Variations in Sagitta Observed Between Contact Lenses of the Same Base Curve

Clinicians may take CL-SAG into consideration when adjusting fit or switching patients to different brands with identical base curves.

Soft contact lens sagita values (CL-SAG) vary greatly between different lenses, even when those lenses have the same base curve (BC), according to a study published in Contact Lens and Anterior Eye.

Researchers assessed differences in CL-SAG among a variety of daily disposable (DD), reusable 2 to 4 week replacement, and toric lenses using an instrument derived from optical coherence tomography (OCT) technology that measured posterior CL-SAG in a hydrated milieu. 

The investigators found that the total range between the flattest and steepest lens tested was 514 µm in DD lenses. The maximum difference between DD lenses with the same BC of 8.7 mm was 264 µm. 

The total range between the flattest and steepest reusable lenses was 632 µm and a maximum difference of 418 µm was noted in 5 reusable lenses with a labelled BC of 8.4 mm.

The range between the flattest and steepest toric lenses was 621µm, with a maximum difference of 345 µm in 4 toric lenses with BCs of 8.5 mm. 

“[Clinicians] who want to interchange lenses [cannot do so] based on BCs alone, as for lenses with the same labelled BCs the CL-SAG values of these lenses are not identical,” according to investigators. “Lens diameter plays a role in this too, although the bulk of the lenses in each of the three analysed categories fell into a narrow range of 0.2 mm from each other.”

Study limitations include confounding due to lens temperature, utilization of 3 lens types from the same batches in all samples, and the use of only 1 investigator to gather data, with no masked reader providing a double check.

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


van der Worp E, Lampa M, Kinoshita B, et al. Variation in SAG values in daily disposable, reusable and toric soft contact lenses. Cont Lens Anterior Eye. 2021;44(6):101386. doi:10.1016/j.clae.2020.11.006