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Radial Keratotomy Clear Zone Diameter Errors

PURPOSE

To examine the variability of achieved clear zone diameters following radial keratotomy and to determine if refractive outcomes are correlated to clear zone diameter errors.

METHODS

Twenty-six patients with radial keratotomy (51 eyes) were studied retrospectively. The central clear zone diameter for each radial incision meridian was measured using a slit-lamp and a photograph. The achieved clear zone diameters were statistically compared to the intended clear zone sizes and to the refractive outcomes.

RESULTS

Twenty-nine of the 51 eyes met various exclusion criteria. Ninety individual slit-lamp clear zone measurements were obtained for the remaining 22 eyes. Sixty-two of 90 (69%) achieved clear zone diameters were more than 0.25 mm different than the intended clear zone size. A maximum difference of +/- 0.80 mm from the intended clear zone marker size was observed. The average clear zone diameter error did not statistically differ between the three refractive outcome groups (undercorrection, emmetropia, and overcorrection).

CONCLUSIONS

In selected cases of centripetal radial keratotomy, the achieved clear zone diameter can vary widely from the intended clear zone size despite extensive surgeon experience.

Measurement of Radial Keratotomy Clear Zone Diameters

BACKGROUND

To compare the accuracy of photographic measurements to slit-lamp measurements of radial keratotomy clear zone diameters in order to develop an independent, objective, unbiased, and reproducible method of verifying clinical observations.

METHODS

Twenty-five patients (48 eyes) following radial keratotomy had matched slit-lamp and photographic measurements of the diameter of the central clear cornea between the ends of opposite radial incision pairs. Matched slit-beam, photographic, and pathologic observations were compared statistically.

RESULTS

Two hundred fifty-four slit-lamp clear zone diameter measurements were obtained. In twenty instances (8%), the radial incision end-point could not be identified on the photograph. For the remaining 234 measurements, the mean slit-lamp clear zone diameter was statistically smaller than the photographic measurement by 0.03 mm (t-test, p = 2.2 x 10(-5)). The slit-lamp and photographic clear zone measurements were strongly positively correlated (Pearson r = 0.99, p < 1.0 x 10(-15)). Matched slit-lamp, photographic, and pathologic clear zone measurements (N=8) in one excised corneal button were not statistically different.

CONCLUSIONS

For radial keratotomy clear zone diameters, slit-beam measurements and photographic caliper measurements yield indistinguishable results that are highly concordant over a wide range of diameters. Both slit-beam and photographic measurements yield accurate and reliable results that reflect the true pathologic achieved clear zone diameter following radial keratotomy surgery.