Medical services

Computer refractometry

Computer refractometry is usually prescribed as part of a routine eye exam. This study tells the eye doctor exactly what the prescription is for a patient with glasses or contact lenses.

What is eye refractometry is an interesting question, but it does not have a very simple answer. This requires some understanding of the principles of optics. A computerized eye test machine is called an autorefractometer. The actual technologies in each machine are very different, but basically all computer refractometers have the following three properties: infrared light, the purpose of fixation, the lens.

Infrared light is used in these machines because it has the smallest scattering potential, so it can spread over long distances without scattering (for the context, a laser pointer). This is ideal for such a machine (which measures the difference in polarization).

The fixation target is used to relax the placement of the eye (focusing power of the eye). It uses the fog method to perform this action. He blurs the target image before he takes objective measurements.

The lens takes measurements. The relative distance between the lens and the eye is linearly dependent on the refractive power of the eye.

An auto refractor is a machine that measures the ability of the eyes to focus and gives a rough estimate of the state of refraction.

Physical Basics of Computer Refractometry

The actual measurement process involves sending a thin beam of infrared light into the eye, which will be reflected back from the retina. The light sensor in the car detects the polarization of the reflected light and compares it with the incident light. The lens is now shifting to equalize the polarization. The analog displacement of a defective lens is captured by the computer and converted to digital readout.

Of course, modern machines use more complex designs and principles to be more accurate, and the explanation for this is beyond the scope of this answer.

It is also necessary to understand that the autorefractometer gives an objective measurement of the refractive error, but glasses and contact lenses are given after subjective refractometry - this is the force that the patient feels comfortable with, checked by an ophthalmologist with lenses. Thus, human involvement is also required to assign points. Automated refraction just speeds up the process.

What is a refraction disorder?

Refractometry is the process that the ophthalmologist uses to measure refractive errors, or vision problems.

A refractive anomaly is an optical defect that prevents light from focusing on the retina, leading to blurred or distorted vision.

A refractive error occurs because the shape of the eye does not bend the light correctly, leading to a blurred image. Examples of refractive errors are myopia, hyperopia and astigmatism. Refractive error can lead to symptoms such as blurred vision, difficulty in reading, as well as crossing the eyes in children (esotropia).

Indications for the procedure

This test tells the doctor whether the patient needs glasses, or prescription lenses, and which prescription lenses the patient will see best.

The results of computer refractometry are used to diagnose the following conditions:

  • astigmatism, a refractive eye problem associated with the shape of the lens that causes blurred vision;
  • farsightedness, which is also known as hyperopia;
  • myopia, which is also known as myopia;
  • Presbyopia, a condition associated with aging, which causes the lens of the eye to experience problems with focusing.

Test results can help diagnose the following conditions:

  • degeneration of the macula, a condition associated with aging, which affects acute central vision;
  • retinal vessel occlusion, a condition that causes small blood vessels near the retina to block;
  • retinitis pigmentosa, a rare genetic condition that damages the retina;
  • retinal detachment when the retina is separated from the rest of the eye.

Who needs research?

Healthy adults under the age of 60 who do not experience vision problems should take a refractive test every two years. Children should take a refraction test every one to two years, starting no later than 3 years.

If the patient is wearing glasses or contact lenses, he should be examined every one to two years. This will allow the doctor to figure out which recipe is needed as the eyes change. If you have problems with vision between studies, then you need to consult a doctor for another refractive examination.

If the patient has diabetes, an examination should be carried out every year. A number of eye conditions are associated with diabetes, such as diabetic retinopathy and glaucoma. According to the American Diabetes Association, people with diabetes are at greater risk of blindness than other people.

If a patient is over 60 years old or has a family history of glaucoma, then he should also undergo computer refractometry every year. Glaucoma occurs when pressure rises in the eye, damaging the retina and optic nerve. Regular examinations will help the ophthalmologist detect diseases such as glaucoma and other eye conditions associated with aging, and, if possible, treat them early.

What happens during the study?

The patient will be asked to look at the car through two lenses in the picture, for example, on a balloon at the end of a long straight road, and focus on the picture. The machine brings and removes the balloon. In this case, the machine calculates an estimate of the need for vision correction with the results of how well the eyes focus on the image.

