Corneal topography is a complementary diagnostic and therapeutic examination that measures the curvature and thickness of the cornea over its entire surface, allowing for a detailed mapping of this structure.
This examination is performed in a computerised form, which allows measurements at multiple points on the cornea and its analysis. It can be represented in the form of colour charts in order to simplify its reading and interpretation.
Corneal topography is a non-invasive examination that can be performed quickly and requires no prior preparation. To obtain a more reliable examination, it is important to treat dry eye and contact lens wearers should take a break from wearing them for 2 to 4 weeks (depending on the type of contact lens worn), since both prolonged contact lens wear and the quality of the tear film may cause temporary changes to the anterior surface of the cornea, especially induced astigmatism.
The devices used allow us to evaluate the anterior and posterior surfaces, as well as the thickness of the cornea, creating a three-dimensional map and therefore the most correct term is corneal "tomography".
The corneal topography methodology was developed by an ophthalmologist and physicist, António Plácido da Costa (1848 - 1915) and has been maintained to this day. A pattern of alternating black and white concentric circles is projected onto the cornea and its reflection is analysed. Any alteration in the spherical surface of the cornea causes distortion of the projected circles.
The first topographers started to be commercialised in the 1980's and have been evolving and improving their quality, even so, some still use the placid ring system. There are other techniques, used in more recent topographers, which use Scheimpflug rotating images and optical coherence tomography.
