Introduction
An autorefraction test is an exam conducted to detect a refractive error. A refractive error is defined as an optical imperfection with how the eye focuses and bends light on the retina. This results in a distorted/blurred image output.
The autorefraction test is carried out via a device known as the autorefractor (short for automatic refractor). An autorefractor is a computer-controlled device used to examine and give an objective assessment of a person’s refractive error. Autorefractors are highly reliable when it comes to measuring lenses. The device can determine the right measurement for a glasses or contact lens prescription. A prescription is represented as numbers that describe the powers of the lenses needed by the patient.
The eye's ability to sharply focus on sources of light is based on three eye anatomy characteristics:
- The curvature of the cornea
- The overall length of the eye
- The curve of the eye’s lens
Perfect vision is given as a value of 20/20. People who have 20/20 vision can read characters that are 3/8 of an inch tall from 20 feet away. People who do not have 20/20 vision are diagnosed as having a refractive error.
Purpose
An autorefraction test is a simple, routine test that can be conducted by anyone as it is an automated process. However, for more accurate results, it is typically done at the eye doctor’s office by:
- A technician
- An ophthalmologist
- An optometrist
A patient may present various symptoms that indicate the presence of a refractive error. These symptoms include:
- Blurred/distorted vision
- Esotropia - Crossing of the eyes in children
- Having a problem reading or seeing things that are up close
These are the four types of refractive errors:
Myopia/Near-sightedness:
This is where nearby objects are clear, but distant ones are blurry. This disorder is usually inherited and tends to worsen when the patient reaches their teenage years.
Hypermetropia/Far-sightedness:
This is where distant objects are clearer than close ones. Advanced hypermetropia could also mean that the patient cannot see objects that are both close and far. It can also be inherited from one’s parents.
Astigmatism:
As we age, so do our eyes. At the age of 40, the eyes start to become more rigid. This ultimately means that they lose their ability to focus, which causes an inability to read things that are nearby. This condition is known as astigmatism.
Presbyopia:
Usually, the cornea is smooth and curved. Presbyopia is caused by the irregular and asymmetrical curve of the cornea. This results in distorted, wavy vision.
Autorefractors work by calculating the patients’ exact vision correction through sensors that detect the reflections from a cone of infrared light. It measures the size and shape of the retina and determines at which point the patient can adequately focus on an image. The autorefractor does this by changing its magnification until the image comes into focus. It then calculates the refraction of the eye, sphere, cylinder, and axis.
Preparation & Expectation
Autorefraction testing is painless and only lasts a couple of seconds. Due to this, autorefractors are especially helpful when dealing with children or the differently-abled. However, if the patient wears glasses or contact lenses, they will be required to take them off during the exam.
Procedure
The patient will be required to take a seat, rest their chin on the chin rest and forehead on the forehead rest. S/he will be required to look at the moving images that will be shown to them inside the autorefractor. Each eye is tested separately.
As the images move in and out, they keep changing their level of focus until the patient can clearly see the photos. The machine repeats this process in at least three meridians of the eye. The autorefractor takes several readings and the average determines the glasses prescription.
To refine the prescription strength, the eye specialist may decide to use the autorefractor together with a machine called a phoropter. When using the phoropter, the patient will sit behind the phoropter, with an eye chart ahead. The eye specialist manually switches multiple lenses in front of the patient’s eyes, constantly asking how well the patient can see the elements on the chart. The answers, in conjunction with the phoropter’s readings, will determine the perfect prescription.
Outcome
Normal results:
If the standard vision is normal (i.e., without glasses or contact lenses), then the refractive error is zero, meaning that the patient’s vision is 20/20.
Abnormal results:
Abnormal results reveal that the patient has a refractive error. S/he will need a combination of lenses to see clearly. Abnormal results will help to diagnose the patient with one or several of these conditions:
- Myopia
- Hypermetropia
- Presbyopia
- Astigmatism
The results can also help diagnose:
- Retinal detachment - The separation of the retina from the rest of the eye.
- Macular degeneration - The gradual vision loss from advanced age.
- Corneal ulcers and infections
- Retinal vessel occlusion - The blockage of small blood vessels located near the retina
- Retinitis pigmentosa - The breakdown and loss of cells in the retina.
After interpreting the results, the eye specialist will decide what glasses or contact lenses suit the patient. Another treatment for refractive error is LASIK. LASIK is a vision correction surgery that seeks to correct refractive errors by changing the cornea’s shape.
Everyone needs to get an autorefraction test done every 3 to 5 years. It is important because eyes tend to change over time. Even for those who already wear glasses, it is an important test because it assesses the progression of refractive error. However, there are certain groups of people who are required to do the autorefraction test more regularly. They are:
- People above the age of 60
- People who have been diagnosed with glaucoma
- People diagnosed with diabetes
- People over 40 years with a family history of glaucoma
Risks & Complications
There are no risks or complications associated with this test.