The doctor will first evaluate how the light rays of light move through the cornea and lens of the eye. This will help the eye doctor determine if the patient needs corrective lenses, and if so, what type of prescription is needed. The doctor may use a computerized refractor for this part of the test, or they may simply shine the light in their eyes.

In a computerized method, the patient looks into a car that measures the amount of light reflected by the retina.

A doctor can also perform this test without a machine. In this case, the doctor will direct a beam of light into each of the eyes and look at the amount of light that bounces off the retina to measure the refractive index.

Complex refractometry

During a comprehensive eye examination, the doctor uses refractometry to determine how much energy is needed to give the eyes normal, perfectly focused vision. The doctor will decide which glasses, contact lenses or laser vision correction will give the patient the most clear vision. Refractometry consists of two parts, objective and subjective.

Objective refractometry

Objective refractometry is refraction obtained without receiving feedback from the patient. Objective refraction is obtained by using different tools. The doctor will use a retinoscope or an auto-refractor to measure refraction without asking for subjective responses from the patient.


Sometimes ophthalmologists prefer to use this method, especially when trying to get accurate refraction in young children, who may distort the results of refraction by adjusting their eyes. Cycloplegic eye drops are applied to the eye to temporarily paralyze the ciliary muscle of the eye.

There are three main types of patients for whom doctors like to perform cycloplegic refraction:

  1. Children: Children tend to focus at close range and cannot control the focus when asked to look at long distances during an exam. The physician can be sure that they measure their vision correctly when performing this method.
  2. Adults with presbyopia: Presbyopia is a condition that affects the ability to focus on close objects, mainly in people over 40 years of age.
  3. Candidates for laser vision correction or other refractive surgery must undergo cycloplegic refraction so that the surgeon knows exactly which part of the vision problem should be corrected with a laser.


One of the most common tools used for objective refraction is the retinoscope. Using a retinoscope, the doctor projects the light of the pupil. The doctor can study the light reflex of the pupil. Based on the movement and orientation of this reflection of the retina, the refractive state of the eye is measured.


Another tool used for objective refraction is the autorefractor. An auto refractor is a computer tool that shines in your eyes. Light travels through the front of the eye to the back of the eye, and then back. The information bounces back to the instrument, giving an objective measure of refractive power. Autorefractors are quick and easy to use and do not require feedback from the patient.

Subjective refraction

Subjective refraction requires responses from the patient. A physician can use a phoropter to measure a subjective refractive error to determine the prescription of glasses. As a rule, the patient will sit at the phoropter and look at the eye chart. The doctor will change the lenses and other settings by giving feedback to determine which settings give the patient the best vision.

Online Refractometry

Many websites now offer online refractometry, which pretend to determine which prescription for glasses is needed. Companies claim to provide quick and easy eye examinations that will lead to a complete and accurate description of the vision needs of the eyes. Although these online tests can lead to an accurate prescription, online refractometry cannot replace professional eye health examinations.

The relevance of the method

Sometimes an autorefractor can be used for an initial assessment of vision. Autorefractometry can save time and is useful in examining young children or people who have problems with eye examinations, but are not necessarily accurate enough to complete the definition of a prescription.

There is subjective refractometry - the oculist will always discuss the patient's responses and their conclusions with him, based on the results, they can determine the stage of myopia, hyperopia or astigmatism, if any.

Sometimes, when patients cannot respond orally or to determine more complex prescriptions, eye drops are used. These drops temporarily prevent the eyes from changing focus when performing refraction. Drops are usually not required for refractometry, as the ophthalmologist is interested in how the eyes react under normal visual conditions.

After computer refractometry, the doctor will determine the prescription and prescribe glasses, contact lenses, based on the specific needs of the patient. Refractometry can also detect visual impairment and tells the eye doctor about eye health, an important aspect of the examination. An optometrist can also perform tests to check the focus and how well the eyes work together, which is important for everyday tasks.

Regular eye examinations are crucial to maintaining healthy eyesight. They are a common part of visiting an eye doctor and do not require any preparation from the patient. They can help the doctor diagnose and treat conditions such as glaucoma, and, among other things, determine the need for corrective lenses. Healthy adults should take a refraction test every two years, while children need them every one or two years, starting at 3 years of age.

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