Transcript ACHIEVING REFRACTIVE TARGET IN PHAKIC IOLs.

Minimizing Risk
in Visian ICL Implantation.
NO FINANCIAL DISCLOSURE
Dr. MATHEW KURIAN
Dr. ROHIT SHETT Y, Dr. HEMAMALINI M. S., Dr. SHETT Y BHUJANG K.
CATARACT & REFRACTIVE LENS SURGERY SERVICES
NARAYANA NETHRALAYA, BANGALORE
Implantable
Collamer Lens
• The ICL(Staar Surgical AG) is FDA approved for myopia
• It is a plate haptic lens implanted in the sulcus with an aqueous
layer separating it from the lens.
• This requires accurate intraocular sizing calculations.
• Horizontal white to white diameter (Orbscan II) estimates sulcus
(Recommended method)
• However, estimating sulcus size through white to white
measurements could lead to improper sizing1 that would only
be detected in the postoperative period.
• Recent literature: UBM is more reliable2.
1. Werner L, et.al,“Correlation between different measurements within the eye relative to phakic intraocular lens implantation” JCRS 30:1982–8
2. Choi KH, et.al, “Ultrasound biomicroscopy for determining visian implantable contact lens length in phakic IOL implantation.” JRS. 362-7.
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AIMS AND OBJECTIVES
• To study the sizing of the Visian implantable Collamer® lens (ICL™)
– by white to white measurement using the Orbscan II and
– sulcus diameter using ultrasound biomicroscopy (UBM)
• To correlate the results to the postoperative vaulting assessed by
– Slit lamp evaluation
– UBM measurement from the anterior capsule to the posterior ICL surface.
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MATERIALS AND METHODS
• Prospective study with IERB clearance & informed consent
• All cases which underwent Implantable Collamer Lens (ICL)
implantations for the correction of myopia from Jan to Dec 2007
• Standard inclusion and exclusion criteria for ICL implantation
• Surgeries performed by a single surgeon.
• Standardized UBM scans (single examiner)
ICL POWER CALCULATION
• Refraction (manifest/cycloplegic)
• Keratometry
• Desired target post-operative
refraction
• Corneal thickness
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ICL SIZING
• Horizontal white to white (Orbscan)
• Horizontal sulcus diameter (UBM).
• ACD
SULCUS ESTIMATION
ORBSCAN
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UBM
POST-OPERATIVE FOLLOW UP
•
Reviewed on day 1 & 7, 6 weeks
•
Thorough ocular examination
•
Correction of residual refractive error
•
ASSESSMENT OF VAULT
•
Central distance between anterior surface of
the crystalline lens and posterior surface of the
ICL
•
Ideal sized ICL will provide a vault of 0.250 to
0.750 mm ( ½ CT to 1 ½ CT)
•
An undersized ICL (less than 0.125 mm vault)
may increase the risk of anterior subcapsular
opacification.
•
An oversized ICL (more than 1 mm vault) may
cause angle closure glaucoma, endothelial
damage and glare.
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RESULTS
•
• Twenty one eyes of 17 patients
– 11 men and 6 women
– 11 right & 10 left eyes
• Mean age was 25.24yrs + 5.72
• Mean refractive spherical equivalent
– PREOP: 16.51 D + 3.68
– POSTOP: -1.16 D + 0.87
• Vault
– NO LOW VAULTS
– 1 High vault: 1.51mm
– Mean Vault (UBM):
• 0.67 + 0.29
•
The mean for the measurements
– Orbscan II (white to white) =
11.63mm + 0.35
– UBM (sulcus diameter) =
11.73mm + 0.30
Paired measures one by each
technique and analyzed by the
Bland Altman Technique3,4 that
plotted the difference between the
results by the two measuring
instruments against their means.
3. Altman DG and Bland JM “Measurement in Medicine: the Analysis of Method Comparison Studies,” The Statistician, 32, 307-317.
4. Bland JM and Altman DG “Statistical Methods for Assessing Agreement between 2 Methods of Clinical Measurement,” Lancet, 986, 307-310.
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HIGH VAULT
ICL to Anterior Capsule = 1.51mm
ICL
Iris
Anterior
Capsule
Cornea
ICL
• Shallow anterior chamber
• Large gap between
ICL & Anterior Capsule
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Anterior
Capsule
Endothelium to ICL = 1.32 mm
Bland Altman Plot
BLAND ALTMAN PLOT
Orbscan WTW - UBM STS (mm)
1.00
0.80
0.60
+ 0.592
0.40
0.20
0.00
11.0
11.2
11.4
11.6
11.8
12.0
12.2
-0.20
-0.40
-0.60
Average
12.4
12.6
Mean Difference = -0.10 + 0.35
Limits of Agreement = -0.790 and + 0.592
Pitman’s test of difference in variance
p = 0.426
- 0.790
• X- Axis: Mean of a pair of values obtained by Orbscan and UBM
• Y- Axis: Difference between each pair of measurements
• 95% of the values fall within Mean Difference + 2 standard deviations
• Good agreement between the values obtained by the 2 instruments
• However the trendline indicates that Orbscan would
• Underestimate in small eyes
• Overestimate in large eyes
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IMPACT ON ICL SIZING
DIAMETER OF ICL (ORBSCAN vs UBM)
VAULT ASSESSMENT
Difference in ICL size (mm)
Orbscan-UBM
2.00
1.50
Slit Lamp
UBM
1.00
1.51
High
0.54
Normal
0.65
Normal
0.63
Normal
0.50
0.00
11.00
-0.50
11.50
12.00
12.50
13.00
-1.00
13.50
14.00
ICL diameter by Orbscan (mm)
• X- Axis: ICL diameter as calculated by Orbscan
• Y- Axis: Difference between Orbscan & UBM ICL diameters
• The trendline indicates that Orbscan ICL diameter is
Underestimated in small eyes; Overestimated in large eyes
• The vault assessment by slit lamp & UBM are denoted alongside
• Normal vault: Difference in ICL diameter as calculated by the 2 techniques is < 0.5mm
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DISCUSSION
• All techniques have some measurement error
• "Do the two methods of measurement agree closely?"
• Does the technique used influence the ICL diameter?
• How does the difference affect the vault?
• Same ICL diameter irrespective of the technique in 12 of 21 eyes (57.14%)
• The height of the vault remains within normal limits if ICL diameter does not
vary by > + 0.5mm (20 of 21 eyes; 95.24%)
• If Orbscan underestimates then the vault would be lower.
• If Orbscan overestimates then the vault would be high (1 eye; 4.76%)
• Caution for larger eyes; as Orbscan seems to over estimate
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CONCLUSION
• The Visian implantable contact lens (ICL) requires accurate
measurements of sulcus to sulcus diameter for implantation.
• There was good agreement between the UBM & OrbscanII
• UBM may be better in relative anterior megalophthalmos as
Orbscan tends to over estimate in larger eyes.
• UBM should be mandatory in the preoperative evaluation as
it increases the predictability of the postoperative vault and
thus enhances the safety of the procedure.
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