Can Ultrasound Biomicroscopy Match the Gold Standard Ultrasound Pachymetry for the Measurement of Central Corneal Thickness?

Neeharika P. Shah

Volume : V, Issue : III, March - 2015

Can Ultrasound Biomicroscopy Match the Gold Standard Ultrasound Pachymetry for the Measurement of Central Corneal Thickness?

Neeharika P. Shah

Abstract :

Aim: Ultrasound Biomicroscopy (UBM) has emerged as a valuable tool in the diagnosis of various Ophthalmological conditions. Some applications in Glaucoma include measurement of Central Corneal Thickness (CCT), lens thickness, anterior chamber depth and angle, trabecular iris angle, angle recess area, etc. CCT acts as a confounding factor for the diagnosis of primary open angle glaucoma because while measuring intraocular pressure (IOP) by Applanation tonometry, a thicker cornea leads to overestimation of IOP and a thinner cornea leads to underestimation of IOP. Our study aims to assess the accuracy with which UBM measures the CCT vs. the gold standard Ultrasound Pachymetry (USP). Method: Our study was a prospective study undertaken during the period from June 2009 to June 2011. We studied 120 eyes of 60 patients diagnosed with Primary open angle Glaucoma. Imaging using UBM with a 50 MHz probe was done to measure CCT. Pachymetry using Ultrasonic Pachymeter was done till 3 consistent reliable readings were obtained and the average of these readings were taken as the final CCT reading. Result: After analyzing by means of statistical principles, the coefficient of correlation between UBM and USP values was 0.76. UBM overestimates CCT in the range of 25 –30 microns. Applying paired ‘t’ test, the p value came out to be 3.48387 x e –21 (p< 0.05), implying that there is a statistically significant difference between the values of CCT as measured via UBM and USP. Conclusion: UBM has various utilities in the field of Glaucoma – it provides us with high resolution images of structures such as a trabeculectomy site, a peripheral iridectomy, etc and allows us to measure various anterior segment parameters. UBM is not as accurate as USP in the measurement of CCT. Hence, more research is needed to standardize the techniques in order to make UBM accurate and reliable for CCT measurement.