COMPARISON OF HORIZONTAL ANTERIOR CHAMBER ANGLE-TO-

ANGLE MEASUREMENTS OBTAINED USING OPTICAL COHERENCE

TOMOGRAPHY AND HIGH-FREQUENCY ULTRASONIC

BIOMETRY

Paul “Butch” Harton, MDHarbin Clinic Eye Center

Rome, GA USAASCRS Boston Poster, 2010

The Author has no financial interest in the subject matter of this poster

Purpose

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

Methods – UBM ATA 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

UBM - ATA

Methods – OCT ATA 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)

Methods OCT - ATA 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)

OCT - ATA

Results 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)

UBM OCT VM OCT LP11.5

11.6

11.7

11.8

11.9

12

12.1

12.2

12.3

Chart Title

Mean (mm) N=30

Results Mean Difference (mm)

UBM-OCT VM -0.494*UBM-OCT LP -0.097OCT VM – OCT LP +0.397*

Correlation Coefficient (r)UBM-OCT VM 0.865UBM-OCT LP 0.873OCT VM-OCT LP 0.902 Mea

n Differe

nce (m

m)

Corre

lation

C

oefficie

nt

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

UBM - OCT VMUBM - OCT LPOCT VM - OCT LP

* Statistically Significant p< .0001

Conclusions 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.

Conclusions 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

Conclusions 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.