Answer to Question #11378 Submitted to "Ask the Experts"
Category: Lasers and Infrared
The following question was answered by an expert in the appropriate field:
Optometrists now commonly use a device called an autorefractor to get a patient's prescription for glasses. This device uses infrared radiation. Could this machine cause damage to the eye since it uses radiation? Would it be safer to opt for only an old-fashioned eye exam without the machine?
An autorefractor (or automated refractor) is a computer-controlled machine used during an eye examination to provide an objective measurement of a person's refractive error and prescription for glasses or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye. The infrared radiation used in autorefractors is similar to heat waves and does not cause harm to the eyes.
You may already know something about the electromagnetic (EM) spectrum. The light we see is part of the EM spectrum. Radio waves, microwaves, and x rays are part of it, too. Another part is called infrared.
Like all parts of the EM spectrum, infrared is a kind of energy that moves in waves. Our eyes can't see infrared waves. We can't see radio, microwaves, or x rays either. Infrared waves act in the same ways that light does. Infrared is reflected (or bounces off) light things better than dark things. It is absorbed by dark things better than by light things. Light travels in a straight line and so do infrared waves.
Your TV remote sends out a beam of infrared waves. Infrared is also used in a sauna. The heating effect there is due to wavelengths greater than 1,500 nanometers (nm). The infrared wavelength in the autorefractor is only around 900 nm, so there are no observable heating effects.
In the autorefractor, the infrared waves are machine generated. Near infrared radiation (NIR, specifically 880 ± 80 nm) is used. The reason this is used is because the fundus efficiently reflects back NIR, and this NIR is invisible to our visual system. The NIR travels through the cornea, lens, vitreous, etc.; bounces off the retina to travel back through the eye media; and is read by a sensor in the machine.
Scientists believe that autorefractors are a completely safe technology, and there is no evidence of documented injury. Ophthalmologists use them all the time to get a rough estimate of the patient’s refraction, prior to checking refraction with the chiropter (lenses). Autorefraction is generally regarded as a screening test and therefore is beneficial to the optometrist. The results still have to be fine-tuned with a traditional refraction test (old-fashioned exam), so there would be no loss to you if you refused the autorefractor test.
As a radiation-emitting product, ophthalmic autorefractors are regulated by the U.S. Food and Drug Administration (FDA). Most ophthalmic autorefractors are classified as FDA Class 1 Exempt Devices. For more information on this, you can access the FDA process at the following website: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/315.cfm.
Ninni Jacob, CHP