MANY DISPOSABLE SOFT CONTACT LENSES are available in single diameters for each brand, and a few have different base curve (BC) options. Traditionally, central corneal curvature (K) measurements guide soft lens BC selection, based on the assumption that steeper corneas have larger sagittal heights and would be better fit with lenses of deeper sagittal heights. However, using Ks to pick the BC oversimplifies the process of aligning the lens to the ocular surface, and trial fitting is still utilized (Young et al, 2010). Keratometry only covers the central 3 mm of the cornea, and sagittal depth is diameter dependent.

To explore this, van der Worp and colleagues (2021) measured the contact lens sagittal heights (CL-SAG) of 44 commercially available soft lenses, including daily disposable and reusable spherical and toric designs. They found large differences in CL-SAG values between lenses with the same BC across different manufacturers (maximum difference of 264 µm in daily disposables, 418 µm in resuable, 345 µm in toric lenses). The CL-SAG differences between lens designs from the same manufacturer with 2 available BCs (average CL-SAG difference of 276 µm) were not much different than lenses labeled with the same BC. Therefore, even if the same lens has 2 BCs to choose from, lens fit changes are modest. Another interesting finding is that, with the same lens type and manufacturer, switching from a spherical to a toric lens may have a large impact on CL-SAG—as much as a 500 µm difference.

Cruz-Crespo and coworkers (2025) suggest a sagittal height-based approach to fitting soft contact lenses. They looked at the correlation of sagittal difference (δ-sag) between ocular sagittal height (OC-SAG) and CL-SAG and its effect on optimal lens fit. Thirty subjects were fitted with 8 daily disposable lenses with known CL-SAG. Using both objective (with imaging software) and subjective assessments (by 2 eyecare professionals), they determined that a δ-sag range of 120 µm–280 µm (CL-SAG deeper than OC-SAG) yielded a satisfactory lens fit and may improve patient comfort.

Sagittal height may also play a role in soft contact lens complications. Contact lens use is a well-established risk factor for developing microbial keratitis (MK) (Waghmare and Jerea, 2022). Suboptimal fit of extended-wear silicone hydrogel lenses, namely reduced lens movement, is associated with developing inflammatory events (Ozkan et al, 2010).

Andrew and colleagues (2025) studied 25 participants who were diagnosed with a contact lens-related corneal infiltrative event (CIE) or MK. They found that these patients had flatter OC-SAGs compared to the population mean (control group of more than 18,000 contact lens wearers). The authors hypothesized that having a shallow OC-SAG is a risk factor for adverse lens events with soft lens wear due to an excessively steep contact lens fit when using “one-size-fits-most” commercial soft lenses.

Current research may suggest a paradigm shift in soft contact lens fitting. Rather than using corneal keratometry readings to choose a BC, measurements such as ocular sagittal height can be useful in optimizing lens fit, which is related to comfort and reducing the risk of adverse events.  

References

1. Young G, Schnider C, Hunt C, Efron S. Corneal topography and soft contact lens fit. Optom Vis Sci. 2010 May;87(5):358-366. doi: 10.1097/OPX.0b013e3181d9519b

2. van der Worp E, Lampa M, Kinoshita B, Fujimoto MJ, Coldrick BJ, Caroline P. Variation in sag values in daily disposable, reusable and toric soft contact lenses. Cont Lens Anterior Eye. 2021 Dec;44(6):101386. doi: 10.1016/j.clae.2020.11.006

3. Cruz-Crespo JJ, Ortiz-Peregrina S, García-Gamero A, Rodríguez-Farfach F, Bolívar-Parra J, Ghinea R. Changing the paradigm of soft contact lens fitting: A sagittal height-based approach. Ophthalmic Physiol Opt. 2025 May;45(3):607-617. doi: 10.1111/opo.13487

4. Waghmare SV, Jeria S. A review of contact lens-related risk factors and complications. Cureus. 2022 Oct 10;14(10):e30118. doi: 10.7759/cureus.30118

5. Ozkan J, Mandathara P, Krishna P, et al. Risk factors for corneal inflammatory and mechanical events with extended wear silicone hydrogel contact lenses. Optom Vis Sci. 2010 Nov;87(11):847-853. doi: 10.1097/OPX.0b013e3181f6f97d

6. Andrew M, Zimmerman AT, Bailey MD. The relationship between soft contact lens adverse events and corneal sagittal depth. Cont Lens Anterior Eye. 2025 Jul;48(4):102413. doi: 10.1016/j.clae.2025.102413