Diagnostics before laser vision correction or lens implantation

There is not the slightest doubt: the more thorough the preliminary research, the better the outcome of the operation. Research is needed for two reasons.

First, to determine whether the patient’s eyes can be subjected to the laser vision correction or whether he or she qualifies for artificial lens implantation, and secondly, to precisely plan the operation. The more multifaceted the operation, such as simultaneous removal of cataracts and a visual defect, correction of a complicated form of astigmatism co-occurring with another visual defect and/or eye disease, etc., the more detailed the tests needed.

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.

Among the guidelines for preparing patients for eye surgery, it is mandatory to perform m. in. Such studies as:

• corneal topography
• corneal tomography
• pupil width
• intraocular pressure (IOP measurement) with corneal hysteresis
• autorefraction
• subjective refraction
• examination of binocular vision
• optical biometry
• Optical coherence tomography (OCT) / macula and optic nerve imaging of the posterior segment of the eye
• endothelial cell density
• biomicroscopic ophthalmic examination

One of the most important tests necessary for planning laser corneal procedures or laser vision correction is corneal topography (3D).

It is worth remembering that we must stop wearing contact lenses (soft lenses for 1 week, hard lenses for 4 weeks) before the examination. Contact lenses change the shape of the cornea in the long term. It is after two weeks after contact lens removal that the cornea can return to its natural shape. If the contact lens is not removed long enough before the examination, this can result in poor surgical planning, as the ophthalmologist will not have the opportunity to take into account the actual parameters of the eye. The consequence would be, predictably, an unsatisfactory surgical result.

Corneal topography, or computerized keratometry

Corneal topography makes it possible to accurately assess the surface of the eye and detect many anterior segment pathologies, and thus properly prepare the patient for surgery.

There is a perception that it is the test that determines whether a patient can be admitted to surgery. This is why patients fear that a cornea that is too thin is tantamount to disqualification.

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).

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.

Corneal tomography also allows us to determine the depth of the anterior chamber, the corneal-ocular angle, the size of any shape changes, scars, inhomogeneities.

During computerized keratometry, the doctor can see:

• The surface of the eye: thus gaining additional information about each corneal curvature and its features. On this basis, he assesses whether the planned correction is possible and will bring the results expected by the patient.
• The posterior surface of the cornea: it should be healthy for a decision to operate.
• Corneal thickness: decides which special incisions can be made to remove existing corneal curvature during surgery or whether Femto-LASIK is possible.
• The depth of the anterior chamber and the diameters of the cornea: this is important when implanting phakic lenses.

Other important diagnostic tests include:

Measuring pupil width

Normally, laser correction is performed on an area slightly larger than the pupil of the eye in the dark. This ensures that after laser vision correction, the eye will see equally well in all lighting conditions. A surgical field that is too small would result in strong halo and glare effects and poor vision after dark and at night.

Measurement of intraocular pressure (IOP), or tonometry

IOP testing before deciding on laser vision correction is designed to determine whether the procedure poses any risk to the patient. Modern non-contact tonometers measure not only corneal thickness and intraocular pressure (IOP), but also the biomechanical properties of the cornea after an air pulse is applied to it.

Optical biometrics

Optical biometry provides information about the length of the eyeball and the distances between successive elements of the eye. During the examination, the cornea, lens, and retina can also be imaged along the measuring beam. Biometrics can identify any differences in the length of the eyeballs.

Optical coherence tomography (OCT)

It is an examination of the retina or anterior segment of the eye to rule out degenerative diseases of the retina, detachments, dilation, macular holes and glaucoma. State-of-the-art CT scanners make it possible to characterize the thickness of the cornea, see the successive layers of the cornea and all the features of their structure.

Epithelial cell density study

With this test, dystrophic (atrophic) diseases of the cornea of the eyes can be diagnosed, which are contraindicated in laser treatments.

Diagnosis of optical system aberrations

Aberrations are deviations that can be responsible for glare and reflections around light sources, such as in the dark (higher order aberrations cannot be corrected with glasses). They reflect any irregularities in the eye’s optical system (cornea, natural lens). They are diagnosed with modern aberrometers, which allow simultaneous measurement of aberrations of the entire optical system, visual axis and keratography. The resulting high-precision results are then incorporated into the calculation of individually designed laser or lens surgery.

It is worth remembering that 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.