Corneal Metrics Affect Ability to Detect Keratoconus on Tomography

Macro close up eye.
Current single corneal topography or tomography devices can produce false-negative results, possibly keeping patients from being cleared for surgery.

Horizontal corneal diameter and central corneal thickness can influence clinicians’ ability to detect suspect keratoconus using corneal tomography, according to findings published in BMC Ophthalmology.

Screening patients for suspicious keratoconus is a standard practice before corneal refractive surgery. Previous keratoconus screening studies, based on findings using older diagnostic methods, had a high false-negative rate. 

According to investigators, recent studies using corneal tomography have provided more accurate estimates of the prevalence of the condition. However, current single corneal topography or tomography devices — no matter which indices are used — still can produce false-negative results, potentially excluding patients from being cleared for surgery.

Because tomographic parameters vary among geographic and ethnic populations, investigators studied the possible causes of tomography-suspect keratoconus (TSK) marked by tomography in screening keratoconus in a Chinese cohort. 

The research team conducted a nested, case-control study of patients, including those with myopia, seeking corneal refractive surgical corrections since 2013. 

Patients were divided into 2 groups: a TSK group (with abnormal screening examinations) and a control group (with unremarkable screening examinations). After at least 2 years, none of the patients developed abnormalities after having excimer laser corneal refractive surgery. 

Of 183 TSK eyes (109 patients) and 160 control eyes (83 patients), the mean age of patients was 28.0 and 26.3 years old, respectively. The horizontal corneal diameter was 11.5 mm to 11.8 mm in the TSK group and 11.8 mm to 12.0 mm in the control group. The central corneal thickness was nearly 520 μm in the TSK group and 550 μm in the control. 

These results show that corneal diameter and thickness both have a statistically significant effect on tomography screenings and can result in false positive results.


Feng K, Zhang Y, Chen YG. The possible causes for tomography suspect Keratoconus in a Chinese cohort. BMC Ophthalmol. 2021;21(1):47. doi:10.1186/s12886-021-01806-9