AUTOREFRACTOMETER
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.
Technique
The majority of autorefractors
calculate the vision correction a patient needs (refraction) by using sensors
that detect the reflections from a cone of infrared light. These reflections
are used to determine the size and shape of a ring in the retina at the back of
the eye. By measuring this zone, the autorefractor can determine when a
patient’s eye properly focuses an image. The instrument changes its
magnification until the image comes into focus. The process is repeated in at
least three meridians of the eye and the autorefractor calculates the
refraction of the eye, sphere, cylinder and axis. Modern autorefractors are
based on the idea patented by Medina.
Uses
In some offices, this process is
used to provide the starting point for the ophthalmologist or optometrist in subjective refraction tests.
Here, lenses are switched in and out of a phoropter and the patient is asked
"which looks better" while looking at a chart. This feedback refines
the prescription to one which provides the patient with the best vision.
Automated refraction is particularly
useful when dealing with non-communicative people such as young children or
those with disabilities.
Retinoscopy
Retinoscopy performed by an experienced
clinician has been found to provide a more accurate estimation of refractive
error than autorefraction. Recent studies report that autorefractor
measurements without application of cycloplegia can result in significant
overestimation of myopia.
References
· Jorge J, Queiros A, Almeida JB, Parafita
MA. "Retinoscopy/autorefraction: which is the best starting point for a
noncycloplegic refraction?" Optom Vis Sci. 2005 Jan;82(1):64-8. PMID 15630406.
· Choong YF, Chen AH, Goh PP.: A comparison
of autorefraction and subjective refraction with and without cycloplegia in
primary school children. Am J Ophthalmol. 2006 Jul;142(1):68-74. PMID 16815252.
· Fotedar R, Rochtchina E, Morgan I, Wang JJ,
Mitchell P, Rose KA.: Necessity of cycloplegia for assessing refractive error
in 12-year-old children: a population-based study. Am J Ophthalmol. 2007
Aug;144(2):307-9. PMID 17659966.
External links
Trusit Dave "Automated refraction - Design and
applications" in "Optometry Today" 04/06/04
- "This
Company Is Bringing Eye Exams (And Glasses) To People Who Can't Afford Healthcare".
Read about Smart Vision Labs in "Business Insider" 09/29/14
- PIKE
Ophthalmic, image
