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. dr.mkurian@gmail.com

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. dr.mkurian@gmail.com

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 ICL SIZING Horizontal white to white (Orbscan) Horizontal sulcus diameter (UBM). ACD dr.mkurian@gmail.com

SULCUS ESTIMATION ORBSCAN UBM dr.mkurian@gmail.com

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. dr.mkurian@gmail.com

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. dr.mkurian@gmail.com

ICL to Anterior Capsule = 1.51mm HIGH VAULT ICL to Anterior Capsule = 1.51mm Endothelium to ICL = 1.32 mm ICL Iris Anterior Capsule Cornea ICL Anterior Capsule Shallow anterior chamber Large gap between ICL & Anterior Capsule dr.mkurian@gmail.com

Bland Altman Plot 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 + 0.592 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 dr.mkurian@gmail.com

IMPACT ON ICL SIZING VAULT ASSESSMENT Slit Lamp UBM 0.54 Normal 0.65 1.51 High 0.54 Normal 0.65 0.63 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 dr.mkurian@gmail.com

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 dr.mkurian@gmail.com

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. dr.mkurian@gmail.com