Topography — Prior Radial Keratotomy.

For RK, averaging the 0 mmm, 1 mm and 2 mm annular power rings of the Numerical View of the Zeiss Humphrey Atlas topographer (below) will typically a useful estimate of central corneal power.

Transient Hyperopia

Following cataract surgery and prior radial keratotomy, patients with previous 8-incision radial keratotomy will commonly show variable amounts of hyperopia in the immediate post- operative period following cataract surgery.

This is felt to be due to stromal edema in the areas of the radial incisions, producing a temporary enhancement of central corneal flattening. While this central corneal flattening is usually transient, it can be as much as +4.00 D, and is further accentuated by greater than eight incisions, or an optical zone of less than 2.0 mm. If a patient exhibits any of the above, significant unanticipated hyperopia may be seen in the immediate post-operative period, which should gradually resolve after eight to twelve weeks. Sometimes, due to a lack of corneal stability, the post-operative refraction can continue to slowly shift myopic over a several month period. We have seen several patients with myopic shifts as large a -5.00 D over a 12-week period.

If the refractive objective remains elusive, plans for an IOL exchange, or a piggyback IOL, should not be made until at least two months have passed and two consecutive refractions, at the same time of the day, are stable. If more than six months passes before cataract surgery is required for the fellow eye, the corneal measurements should be repeated due to the fact that additional corneal flattening frequently occurs over time following radial keratotomy. For this reason, IOL power calculations are usually targeted for between -0.50 D and -1.00 D and are designed to make the operative eye more myopic than usual, so that five to ten years from now, the post-cataract surgery refractive error does not drift into hyperopia. This also helps to avoid hyperopic refractive results, which are quite common in spite of every precaution being taken.