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The refraction test is an eye exam that measures a person's prescription for eyeglasses or contact lenses.
Alternative NamesEye test - refraction; Vision test - refraction
How the test is performedThis test is performed by an ophthalmologist or optometrist, or "eye doctor."
You sit in a chair that has a special device (called a phoroptor or refractor) attached to it. You look through the device and focus on an eye chart about 20 feet away. The device contains lenses of different strengths that can be moved into your view.
The eye doctor performing the test will ask if the chart appears more or less clear when different lenses are in place.
How to prepare for the testIf you wear contact lenses, ask the doctor how long they should be left out before the test.
How the test will feelThere is no discomfort.
Why the test is performedThis test can be done as part of a routine eye test to determine if a person has normal vision.
When a person complains of blurred vision, this test can help determine the extent of poor vision. It can also be done to monitor a person who is being treated for an eye disease.
The test is used to prescribe glasses, if needed. It also will determine if you need bifocals.
Normal ValuesA normal value is 20/20 vision (perfect vision - able to read 3/8 inch letters at 20 feet). A small type size is also used to determine normal near vision.
What abnormal results meanAbnormal results may be due to:
- Astigmatism
- Hyperopia (farsightedness)
- Myopia (nearsightedness)
- Presbyopia (inability to focus on near objects that develops with age)
Additional conditions under which the test may be performed:
- Corneal ulcers and infections
- Macular degeneration
- Retinal detachment
- Retinal vessel occlusion
- Retinitis pigmentosa
There are no risks.
Special considerationsA complete eye examination should be done every 3 - 5 years if there are no problems. If vision becomes blurry, worsens, or if there are other noticeable changes, an eye examination should be scheduled immediately.
After age 40 (or for people with a family history of glaucoma), eye examinations should be scheduled more frequently to test for glaucoma. Anyone with Diabetes should have an eye exam at least once a year.
People with refraction problems should have an eye examination every 2 - 3 years.
ReferencesYanoff M, Duker JS, Augsburger JJ, et al. Ophthalmology. 2nd ed. St. Louis, Mo: Mosby; 2004:71-77.
Behrman RE. Nelson Textbook of Pediatrics. 17th ed. Philadelphia, Pa: WB Saunders; 2004; 2084-2085.
What else can I help you with?
What is an optical refraction test?
An optical refraction test is a procedure performed by an eye care professional to measure how your eyes refract light. This test helps determine your prescription for glasses or contact lenses by assessing how well your eyes focus and how strong of a lens correction you may need.
How is astigmatism diagnosed?
The standard eye examination with a refraction test, given by an optometrist or ophthalmologist, is used
Which principle of light behavior does a telescope use?
It would be reflection, if you are doing a study island test. :)
Which of the following values represents an index of refraction of an actual material A 0 B1 4 C 1 2 D 5 4?
Index of refraction values are typically greater than 1 for actual materials. Therefore, value B - 1.4 could represent the index of refraction of an actual material. Values A, C, and D are not realistic index of refraction values for materials.
What are difficulties in measuring the angle of refraction for large angles of incidence?
Difficulties in measuring the angle of refraction for large angles of incidence include inaccuracies due to significant refraction occurring close to the critical angle, which can lead to total internal reflection instead of refraction. Additionally, there may be challenges in distinguishing the refracted ray from the reflected ray, especially when using equipment with limited precision. Finally, for very large angles of incidence, the refraction angle may become difficult to measure accurately due to the rapid change in direction of the refracted ray.
What has the author Frank William Marlow written?
Frank William Marlow has written: 'The relative position of rest of the eyes and the prolonged occlusion test' -- subject(s): Accommodation and refraction, Eye
How can you test a rainbow?
A rainbow is a natural phenomenon caused by the reflection, refraction, and dispersion of light in water droplets, usually after a rain shower. You cannot test a rainbow in a traditional scientific sense, but you can observe, photograph, and study it to understand its formation and properties.
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How can the refractive index of water in a glass bottle be determined?
Perhaps the easiest way to determine this would be by using Snell's law. This requires that you shine a beam of light incident at some angle to the normal of your bottle (let this angle be "theta 1", or Th1). By then observing where the beam of light is refracted to once inside the bottle, you can then measure a second angle to the normal, this time inside the bottle (Th2). You can then use Snell's law to equate n1*sin(Th1)=n2*sin(Th2), where n1 and n2 are the indices of refraction of your two respective media. Since the index of refraction of air is known (n1=1.0002926 at standard conditions, it is often approximated as 1), and the two angles are known, you can then solve for the remaining unknown, n2, the index of refraction of water. It is likely that for best accuracy you will want to test this at various angles of the incident light, which would then allow you to take an average of your calculated values for n2, which is likely more correct than a single measurement. Light will be refracted by the glass of the bottle, but luckily the light leaves the glass at the same angle that it entered it at, and the refraction effects at both sides of the glass interface cancel out and can be ignored in calculating the index of refraction of water
When a glass rod is immersed in the colourless liquid the glass rod seems to be deappeared why?
Hey! The reason it seems to disappear is because of the refraction and absorption of light and colour. When light enters the colourless liquid, colour is obviously absorbed. The light waves refract ("bounce") off the glass test tube and leave the glass beaker (containing the colourless liquid). Because the liquid and solid are the same colour, it creates the illusion of the test tube disappearing.
What is considered normal eye vision and how can it be measured or assessed?
Normal eye vision is typically defined as 20/20 vision, which means a person can see at 20 feet what a person with normal vision can see at 20 feet. This can be measured through a visual acuity test, where a person reads letters on a chart from a specific distance. Other assessments may include a refraction test to determine the need for corrective lenses, and a visual field test to check peripheral vision. Regular eye exams are important to monitor and maintain good eye health.
Why does a test tube filled with glycerol disappear in a beaker filled with glycerol?
Glycerin has essentially the same refractive index as glass, so any light passing through the two is bent equally. Since both are transparent it's not possible for your eye to distinguish the boundary by a change in the angle of refraction, and the glass seems to vanish.
