Abstract
Abstract: :
Purpose: To investigate the distribution of the eye's higher order aberrations in postoperative laser refractive surgery patients with visual complaints and highly irregular corneal shapes. Methods: Postoperative wave aberrations were measured for 33 symptomatic postoperative LASIK and/or PRK eyes using a Shack–Hartmann wavefront sensor (Zywave, Bausch & Lomb) over a 6 mm pupil. These measurements were averaged across patients with similar corneal topographic diagnoses (central islands, decentered ablations, a new group we termed "baby bowties" and irregularly irregular corneas) and were compared with 46 pre– and successful postoperative LASIK eyes. Point spread functions and Strehl ratios were computed for each. 14 eyes had ultrasound corneal pachymetry measured. Results: The average higher order rms wavefront error (3rd, 4th and 5th orders) for the symptomatic patients was 1.31 ± 0.58 µm and was significantly elevated (p<0.001) relative to both normal preoperative (0.38 ± 0.14 µm) and successful postoperative LASIK eyes (0.58 ± 0.21µm) over a 6 mm pupil. Higher order rms wavefront error increased with pupil size, roughly doubling for each millimeter of increasing pupil diameter. On average,eyes with central islands (n=6) had the most vertical coma (mean –1.35 ± 0.43µm) while eyes with decentered ablations (n=2) had the most horizontal coma (mean of –0.93 ± 0.13 µm) while both had elevated spherical aberration (means of 0.83 ± 0.11µm and 0.69 ± 0.29 µm, respectively) compared with other symptomatic patients (0.27 ± 0.53 µm) and successful post–LASIK eyes (mean of 0.42 ± 0.20 µm). Eyes with a topographic central "baby bowtie" demonstrated the most secondary astigmatism (combined mean rms = 0.56 ± 0.17 µm). In 10 symptomatic patients with bilateral laser refractive surgery, there was significant mirror symmetry between higher order Zernike terms in fellow eyes (R = 0.66, p<0.001) which could be observed in the point spread function (PSF). Pachymetry of 14 symptomatic eyes revealed an inverse correlation between corneal thickness and higher order rms (R = –0.67, p<0.01.) Conclusions: Symptomatic post–laser refractive surgery patients with irregular corneas have significant higher order aberrations that correlate with corneal topography. In patients with symptoms in both eyes, there is significant mirror–symmetry between left and right eyes, suggesting a non–random reason for the undesirable outcome. Low residual corneal thickness may be a predictor of increased higher order rms wavefront error.
Keywords: refractive surgery: complications • refractive surgery: corneal topography • refractive surgery: optical quality