Autorefractor: What, Working, How To Use,Uses,Types

What is an autorefractor?

An automated refractor or an autorefractor is a digitally-controlled instrument used for providing an objective measurement of a refractive error, vision defects, and prescription for eyeglasses or contact lenses during an eye inspection. This method is carried out by analyzing the change in the path of light rays when it enters the eye. Antonio Medina Puerta patented the idea of modern automated refractors.

How does an autorefractor work?

The automated refractor displays an image into the eye. The infrared light rays from the image then pass through the autorefractor lens and strike the retina. Light rays get reflected from the retina, the eye, and pass through the optical lens. The defectiveness in the eye lens distorts and defocuses the reflected image. The autorefractor senses these defects/imperfections. 

The instrument then uses its lenses and software to rectify the returned image until no imperfections remain. This process is carried out thrice, and the autorefractor’s software provides the corrected lens prescription for the eye. The automatic refractor is used for measuring the axial, spherical, and cylindrical lens components. 

How to use an autorefractor?

Steps to use a table-top autorefractor:

  1. The patient should align his/her chin and forehead on the chin and forehead rest, respectively.  
  2. The height or level of the rest should be varied depending on the patient’s requirements.
  3. The patient should then focus on the image shown in the automated refractor.
  4. The measurement of each eye focusing should be captured separately by adjusting the sensor level until there is a clear view of the eye on the monitor.
  5. The automated refraction results of the eye can then be printed out after repeating the same process thrice. 

What are the uses of autorefractor?

Ophthalmologists or optometrists use Automated refractors for conducting subjective refraction tests. This instrument calculates the vision correction parameters of a patient’s eye lens. This instrument works on the concept of refraction and reflection for calculating the structural components of the retinal ring.

Types of Autorefractors

Portable autorefractor

US Navy 060527 N 3714J 063 USNS Mercy Deployment 2006
Image source:  US Navy 060527-N-3714J-063 USNS Mercy – Deployment 2006, marked as public domain, more details on Wikimedia Commons

Portable automated refractors are specially designed for people who are unable to reach the clinic of an optometrist for a checkup. This instrument has allowed optometrists to examine at-risk populations and pediatric screening, medical care in remote areas, and calamity areas. This has made eye lens correction more effective and easy to access. 

Handheld autorefractor

Handheld automated refractors are a type of mobile automated refractors that comprises a handheld instrument that can be used for determining the correct measurement of an eye lens. The instrument is placed at the eye level of the person within a 5cm distance, and the person is then instructed to focus on the image projected by the instrument. These automated refractors are easy to use and mobile. 

Table-top autorefractor

Table-top automated refractor
image source: Hans-Jürgen NeubertRodenstock RX900 Autorefractor HaJN 4415CC BY 4.0

Table-top automated refractors can be seen in an optometrist clinic. The patient places their forehead near the device, and the infrared rays are directed from the device to the patient’s eyes. The device then captures the returned rays. These instruments demonstrate accurate measurements of the spherical, cylindrical, and axial components of the eye. 

What are the new improvements in autorefractors?

In recent years, traditional automated refractors have witnessed some variations. One such variant is the aberrometer. It is a developed form of autorefractor that is capable of examining the refraction of light from multiple locations on the eye.

Another improvement on the autorefractor involves merging other eye inspection functions. Certain instruments combine autorefraction with wavefront analyzers and corneal topography measurements in order to get a compact device and save space in an optometrist’s clinic. These instruments also help in conducting a quick and effective checkup. 

Can autorefractors detect astigmatism?

An optometrist uses three instruments to analyze astigmatism. 

(1) Keratometer:

Keratometer or topography device is used for measuring the reflected image of a ring of light on the exterior dome of the eye formed by the iris, cornea, pupil, and lens. This gives us information about the extent of the curvedness of the cornea in every direction.

(2) Autorefractor:

An automated refractor is used for measuring the level of variation in the path of light after it reflects back from the retina. 

(3) Phoropter:

A phoropter is an instrument that has a set of different lenses. The patient is made to try the different lenses to decide precisely which corrective lens is the most suitable for them.

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