1 1 ««««««««««««««««««««««««««««««««««2««««««««««««««««««««««««««««««««««2 Financial Disclosure The authors have no financial interest in the subject matter of this e-poster

Abstract  Purpose To determine if there is a relationship between the difference of scotopic pupil size and ablation zone diameter (Δd) and the perception of halos in scotopic conditions after myopic LASIK as assessed by a questionnaire.  Method This prospective study included 66 myopic patients aged 32.9 ± 8.3 years. The Zeiss Mel-80 LASER platform was used for the surgery. Visual acuity (LogMar), pre and post-operative refractive error, scotopic pupil diameter (measured with the Wasca aberrometer) and ablation zone were computed. At one month post- op, to subjectively evaluate visual symptoms such as halos, patients responded to a psychometric questionnaire consisting of 11 questions related to their quality of vision and dryness symptoms.  Results Mean scotopic pupil diameter was 6.18 ±0. 80 mm, mean Δd was 0.14 ± 0.71 mm. Mean depth of ablation was 92.4 ± 32.6 microns and the post-operative defocus was 0.39 ± 0.35 D. No significant correlation was found between Δd and halos in scotopic condition (r = 0.132) whilst a significant correlation was found between the residual defocus and halos as well as uncorrected visual acuity (UCVA) and halos. No other studied parameters such as SPK or dryness symptoms are correlated with halos. A positive correlation was found between difficulties when driving at night and halos (r = 0. 70).  Conclusion It is important to educate all patients about post-operative halos and risk of driving difficulties at night following LASIK. In addition, surgeons can slightly reduce the ablation zone to remove less tissue without increasing the risk of halos if the postoperative defocus is almost zero.

Introduction  Laser in situ keratomileusis (LASIK) has become the most commonly performed refractive procedure to treat myopia  There is, therefore, a need for greater understanding of the factors that directly affect postoperative visual function  A subset of patients reported nighttime glare, halo and vision disturbance 1-8  The role of pupil size in the appropriate selection of patients for LASIK insofar as risk of visual disturbances under low-light conditions remains controversial 3-8  The effect of increased spherical aberration after myopic LASIK is thought to be partially dependent on pupil size as well as attempted correction. This is supported by clinical findings of increasing incidence of glare, halo, and disturbances in night vision with smaller ablation diameter as well as larger pupil size and attempted correction 5-8  Several recent articles refute an association between pupil size and night vision disturbances. 5-8 Most of the literature that has attempted to address this relationship has reported no demonstrable association  In recent studies, the attempted degree of spherical correction, optical zone, patient age, or postoperative spherical equivalent were major risk factors for glare and halo symptoms as well as patients satisfaction. 6-8

Purpose  Determine if there is a relationship between the difference of scotopic pupil size and ablation zone diameter (Δd) and the perception of halos in scotopic conditions after myopic LASIK as assessed by a questionnaire  Determine if postoperative residual refractive error (defocus), UCVA (LogMar), ablation depth or ocular dryness symptoms or signs are related to the perception of halos  Determine if the perception of halos is correlated to reported difficulties in driving in the evening or at night

Method and materials  Prospective study  66 consecutive patients Age:18 to 40 (mean±SD: 32.9±8.3 years) Refraction: myopia ≤  LASER: Zeiss Meditec MEL80 ™ Wavefront optimized ablation profiles –Aberration Smart Ablation or Tissu Saving  Exclusion criteria Astigmatism > D BSCVA worst than 20/20 Per or postoperative complications  Self-administered psychometric questionnaire Before surgery and 1 month post-op Multiple choice questions (n=7) / visual analogue scale (n=4) addressing –Quality of vision (halos, stars around light, distortion of fine details) –Dryness symptoms –Difficulties in driving (day and night)

Statistical analysis  Data analyzed by the department of statistics (Université de Montréal)  SPSS software  Relations between variables identified by Pearson linear correlation coefficient (r)  The importance of a correlation was defined as: Strong when r ≥ 0.50 Medium when (0.30 ≤ r < 0.50) Low when (0.10 ≤ r < 0.30)  Univariate statistical analysis in order to study the variances in answers of the questionnaire

Results OD Mean ± SD OS Mean ± SD OD/OS Range Defocus (D) 0.40 ± ± to1.75 Ablation depth (microns) ± ± to 167 UCVA (LogMar)-0,01 ± 0, ± to Wasca scotopic pupil diameter (mm) 6.32 ± ± to 7.99 Ablation zone diameter (mm) 6.25 ± 0, ± to 6.5 Δd (mm) 0.07 ± ± to 1.49

