A clinical comparison of optical and ultrasonic pachometry

Abstract

Central corneal thickness (CCT) of normal and oedematous corneae was measured in a study comparing a modified Haag-Streit optical pachometer and an ultrasonic pachometer (Teknar Ophthasonic, preset velocity 1630 m/s). Sixty-eight patients were examined before and after cataract extraction with implantation of an anterior chamber lens. Mean values of CCT before operation were 531 +/- 4.9 (SEM) micron by optical pachometry and 524 +/- 4.7 microns when measured by ultrasound (not significantly different). On the first post-operative day the values were 618 +/- 8.4 and 602 +/- 7.6 microns for optical and ultrasonic measurements, respectively (significantly different, 2P less than 0.001). Correlation analysis showed a high dependence between the methods with coefficients of correlation being 0.955 before and 0.958 after the operation. Linear regression analysis revealed small, but significant differences between the techniques. The difference between the two methods increased with increasing corneal hydration, whereas it could not be ascribed to sex, age, or intraocular pressure. It is concluded that for clinical purposes optical and ultrasonic pachometry techniques are comparable.

Comparison of central corneal thickness estimated by an ultrasonic pachymeter and non-contact specular microscopy

“…Differences in measurement between UP and NCSM devices may be caused by the different working systems of each device. In cases of ultrasound pachymetry, the exact posterior corneal reflection point is not known; it may be located between the Descemet membrane and the anterior chamber (16) . One other factor potentially influencing CCT measurement is tear film.…”

Reliability of Entire Corneal Thickness Mapping in Normal Post-Laser in situ Keratomileusis and Keratoconus Eyes Using Long Scan Depth Spectral Domain Optical Coherence Tomography

“…There are several possible reasons for the corneal thickness underestimates made using the SD-OCT system. Unlike the noncontact measurement in OCT instruments, the ultrasound contact probe displaces the tear film and compresses the corneal surface [58]. The exact location of the posterior corneal reflection using ultrasonic pachymetry is unknown, but it is possibly between the Descemet membrane and the anterior chamber [59].…”

Agreement between Central Corneal Thickness Measured Using Pentacam, Ultrasound Pachymetry, Specular Microscopy and Optic Biometer Lenstar LS 900 and the Influence of Intraocular Pressure

“…For example, PC is used to calculate corneal topography with multiple applications in corneal and refractive surgery, intraocular lens implantation and glaucoma [14,15]; the LE biometer provides information on keratometry, anterior chamber depth, lens thickness or intraocular lens measurements, and SM, whose substantial properties are endothelial cell counting, is essential in assessing the evolution of certain refractive surgical procedures, such as phakic lens implants, cataract surgery or corneal transplants [1,3,6,16]. …”