Corneal topography also called keratometry (computer/digital or manual/manual). During the examination, which is painless and non-invasive, a color map of the local curvature of the eye’s cornea is created, based on which the ophthalmologist can diagnose and assess any abnormalities in the structure and condition of the cornea.
The keratoscope (Placido disc), which is a disc with black and white circles, allows you to observe the shape of the circles’ reflections on the cornea. The use of a manual/manual keratoscope is becoming less common, as ophthalmologists and optometrists have at their disposal a computer/digital videokeratograph – an image of a Placido disc projected onto the surface of the cornea is used for examination, then recorded by a camera, transmitted to a computer and analyzed. The results of the study are a corneal map, a cross-section of the corneal surface, and a map of digital corneal curvature values.
Specialists also still use Javal’s ophthalmometer (keratometer), a handheld keratometer that is used to measure corneal curvature in two main sections. With these measurements, the magnitude and axes of astigmatism can be accurately determined. Manual keratometry is the gold standard for assessing the power and axis of astigmatism in toric lens calculations.
Corneal topography is one of the most important examinations if we plan to select artificial implantable lenses, which are used to treat myopia, farsightedness, astigmatismi cataracts. It is an especially important tool when qualifying for the right type of lens. With it, the corneal cone can also be diagnosed with an assessment of its severity and possible progression. To assess the condition of the patient’s eyes, a comparison is made between the results of an individual corneal topography, such as from a year ago and from the current examination. Depending on the changes that have occurred during this time, measures are taken to stop the changes occurring in the cornea. Corneal topography also allows diagnosis of post-surgical or post-traumatic corneal deformities. Corneal topography, as mentioned, is most often performed using a digital/computerized videokeratograph. The patient rests his chin and forehead on a support in front of a canopy illuminated by a red light. The canopy is covered with concentric black rings that reflect on the cornea during examination. During the examination, you have to look, without blinking your eyes, at the centrally placed light. The reflections of the circles/rings (described above) on the cornea, their widths and distortions are recorded and analyzed by computer, and then converted to corneal radii of curvature. The resulting corneal map can be two- or three-dimensional.
There is a perception that it is the test that determines whether a patient can be admitted to surgery. Patients are concerned that a cornea that is too thin is tantamount to disqualification. Meanwhile, 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!) parameters of the eye planned to be operated on with the laser checked by the specialist are correct, the laser can be programmed in such a way that such an operation can be carried out successfully (depending on the height of the eye defect). We distinguish between the so-called. Scheimpflug or OCT topographies, with which we also measure the thickness of the cornea and other anatomical parameters of the anterior segment of the eye, and the so-called “OCT topography. Placido topographies, with which we measure only the regularity of the anterior part of the cornea (without pachymetry).
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:
Experts believe that a simple slit-lamp examination can cause an ophthalmologist to overlook eye diseases such as epithelial basement membrane corneal dystrophy (EBMD). If the disease goes unnoticed, it can lead to postoperative refractive problems.
Computerized keratometry is a non-invasive and painless examination (the patient sits comfortably, forehead and chin resting on a special support of the apparatus used to perform the test), and the accuracy of the measurement depends on the immobilization of the eyeball of the examined person – hence the need not only to stabilize his head, but also to look centrally in front of him at the light point visible in the apparatus. Indications for corneal topography:
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