Results (questionnaire) Answers Questions Completely disagree (%) Partially disagree (%) Neither agree or disagree (%) Partially agree (%) Completely agree (%) Does not apply (%) No answer (%) Perception of halos ,51.5 Difficulty driving during the day Difficulty driving at night or during the evening More difficulties driving during the day More difficulties driving at night or during the evening % of patients reported no difference in halos following LASIK 18% of patients reported being more bothered by halos after LASIK

Results (correlations/probability) ODHalos (Q2B)Halos (Q5B) Δdr = 0.17p = 0.190r = 0.01p = Ablation depthr = 0,14p = 0.286r = 0.10p = Defocus * r = -0.28p = 0,028r = -0.15p = Dry eye symptomsr = 0.11p = 0.398r = -0.01p = UCVA (LogMar) *r = 0.32p = 0.010r = 0.07p = Night driving * r = 0.70p = 0 OSHalos (Q2B)Halos (Q5B) Δdr = 0.17p = 0.190r = 0.01p = Ablation depthr = 0.14p = 0.267r = 0.02p = Defocus * r = 0.34p = 0.006r = -0.11p = Dry eye symptomsr = 0.11p = 0.398r = -0.01p = UCVA (LogMar) *r = 0.26p = 0.035r = 0.03p = Night driving * r = 0.70p = 0 * Statistically significant correlations are in blue (p = 0.05)

Results and Discussion  There is no significant correlation between Δd and the perception of halos in scotopic conditions when the value of Δd is less than 1.5 mm (all patients included in this study) but residual ametropia (defocus) and UCVA (LogMar) influence the perception of halos in scotopic conditions. Our results are in accordance with the ones of Schmidt et al 8  There is no significant correlation between the perception of halos and parameters such as ablation depth or symptoms of ocular dryness post LASIK  It is not possible to maintain that our results can be applied to ablation zone smaller than 1.5 mm in comparison with the scotopic pupillary diameter  Patients who perceive halos report more difficulties in driving at night (r=0.70 p=0)

Conclusions  It is important to recognize that in this study, while myopic patients with scotopic pupil diameter up to 7.99 mm were included, the ASA (Aberration Smart Ablation) ablation profile of the MEL80™ was chosen for patients with scotopic pupil diameter larger than 6.5 mm in order to reduce the increase in spherical aberration following LASIK  In addition, with today’s Excimer laser profile, surgeons can slightly reduce the ablation zone to remove less tissue without increasing the risk of halos if the postoperative defocus is almost zero and the UCVA is 20/20 (LogMar ≤ 0) or better  It is important to educate all patients about post-operative halos and risk of driving difficulties at night following LASIK.  Further study of risk factors for halos perception in the rapidly evolving field of laser refractive surgery is essential

References 1. Villa C, Gutiérrez R, Jiménez JR, González-MéijomeJM. Night vision disturbances after successful LASIK surgery. British J Ophthalmol 2007;91: Hersh PS, Steinert RF, Brint SF, Summit PRK-LASIK Study Group. Photorefractive keratectomy versus laser in situ keratomileusis: a comparison of optical side effects. Ophthalmology. 2000;107(5): Helgesen A. Pupil size and night vision disturbances after LASIK for myopia. Acta Ophthalmol Scand. 2004;82(4): Fan-Paul NI, Li J, Sullivan Miller J, and Florakis GJ. Night vision disturbances after corneal refractive surgery. Surv Ophthamol. 2002;47(6): Pop M, Payette Y. Risk factors for night vision complaints after LASIK for myopia. Ophthalmology. 2004;111(1): Lee YC, Hu FR, Wang IJ. Quality of vision after laser in situ keratomileusis: influence of dioptric correction and pupil size on visual function. J Cataract Refract Surg. 2003;29(4): Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, Bourque LB. Pupil size and quality of vision after LASIK. Ophthalmology. 2003;110(8): Schmidt GW, Yoon M, McGwin G, Lee PP, Stephen D. Mcleod SD. Evaluation of the relationship between ablation diameter, pupil size and visual function with vision-specific quality-of-life measures after Laser In Situ Keratomileusis. Arch Ophthalmol. 2007: 125: Acknowledgments Tien Hung Nguyen OD & Angela Sun OD for data collection Miguel Chagnon for statistical analysis