Wavefront-guided LASIK tackles mixed astigmatism

The wavefront-guided LASIK procedure was performed using a specific microkeratome (Hansatome, Bausch & Lomb) and excimer laser (Technolas 217z100, Bausch & Lomb). The postoperative uncorrected and best-corrected visual acuities (UCVA and BCVA, respectively) were measured on days 1 and 7 and again at 1, 3, and 6 months after the procedure. The surgical technique and the climate in the operating suite were strictly standardized. The nomogram was adjusted for an expected coupling effect, according to Dr. Thilesen, who is in private practice in Larvik, Norway.

Using the customized platform, Dr. Thilesen and his colleagues treated 43 consecutive eyes with mixed astigmatism. Thirty-eight of the eyes had been followed for 6 months post-procedure.

"At the 6-month follow-up examination, the spherical equivalent [SE] was 0.09 D, the sphere was 0.32 D, and the cylinder was –0.45 D. The cylindrical SD of 0.35 D was noteworthy because it was significantly lower than most published data. We attribute this result to strict standardization of the refractive process," Dr. Thilesen reported.

He presented a case report that illustrated how he and his colleagues achieved their excellent results. A 37-year-old man had a preoperative cylinder of –3.25 D in the right eye and –2.25 D in the left eye. The axes were oblique. The aberrometer (ZyWave, Bausch & Lomb) predicted phoropter refraction was higher for sphere but was compatible with the subjective cylinder. The treatment administered was adjusted according to the customized nomogram used by Dr. Thilesen and colleagues. The refraction 4 weeks postoperatively indicated that there was no subjective cylinder, according to Dr. Thilesen. He noted however, that most of the cases had some residual cylinder.

At the 6-month examination, SE was within ±1.0 D of the attempted correction in 97% of cases, 84% were within ±0.5 D, and almost 70% of the eyes were within ±0.25 D of the SE. Aside from a slight hyperopic shift, sphere and cylinder values were highly stable over time.

In addition, he showed that the cylindrical scattergram was tight, with most of the corrections within 0.5 D of the desired correction. The results from 3 months and at 6 months were similar, he noted.

"We had wished that the achieved correction was a little better for those patients with lower cylindrical corrections," he said.

Vector analysis showed that the mean preoperative cylinder was almost 3.0 D. Most of the patients had with-the-rule astigmatism. "One month after surgery, the mean value showed a slight cylindrical undercorrection of 0.25 D with good centration. This remained stable through to the 6-month examination," he said.

Dr. Thilesen reported that the procedure was both safe and effective. Eighty percent of the patients had a UCVA of 20/20 at the 6-month time point, and almost 40% of patients achieved 20/16. All patients had a BCVA of 20/25, and a BCVA of 20/16 was achieved in almost 80%. No more than one line of BCVA was lost in any eye, and a gain of one or more lines at 6 months was experienced in 60% of eyes.

"Considering the safety of this procedure, [this customized] LASIK performed to treat mixed astigmatism is a safe procedure that yields favorable and reproducible refractive results," Dr. Thilesen said.