A thorough preoperative examination is a prerequisite to ensure the safety and effectiveness of the procedure. In clinical work, patients often ask: What is the use of this test? And what is the test for? The significance of the following preoperative examinations is explained in this question.
I. Medical history
Medical history contains many items. For example, age and occupation are important factors in the design of surgery; generally the refraction is stable for more than 1 year before considering surgery; soft contact lenses need to stop wearing for 1 week, hard contact lenses need to stop wearing for more than 1 month, the test results will be more accurate; the history of drug allergies, previous eye diseases, surgical history, genetic history, etc. are important indicators to determine whether surgery can be performed and which type of surgery to choose.
Visual acuity
Generally, it includes naked eye vision, vision with glasses and near vision. For older patients, near vision will be more meaningful and is a reference indicator for surgical design.
Third, the dominant eye
As the name suggests, the dominant eye is the one that is usually used mainly, just like some people are used to using the right hand and some are used to using the left hand. Generally speaking, the vision of the dominant eye is slightly better than the vision of the non-dominant eye will be more comfortable.
IV. External eye/slit lamp examination
The main purpose is to exclude other diseases of the eye, such as blepharitis, conjunctivitis and other active inflammatory diseases that need to be controlled before surgery, strabismus that needs to be treated by surgery before surgery, and also to check for stones, superfluities, pterygium, KP, anterior chamber reactions, iris adhesions, cataracts and other problems of the anterior segment of the eye.
V. Optometry
Optometry is used to determine the refractive error, which directly affects the final outcome of the surgery. It includes small-pupil optometry, dilated optometry, and comprehensive optometry. Generally, the first two are also divided into photometry and computerized optometry. Small pupil optometry is used to obtain the initial refractive error, dilated pupil optometry removes the effect of adjustment and will give a more accurate spherical lens, and comprehensive optometry will determine the final treatment degree.
Six, corneal topography
Corneal topography is currently the best means of screening potential cone corneas (preclinical cone corneas). Regardless of the manufacturer of which brand of corneal topography, it is best to get both the data of the anterior surface of the cornea and the data of the posterior surface of the cornea (preferably directly detectable, rather than through conversion), because there is a condition of posterior cone, that is, the anterior surface is “very normal”, but the posterior surface has been significantly pre-expansion, if rash surgery This can have very negative consequences. Corneal topography can also check the corneal curvature (of course, computerized optometry can also check this), which is also an indicator of the surgical design. Another indicator is the pupil diameter (also can be checked by optometry), which is a reference factor for the surgical design of the treatment area.
VII. Wavefront aberration
Simply put, the difference between the image formed after the object passes through the optical system and the object itself is called aberration. The refractive system of the eye not only has lower order aberrations (myopia, hyperopia, and astigmatism), but also higher order aberrations, such as spherical aberration, coma, trefoil, and clover, etc. Optical lenses (frames or corneal contact lenses) and conventional excimer laser surgery can only correct these lower-order aberrations of myopia, hyperopia, and astigmatism, but not higher-order aberrations. Only wavefront aberration-guided personalized laser surgery can target the removal of higher-order aberrations, resulting in clearer vision and better visual quality after surgery. Of course, you should not blindly pursue wavefront aberration-guided surgery, but choose rationally according to your actual situation.
Eight, dry eye related tests
It generally includes tear secretion test (Schirmer test) and tear film rupture (BUT test). Simply understood, the tear secretion test is to check whether the amount of tears is enough, and the tear film rupture is to check whether the function of tears is normal. Severe dry eye is a contraindication to myopia surgery.
IX. Intraocular pressure
It generally includes non-contact intraocular pressure (NCT) and contact intraocular pressure. If glaucoma is suspected, further screening is needed to confirm the diagnosis of glaucoma, and myopic surgery can be considered if the IOP is well controlled. Another purpose of preoperative IOP check is to provide reference and comparison for postoperative medication.
X. A ultrasound thickness measurement
Although corneal topography can also be used to measure corneal thickness, the gold standard is now recognized as ultrasonic thickness measurement. The higher the degree, the more tissue is cut, and the remaining corneal thickness must be in a safe range. Therefore, if the corneal thickness is thin relative to the degree of myopia, it is less suitable for laser myopia treatment.
Length of the eye axis
The length of the eye axis is particularly important for high myopia. The eye axis of high myopia generally grows, and each growth of 1mm is greater than an increase of 300 degrees. If the vision decreases after high myopia surgery and a state of re-myopia occurs, the length of the eye axis can be measured (compared with that before surgery) to confirm that the refractive return of the surgery is caused by the growth of the eye axis.
Fundus examination
The purpose of fundus examination is to rule out fundus diseases such as fundus hemorrhage, retinal fissures and detachment, and if necessary, retinal photocoagulation or surgery. However, myopia surgery does not improve or aggravate the complications caused by myopia itself (e.g. vitreous opacities, retinal hemorrhage, degeneration, fissures and detachments, complicating cataracts, etc.), so patients are still advised to have regular fundus examinations after surgery.