Keratometry
Warsaw · Krakow · Vienna · Zurich
Keratometry (ophthalmometry, corneal topography) is a non-invasive, painless diagnostic examination performed when it is necessary to measure the curvature and refractive power of the cornea.
Keratometry (Ophthalmometry, Corneal Topography)
This is a non-invasive, painless diagnostic examination performed when it is necessary to measure the curvature and refractive power of the cornea. Indications for the examination include:
- diagnosis of refractive errors and the need to select eyeglasses/contact lenses
- diagnosis of astigmatism
- preparation for cataract surgery (necessity of calculating the power of the implanted artificial lens)
- before planned laser vision correction procedures and after such procedures to assess the changes in corneal curvature obtained
- in the diagnosis of certain corneal diseases (e.g., keratoconus [keratoconus], megalocornea [megalocornea], keratoglobus [keratoglobus], microcornea [microcornea], cornea plana [cornea plana], or sclerocornea).
Keratometry in the Diagnosis of Astigmatism
Manual keratometry is the gold standard for assessing the power and axis of astigmatism in toric lens calculation. A keratoscope (Placido disc), which is a disc with black and white circles, allows observation of the shape of the reflected circles on the cornea. Specialists also still use the Javal ophthalmometer (keratometer), a manual keratometer used to measure corneal curvatures in two main meridians. These measurements allow for precise determination of the magnitude and axes of astigmatism.
Digital Corneal Shape Examination
Ophthalmologists also have access to a computer videokeratograph (digital) – the examination uses an image of the Placido disc projected onto the corneal surface, which is then recorded by a camera, sent to a computer, and analyzed. The keratometer projects images onto the cornea and analyzes the position of their reflections relative to each other. The central part of the cornea acts as a spherical convex mirror.
What does corneal measurement involve?
If an illuminated object of known size is placed at a known distance from the cornea and the size of the reflected image can be measured, its radius of curvature can be determined. Because the eye is constantly moving, measuring the image size with a linear scale is difficult. The use of two prisms placed base-to-base will create two images separated by a constant distance, which does not change due to minor eye movements (the doubling principle).
Are you eligible for laser surgery?
Corneal topography allows for a precise assessment of the eye’s surface and the detection of many anterior segment pathologies, thereby enabling appropriate patient preparation for surgery. It is believed that this examination is crucial for determining a patient’s eligibility for surgery. A cornea that is too thin may, but does not necessarily, contraindicate the procedure. Corneal thickness is measured during an examination called pachymetry (optically measured non-contact or by contact using an ultrasonic probe). If the cornea is too thin, but other (numerous!) eye parameters checked by the specialist for laser surgery are correct, the laser can be programmed to perform such an operation.
Corneal tomography also allows for determining the depth of the anterior chamber, the iridocorneal angle, the size of any changes in shape, scars, and inhomogeneities.
During computer keratometry, the doctor can see:
- The eye’s surface: this provides additional information about each corneal curvature and its characteristics. Based on this, it is assessed whether the planned correction is possible and will achieve the patient’s desired results.
- The posterior corneal surface: it should be healthy for a decision on surgery to be made.
- Corneal thickness: this determines whether all methods are possible – i.e., surface methods, LASIK, and microlenticular laser vision correction.
- Anterior chamber depth and corneal diameter: this is important for phakic lens implantation.
The result of the examination is a corneal map, a cross-section of the corneal surface, and a map of digital corneal curvature values.
The most important thing is to choose the right method for your vision defect. During initial consultations, we will propose an appropriate laser correction technique.
