question: How are glasses prescriptions determined and then created so precisely?
comment: The lens of your eye focuses an image on the back of your eye where it hits the retina. If it is blurry than it needs to be focused because the point where it's focused is before it hits your eye or it doesn't. That would make you nearsighted or farsighted. Those massive optometrist glasses where they ask this or this, slowly dials in exact shape of the lens needed to make that image on the back of your eye perfectly in focus. Then they just choose the exact lens shape from the pile that they have and then shape them to the frames that you chose
passages: Section::::Manufacture.
  
  Schmidt corrector plates can be manufactured in many ways. The most basic method, called the "classical approach", involves directly figuring the corrector by grinding and polishing the aspherical shape into a flat glass blank using specially shaped and sized tools. This method requires a high degree of skill and training on the part of the optical engineer creating the corrector.
   Eyeglass prescription
  
  An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist or ophthalmologist, 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 examination indicates that corrective lenses are appropriate, the prescriber generally provides the patient with an eyewear prescription at the conclusion of the exam.
   The parameters specified on spectacle prescriptions vary, but typically include the patient's name, power of the lenses, any prism to be included, the pupillary distance, expiration date, and the prescriber's signature. The prescription is typically determined during a refraction, using a phoropter and asking the patient which of two lenses is better, or by automated refractor, or through the technique of retinoscopy. A dispensing optician will take a prescription written by an optometrist or ophthalmologist and order and/or assemble the frames and lenses to then be dispensed and sold to the patient.
  
  Section::::Components of a sphero-cylindrical correction.
   In the early 20th century, Moritz von Rohr and Zeiss (with the assistance of H. Boegehold and A. Sonnefeld), developed the Zeiss Punktal spherical point-focus lenses that dominated the eyeglass lens field for many years. In 2008, Joshua Silver designed eyewear with adjustable corrective glasses. They work by silicone liquid, a syringe, and a pressure mechanism.
   The glass blank pedigree, or "melt data", can be determined for a given glass batch by making small precision prisms from various locations in the batch and measuring their index of refraction on a spectrometer, typically at five or more wavelengths. Lens design programs have curve fitting routines that can fit the melt data to a selected dispersion curve, from which the index of refraction at any wavelength within the fitted wavelength range can be calculated. A re-optimization, or "melt re-comp", can then be performed on the lens design using measured index of refraction data where available. When manufactured, the resulting lens performance will more closely match the desired requirements than if average glass catalog values for index of refraction were assumed.
   However, it was not until computerized corneal topography became available during the 1990s that it became possible to apply the theory to create designs with repeatable results through being able to accurately map the surface curvature of the cornea using a non-invasive, painless imaging procedure. Additionally, the development of new base materials for rigid gas permeable lenses which provided much higher levels of oxygen permeability opened up the possibility of orthokeratology becoming an overnight procedure rather than being used for daytime wear alone. Finally, the introduction of computer-controlled precision lathes meant that lens designs could be manufactured to sub-micrometer levels of accuracy thereby offering the prospect of high volume production becoming commercially viable.
   In the U.S., laws at the federal and state level govern the provision and effective dates of prescriptions for contact lenses and eyeglasses. Federal law requires that eyeglass and contact lens prescriptions be given to every consumer, and that the prescriptions be for a minimum of one year. (FTC Section 456.2 “Separation of examination and dispensing” was reviewed in 2004: FTC 2004 review of section 456.2)).
   An example of figuring is that used in reflecting telescope primary mirrors in a process of converting the smooth spherical mirror produced by earlier stages into the aspherical or parabolic shapes needed to form the correct image. It is done by applying different polishing stroke lengths with different sized and shaped tools. Manual figuring is a very laborious process, since the heat produced by polishing has to be allowed to dissipate before the shape of the mirror can be measured again, and the places for later polishing selected. Testing of the figure is usually done by a Foucault knife-edge test or Ronchi test in amateur telescope making and with very sophisticated null testers on research telescope optics.
   Section::::Training, licensing, representation and scope of practice.:Europe.:Germany.
  
  Optometric tasks are performed by ophthalmologists and professionally trained and certified opticians.
  
  Section::::Training, licensing, representation and scope of practice.:Europe.:Greece.
   Section::::Non-Surgical Visual Correction.:Corrective lens.:Prescription of corrective lenses.
  
  Corrective lenses are typically prescribed by an optometrist. The prescription consists of all the specifications necessary to make the lens. Prescriptions typically include the power specifications of each lens (for each eye). Strengths are generally prescribed in quarter-diopter steps (0.25 D) because most people cannot generally distinguish between smaller increments (ex. eighth-diopter steps / 0.125 D).
  
  Section::::Non-Surgical Visual Correction.:Corrective lens.:Glasses.
  
