1. Field of the Invention
This invention relates to optical instruments for measuring refraction of the eye and of lenses and specifically to an instrument for rapid objective refraction.
2. Description of the Prior Art
Machines to automatically and objectively measure the optics of the eye are essential for eye care, yet these machines, called “autorefractors,” are of limited use. Complexity and high price limit the use of these essential machines to perhaps less than 1% of the world's peoples.
Complexity and high prices also means these machines are used mostly in the advanced, industrial nations. Even in these rich nations, however, large populations are not reached. This includes patients of family physicians, children treated by pediatricians, and students in schools. Family physicians, pediatricians, and schools are unable to afford the high prices of these complex machines.
Most affected are children. In the U.S. an estimated one out of every 20 preschool children has a vision problem, which, if undetected and uncorrected, will affect the child's education and development. Another problem is amblyopia (“dull eye”). Vision in one eye is suppressed, and, if untreated, the child becomes blind in that eye. An estimated 3% of children in the U.S. have amblyopia. Amblyopia must be detected and treated at an early age to prevent blindness.
Adults are affected, too. Much of the world has limited eye care. In large parts of the world many people are vision impaired. Some are almost blind. For many their problem is simply poor refractive vision. The solution is autorefraction and corrective lenses. Our autorefractor provides a way to help solve these vision problems, such that people with poor refractive vision can be restored to useful, productive lives.
Conventional autorefractors typically measure how light rays are bent or “refracted.” Another method (Yancey, U.S. Pat. Nos. 5,329,322 and 5,684,561) used measurement of intensity of light. Yancey, however, neither described a method nor showed an embodiment for achieving full refraction of the eye. Full refraction is “spherocylindrical” and in addition to sphere correction must also include cylinder and axis measurements. Yancey describes a method of “foci”, which requires at least three lenses (a pupil lens and two other lenses acting as small telescopes) to look at areas (“foci”) in different areas of the eye. Yancey requires at least two detectors, and these two detectors must operate in at least two independent optical paths.
To be practical, an autorefractor must have a means of optically aligning the optics of the instrument with the optics of the eye. Additionally, where the eye is looking and focused must be controlled. Where the eye is looking and focused refers to “accommodation.” Accommodation refers to compression and change in the eye lens so as to focus on a nearby object. Conventionally, refraction requires that the eye be looking at a distant target. This target is usually at a standard distance of 20 feet (or five meters). Accommodation, focusing on a nearby object, would cause refraction of the eye to be in error. Therefore, accommodation must be controlled.
Conventional stand-mounted autorefractors typically use a series of sensors and motors to acquire the eye. Another system of sensors and motors is used for fine optical alignment. Still another, third, system of optics and motors is used to control where the eye is looking and focused. These systems are complex, bulky, and expensive.