A phoropter can measure refractive error to determine an individual's spectacle lens prescription during an eye examination.Side of a phoropter that faces the patient
Typically, the patient sits behind the phoropter, and looks through it at an eye chart placed at optical infinity (20 feet or 6 metres), then at near (16inches or 40 centimetres) for individuals needing reading glasses. The eye care professional then changes lenses and other settings, while asking the patient for subjective feedback on which settings gave the best vision. The patient's habitual prescription or an automated refractor may be used to provide initial settings for the phoropter. Sometimes a retinoscope is used through the phoropter to measure the vision without the patient having to speak, which is useful for infants and people who do not speak the language of the practitioner.
Phoropters can also measure heterophorias (natural resting position of the eyes), accommodative amplitudes, accommodative leads/lags, accommodative posture, horizontal and vertical vergences, and more.
The American Optical Ultramatic RxMaster of 1967
The major components of the phoropter are the battery of spherical and cylindrical lenses, auxiliary devices such as Maddox rods, filtered lenses, prisms, and the JCC (Jackson cross cylinder) used for astigmatism measurement. The prismatic lenses are used to analyze binocular vision and treat orthoptic problems.
From the measurements taken, the specialist will write an eyeglass prescription that contains at least three numerical specifications for each eye: sphere, cylinder, and axis, as well as pupillary distance (distance between eyes), and, rarely, prism for one or both eyes.
The lenses within a phoropter refract light in order to focus images on the patient's retina. The optical power of these lenses is measured in 0.25 diopter increments. By changing these lenses, the examiner is able to determine the spherical power, cylindrical power, and cylindrical axis necessary to correct a person's refractive error. The presence of cylindrical power indicates the presence of astigmatism, which has an axis measured from 0 to 180 degrees away from being aligned horizontally.
Phoropters are made with either plus or minus cylinders. Traditionally, ophthalmologists and orthoptists use plus cylinder phoropters and optometrists use minus cylinder phoropters. One can mathematically convert figures obtained from either type of phoropter to the other.
Trademark and origin of the term
Phoroptor is a registered trademark currently owned by Reichert Technologies, filed Apr 25, 1921, by DeZeng Standard of New Jersey, with the USPTO, serial number 71146698. The word was coined at that time for the newest version of their phoro-optometer. DeZeng was purchased in 1925 by American Optical of Massachusetts, which continued to market the product, but the term, often spelled phoropter, has become a generic trademark for all brands of modern vision testers, especially since AO's main competitor, Bausch and Lomb, stopped making their Greens' Refractor in 1970s. Reichert bought AO's refracting equipment division in 1980s, and their current version is named "Ultramatic Rx Master Phoroptor".
History
Very early phoropters. Top, the 1917 Woolf Ski-Optometer of New York City, with cylinder.; bottom, the 1915 DeZeng Phoro-Optometer model 570, Camden, NJ. The mounting arms on both devices attached at the bottom.
The history of the phoropter, as a binocular refracting device which can also measure phorias, ductions, and other traits of binocularity, as distinct from the monocular optometer, which cannot, starts in the mid-1910s, with the introduction of the Ski-optometer by Nathan Shigon, and the Phoro-optometer by Henry DeZeng. These two inventions, as they continued to improve, were accompanied by a third device, the Greens' Refractor, which entered the market in 1934. European manufacturers were working on similar devices as well.[2]
Shigon/Woolf/Genothalmic/Shuron/BRU
In 1909, Nathan Shigon of New York City invented[3] a monocular optometer with a range of +0.25 to +6.00 diopters, consisting of a mechanism where a disc of low-powered lenses advanced a second disc of higher power lenses automatically with each rotation, as in a modern phoropter.
There is no evidence this was ever manufactured, but in 1915 he filed for a patent for a binocular version of this same optometer,[4] and called it the Ski-Optometer, so named for its usefulness in doing skiascopy . This was manufactured by Wm. F. Reimold of Philadelphia. It included a Stevens Phorometer for measuring phorias, and a disc of auxiliary spherical lenses on the back, giving it a range of -12.00 to +12.00. To extend the range, there were clips on the front of each eye hole for the insertion of hand held sphere or cylinder trial lenses, with a mechanism to rotate the axis with the thumb. It weighed 2 lb. 3 oz.
Around 1916 Michael Woolf, also of New York City, bought him out and added his own invention,[5] an innovative battery of cylinder lenses, ranging from 0.25 to 2.00 D to the device, as well as Risley prisms for each eye. Maddox rods were optional. It was also called the Ski-Optometer, and it weighed 3 lb. 13 oz.
