1 or 2?
We don't know whether the question has been asked for hundreds or thousands of years. We do know that it creates unneccesary anxiety for many patients. Luckily, there is new technology attempting to eliminate the need for this question. This article will discuss the process of refraction (1 or 2 test), how it can be simplified to reduce anxiety, and how new technology measures up in its attempt to make it easier and more accurate.
Using the traditional methods of refraction I say "is 1 or 2 better" 150 to 600 times per day. Needless to say, I've put a lot of thought into making the test easier for patients and my vocal cords. I will compare the old fashioned methods with new technology available today.
The traditional (old) process of refraction begins with gathering data. A lensometer is used to measure to correction in the current spectacle prescription. Visual acuity with the spectacles on can be used to estimate how far the prescription is off. Keratometry can be used to measure the curvature of the cornea to estimate location and magnitude of astigmatism. Retinoscopy can be used without spectacles to get a more accurate estimate of the eye's current prescription.
For retinoscopy, a patient sits behind the phoropter and looks at the eye chart while the Eye Doctor focuses a beam of light on the retina. The beam moves the same direction the Eye Doctor directs it when more plus power (less nearsighted) power is needed. The beam moves opposite the direction it was directed when more minus (more nearsighted) power is needed. When different orientations of the beam focus different powers this means astigmatism is present. Once this data is gathered we can begin the refraction (1 or 2 test).
The first part of the 1 or 2 test tries to optimize clarity using sphere. This is the amount of near or farsighted prescription present. When checking sphere the entire image is moved forward and backward from the macula of the retina. For those who are nearsighted the uncorrected image is focused in front of the retina. Minus or nearsighted correction moves the image back to the retina to clarify the image. For those who are farsighted the uncorrected image would focus too far behind the retina. The plus or farsighted lenses move the image forward onto the retina.
During the sphere changes most patients can tell the difference in clarity between the two options. If too much minus power is used the image may appear to shrink in size. Too much plus power can make the images look larger. The most important thing to tell your Eye Doctor is if the image is more or less clear, but if its the same let them know if the size of the image is changing. It could make your new prescription more comfortable and speed up the test.
Once the sphere has been found you will likely hear a different sounding click. This is the Jackson cross cylinder (JCC) clicking into place for the second part of the 1 or 2 test. This step refines the axis or location of astigmatism. The axis is the orientation with the flatest course across the cornea. This part of the test can be tough, especially for patients with small amounts of astigmatism. The closer we get to the location of the astigmatism (axis) the more difficult the choices are. Let your Eye Doctor know when the images look the same, this is when you've reached the desired endpoint or location of the axis.
To start the third and final portion of the 1 or 2 test there is another click as the Eye Doctor shifts the JCC from checking for axis to checking for cylinder or amount of astigmatism. The best letters to focus on are the circular letters O,C, and G. Circular letters are less susceptible to error from astigmatism. Try choosing the option with best clarity and least distortion (streching, shadowing, etc.). Once again the choices become progressively more difficult to distinguish between, so when the options look the same let your Eye Doctor know.
You've passed the 1 or 2 test with flying colors. Your Eye Doctor should supply you with your prescription from the exam. The top set of numbers are for the right eye or OD, and the bottom set of numbers are for the left eye. If a third set of numbers is present below preceded by "Add" this is the reading prescription. The first number in the set is the sphere (-- for nearsighted and + for farsighted). The second number is the cylinder or amount of astigmatism (-- Optometrist script and + for Ophthalmologist script), and the last number is the axis or location of astigmatism.
New methods utilize shortcuts to obtain the same information. Lensometers are now automated to obtain spectacle prescription readings faster. The machine with a picture inside of it is the autorefractor. The autorefractors obtains the same data keratometer and retinoscopy in a fraction of the time. This speeds up the exam and provides a more accurate starting point.
New autorefractors can take wavefront calculations. Wavefront technology takes an extremely precise reading of the curvature of the cornea. It is the technology the produces the calculations needed for modern LASIK (laser assisted insitu keratomileusis) procedures. Modern refraction systems can use wavefront to supply a spectacle or contact lens prescription. In practice, I have noticed three refraction systems which seem to boast the latest and greatest technology available.
Three of the top systems today are the Marco 3D wave / Epic 2100 system, the Veatch OWRx and Vmax PSF. All 3 systems take wavefront readings and utilize them in a computerized refraction. The refractions from these systems can be customized to 0.05 diopters (traditional methods only go to 0.25D). The Vmax PSF system does away with letters. With the Vmax system patients look at a dot and report when distortion is removed.
From my personal experience there is a great deal of variability from individual to individual. Some patients can appreciate small changes in prescription while others have difficulty telling the difference in 0.25D steps. From clinical studies thus far, only about 25% of patients can tell the difference between traditional refraction methods and new incredibly precise wavefront systems. New autorefraction systems help speed up the 1or 2 process a great deal and provide very accurate starting points.
Wavefront systems will play a large role in the future of eyecare. Wavefront systems can provide improved clarity to some, but for most (roughly 75% of patients) traditional methods provide prescriptions with equal clarity without a premium cost.
