The effect of the ablation zone diameter in relationship to the scotopic pupil size on the patient perception of halos after myopic LASIK

1
The effect of the ablation zone diameter in
relationship to the scotopic pupil size on the
patient perception of halos after myopic LASIK
Nadia Marie Quesnel, OD MSc 1-2 Christian
Ferremi, MD, FRCS (c) 2 Martin Boileau MD, FRCS
(c) 2 Laurent Lalonde MD, FRCS (c) 2

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

1
2
Abstract

• Purpose
• To determine if there is a relationship between
  the difference of scotopic pupil size and
  ablation zone diameter (?d) 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 ?d 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 ?d 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.

3
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

4
Purpose

• Determine if there is a relationship between the
  difference of scotopic pupil size and ablation
  zone diameter (?d) 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

5
Method and materials

• Prospective study
• 66 consecutive patients
• Age18 to 40 (meanSD 32.98.3 years)
• Refraction myopia -10.00
• LASER Zeiss Meditec MEL80
• Wavefront optimized ablation profiles
• Aberration Smart Ablation or Tissu Saving
• Exclusion criteria
• Astigmatism gt -3.00 D
• BSCVA worst than 20/20
• Per or postoperative complications
• Self-administered psychometric questionnaire
• Before surgery and 1 month post-op
• Multiple choice questions (n7) / visual
  analogue scale (n4) addressing
• Quality of vision (halos, stars around light,
  distortion of fine details)
• Dryness symptoms
• Difficulties in driving (day and night)

6
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 lt 0.50)
• Low when (0.10 r lt 0.30)
• Univariate statistical analysis in order to study
  the variances in answers of the questionnaire

7
Results
OD Mean SD OS Mean SD OD/OS Range
Defocus (D) 0.40 0.33 0.39 0.36 0.00 to1.75
Ablation depth (microns) 94.39 32.73 90.40 32.45 31 to 167
UCVA (LogMar) -0,01 0,09 -0.01 0.09 -0.15 to 0.30
Wasca scotopic pupil diameter (mm) 6.32 0.79 6.04 0.81 4.07 to 7.99
Ablation zone diameter (mm) 6.25 0,24 6.25 0.24 5.80 to 6.5
?d (mm) 0.07 0.66 -0.21 0.71 -1.93 to 1.49
8
Results (questionnaire)
Answers Questions Completely disagree () Partially disagree () Neither agree or disagree () Partially agree () Completely agree () Does not apply () No answer ()
Perception of halos 25.8 12.1 4.5 37.9 16.7 1,5 1.5
Difficulty driving during the day 93.9 0 0 0 1.5 0 4.5
Difficulty driving at night or during the evening 48.5 21.2 0 21.2 3.0 0 6.1
More difficulties driving during the day 92.4 1.5 0 1.5 0 0 4.5
More difficulties driving at night or during the evening 54.5 10.6 0 19.7 9.1 0 6.1
73 of patients reported no difference in halos
following LASIK 18 of patients reported being
more bothered by halos after LASIK
9
Results (correlations/probability)
OD Halos (Q2B) Halos (Q2B) Halos (Q5B) Halos (Q5B)
?d r 0.17 p 0.190 r 0.01 p 0.306
Ablation depth r 0,14 p 0.286 r 0.10 p 0.451
Defocus r -0.28 p 0,028 r -0.15 p 0.234
Dry eye symptoms r 0.11 p 0.398 r -0.01 p 0.939
UCVA (LogMar) r 0.32 p 0.010 r 0.07 p 0.596
Night driving --------- --------- r 0.70 p 0
OS Halos (Q2B) Halos (Q2B) Halos (Q5B) Halos (Q5B)
?d r 0.17 p 0.190 r 0.01 p 0.306
Ablation depth r 0.14 p 0.267 r 0.02 p 0.879
Defocus r 0.34 p 0.006 r -0.11 p 0.383
Dry eye symptoms r 0.11 p 0.398 r -0.01 p 0.939
UCVA (LogMar) r 0.26 p 0.035 r 0.03 p 0.806
Night driving --------- --------- r 0.70 p 0
Statistically significant correlations are in
blue (p 0.05)
10
Results and Discussion

• There is no significant correlation between ?d
  and the perception of halos in scotopic
  conditions when the value of ?d 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 (r0.70 p0)

11
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 todays 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

12
References
Acknowledgments

• 1. Villa C, Gutiérrez R, Jiménez JR,
  González-MéijomeJM. Night vision disturbances
  after successful LASIK surgery. British J
  Ophthalmol 2007911031-1037
• 2. 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. 2000107(5)925-933.
• 3. Helgesen A. Pupil size and night vision
  disturbances after LASIK for myopia. Acta
  Ophthalmol Scand. 200482(4)454-60.
• 4. Fan-Paul NI, Li J, Sullivan Miller J, and
  Florakis GJ. Night vision disturbances after
  corneal refractive surgery. Surv Ophthamol.
  200247(6)533-46.
• 5.Pop M, Payette Y. Risk factors for night vision
  complaints after LASIK for myopia. Ophthalmology.
  2004111(1)3-10.
• 6. 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.
  200329(4)769-777.
• 7. Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J,
  Laurent J, Bourque LB. Pupil size and quality of
  vision after LASIK. Ophthalmology.
  2003110(8)1606-1614.
• 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 1037-1042.

• Tien Hung Nguyen OD Angela Sun OD for data
  collection
• Miguel Chagnon for statistical analysis