Refractive Surgery

PATIENT'S CORNER
The authors report their findings in blind eyes which underwent laser thermokeratoplasty (LTK) for hyperopia. Refractive surgery using excimer laser has been shown effective for moderate levels of hyperopia and astigmatism. LTK is a different method for affecting the central corneal curvature. In hyperopia, the cornea is too flat, causing the focal point of the eye to be "behind" the fovea. By steeping the cornea, light is refracted more, resulting in the anterior movement of the focal point. Nomograms are used to determine how much laser energy and where this energy should be applied to achieve the desired shift in the eye's focal point. The goal is to make the focal point rest on the central portion of vision when the eye is completely at rest and not focusing. The authors report their one year results using LTK: it is safe and effective. Best results are achieved using two rings of laser placed deep within the mid corneal position and using the wavelength of 1.870 micronmeters (instead of 1.854 micrometers). Look for this modality to make its way into the armamentarium of the refractive surgeon in the next five to ten years.

CLINICIAN'S CORNER
LTK research has shown a single laser spot application may not be the best or even an effective way of reversing hyperopia. Using a diode laser, one can apply a continuous emission of laser energy to the corneal stroma, allowing temperatures to reach a high enough point where collagen coagulates and refractive changes can be realized. This is a pilot study on eight blind eyes.

METHODS: Using a diode laser, 8 legally blind eyes were treated in two groups.
Group 1 had a lower wavelength/high frequency beam applied in one ring. The higher wavelengths applied in Group 2 were applied in two rings instead of one. The power settings used were not consistent between patients within a group. Although Group 2 had two rings instead of one, the size and positioning of the rings were different in all patients.

RESULTS: Up to 5.66D of hyperopia may be correctable with the diodeLTK technique. There were variable but occasionally considerable amounts of induced astigmatism. Endothelial damage occurred in Group 1.

DISCUSSION: This pilot study shows continuous diode laser may become an effective method for the correction of hyperopia and astigmatism. The sample sizes are too small and the parameters betwen subjects varied such that specific conclusions can not be made.

The general trend of the paper is that diode LTK can lower hyperopia and astigmatism. The wavelength, spot placement and number of rings applied are factors which will influence future studies and eventually clinical nomograms.

Finally, there is significant damage to the corneal endothelium with certain parameters. Work needs to be done to further elucidate these concerns before any "normal" eyes are considered for inclusion into a study protocol.

Raymond Magauran, MD
Boston, MA