Summary - for the best results on your 1 or 2 test
Focus on circular letters on the chart
Choose the option that it most clear
Options can look the same, if they do report any magnification, minification, or distortion
Autorefractors speed up the exam and provide an accurate starting point
Wavefront systems provide better vision for 25% of patients, equal vision to the other 75%
Using the traditional methods of refraction I say "is 1 or 2 better" 150 to 600 times per day. Needless to say, I've put a lot of thought into making the test easier for patients and my vocal cords. I will compare the old fashioned methods with new technology available today.
The traditional (old) process of refraction begins with gathering data. A lensometer is used to measure to correction in the current spectacle prescription. Visual acuity with the spectacles on can be used to estimate how far the prescription is off. Keratometry can be used to measure the curvature of the cornea to estimate location and magnitude of astigmatism. Retinoscopy can be used without spectacles to get a more accurate estimate of the eye's current prescription.
For retinoscopy, a patient sits behind the phoropter and looks at the eye chart while the Eye Doctor focuses a beam of light on the retina. The beam moves the same direction the Eye Doctor directs it when more plus power (less nearsighted) power is needed. The beam moves opposite the direction it was directed when more minus (more nearsighted) power is needed. When different orientations of the beam focus different powers this means astigmatism is present. Once this data is gathered we can begin the refraction (1 or 2 test).
The first part of the 1 or 2 test tries to optimize clarity using sphere. This is the amount of near or farsighted prescription present. When checking sphere the entire image is moved forward and backward from the macula of the retina. For those who are nearsighted the uncorrected image is focused in front of the retina. Minus or nearsighted correction moves the image back to the retina to clarify the image. For those who are farsighted the uncorrected image would focus too far behind the retina. The plus or farsighted lenses move the image forward onto the retina.
During the sphere changes most patients can tell the difference in clarity between the two options. If too much minus power is used the image may appear to shrink in size. Too much plus power can make the images look larger. The most important thing to tell your Eye Doctor is if the image is more or less clear, but if its the same let them know if the size of the image is changing. It could make your new prescription more comfortable and speed up the test.
Once the sphere has been found you will likely hear a different sounding click. This is the Jackson cross cylinder (JCC) clicking into place for the second part of the 1 or 2 test. This step refines the axis or location of astigmatism. The axis is the orientation with the flatest course across the cornea. This part of the test can be tough, especially for patients with small amounts of astigmatism. The closer we get to the location of the astigmatism (axis) the more difficult the choices are. Let your Eye Doctor know when the images look the same, this is when you've reached the desired endpoint or location of the axis.
To start the third and final portion of the 1 or 2 test there is another click as the Eye Doctor shifts the JCC from checking for axis to checking for cylinder or amount of astigmatism. The best letters to focus on are the circular letters O,C, and G. Circular letters are less susceptible to error from astigmatism. Try choosing the option with best clarity and least distortion (streching, shadowing, etc.). Once again the choices become progressively more difficult to distinguish between, so when the options look the same let your Eye Doctor know.
You've passed the 1 or 2 test with flying colors. Your Eye Doctor should supply you with your prescription from the exam. The top set of numbers are for the right eye or OD, and the bottom set of numbers are for the left eye. If a third set of numbers is present below preceded by "Add" this is the reading prescription. The first number in the set is the sphere (-- for nearsighted and + for farsighted). The second number is the cylinder or amount of astigmatism (-- Optometrist script and + for Ophthalmologist script), and the last number is the axis or location of astigmatism.
New methods utilize shortcuts to obtain the same information. Lensometers are now automated to obtain spectacle prescription readings faster. The machine with a picture inside of it is the autorefractor. The autorefractors obtains the same data keratometer and retinoscopy in a fraction of the time. This speeds up the exam and provides a more accurate starting point.
New autorefractors can take wavefront calculations. Wavefront technology takes an extremely precise reading of the curvature of the cornea. It is the technology the produces the calculations needed for modern LASIK (laser assisted insitu keratomileusis) procedures. Modern refraction systems can use wavefront to supply a spectacle or contact lens prescription. In practice, I have noticed three refraction systems which seem to boast the latest and greatest technology available.
Three of the top systems today are the Marco 3D wave / Epic 2100 system, the Veatch OWRx and Vmax PSF. All 3 systems take wavefront readings and utilize them in a computerized refraction. The refractions from these systems can be customized to 0.05 diopters (traditional methods only go to 0.25D). The Vmax PSF system does away with letters. With the Vmax system patients look at a dot and report when distortion is removed.
From my personal experience there is a great deal of variability from individual to individual. Some patients can appreciate small changes in prescription while others have difficulty telling the difference in 0.25D steps. From clinical studies thus far, only about 25% of patients can tell the difference between traditional refraction methods and new incredibly precise wavefront systems. New autorefraction systems help speed up the 1or 2 process a great deal and provide very accurate starting points.
Wavefront systems will play a large role in the future of eyecare. Wavefront systems can provide improved clarity to some, but for most (roughly 75% of patients) traditional methods provide prescriptions with equal clarity without a premium cost.
Summary - for the best results on your 1 or 2 test
Focus on circular letters on the chart
Choose the option that it most clear
Options can look the same, if they do report any magnification, minification, or distortion
Autorefractors speed up the exam and provide an accurate starting point
Wavefront systems provide better vision for 25% of patients, equal vision to the other 75%
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