Around 1924 the patents and rights were transferred to General Optical Company of Mount Vernon, NY, which had been making a much larger, heavier and more solidly encased instrument, called the Genothalmic Refractor, since around 1920, using Woolf's 1917 patent number, and with a user's manual dated 1921. This instrument had a range of +17.75 to - 22.50 sphere, and up to 3.75 cylinder, Maddox rods, Risley prisms, and a Steven's phorometer. It weighed 7 pounds 5 ounces, and unlike all earlier devices of this kind, it hung from a horizontal mounting bar instead of being supported from the bottom. Like the Woolf, it had no Jackson cross-cylinders (JCC) at first, so a separate hand-held one was required. Late models of the Genothalmic were fitted with JCCs.
General Optical sold out to Shuron Optical of Geneva, New York, in 1927, which sold the refractor until the late 1930s.[2] A refined and improved version of the Genothalmic Refractor was manufactured in London starting around 1932, and sold in the UK by S. R. Stearman, S. Pulzer & Son Ltd., and others, as the British Refracting Unit (B.R.U.).
DeZeng/American Optical/Reichert
The early DeZeng/AO lineage. Top row: Model No. 570, 1917 or earlier, No. 584, 1922. Bottom row: No. 589, 1934, No. 590, 1948.
Also in 1909, Henry DeZeng got a patent for what looks remarkably like a modern phoropter,[6] but the patent illustrations look nothing like the manufactured product, which was introduced around 1915—the DeZeng Phoro-Optometer model 570. This was a device produced in Camden, New Jersey, which contained a battery of convex lenses for each eye, a battery of concave lenses for each eye, and auxiliary lenses which gave it a total power range of +15.75 to -19.75, as well as a Maddox rod and Risley prism for each eye, and a Steven's phorometer.
There were no cylindrical lenses, so testing for astigmatism required the use of manual trial-lenses, for which there were rotating holders on the front of each eye hole, and there were stationary ones on the backs as well. Cross-cylinders were optional, but they did not flip like a Jackson cross cylinder, they rotated in the same plane, so they were probably meant for the near point cross-cylinder test for reading.[7] It weighed 3 lb. 2 oz. Around 1920 an improved model, No. 574, was introduced, reduced in size but with the same range (lenses reduced from 1 inch to 3⁄4 inch). The forehead rest was removed, and the rear trial lens clips were replaced with rubber eye guards. It weighed 2 lbs. 12 oz.
In 1922, DeZeng replaced No. 574 with No. 584, and shortened the name to Phoroptor. This device became so popular that its name became genericized, though often spelled phoropter. The Phoroptor was smaller (lenses reduced again, to 9/16 inch diameter), with a similar power range, and the front clips for hand-held trial lenses were removed and replaced with batteries of cylinder lenses ranging from 0.25 D to 4.75 D. The Steven's phorometer was dropped, and there were no Jackson cross cylinders. It weighed 2 lb. 8 oz.
In 1925, American Optical bought DeZeng, and in 1927 introduced No. 588, the AO Wellsworth DeZeng Phoroptor, which was slightly larger; the lenses were increased to 11/16 inch and it weighed 3 lb. 2 oz. This was the first in the DeZeng/AO line to hang from a horizontal mounting bar, the earlier ones were supported from a bar below it. This phoroptor was unique in that it was calibrated in 1/8 diopter steps throughout its whole range.
In 1934, AO introduced No. 589, the Additive Effective Power Phoroptor, once again enlarged and improved. The lenses were increased to 3⁄4 inch diameter, the permanent size, and the unit was much more massive, with a weight of 7 lb. 9 oz., and with a range of +16.87 to -19.12 sphere and 6.00 cylinder, with auxiliary lenses to increase these to +18.87/-21.12 sphere and 8.00 cylinder. All these models resembled the original DeZeng model in design, but No. 590 of 1948 was a completely re-designed device, much larger and heavier, and more modern. It weighed 10 lbs. 7 oz. This was followed by another complete re-design in 1956, the RxMaster,[2] which became the prototype of all modern phoropters, and was updated to the Ultramatic RxMaster in 1967, which is the current model.
AO sold their phoroptor division to Reichert in 1982, who still make the Ultramatic.
Greens'/Bausch and Lomb
What was available in 1934. Top left, the Genothalmic Refractor; top right, the AO 589 Phoroptor; bottom, the B&L Greens' Refractor, still much in use today.
In the early 20th century, ophthalmologists A. S. Green, L. D. Green, and M. I. Green, of San Francisco, CA, designed an optometer,[8] which they developed slowly over many years. The Greens teamed up with inventor Clyde L. Hunsicker of San Francisco, who applied for a patent on October 25, 1926. The title of their invention was simply an "optometrist instrument", and the text described it as an optometer. Patent 1,804,690 was granted to the Greens and Hunsicker in 1931, and sold to Bausch & Lomb (B&L), which had them redesign it (patent 1,873,356, granted 1932).
