Automated refractor
Encyclopedia
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.
in relaxed position and avoid the erroneous diagnosis of a pseudomyopia
, the patient takes a seat and places their chin on a rest. One eye
at a time, they look into the machine at a picture inside. The picture moves in and out of focus as the machine takes readings to determine when the image is on the retina
. Several readings are taken which the machine averages to form a prescription. No feedback is required from the patient during this process.
Within seconds an approximate measurement of a person's prescription
can be made by the machine and printed out or shared electronically with an Automated Refraction System
.
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.
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
.
Eye examination
An eye examination is a battery of tests performed by an ophthalmologist, optometrist, or orthoptist assessing vision and ability to focus on and discern objects, as well as other tests and examinations pertaining to the eyes....
to provide an objective measurement of a person's refractive error and prescription
Eyeglass prescription
An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist or ophthalmologist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.If an examination indicates that...
for glasses
Glasses
Glasses, also known as eyeglasses , spectacles or simply specs , are frames bearing lenses worn in front of the eyes. They are normally used for vision correction or eye protection. Safety glasses are a kind of eye protection against flying debris or against visible and near visible light or...
or contact lenses. This is achieved by measuring how light is changed as it enters a person's eye.
Technique
The automated refraction technique is quick, simple and painless. After application of a cycloplegic agent to keep the ciliary muscleCiliary muscle
The ciliary muscle is a ring of striated smooth muscle in the eye's middle layer that controls accommodation for viewing objects at varying distances and regulates the flow of aqueous humour into Schlemm's canal. It changes the shape of the lens within the eye not the size of the pupil which is...
in relaxed position and avoid the erroneous diagnosis of a pseudomyopia
Pseudomyopia
Pseudomyopia refers to an intermittent and temporary shift in refraction of the eye towards myopia, in which the focusing of light in front of the retina is due to a transient spasm of the ciliary muscle causing an increase in the refractive power of the eye...
, the patient takes a seat and places their chin on a rest. One eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
at a time, they look into the machine at a picture inside. The picture moves in and out of focus as the machine takes readings to determine when the image is on the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
. Several readings are taken which the machine averages to form a prescription. No feedback is required from the patient during this process.
Within seconds an approximate measurement of a person's prescription
Eyeglass prescription
An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist or ophthalmologist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.If an examination indicates that...
can be made by the machine and printed out or shared electronically with an Automated Refraction System
Automated Refraction System
An automated refraction system is a group of ophthalmic devices used during an eye examination to aid in the determination of a person's refractive error and prescription for glasses or contact lenses....
.
Uses
In some offices this process is used to provide the starting point for the optometrist in subjective refraction tests. Here, lensesLens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
are switched in and out of a phoropter
Phoropter
A phoropter is an instrument commonly used by eye care professionals during an eye examination, containing different lenses used for refraction of the eye during sight testing, to measure an individual's refractive error and determine his or her eyeglass prescription.Typically, the patient sits...
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
RetinoscopyRetinoscopy
Retinoscopy is a technique to obtain an objective measurement of the refractive error of a patient's eyes. The examiner uses a retinoscope to shine light into the patient's eye and observes the reflection off the patient's retina...
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
Myopia
Myopia , "shortsightedness" ) is a refractive defect of the eye in which collimated light produces image focus in front of the retina under conditions of accommodation. In simpler terms, myopia is a condition of the eye where the light that comes in does not directly focus on the retina but in...
.
External links
- Trusit Dave "Automated refraction - Design and applications" in "Optometry Today" 04/06/04 http://www.optometry.co.uk/articles/docs/ae331f5e9f3c12ab8e23e345f22b45d4_dave20040604.pdf