Posters

Comprehensive analysis of horizontal corneal diameter measured by six clinical methods

Poster Details

First Author: D.Meda INDIA

Co Author(s):    H. Matalia   A. Ranganath           

Abstract Details

Purpose:

To measure and compare horizontal corneal diameter (white to white) measured by 6 different methods i.e. Pentacam (Scheimpflug based topography), Keratograph( Placido based), IOL master(partial coherence interferometry biometry device), iDesign(aberrometer) and iTrace (Ray tracing) and manual digital caliper.

Setting:

Tertiary eye care centre and teaching institute, South India

Methods:

In this prospective study, 60 eyes of 30 consecutive volunteers were included. All of them underwent horizontal white to white measurement by Pentacam, Keratograph, IOL master, iDesign, iTrace and manual digital caliper. All measurements were taken 3 times to evaluate intrasession repeatability, except for the manual caliper measurement. The values were directly taken as measured by the instrument for Keratograph, I trace, I design and IOL master. For Pentacam, the white to white was manually measured from the horizontal inversed Scheimpflug image using the digital caliper by a single examiner. Manual measurements were taken using a digital caliper again by a single examiner. Bias was avoided as none of the examiners were aware of the results of the other tests.

Results:

The mean horizontal corneal diameter was 11.88 +/-0.44 (P value <0.05) with the IOL master,11.73 +/- 0.43(P value <0.05) with the Pentacam, 12.31 +/- 0.34 (P value <0.05) with iDesign ,10.88 +/- 0.5(P value <0.05) with iTrace, 12.06 +/- 0.35(P value <0.05) with the Keratograph and 11.33+/- 0.35(P value <0.05) with manual measurement. Annova statistical analysis showed statistically significant difference (P value <0.05) between measurements made by all the methods. Measurements made by the iTrace are smallest and those by iDesign are comparatively largest. Repeatability was best for Pentacam (Intra class correlation of 0.988) and least for iTrace (Intraclass correlation of 0.769). Highest correlation was found between Pentacam and iDesign ( Correlation coefficient of 0.754)iTrace showed poor correlation with all the other instruments with correlation coefficient of -0.07 with iDesign ,-0.027 with Keratograph,0.092 with IOL Master , -0.132 with manual caliper measurement and -0.16 with Pentacam. Manual digital measurement which is the gold standard for the surgeon showed best correlation with iDesign(Correlation coefficient of 0.675) and Pentacam (correlation coefficient of 0.611)

Conclusions:

Among all the instruments described, repeatability of horizontal corneal diameter is best with Pentacam and worst with iTrace. Measurements made by iTrace are smallest and those by iDesign are largest. Over all iTrace had the worst Correlation coefficient. Manual measurements (which is the surgeons preferred method) had moderate correlation with iDesign and Pentacam. As of now none of the methods described can be used interchangeably and each surgeon has to decide the best method depending on his results. FINANCIAL INTEREST: NONE