  Glasses (also called eyeglasses or spectacles) are frames bearing lenses worn in front of the eyes, normally for vision correction, eye protection, or for protection from UV rays.
   Optician
  
  An optician, or "dispensing optician", is a technical practitioner who designs, fits and dispenses corrective 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.
   August Müller (inventor)
  
  August Müller (1864 – 1949), born in Mönchengladbach, was a medical student at the University of Kiel, Germany, and a pioneer in the manufacture of contact lenses. In 1889, he presented at the university his doctoral thesis titled "Eyeglasses and corneal lenses" in which he described his efforts to grind scleral lenses from blown glass. Refinements in his process led him to be able to correct his own severe -14 dioptre myopia to within 0.50 D.
   The cornea experiences a significant degree of adaptation within hours to days, although full adaptation often requiring 2 – 3 weeks. During this initial period vision may be affected for some people. Once adapted, FDA trials showed over 65% of patients achieved 20/20 eyesight and over 90% achieved 20/40 or better (the typical US requirement for driving without glasses).
   BULLET::::- Research has confirmed that when nearsighted subjects remove their corrective lenses, over time there is a limited improvement (termed "blur adaptation") in their unaided visual resolution, even though refraction indicates no corresponding change in refractive error. This is believed to occur due to adjustments made in the visual system. One who has been practicing Bates' techniques and notices such improvement may not realize that simply leaving the glasses off would have had the same effect, which may be especially pronounced if the prescription was too strong to begin with.
   Section::::Women and the family.
   Lenses can first be designed using paraxial theory to position images and pupils, then real surfaces inserted and optimized. Paraxial theory can be skipped in simpler cases and the lens directly optimized using real surfaces. Lenses are first designed using average index of refraction and dispersion (see Abbe number) properties published in the glass manufacturer's catalog and though glass model calculations. However, the properties of the real glass blanks will vary from this ideal; index of refraction values can vary by as much as 0.0003 or more from catalog values, and dispersion can vary slightly. These changes in index and dispersion can sometimes be enough to affect the lens focus location and imaging performance in highly corrected systems.
   The base curve (usually determined from the profile of the front surface of an ophthalmic lens) can be changed to result in the best optic and cosmetic characteristics across the entire surface of the lens. Optometrists may choose to specify a particular base curve when prescribing a corrective lens for either of these reasons. A multitude of mathematical formulas and professional clinical experience has allowed optometrists and lens designers to determine standard base curves that are ideal for most people. As a result, the front surface curve is more standardized and the characteristics that generate a person's unique prescription are typically derived from the geometry of the back surface of the lens.
   The Association of Regulatory Boards of Optometry (ARBO) assists these state board licensing agencies in regulating the practice of optometry.
  
  Section::::Training, licensing, representation and scope of practice.:North America.:United States.:Licensing.
  
  Optometrists must complete all course work and graduate from an accredited College of Optometry. This includes passage of all parts of the national board examinations as well as local jurisprudence examinations, which vary by state.
  
  Section::::Training, licensing, representation and scope of practice.:North America.:United States.:Education and Training.
   DITTO
  
  DITTO is a company that sells software that aids eyewear companies sell their products online using virtual fitting. Originally DITTO was a retailer that sold designer prescription eyeglasses and sunglasses. The company used virtual fitting technology to let customers try on frames from a computer. The technology measures a user’s face by homing in on pupils, ears, cheekbones, ears and other facial landmarks, and then came back with images of dozens of different pairs of glasses that might be a good fit.
  
  Section::::History.
   Swedish goggles require complete user assembly, which results in a fit that is specifically tailored to their owner. Proper assembly generally requires some skill and practice, as well as precision. Before assembly, the inside edges of the lenses are often filed down to remove any sharp edges and thus improve comfort.
   In addition, there is an accommodating lens that was approved by the US FDA in 2003 and made by Eyeonics, now Bausch & Lomb. The "Crystalens" is on struts and is implanted in the eye's lens capsule, and its design allows the lens' focusing muscles to move it back and forth, giving the patient natural focusing ability.
   He held U.S. patent number 1,505,878 for “a new and useful Telescope” with a prism system containing “two lateral boundary surfaces, parallel to each other and an optional number of reflecting surfaces, inclined to these boundary surfaces.” This makes it possible to look “in two different directions in succession.”
   The most common way to treat forms of aniseikonia, including macropsia, is through the use of auxiliary optics to correct for the magnification properties of the eyes. This method includes changing the shape of spectacle lenses, changing the vertex distances with contact lenses, creating a weak telescope system with contact lenses and spectacles, and changing the power of one of the spectacle lenses. Computer software, such as the Aniseikonia Inspector, has been developed to determine the prescription needed to correct for a certain degree of aniseikonia. The problem with correction through optical means is that the optics do not vary with field angle and thus cannot compensate for non-uniform macropsia. Patients have reported significantly improved visual comfort associated with a correction of 5-10% of the aniseikonia.
   BULLET::::- if the cylinder power is negative, the lens is most divergent 90° from the axis
  
  BULLET::::- if the cylinder power is zero, the lens is spherical and has the same power in every meridian
  
  Section::::Components of a sphero-cylindrical correction.:Axis component.:Summary.:Sample prescription.
  
  A prescription of "−1.00 +0.25 x 180" describes a lens that has a horizontal power of −1.00 D and a vertical power of −0.75 D.
  
  Section::::Abbreviations and terms.
  
  Similar to medical prescriptions, eyeglass prescriptions are written on paper pads or included in a patient's electronic health record, and contain a number of different abbreviations and terms:
   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 (16 inches 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 don't speak the language of the practitioner.
  