Corneal Measurement Devices Show Agreement, No Diurnal Variations Noted

Corneal diameter measurements are repeatable and show agreement between manual and automated methods, according to a study published in Clinical Optometry. No diurnal variations are noted when these measurements are performed at different times of the day. 

Researchers enrolled 20 participants (60% women; mean age, 26.5 years) and measured their white-to-white corneal diameter 3 times per day (8 AM, 11 AM and 2 PM) with 2 automated procedures (Scheimpflug imaging and placido based topography) and 1 manual method (image analysis software with a slit lamp). Each individual measurement was performed 3 times with each instrument by the same examiner.

According to the report, there was good agreement between devices, good repeatability, and no diurnal variation. There was no significant effect between the different instruments (P =.117), the different time points (P =.506), or the interaction between instrument and time point (P =.182). 

There were also no significant differences in the corneal diameters measured in men and women with different devices (placido based topography: P =.427; Scheimpflug imaging: P =.473; slit lamp: P =.970).

Although good repeatability was reported for all 3 devices, manual slit lamp measurements showed a higher quartile coefficient of dispersion than the automatic measurements taken with placido based topography (ρ, 0.767; P <.001) and Scheimpflug imaging (ρ, 0.707; P <.001) at all measurement times.

“The manual and automated methods used in the study to determine corneal diameter showed good agreement and repeatability,” according to the researchers. “No significant diurnal variations of corneal diameter were observed during the period of time studied.”

Study limitations include small sample size, a single center design, and potential volunteer bias.