Auto refractometer is used to determine an individual’s prescription by measuring how light is affected as it reflects through the eyeball. The process is quick and painless for the patient, and the data ensures a baseline to determine the correct eyeglass or contact lens prescription.
What is Autorefractor keratometer?
Autorefractor/keratometers (ARKs) are computerized devices that provide both refractive testing and keratometry measurements. This allows eyecare professionals to determine both a baseline for the patient’s prescription as well as the curvature of the cornea for contact lenses.
What is Autorefractometry?
INTRODUCTION S Refractometry is the estimation of refractive error with a machine, called refractometer or optometer. S Automated Refractometers (AutoRefractors) are designed to objectively determine the refractive error & are of various types depending upon the underlying principle they are based on.
How does a refractometer work?
Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to refractive index (nD) values that have been established. Measurements are read at the point where the prism and solution meet.
The chart projector is an AC-powered device intended to project an image on a screen for vision testing.
Ophthalmic examination chart projector including a rotatable chart carrying disc and a mask plate which are co-axial with each other. A light source and a projecting lens assembly are provided for projecting one of the charts on the disc and one of the mask openings onto a screen. An index tube is rotatably mounted in the projecting optical path and carrying a colored filter on the inner periphery thereof. Thus, an astigmatic index can be projected on the peripheral portion of the astigmatic examination chart. The chart carrying disc, the mask plate and the astigmatic index tube can be controlled by knobs all provided on the front panel of the projector.
There are important applications for a handheld autorefractor in the clinical setting. A portable but powerful handheld autorefractor such as the SVOne (Smart Vision Labs; Figure 1) can be used in place of a desktop unit if, for instance, the desktop unit malfunctions or needs servicing. The SVOne adds flexibility to the clinic because it is transportable. This can improve patient flow dynamics, taking the testing modality to the patient rather than having the patient leave the exam room to go to a testing station. A handheld autorefractor serves to relieve bottlenecks if a testing station is occupied; it also allows clinicians to carry the technology to satellite offices that may not have the same diagnostic equipment as the main office.
Where a handheld autorefractor such as the SVOne could have its greatest impact, however, is in teleophthalmology settings. In certain rural areas, there are coverage gaps where patients often have to travel great distances to be seen by an eye care provider. Using the SVOne, which is a Hartmann-Shack wavefront sensor affixed to an iPhone, it would not take much to design a protocol to remotely screen patients to detect refractive errors in need of follow-up.
Understanding and caring for a lensmeter
A lensmeter or lensometer is an instrument used to verify the prescription of eyeglasses or spectacles. Many lensmeters can also verify the power of contact lenses with the addition of a special lens support. The values obtained from a lensmeter are the values specified on the patient's eyeglass prescription: sphere, cylinder, axis, add, and in some cases, prism. It is commonly used prior to an eye examination to obtain the last prescription the patient was given, in order to expedite the examination.
In one commonly used type of lensmeter the target seen through the eyepiece consists of a set of three wide lines with wide spacing between them and another set of three narrow lines with smaller spacing between them. These two sets of lines intersect at right angles. The closely spaced lines represent the sphere component of lens power and the thicker, widely spaced lines represent the cylinder power. In the case of a spherical lens, all of the lines of the target will focus at the same time, while in the case of a sphero-cylindrical lens, the lines will focus separately at different power drum readings (see illustration).
In another type of lensmeter, a series of light dots forming a circle is used as a target instead of the two sets of parallel lines described earlier. If a spherical lens is measured, the circle remains a circle and the power drum is adjusted to obtain a sharp image of the dots. For sphero-cylindrical lenses the dots, when focused, will display a sharp ellipse. The major and minor axes of the ellipse can be read on the scale provided in the instrument.