B&L trademarked it as "Greens' Refractor" and introduced it in 1934. It was far more advanced than the competition in many ways. The power could be read right off the dial without having to do mental calculations, the range was far higher, from +19.75 to -28.00 and with cylinders up to 7.50, the battery of cylinders was much more intuitive and easy to use, and it was the first to have Jackson cross cylinders affixed, (the first AO Phoroptors with JCC's were late models of the Additive, and very late Genothalmic Refractors also had them). It weighed 13 lbs. 1 oz. The Greens' Refractor soon became the gold standard among eyecare professionals. It helped put the Shigon/Woolf/Genothalmic line out of the market and forced AO to completely redesign their phoroptor from scratch, not once, but twice, (the 590 failed to compete).
The Greens' Refractor remained unchanged for over four decades, but sales slipped when AO introduced the Ultramatic RxMaster with its revolutionary yoked JCC in 1967, and production of the Greens' Refractor finally ended in the mid-1970s. In 1978, B&L introduced the Greens II refractor, also called the Bausch and Lomb Refractor, or the Greens' Mark II Refractor.[9] It included yoked JCC, but AO had already patented the yoking of the JCC, and production of the Greens' II was halted. Very few were made, and they are a rarity. It weighed 11 pounds 13 ounces. As for the original Greens' Refractor, in spite of the fact that production stopped decades ago, many are still being used today, as they are virtually indestructible, and have a devoted rank who still swear by them.[2]
Europe and Asia
Starting in the mid-20th century, companies in Europe and Asia have made phoropters of their own design, as well as copied American models. The Moeller Wedel Visutest of Germany, the Magnon RT 500 of France, and the Nikon Optester and Takagi MT3, both of Japan, are all of original design. The Topcon VT S of Japan is of original design, but Topcon has also made knock-offs of the Greens' Refractor and the AO Ultramatic. Rodenstock in Germany has developed many of their own models, as well as copied the Ultramatic with their Phorovist 200. The Marco RT-300 of Japan is an original design which borrows heavily from the Ultramatic. In the 1930s, Stearman in the UK and Ellis Optical Co., also in the UK, both made an improved version of the Genothalmic Refractor called the British Refracting Unit, and Stearman also made a knockoff of the Greens Refractor. China makes numerous unbranded knockoffs of the Ultramatic.
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.
Bausch + Lomb is an eye health products company based in Vaughan, Ontario, Canada. It is one of the world's largest suppliers of contact lenses, lens care products, pharmaceuticals, intraocular lenses, and other eye surgery products. The company was founded in Rochester, New York, in 1853 by optician John Bausch and cabinet maker turned financial backer Henry Lomb. Until its sale in 2013, Bausch + Lomb was one of the oldest continually operating companies in the United States.
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes when viewing distant objects. Most binoculars are sized to be held using both hands, although sizes vary widely from opera glasses to large pedestal-mounted military models.
A dioptre or diopter is a unit of measurement with dimension of reciprocal length, equivalent to one reciprocal metre, 1 dioptre = 1 m−1. It is normally used to express the optical power of a lens or curved mirror, which is a physical quantity equal to the reciprocal of the focal length, expressed in metres. For example, a 3-dioptre lens brings parallel rays of light to focus at 1⁄3 metre. A flat window has an optical power of zero dioptres, as it does not cause light to converge or diverge. Dioptres are also sometimes used for other reciprocals of distance, particularly radii of curvature and the vergence of optical beams.
An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient. If an eye examination indicates that corrective lenses are appropriate, the prescriber generally provides the patient with an eyewear prescription at the conclusion of the exam.
An optician, or dispensing optician, is a technical practitioner who designs, fits and dispenses lenses for the correction of a person's vision. Opticians determine the specifications of various ophthalmic appliances that will give the necessary correction to a person's eyesight. Some registered or licensed opticians also design and fit special appliances to correct cosmetic, traumatic or anatomical defects. These devices are called shells or artificial eyes. Other registered or licensed opticians manufacture lenses to their own specifications and design and manufacture spectacle frames and other devices.
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a-) meaning "without" and στίγμα (stigma), "a mark, spot, puncture".
Gradient-index (GRIN) optics is the branch of optics covering optical effects produced by a gradient of the refractive index of a material. Such gradual variation can be used to produce lenses with flat surfaces, or lenses that do not have the aberrations typical of traditional spherical lenses. Gradient-index lenses may have a refraction gradient that is spherical, axial, or radial.
A telescopic sight, commonly called a scope informally, is an optical sighting device based on a refracting telescope. It is equipped with some form of a referencing pattern – known as a reticle – mounted in a focally appropriate position in its optical system to provide an accurate point of aim. Telescopic sights are used with all types of systems that require magnification in addition to reliable visual aiming, as opposed to non-magnifying iron sights, reflector (reflex) sights, holographic sights or laser sights, and are most commonly found on long-barrel firearms, particularly rifles, usually via a scope mount. The optical components may be combined with optoelectronics to add night vision or smart device features.
