Index
1 Objective exams
2 Subjective exams

Vision grading determines the amount of optical correction that a person with one or more refractive problems (also called ametropia) needs: myopia, hyperopia and / or astigmatism and presbyopia or tired eyesight. This graduation is what the glasses or contact lenses of that patient must have to normalize their vision, both from afar and up close. Upon graduation, the optician or ophthalmologist will determine if the patient suffers from any of these refractive problems and to what degree. The vision graduation must be carried out in a personalized way, since it adapts to the visual defects of each person.

When determining if a patient is a candidate for laser refractive surgery, it is very important to make a correct graduation during the first preoperative consultation, since these values, along with other additional tests that analyze the general state of the visual system, the fundus of the eye and, specifically, the conditions and characteristics of the patient's cornea, will determine if he can correct his refractive problems and what technique the surgeon should apply in his case.

The graduation of the vision is carried out as a complement to the analysis of the visual acuity of the patient (ability of the visual system to clearly capture the details of an object at a certain distance with good lighting conditions) and is developed through two types of simple, painless tests that hardly cause discomfort to the patient. It is very important to evaluate the diopter number of each eye (unit of measurement of the graduation) independently.

Objective exams
They are used to take starting values   (guide values) through techniques that do not require the patient's response as a guide. Usually, they are carried out through these tests:

Autorefractor. It is a technique that is used to determine the graduation of sight quickly and easily. The patient, sitting and with the chin correctly resting on the machine, observes a photograph that focuses and blurs. The autorefractometer analyzes when and how the image is projected onto the retina. With these data, calculate the value of the refraction in each eye.
Retinoscopy. It is a non-invasive test that does not produce any pain or flashes that is usually performed by the ophthalmologist inside the office to measure the refractive power of the eye by interpreting the light reflected on the retina when illuminated with the retinoscope. Usually the consultation is left in semi-darkness and the patient looks at a distant distance (on several axes: up, down ...) while a light is projected on his pupil.
Evaluation of the prescription of the glasses or contact lenses worn by the patient, if this is the case.

Subjective examinations
They are used to determine the refractive value of the patient in distant vision, taking into account the assessments made by the patient himself. A trial mount is placed on which diverging and converging (for myopia and farsightedness) or cylindrical (for astigmatism) spherical lenses are placed and the patient must read the letters or symbols on a panel that is placed at a certain distance (optotype). To measure the near view this panel will be placed at a distance of between 30 and 40 centimeters and to measure the distance view, the optotype will be located about five meters. First it will be tested in one eye by covering the opposite and then in the other. This process, in addition to being carried out with a trial frame on which the lenses are placed, can also be carried out with an apparatus known as a phoropter.

The graduation can vary based on multiple factors, such as the time of day, the visual fatigue that the patient accumulates, his general state of health at the time of graduating his sight, the lighting conditions or the taking of certain medications, among others .