Laser vision correction — Is it worth aiming at “zero”?

Upon registration for the preliminary examination qualifying for a laser vision correction procedure, patients frequently ask us a question whether it is possible to correct a refractive error to zero. What is the “zero” they are searching for?

During the qualifying examination, an ophthalmic surgeon selects the most beneficial correction method for each patient. At this stage, it is already known approximately to what degree the patient’s vision defect can be corrected and whether the patient is satisfied with the expected result.

Laser vision correction cannot be used to treat eye degeneration or eye diseases. Like glasses and contact lenses, it is simply one of the available correction methods. The predicted result is that after the procedure the patient should see exactly the same as they would in the most appropriately chosen glasses or contact lenses, but without them.

“Zero”on a printout from a refractometer – does it mean perfect vision?

The result of the so-called objective examination with the use of the refractometer (computer vision test) determines only the approximate optical correction (power of glasses or contact lenses) which can be applied. The result of the measurement is affected by many factors – the degree of hydration, eye fatigue, possible infection of the body or eyes.

If “0” is not the only value on the printout from the refractometer, it is not necessarily equivalent to the patient seeing incorrectly. “Zeros” on printouts from refractometer tests are almost never found in people who do not have vision problems either.

This means that the values on the printouts do not fully reflect the actual visual acuity.

The choice of correction during the examination qualifying for a laser vision correction procedure

The adequate selection of the correction method is based primarily on a subjective examination conducted with the use of an ophthalmological chart (Snellen chart), on which symbols are displayed. Following the laser vision correction surgery, the patient reads the chart as in the best-chosen correction during the qualifying examination, but without glasses or lenses.

Sometimes a vision defect cannot be fully corrected. It is determined by numerous factors, such as amblyopia or inadequate corneal parameters.

Another issue is so-called presbyopia. It affects people over the age of 40-45 and manifests itself as the need to wear glasses with plus lenses for reading. It cannot be corrected with a laser.

Laser operating range and correction chances in a given patient

In our Centre, the ophthalmic surgeons perform vision correction surgeries with the use of the Wavelight EX500 laser. It enables the correction of short-sightedness up to -14 dioptres, far-sightedness up to +6 dioptres, astigmatism up to 6D as well as a combination of the above defects.

The severity of the refractive error is not a decisive factor, for even if its value fits within the operating range of the laser, corneal parameters may not meet certain criteria (e.g. corneal thickness, shape or curvature) for the defect to be fully, or in same cases even partly, corrected.

In order to definitely assess the possibility of performing the procedure and the degree to which a given defect can be corrected and to select the most suitable correction method, the patient has to undergo a preliminary qualifying examination.

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