A preoperative assessment is necessary to confirm that your condition is operable,
- by ensuring the absence of any general or ophthalmological contraindications
- -by making very precise measurements of your correction
- by analyzing together with you what type of surgical option will be the most suitable depending on your refractive disorders and your expectations.
Your eye surgeon and his/her team of orthoptists will perform the most comprehensive clinical and paraclinical assessments possible, which will allow them to propose the solution best suited to your situation and requests.
A very accurate measurement of many parameters is required. In order to determine the correction, different checks may often be required, including those performed after momentary dilation of the pupil with cycloplegic eye drops.
Lens wearers should stop wearing lenses during the week prior to the assessments so that eye tests can be performed in the best conditions.
Measurement of corneal thickness or pachymetry is an essential part of the exam. In fact, a cornea which is too thin may contraindicate femtolasik surgery and suggests a move towards a different alternative treatment. Pachymetric measurement can be ultrasonic or optical, using different devices.
Many painless and technologically sophisticated tests will complete the analysis as part of the clinical exam performed with a slit light.
Finally, the patient is given all necessary information, in particular about the potential risks, to make his/her decision and this discussion completes the assessment.
As for the administrative part, you will receive two documents at the end of the consultation:
- an estimate of the procedure that you can send to your health insurance company,
- a statement of informed consent which must be signed prior to the procedure.
Corneal topography is a key element in the preoperative assessment. This examination is crucial to understand the specific anatomy and the exact shape of your cornea that is to receive the laser treatment. With representations in the form of color cards, you will easily understand the interpretations given by your surgeon.
Specular corneal topography:
To sum up the principle of the test, the analysis is based on the projection of concentric light rings on the cornea that measure the radii of curvature of the cornea.
The purpose of the test is to find out the exact powers of the radii of curvature, to check their regularity or symmetry and to exclude the possibility of an underlying subclinical Keratoconus-type disease.
Corneal elevation topography: Pentacam*
Based on the principle of a Scheimpflug camera with rotating scanning slit light, this topograph analyzes the anterior and posterior faces of the cornea, the radii of curvature, the three-dimensional coordinates of each point and is used to find out the corneal pachymetry without contact. Accurate cartographic representations and a precise analysis of many indicators are also a major diagnostic complement in the detection of the preoperative corneal abnormalities.
Indeed certain diseases, which are totally asymptomatic in their early stages such as Keratoconus for example, are a contraindication for LASIK surgery. Eventually, in these cases, the cornea would be at risk of asymmetric shape changes with appearance of ectasia and modification of refraction which is detrimental to vision.
Finally, this type of device also allows a "scan-like" analysis of the anterior segment of the eye, with visualization of anatomical structures, cornea, iridocorneal angles, iris, lens, which provides additional information, essential in surgical alternatives to Femtolasik-type corneal treatment.
In some cases, one eye may have too many so called high order optical aberrations that can be specifically treated. In the normal state, any eye has abnormalities like high order aberrations because these give the human eye its own optical characteristics, in particular a specific depth of field. However, if the order of aberrations during the aberrometric measurement is not normal, these can be reduced as part of the same treatment. However, this situation is not common.
-Analysis of lens diffraction: OQAS2
An additional test may be offered in some cases to help confirm the presence or absence of associated lens disorders. The Optical Quality Analyzing System allows us to understand both the high order spherical aberrations and to analyze the transparency of ocular media.
- Optical biometry: IOL MASTER 500
To complete the assessment, this test is a non-contact measurement of the axial length, depth of the anterior chamber of the eye and keratometry, which enables, if necessary, an accurate calculation of the exact substitute lens power that may be necessary if alternative non-corneal surgery was proposed.
-Analysis using Optical Coherence Tomography:
The spectral domain OCT is an ultra precise test which gives vital information on the anatomical state of the optic nerve and the retina that are necessary to check or quantify in some refractive surgery indications to exclude any prior disease that would be detrimental to optimal functional postoperative result.