In our September Case Reports column, we described how elevation display corneal topography maps can provide a new level of accuracy and understanding when fitting corneal GP lenses for keratoconus. This month, we will describe the use of elevation display maps in a group of patients who have unique physiological requirements—those following penetrating (PK) or lamellar keratoplasty (LKP). In our experience, approximately 80% of these patients will require contact lenses to correct their high regular and irregular astigmatism as well as any refractive anisometropia that may exist.
A Case of Bilateral PK
Our patient is a 24-year-old male who has a longstanding history of bilateral bilateral keratoconus. He underwent a PK OD in 2014 and OS in 2016. Post-surgical K readings were OD 44.00 @ 044/47.37 @ 144, and OS 43.25 @ 088/47.50 @ 178.
Figure 1 shows the elevation display topography map of the patient’s right eye. Remember that with these maps, the red, orange, and yellow colors represent areas of the cornea where the elevation is the highest—in this case, 56 microns above a theoretical best-fit-spherical surface. This is where the fluorescein will be the “thinnest/darkest” and the lens will be in closest apposition to the cornea. The blue and green colors represent areas of the cornea where a depression is present—in this case, 78 microns below the spherical surface. This is where the fluorescein will be the “thickest/brightest” and the lens will be furthest away from the cornea.
Figure 2 shows how the elevation map and the actual fluorescein pattern are a perfect match.
Figure 3 shows the elevation display map for the patient’s left eye, with an elevation on the temporal side rising above the spherical surface by 73 microns and a depression along the nasal portion descending 35 microns below the best-fit-sphere. As we discussed in our September column, if the differential in elevation/height is less than 350 microns, we consider a corneal contact lens design. If the differential is in excess of 350 microns, the patient may be a better candidate for a scleral lens design.
In Figure 4, we again see how the elevation display map and the actual fluorescein pattern are a near perfect match.
In this patient, the elevation display maps showed a height differential OD of 134 microns and a differential OS of 108 microns. This made the patient an excellent candidate for corneal GP contact lenses, our lens design of choice post-PK. CLS