Review of refraction
Review of refraction is intended to characterize and measure the importance of the optical defect of the eye. Refractive surgery can correct the myopia, theastigmatism and hyperopia. These optical eye defects and are grouped under the term of "defective vision" or "anomalies of refraction. Review of refraction makes it possible to determine and quantify the importance of the ametropia. The unit of measure of the importance of a defective vision is the diopter (D).
The ametropic subject is blurred vision from a distance (measured loss of tenths of Visual acuity in the absence of lens correction). Presbyopia is a reduction in the ability of the eye to do the update in near vision, between 40 and 45 years old. It leads to the need to carry a specific correction for reading or near vision.
Principles of ocular refraction measurement
The extent of the anomalies of refraction begins with a measure automated by a machine called Auto-refractometre which allows to estimate the degree of myopia; hyperopia and astigmatism. The patient fixes a focus in an eyepiece (usually a road or a distant landscape) the doctor moves successively on each eye. An infrared beam is emitted and then collected by the instrument after reflection on the retina. Results provided serve as initial benchmark providing an often quite accurate estimate of the power of the optical defect to correct.
However, only the examination ofVisual acuity directed by a professional measurement of refraction to determine with precision the degree of optical correction that allows to obtain the best visual acuity. This correction will be performed by the surgeon using a suitable refractive surgery technique.
Measure for refraction
This review is carried out through a mount automated on which variable power correction lenses may be present, and with a projection of letters on a screen located to 5 meters. The reviewer uses special techniques tell of "interference" to get reliable measures and undisturbed by unconscious accommodation efforts. The measurements are performed one eye, and then in binocular vision. They are carried out at the beginning of the consultation, and repeated later after instillation of two or three drops of eye drops said «» cycloplegic ».
This cycloplegic eye drops has the effect of temporarily paralyze accommodation (effort by certain muscles intraocular to allow the development in vision closely). Indeed, some (often intermittent but sometimes permanent) accommodation efforts exist in far vision patients and may reduce the accuracy of the measurement of refraction performed initially. Moreover, these eye drops to induce a expansion of the pupil later, which will be useful to the surgeon to examine certain eye structures such as the lens and the retina (examination of the fundus). Their effect generally lasts two or three hours and eventually disappears completely. In that time, they can however make it difficult to read and reduce Visual acuity by far.
In the review of refraction, the determination of the eye is done by observing a distant point of light through a circle held at arms length. The eye is the one who will be favored for the vision by far in procedures for the compensation of presbyopia.
Review of refraction data will be used to establish treatment issued by the refractive surgery laser.