Central Corneal Thickness Measurements: Using an Ultrasonic Instrument and 4 Optical Instruments

Abstract

Of the 4 instruments that are commercially available, the UP was the most repeatable for within sessions, and the OCT was the most repeatable for between sessions.

Comparison of Central Corneal Thickness Measurements Obtained by RTVue OCT, Lenstar, Sirius Topography, and Ultrasound Pachymetry in Healthy Subjects

“…3 Today, ultrasound pachymetry (UP) is widely recognized as the gold standard because of its low cost, compact design, ease of use, and high repeatability. 4 However, this technique has disadvantages, including the need for topical anesthesia and contact with the cornea, with a risk for epithelial abrasions and infection. 5 Moreover, the measurements of corneal thickness may also vary among different examiners because of the application of different amounts of pressure on the cornea.…”

Comparison of central corneal thickness: ultrasound pachymetry versus slit-lamp optical coherence tomography, specular microscopy, and Orbscan

“…Ultrasound pachymetry (US pachymetry) is the most common method used for CCT measurements 1. This is performed by direct apposition of an ultrasound probe to the anterior corneal surface 2. However, limitations of this method include contact with the corneal surface, misalignment of ultrasound probe perpendicularly to corneal surface, and insufficient tear film displacement after probe compression.…”

“…Orbscan II2 uses a scanning-slit principle in order to measure the corneal thickness. Specular microscopy uses reflections of light from the anterior and posterior corneal surface as a means to distinguish corneal layers and measure corneal thickness 5.…”

Estimating the Osmolarities of Tears During Evaporation Through the “Eyes” of the Corneal Nerves

“…In contrast, entirely different approaches to attempt to measure tear osmolarity on the cornea have been applied in studies 14–18 that took advantage of the ability in human tears to break up and/or thin as they evaporate from the corneal surface and of the mathematical models derived from these measurements. The results from these studies of normal individuals have provided much higher values of tear osmolarities, ranging from approximately 600 to 900 mOsm/L, than those using the other methods described above.…”