rather than subjective perceptions.
While there are several advanced devices to measure the refractive characteristics of an optical system having an inaccessible image, including the human eye, those devices are double pass systems in which light reflects off the image, or retina and diffuses prior to reaching the device, so those systems are unable to account for irregularities of the eye. Also, most therapeutic lenses continue to be specified according to tests where an individual is asked to identify high contrast objects, usually for a single pupil diameter or object distance; often the Snellen Chart, or one similar, is employed for this task. However, this is a subjective test because it depends on the user's judgements, meaning numerous prescriptions can be identified in numerous examinations for the same individual. Typically, these subjective tests measure a first approximation to the optical power of the eye, expressed as diopters of spherical and cylindrical optical power.
Most optical systems provide an image that is accessible by viewing through a lens. However, there are some optical systems through which a third party is unable to look and in which the image must be observed through the optical system itself, thus making it inaccessible for measurement. These are referred to as double pass systems. The eye is one such system: because the retina itself is composed of different cell layers, many of which reflect both specularly and diffusely, the wavefront at the exit pupil of the eye is not set when the image is formed, but rather continues to be modified by the observing system. Furthermore, the eye itself is neither homogeneous, nor solid, so wavefronts for forming and viewing the image are not necessarily the same. As a result, ordinary image quality tests cannot be relied on to describe the images obtained from the retina or other double pass systems. Therefore, the common practice is for vision to be tested under varying conditions from which an assessment from visual acuity is subjectively determined. There are other double pass systems which use reflected light from the retina to calculate refraction, but the light paths to and from the retina are different because irregularities in the surface of the eye make it so the ray enters one part of the pupil but leaves through another. To account for this, these systems must take an average of different refractive properties, leading to imprecise aggregate refraction measurements.
There are many patents describing devices for the purpose of measuring the refractive characteristics of the human eye, but none for any double pass optical system containing a diffusive image surface. U.S. Pat. No. 7,255,442 B2 describes a device which particularly addressed the problem of stray illumination. It includes a filtering device to reduce the size of the pupil but does not disclose any means of restricting illumination to only one segment of the pupil. U.S. Pat. No. 9,192,296 B2 describes a system having separate testing and sighting optical systems: a Hartman-Shack wavefront analyzer is described wherein the individual lenslets have short focal lengths to permit measurement of large aberrations and a provision for combining lenslets is described wherein only selected lenslets receive illumination from the retinal image. The limitations of the Hartman-Shack wavefront measuring device are also minimized by lenslet spacing and focal length. The entire pupil of the eye is filled by the illumination system, however, which provides undesirable stray light. Additionally, the natural movement of the human pupil is unaccounted for and requires unnecessary movement in the device to correct. U.S. Pat. No. 10,201,276 B2 describes a system for measuring the aberration of the eye in which a variable focal length lens is used to provide focusing under varying conditions of the eye. However, the entire pupil of the eye is illuminated, thus generating undesirable stray light. U.S. Pat. No. 9,668,651 B2 describes a system for obtaining refractive measurement of the eye objectively and subjectively. While it provides a focusing motion for refractive measurement using an angular target, it does not show segmentation of the pupil to improve measurement accuracy. U.S. Pat. No. 9,572,486 describes a system to provide objective refractometry. A separate focusing system determines accommodation, but, again, there is no segmentation of the pupil, nor is the pupil function measured directly. Furthermore, the prior art all pertains specifically to the measurement of refractive errors in the eye rather than measurements of refraction in any double pass system.
The two primary difficulties presented when observing an image formed by a double pass optical system that contains a diffusive image surface (such as the retina) are specular reflection and general scattering. If the pupil is divided into segments, each of which is represented by a center ray, then when transmitting through a segment onto the image surface and viewing through the same segment, the refraction of that center ray will be identical to the center ray viewing the image via the optical system. The issue of specular reflection is solved because the angles for forming and viewing the image are not opposite, as indicated by the well-known requirement that the angle of incidence is equal to the angle of reflection.
The concept of the invention as applied to human eye is illustrated in
A second illuminating source (216) is used for sighting and providing a change of accommodation. This source can be focused by the lens (217) to present different virtual object positions to the eye, and it can be composed of various shapes and colors because a beamsplitter (218) selectively restricts light from the source (216) so as to not be received by the sensor (213).
