Anterior Segment Imaging Devices Not Necessarily Interchangeable

Corneal topography. Ophthalmologist scanning a patient’s eye to obtain a three-dimensional image of the cornea.
Research shows keratoconus patients may require various methods of image acquisition.

While 2 optical imaging systems may be used interchangeably to collect several measurements in both normal and keratoconus eyes, results are not equal when looking at white-to-white corneal diameter (WTW), anterior chamber depth (ACD), pupil diameter, or central corneal thickness (CCT), researchers say.

Several instruments can provide detailed analyses of anterior segment structures and corneal shape. Although multiple studies have compared the measurements between these different devices in healthy patients, few have studied the results on keratoconus patients, according to investigators.

Researchers compared the anterior segment parameters captured by the Pentacam® (Oculus) Schiempflug imaging device and the IOL Master 700® (Carl Zeiss Meditec) swept-source optic coherence tomography biometry in patients with and without keratoconus. They looked at several measurements, including CCT, keratometry, WTW, and ACD.

Their analysis included 88 eyes of 50 keratoconus patients and 87 eyes of 50 patients without keratoconus. Biometry was performed using the IOL Master 700, and topography was performed using the Pentacam. The keratometry values, ACD, WTW, CCT, axial length (AL), anterior chamber angle (ACA), and lens thickness (LT) were evaluated. Bland–Altman plots evaluated levels of agreement between devices with 95% limits of agreement.

They found that the IOL Master 700 showed higher WTW, ACD, pupil diameter, and CCT values than Pentacam in both the keratoconus and control groups. However, there were no statistically significant differences in flat keratometry and steep keratometry values between the groups.

The research shows that, although the 2 devices may be used interchangeably in healthy and keratoconus eyes to measure keratometry values and axis, they should not be considered interchangeable for WTW, ACD, pupil diameter, and CCT measurements for either healthy patients or those with keratoconus.

The study’s authors noted several limitations of their study, including that the mean posterior corneal astigmatism magnitude was not evaluated and that only a small sample was included in the study.


Güçlü H, Akaray İ, Kaya Sultan, et al. Agreement of anterior segment parameters between Schiempflug topography and swept-source optic coherence based optic biometry in keratoconus and healthy subjects. Eye & Contact Lens. Published online March 31, 2021. doi:10.1097/ICL.0000000000000787.