Qualification of vision defect for laser correction
About. 90% of patients presenting to ophthalmologists with a specialty in refractive surgery qualify for laser vision correction. However, each case is different, and while it is accepted that myopia, hyperopia and 99% of cases of astigmatism are laser-correctable defects, there may always be an exception.
The type of vision defect, the anatomical condition of the eyes, age and any eye diseases, as well as general health, determine whether our eyes can undergo laser surgery. Analysis of all the mentioned data allows the doctor to qualify (or not) the patient for laser treatment. Ophthalmic problems that prevent laser vision correction are primarily:
- Some corneal lesions: corneal cone, too thin cornea, congenital corneal pathologies, dystrophic diseases, corneal scars,
- too high a visual defect: nearsightedness above -10 diopters and farsightedness above +4 diopters,
- Difficult to treat irregular astigmatism.
Short-sightedness
In addition to too many diopters, corneal thickness can be a contraindication to laser surgery. A cornea that is too thin may or may not be a contraindication to the procedure. Corneal thickness is measured during an examination called pachymetry (optical measured by non-contact or touch using an ultrasound probe).
Evaluation of its thickness is a mandatory examination in patients with glaucoma and ocular hypertension, and is also performed before surgical procedures, including laser procedures, on the cornea, as well as in the diagnosis of corneal cone and other corneal disorders.
If the cornea is too thin, but the other (very many!) eye parameters checked by the specialist, which are planned to be operated on with the laser, are correct, the laser can be programmed in such a way that such an operation can be carried out successfully.
Read more about myopia treatment at “ Myopia treatment “.
The ratio of corrected diopters to corneal thickness determines whether correction is possible. Laser vision correction has what’s known as a “laser eye”. architecture of the procedure. Let’s consider this with a concrete example:
The patient has a corneal thickness of 510 microns.
With the femtolasik technique, we need a corneal flap (called flap) – this one is 100-110 microns thick. After the procedure, the thickness of the cornea under the flap should be at least 300 microns. That is, we have a situation: 510-110-300=100 microns for vision correction.
Here we can choose a variety of so-called “”new” products. zons of optics of the procedure, which wear out the cornea differently. For example, a 6.5mm zona uses 16 microns per diopter, so 100:16= 6.25 diopters for correction. The 7.0mm Zona uses about 18 microns, or 100:18=5.5 diopters.
The larger the zona, the more we use the cornea, but also – the larger the zona, the better the quality of vision and the lower the risk of photophobia.
That is, there are several factors that play a significant role.
NOTE: the calculations given depend on the laser model used
However, if all test results and your current vision defect do not allow you to undergo laser vision correction, you can always undergo refractive lens exchange (RLE) or CLE (clear lens extraction).
Refractive lens replacement involves removing the patient’s own natural lens and replacing it with a technologically advanced artificial lens to correct the visual impairment. It is also possible to implant an artificial lens (in addition to our natural one): phakic lens.
CLE is an irreversible procedure. Phakic lens replacement is a reversible procedure.
Farsightedness
Most often, farsightedness up to +4 diopters is corrected by laser, sometimes, if the anatomy of the cornea allows it – up to +5 diopters. Surgery for higher defects carries the risk of the emergence of impaired vision.
Those who do not qualify for laser vision correction surgery can therefore opt for phakic lenses (special lenses made of Collamer material (Visian ICL) or CLE, which also allow for the correction of astigmatism and severe vision disorders with diopter counts greater than -8 and +3. The method of treatment always depends on the number of diopters and is determined individually during the initial examination and consultation with the doctor.
Read more about farsightedness treatment at “ Farsightedness treatment “.
Astigmatism
If neither spectacle lenses nor contact lenses bring the desired result, one has to turn to traditional surgery methods (implantation of single, bifocal or trifocal toric intraocular lenses) or laser surgery, or to implant a phakic lens.
Laser correction, aims to even out the curvature of the cornea, bringing the rays back into focus and making the patient see more clearly. 99% of astigmatism cases are laser-correctable defects.
The problem arises when a complicated form of astigmatism co-occurs with another visual defect and/or eye disease.
Qualification of an eye defect for laser correction must always be preceded by qualifying examinations.
As part of the qualifying examination, the ophthalmologist conducts an in-depth interview with the patient to get an idea of whether there are any contraindications to the procedure.
Patients can expect a consultation with an optometrist, who consults with a surgeon if necessary, an initial ophthalmological examination, the establishment of an individualized strategy for the correction of vision defects, and discussion of the details of possible treatments.
Read more about astigmatism treatment at “ Astigmatism treatment “.
The latest surgical technologies make it possible to combine short/long-sightedness surgery with the simultaneous removal of other visual defects, such as astigmatism. There is no objectively best method of laser vision correction. We can only talk about technologically more or less advanced or more or less precise methods.
For each patient, the best method is the one recommended by the doctor after an in-depth interview and a series of detailed tests.
Different eye defects are corrected with different laser vision correction methods. For example, surface methods are not suitable for the correction of farsightedness or high astigmatism. The lasik/femtolasik method, on the other hand, is not suitable for correcting vision defects with thin corneas.
Does the defect return after laser vision correction?
