1. Poster# P36 Comparison of Techniques of Measuring Anterior Chamber Depth and Corneal Curvature in Indian Eyes Sujata Das, MS, FRCS Anjula Kumari, B.Optom Mukesh Kumar, Dip. Optom L V Prasad Eye Institute Bhubaneswar, India, 751024 sujatadas@lvpei.org Authors do not have any financial or conflicting interests to disclose

2. Poster# P36 Introduction  Accurate prediction of postoperative refraction is a major challenge in cataract surgery.  Postoperative refraction is determined by three main factors: corneal curvature, corneal curvature, axial length, axial length, postoperative anterior chamber depth (ACD) or pseudophakic effective lens position. postoperative anterior chamber depth (ACD) or pseudophakic effective lens position.  Several instruments are available for measuring ACD and corneal curvature; some are ultrasound-based and the others are optical-based.

3. Poster# P36 Introduction  Limitation of ultrasound-based methods include: inadvertent corneal applanation when using the contact method, inadvertent corneal applanation when using the contact method, off-axis measurement, off-axis measurement, moderate precision and resolution. moderate precision and resolution.  The IOL Master ( Carl Zeiss Jena GmbH, Germany ) uses methods based on image analysis for corneal radius and ACD measurements in which distances between light reflections on cornea, iris and lens are measured.  The manual keratometry method measures corneal curvature by assuming the cornea to be a convex mirror.

4. Poster# P36 Purpose The purpose of the study was to compare measurements of anterior chamber depth (ACD) and corneal curvature obtained with the IOL Master to those with ultrasound A- scan and manual keratometry respectively in Indian eyes.

5. Poster# P36  Statistical significance of the inter-device differences for each parameter was evaluated by the F-test.  Inter-device correlation was evaluated by Pearson correlation coefficient.  Statistical significance of the intra-patient differences for each device was evaluated by the paired t-test.  To assess inter-device agreement and interchangeability, Bland and Altman method was used. Statistical Analysis

6. Poster# P36  Seventy eyes of 35 patients (Male : Female = 23 : 12) with mean age 60.8±11.3 years were recruited for the study. Results CharacteristicUltrasound A-Scan IOL Masterp-Value (F-test) Anterior Chamber Depth (mm)3.205±0.3823.165±0.3850.951 CharacteristicManual Keratometry IOL Master p-Value (F-test) Corneal Curvature (Diopters)44.489±1.49744.514±1.4520.718 The inter-device difference was 0.04±0.42 mm The inter-device difference was 0.02±0.90 D

7. Poster# P36 Anterior Chamber Depth (in mm) CharacteristicUltrasound A-Scan IOL Masterp-Value (F-test) a.Right Eye3.19±0.403.06±0.440.558 b.Left Eye3.22±0.373.27±0.280.140 c.Intra-patient Difference [a-b]-0.04±0.37-0.21±0.52 d.p-Value (Paired t-test)0.5610.020 Corneal Curvature (in Diopters) CharacteristicManual Keratometry IOL Masterp-Value (F-test) a.Right Eye44.49±1.5144.51±1.460.804 b.Left Eye44.49±1.5044.52±1.450.796 c.Intra-patient Difference [a-b]-0.01±0.55-0.02±0.58 d.p-Value (Paired t-test)0.9080.826Results

8. Poster# P36 Results Pearson Correlation for Anterior Chamber Depth Ultrasound A-Scan vs. IOL Master a.Sample Size (n):70 b.Pearson Correlation Coefficient (r):0.399 c.p-Value:0.0006 d.95% Confidence Interval for r:0.181 to 0.580 Pearson Correlation for Corneal Curvature Manual Keratometry vs. IOL Master a.Sample Size (n):140 b.Pearson Correlation Coefficient (r):0.815 c.p-Value:< 0.0001 d.95% Confidence Interval for r:0.751 to 0.864

9. Poster# P36 For measurements of ACD, 95% limits of agreement were -0.78 to 0.86 mm Results Mean Anterior Chamber Depth (in mm) [ Ultrasound A-Scan and IOL Master ] Inter-device difference (mm) [ Ultrasound A-Scan minus IOL Master ]

10. Poster# P36 For measurements of corneal curvature, 95% limits of agreement were -1. 8 to 1.7 D Results Inter-device difference (D) [ Manual Keratometry minus IOL Master ] Mean Corneal Curvature (D) [ Manual Keratometry and IOL Master ]

11. Poster# P36  Contact ultrasound is the most common method used for measurement of anterior chamber depth.  Ultrasound measurements can be affected by various factors such as experience of the operator, the differences of probe handling, alignment error, etc.  Higher intra- and inter- observer variability in measurements with applanation ultrasound, increased chance of corneal abrasion and difficulty in quick sterilization of the contact probe make non-contact optical device a popular alternative.  Disparity of keratometry by various techniques have been reported. However, none of the previous studies compare IOL Master with manual keratometry. Discussion

12. Poster# P36 Conclusion Measurements of anterior chamber depth and corneal curvature with the IOL Master do not vary significantly with that of ultrasound A-scan and manual keratometry respectively, and therefore may be used interchangeably. Thank You !