An optical instrument is a device that processes light waves, either to enhance an image for viewing or to analyze and determine their characteristic properties. Common examples include periscopes, microscopes, telescopes, and cameras.
An otoscope or auriscope is a medical device which is used to look into the ears. Health care providers use otoscopes to screen for illness during regular check-ups and also to investigate ear symptoms. An otoscope potentially gives a view of the ear canal and tympanic membrane or eardrum. Because the eardrum is the border separating the external ear canal from the middle ear, its characteristics can be indicative of various diseases of the middle ear space. The presence of earwax (cerumen), shed skin, pus, canal skin edema, foreign body, and various ear diseases can obscure any view of the eardrum and thus severely compromise the value of otoscopy done with a common otoscope, but confirm the presence of obstructing symptoms.
In optics, optical power is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the focal length of the device: P = 1/f. High optical power corresponds to short focal length. The SI unit for optical power is the inverse metre (m−1), which is commonly called the dioptre.
A lensmeter or lensometer , is an ophthalmic instrument. It is mainly used by optometrists and opticians to measure the back or front vertex power of a spectacle lens and verify the correct prescription in a pair of eyeglasses, to properly orient and mark uncut lenses, and to confirm the correct mounting of lenses in spectacle frames. Lensmeters can also verify the power of contact lenses, if a special lens support is used.
A cylindrical lens is a lens which focuses light into a line instead of a point, as a spherical lens would. The curved face or faces of a cylindrical lens are sections of a cylinder, and focus the image passing through it into a line parallel to intersection of the surface of the lens and a plane tangent to it along the cylinder's axis. The lens converges or diverges the image in the direction perpendicular to this line, and leaves it unaltered in the direction parallel to its cylinder's axis.
Eye care professionals use prism correction as a component of some eyeglass prescriptions. A lens which includes some amount of prism correction will displace the viewed image horizontally, vertically, or a combination of both directions. The most common application for this is the treatment of strabismus. By moving the image in front of the deviated eye, double vision can be avoided and comfortable binocular vision can be achieved. Other applications include yoked prism where the image is shifted an equal amount in each eye. This is useful when someone has a visual field defect on the same side of each eye. Individuals with nystagmus, Duane's retraction syndrome, 4th Nerve Palsy, and other eye movement disorders experience an improvement in their symptoms when they turn or tilt their head. Yoked prism can move the image away from primary gaze without the need for a constant head tilt or turn.
Subjective Refraction is a technique to determine the combination of lenses that will provide the best corrected visual acuity (BCVA). It is a clinical examination used by orthoptists, optometrists and ophthalmologists to determine a patient's need for refractive correction, in the form of glasses or contact lenses. The aim is to improve current unaided vision or vision with current glasses. Glasses must also be comfortable visually. The sharpest final refraction is not always the final script the patient wears comfortably.
The optometer was a device used for measuring the necessary spherical and/or cylindrical corrections to be prescribed for eyeglasses, from the middle of the 18th century until around 1922, when modern instruments were developed. The term, coined in 1738 by W. Porterfield to describe his Scheiner slit optometer, and used for 200 years to describe many different inventions to measure refractive error of the eye, has completely fallen out of usage today as the task of measuring eyes for spectacles is done with modern instruments, such as the phoropter.
Ernest Edmund Maddox was a British surgeon and ophthalmologist. He was a specialist in abnormal binocular vision and phorias. He made advances in optical treatments and invented several devices to better investigate eye conditions, including Maddox rod, double prism Maddox, red glass Maddox, Maddox cross and Maddox wing. As a keen amateur astronomer he also invented the starfinder, a device to home in on stars and constellations.
The Jackson cross cylinder (JCC) is an instrument used by ophthalmologists, orthoptists and optometrists in their routine eye examination, particularly in determination of corrective lens power in patients with astigmatism. It is also used for testing near point of the eye.
An Uppendahl prism is an erecting prism, i.e. a special reflection prism that is used to invert an image. The erecting system consists of three partial prisms made of optical glass with a high refractive index cemented together to form a symmetric assembly and is used in microscopy as well as in binoculars technology.
References
↑ Dictionary.com, Definition of "phoropter", American Heritage Stedman's Medical Dictionary. Retrieved 10-10-10.
1 2 3 4 "Phoroptors, Early American Instruments of Refraction, and Those Who Used Them", Gary L. Campbell O.D., 2008, Wheaton, Illinois.
↑ Meyrowitz Catalogue of Ophthalmic Equipment, 6th edition, New York City, 1920
↑ Bauch and Lomb Greens' Refractor Reference Manual, date uncertain
↑ Clinical and Experimental Optometry Volume 61, 1978 - Issue 2 p. 73, 74 "The Greens' II Refractor", O. Ashley Williams
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