1. Paul “Butch” Harton, MD Harbin Clinic Eye Center Rome, GA USA ASCRS Boston Poster, 2010 The Author has no financial interest in the subject matter of this poster

2.  Accurate Horizontal Anterior Chamber Angle- to-Angle (ATA) measurements are necessary for the implantation of both phakic and aphakic IOLs.  The general purpose of this pilot study was to determine the degree of correlation between the OCT and UBM methods of measuring ATA

3.  30 Eyes of 15 healthy volunteers  Each eye was scanned with the Sonomed VuMaxII High Resolution Ultrasound (UBM) by a single Technician  The Author, blind to the on-screen identity of each eye analyzed the UBM video  Using the on-screen calipers, the best visible ATA dimension was recorded

5.  Each eye was also scanned with the Visante OCT by a single Technician. The Author, again blind to the identity of each eye, used the on-screen calipers to measure OCT ATA  However the OCT ATA was measured 2 ways. The first was similar to UBM, the second used a rule developed for this study  This rule was suggested after personal communications indicated OCT might over- estimate ATA when measured with similar landmarks as UBM (This theory has been subsequently supported by Kim, Kim and Song in J Refract Surg. 2010;26:120-126)

6.  The two values of OCT recorded are described below:  One caliper line simply measured the visible extent of ATA in a manner similar to the UBM  (OCT ATA – Visible Margins or VM)  The other method determined OCT ATA using a rule where the caliper line was always drawn tangential to the anterior lens surface. The ATA was determined where this line then intersected the inner aspect of the cornea.  (OCT ATA-Lens Plane or LP)

8.  Mean ATA in millimeters (N=30) UBM OCT VM OCT LP 11.76 12.26 11.86 ( SD 0.47) (SD 0.48) (SD 0.58)

9.  Mean Difference (mm) UBM-OCT VM -0.494* UBM-OCT LP -0.097 OCT VM – OCT LP+0.397*  Correlation Coefficient (r) UBM-OCT VM0.865 UBM-OCT LP0.873 OCT VM-OCT LP0.902 * Statistically Significant p<.0001

10.  OCT and UBM show close correlation with one another in their determination of the horizontal anterior chamber angle-to-angle measurement (ATA)  The absolute value of ATA is however significantly different between the two technologies when measuring from the visible margins of ATA. OCT VM consistently gives larger ATA values vs. UBM.

11.  These findings are similar to the recent article by Kim, Kim and Song in the Journal of Refractive Surgery.  This article found a high degree of correlation between UBM and OCT ATA measurements  The OCT measurements defined in their study were the same as theVisible Margin (VM) type in our study and similarly showed the OCT ATA to be consistently larger than the UBM ATA.  This may indicate the OCT overestimates ATA using this criteria

12.  Our adjustment in the OCT ATA measurement (OCT LP) has close correlation with UBM and produces similar absolute values as UBM  Further studies are needed to better define the degree of correlation and the accuracy of these technologies with respect to phakic and aphakic IOL sizing.  Further studies are needed to confirm which technology provides a better determination of the actual ATA value.