Visual outcome after correcting the refractive error of large pupil patients with wavefront-guided ablation

Abstract

Purpose: To investigate the efficacy and predictability of wavefront-guided laser in situ keratomileusis (LASIK) treatments using the iris registration (IR) technology for the correction of refractive errors in patients with large pupils.

Setting: Horus Vision Correction Center, Alexandria, Egypt.

Methods: Prospective noncomparative study including a total of 52 eyes of 30 consecutive laser refractive correction candidates with large mesopic pupil diameters and myopia or myopic astigmatism. Wavefront-guided LASIK was performed in all cases using the VISX STAR S4 IR excimer laser platform. Visual, refractive, aberrometric and mesopic contrast sensitivity (CS) outcomes were evaluated during a 6-month follow-up.

Results: Mean mesopic pupil diameter ranged from 8.0 mm to 9.4 mm. A significant improvement in uncorrected distance visual acuity (UCDVA) (P < 0.01) was found postoperatively, which was consistent with a significant refractive correction (P < 0.01). No significant change was detected in corrected distance visual acuity (CDVA) (P = 0.11). Efficacy index (the ratio of postoperative UCDVA to preoperative CDVA) and safety index (the ratio of postoperative CDVA to preoperative CDVA) were calculated. Mean efficacy and safety indices were 1.06 ± 0.33 and 1.05 ± 0.18, respectively, and 92.31% of eyes had a postoperative spherical equivalent within ±0.50 diopters (D). Manifest refractive spherical equivalent improved significantly (P < 0.05) from a preoperative level of -3.1 ± 1.6 D (range -6.6 to 0 D) to -0.1 ± 0.2 D (range -1.3 to 0.1 D) at 6 months postoperative. No significant changes were found in mesopic CS (P ≥ 0.08), except CS for three cycles/degree, which improved significantly (P = 0.02). Magnitudes of primary coma and trefoil did not change significantly (P ≥ 0.34), with a small but statistically significant increase in primary spherical aberration.

Conclusion: Wavefront-guided LASIK provides an effective correction of low to moderate myopia or myopic astigmatism in large pupil patients without deterioration of visual quality.

Keywords: LASIK; large pupil; wavefront.

Figure 1

Pentacam (Oculus Inc, Wetzlar, Germany) axial curvature difference map comparing pre- and postoperative curvature to assess treatment centration.

Figure 2

Comparative distribution of the preoperative CDVA and the UDVA at the end of the follow-up. Abbreviations: CDVA, corrected distance visual acuity; UDVA, uncorrected distance visual acuity.

Figure 3

Distribution of changes in postoperative CDVA during follow-up. Abbreviation: CDVA, corrected distance visual acuity.

Figure 4

Distribution of the postoperative spherical equivalent during the whole follow-up. Abbreviation: D, diopters.

Figure 5

Scattergram showing the relationship between the achieved postoperative spherical equivalent correction and the intended. Abbreviations: SE, spherical equivalent; D, diopters.

Figure 6

Mean monocular contrast sensitivity function measured under mesopic conditions preoperatively (gray line) and postoperatively (red line).

Figure 7

Scattergram showing the relationship between the change with surgery in spherical equivalent (ΔM) and the associated change in the magnitude of the Zernike coefficient corresponding to the primary spherical aberration (ΔZ₄⁰). Note: The adjusting line to the data obtained by means of the least-squares fit is shown (R²: 0.20): ΔZ ΔM ₄⁰ =0.030 − 0.052×. Abbreviation: D, diopters.

Figure 8

CustomVue™ software (Abbott Medical Optics Inc, Santa Ana, CA) showing the aberrometric outcomes in one patient that presented an improvement/ maintenance of HOA. (A) Shows wave-front maps, and (B) shows Zernike polynomials differences. Note: Images used with permission of Abbott Medical Optics Inc, Santa Ana, CA. Abbreviation: HOA, higher order aberrations.