1. Adriana S. Forseto1, MD Walton Nosé1,2, MD
Changes in IOL Positioning and Refraction after Neodymium:Yag Laser Posterior Capsulotomy
Adriana S. Forseto1, MD
Walton Nosé1,2, MD
1Eye Clinic Day Hospital
2Federal University of São Paulo - UNIFESP
São Paulo - Brazil
The authors have no financial interest in the subject matter of this poster

2. Introduction
Intraocular lens (IOL) positioning alteration is a possible complication of Neodymium:YAG laser posterior capsulotomy (Nd:YAG).
Some studies have already been proposed to quantify IOL positioning changes after Nd:YAG by measuring the anterior chamber depth (ACD) pre and after the treatment. Using the Scheimpflug’s principle we can determine not only the ACD changes but also the actual value of IOL decentration and tilt.
Purpose
The purpose of this study is to evaluate the effect of Neodymium:YAG laser posterior capsulotomy (Nd:YAG) on intraocular lens (IOL) positioning and refraction

3. Methods Prospective study: 25 eyes (20 patients)
Inclusion criteria
Presence of posterior capsule opacification (PCO)
Minimum post cataract surgery follow-up: 3 months
The anterior chamber depth (ACD) and the IOL positioning changes (tilt and decentration) were measured using a Scheimpflug camera (EAS-1000; NIDEK):
4 measurements were obtained from each eye within 15 days prior to Nd:YAG and 30 days post treatment to assess the method’s reproducibility
Changes in refraction and best corrected visual acuity (BCVA) were analyzed
Statistical analysis: parametric and nonparametric testing (significant level: p < 0.05)

4. Example of decentration and tilt analysis of a posterior chamber IOL pre Nd:YAG using the Scheimpflug camera
Two images of the anterior segment of the eye were obtained with the rotating CCD camera at the 45º and 135º angles
The images were transferred to the computer for storage and analysis
Measurements of the extension and direction of decentration (mm) and the degree of tilt (°) of the implanted IOL, were calculated through the IOL image modes of the apparatus

5. Results The mean time between cataract surgery and Nd:YAG: IOL type:
24 ± 20 months (range, 3 to 60 months)
IOL type:
3-piece IOL: 12 eyes
1-piece IOL: 12 eyes
unknown: 1 eye (impossible to evaluate: insufficient mydriasis)
Nd:YAG energy power for 4.00mm capsulotomy opening:
1.7  0.3 mJ (range, 1.0 to 2.2 mJ)
Complications: Retinal detachment (n = 1)
Excluded because of poor post Nd:YAG eye fixation for evaluation

6. Results
No statistically significant changes were observed comparing the mean pre and post Nd:Yag ACD (p=0.327) :
Pre Nd:YAG: 4.14  0.39 mm
Post Nd:YAG: 4.11  0.46 mm
ACD pre Nd:YAG = 3.87mm
ACD post Nd:YAG = 3.84mm

7. Results
Reproducibility test of the Scheimpflug camera for IOL decentration and tilt
Pre-Nd:YAG Decentration
(mm)
Post-Nd:YAG Decentration
Pre-Nd:YAG
Tilt
(o)
Post-Nd:YAG
Measurements
Mean 
S.D. 1
0.34
0.31
0.38
0.26
3.40
2.39
3.27
1.73 2
0.32
0.28
0.33
0.20
2.98
2.21
2.79
1.71 3
0.17
3.36
2.92
2.53
1.52 4
0.36
0.35
3.49
3.07
1.65
Comparison
2 r = 0.41
p= 0.937
2 r = 1.39
p= 0.709
2 r = 4.85
p= 0.183
2 r = 6.45
p= 0.092
The four IOL positioning measurements taken from each eye were similar

8. Results
Posterior chamber IOL decentration and tilt pre and post Nd:YAG
Exam
Decentration
(mm)
Tilt
(o)
Pre Nd:YAG
0.34  0.25
3.30  2.55
Post Nd:YAG
0.34  1.18
2.78  1.44
z= p= 0.808
z= p=0.235
There were no statistically significant differences between pre and post laser measurements

9. Results
Correlation between the number and the power of laser shoots used and the post Nd:YAG IOL positioning percent variation
Variation
Number of laser shoots
Power of laser shoots
(mJ)
Tilt
rs= 0.08
p= 0.736
rs= 0.11
p= 0.651
Decentration
rs= -0.01
p= 0.980
rs= 0.31
p= 0.166
No statistically significant correlation was observed between the number and power of laser shoots used and the IOL positioning percent variation

10. Results
Association between the IOL type and its post Nd:YAG positioning percent variation (mean  standard deviation)
IOL
Decentration
Tilt
1-piece
17.76 
31.77 
3-piece
14.67 
13.35  75.27
U= p=0.347
U=58.0 p= 0.651
No association was demonstrated between the type of the IOL and its positioning change post laser

11. Results
No statistically significant changes were observed comparing the mean pre and post Nd:YAG mean Sph Eq refraction (p=0.362):
Pre Nd:YAG: –0.65  1.47 D (range, to +2.00D)
Post Nd:YAG: –0.59  1.44D (range, to +2.40D)
The BCVA remained unchanged in 8 eyes and improved in 14 eyes. Only the case with retinal detachment lost lines of BCVA

12. Conclusions
No statistically significant changes of the IOL positioning and refraction were induced by the Nd:YAG laser posterior capsulotomy