Corneal topography

Corneal Topography

Just like a topographic land map shows the shape of the land, corneal topography shows the
shape of your cornea. The corneas are the clear “domes” at the front of our eyes. They’re directly in front of the iris (which gives the eye its colour), and they’re where we place contact lenses.

Corneal topography is quick and easy, and is used routinely at ICU, for all children’s visits, all routine contact lens visits and, for (non-contact-lens-wearing) adults, at least for the first visit. We use it to screen for irregularities that may cause distortions in your vision. Most people have a perfectly smooth, regularly-shaped cornea. Fairly frequently though, we’ll come across corneas that have distortions on them that can affect vision. These distortions are often reversible, and some of them indicate disease conditions that can progress and cause severe vision problems.

This cornea is perfectly normal. The “hotter” colours represent steeper curves, where the cornea changes direction more quickly than in other places. Similarly, the “cooler” colours are flatter, more gently-sloping areas. We usually see steeper curves towards the centre, flatter curves in the periphery, and typically most people have a little corneal astigmatism, where there is a different colour scheme in one direction than there is in the other. One of the best indicators for the quality of the cornea’s optics, and therefore the quality of the person’s vision, is the degree of symmetry of the colour spread in the central circle. This circle represents your pupil in daylight conditions, which in turn represents the area through which light will travel to form the image on your retina.

This cornea has keratoconus, which literally translates from the Latin for conical cornea. Keratoconus is common, and is more likely to occur when a patient has a history of asthma and/or eczema. The steeper (red) parts are associated with eye rubbing – the collagen in the cornea doesn’t respond well to this external pressure, and it becomes thinner over time. Then the fluid forces inside the eye “lean” on the thin parts, causing them to bulge outwards. Keratoconus can cause severe vision problems – for this reason, we like to screen all children (and first-visit adults) for this condition, and to offer strategies to make the eyes more comfortable. In this way, we have the opportunity to keep patient’s rubbing hands away from their eyes, which will hopefully stop or reverse the keratoconus. We can in no way guarantee this, as there are other factors at play, but it’s a positive step we can take and (at least anecdotally) it can reverse early “cones”.

This patient has little “pseudocones.” Is it early keratoconus? It’s hard to say without some background. Our usual strategy is to err on the side of caution, advising the patient that it may be a progressive problem, and to put strategies in place to minimize the risk of progression. Often, all it takes is one month of no eye rubbing to see these “cones” regress.