In its most basic embodiment, applicable to any double pass optical system containing a diffusive image surface, movement of only one lens group is required to determine the refractive power of each pupil segment. Referring to
Light from the object source transmitting through any segment and focused at (5) is reimaged by the double pass optical system under test. In the absence of defects concerning the lens of the system (such as myopia, hyperopia, presbyopia or astigmatism for the eye), an image will be formed at the optical system's diffusive surface. When the image is not formed at the diffusive surface, the moving lens group (9), part of the focusing objective (6), is moved from its nominal position and reimages the particular segment image at (5) to a virtual distance that will be focused by the system at the sensor. Because the segmented aperture stop is conjugate to the pupil, only the corresponding segment of the pupil will be illuminated. The optical design of the focusing objective (6) can have many forms. However, it must be well corrected for all pupil segments and also must image the aperture stop (4) accurately into the pupil. It can compensate for significant refractive errors, limited only by the complexity of the optical system and its manufacturing cost. The image formed at the sensor is imaged by the relay lens back toward the source, but that image path is intercepted by a beam splitter near an image sensor (2). This image sensor determines the best-focus of the focusing objective. A measure of an appropriate metric, such as point spread function can be transmitted to a focus control mechanism which then directs the focus group to move appropriately. This moving portion comprises few lens elements, whose motion is within conventional camera lens focusing technology. To increase the extent of focusing, greater complexity of the optical components and associated movements may be necessary. The movement of the lens unit (9) is calibrated according to a corresponding deviation from the position of a perfect system.
In a second configuration intended to measure the optical characteristics of an eye, a provision for sighting and testing for different accommodations may be desired, and, therefore, a second beam splitter (12) can be provided so that a sighting source (10) can be viewed by the subject. The beam splitter can be a dichroic mirror so that light projected into the system will be a different wavelength than that which is emitted by the object source. By moving a lens group (11) the sighting system provides an image at set distances from the eye, and thus allows the subject to accommodate the eye under test. The illuminated test object viewed by the subject, and formed at the retina can have different shapes and durations during the test because it is not imaged on the sensor and has a wavelength of light that is not passed by the dichroic beam splitter (12). If the sighting source is programmable, such as an LED, various types of moving targets can be used to prevent movement during the few seconds required to measure the pupil function for any accommodation distance. The programmable sighting source allows the subject to focus on a specific image, which significantly reduces the natural darting motion of the eye and enables refractive power to be calculated accurately. The whole eye views the LED sighting source, which differs from the LED object source that a single pupil segment views. Additionally, monochromatic filters must be used in the optical system of the object source, so that none of the light from the sighting source is seen by the object sensor. By using two different colors of light, monochromatic filters could eliminate any stray light entering the object source from the sighting source. In this way, the eye can be distracted by whatever image, movement or color the LED sighting source is programmed for, but this light never reaches the focus sensor of the object source because it is filtered out prior to its arrival.
Additionally, by using LEDs, the color of the object source could be modified to measure the refractive power of the eye having been exposed to different wavelengths of light. Furthermore, a programmable sighting source would allow the accommodation of the eye to be measured under different stimuli. This would be a valuable source of research to help determine the relation between refractive errors in response to different wavelengths of light and various ophthalmological diseases such as keratoconus or retinitis pigmentosa. The LED object source can also be aimed to image at various off-axis positions to provide a different angle which enables us to inspect different spots on the retina. This would provide for the comparison with respect to color and surface texture of specific locations on the retina. From these data, we could possibly detect the presence of eye related disease such as macular degeneration and retinitis pigmentosa at an early stage.
The device disclosed measures the pupil function expressed in wavefront deviations. The pupil function can be measured for different pupil openings, particularly important concerning large aberrations and for determining acuity for night vision. Also, asymmetries of a double pass optical system, and line of sight deviations can be determined using conventional computational methods of analysis and interpolation. In addition, conventional optical design software can use the pupil function for optimization of any lens to be added or inserted into the system, such as custom contact lenses for the eye. Aberrated objects and aspherical correcting lenses are well known.
A third embodiment, also meant for the eye, is shown in
A further embodiment to be used with the eye is shown in
The device described herein can be used to measure the pupil function of a fully opened pupil, and because measured wavefront data are not functionally instrument dependent, conventional optical design software can be used to add or replace components as needed to improve vision.
Optical design prescription data for the focusing objective are given in Table 1. Conventional optical design terminology is used. Each configuration represents a different focal length, object or image position.
In Table 2, the optical design prescription data are given for a symmetrical relay lens. If a reflex-type is desired, then only those lens elements on one side of the aperture stop are needed and the aperture stop surface is a mirror.
The design is limited only by chromatic aberrations which can be reduced upon the selection of the illumination wavelengths to be used in the system. There are many types of 1:1 lenses that can include an accessible segmented aperture stop, and, when designed correctly, satisfy the requirements of the invention.
A further example showing how the invention can be used to measure the refractive characteristics of the human eye employs the OSLO optical design software, available from Lambda Research Corporation, Littleton, Mass. 01460, United States. A model is set up with the BW eye from their lens database. There are other models available that more accurately represent the human eye, but this one is very simple and adequate for the following demonstration of computing procedure. The prescription data are shown in Table 3. Surface 1, as specified in the model eye specification, is modified so as to induce a focus error. In addition to the base radius change, the surface is designated at a toric having a curvature in the x direction of 0.12. In addition, the surface is rotated 45 degrees. An entrance pupil is divided into thirteen circular segments shown in
This application claims the benefit of U.S. Provisional Application No. 63/283,442, filed on Nov. 27, 2021, which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63283442 | Nov 2021 | US |
