New Soft Lens Designs for the ‘Not-So-Standard Eye’

Introduction

The notion that each individual eye has its own unique fingerprint could not be truer. Though soft contact lenses (SCLs) may be more forgiving than rigid gas permeable (GP) contact lenses when there is a mismatch between the contact lens shape and the cornea, dropout due to discomfort or vision remains a troublesome reality in eye care. [1-4] Today we can measure ocular shape to obtain sophisticated comprehensive topography of the anterior eye. Following the advancement of such technology, research has also resulted in an evolution in the understanding of ocular shape. [5-7] The present academic, industry, and clinical task is to best determine how to successfully translate this knowledge into modern and optimal contact lens designs.

A Clinical Challenge…

LASIK and PRK are common corneal refractive surgeries for myopia that can potentially regress post-operatively. Due to the nature of ablation, the resultant oblate-shaped cornea often leads to an unstable fit with conventional SCLs, resulting in inadequate vision and discomfort. Additionally, other post-LASIK complications such as dry eyes and post-refractive ectasia can result in unique challenges to contact lens fitting options for patients who may be reluctant to return to vision correction after refractive surgery.[8-10] Post-surgical corneas are oblate, with a flatter central curvature relative to the peripheral curvature. Modern mass-produced soft contact lenses have a constant base curve (BC) that is prolate they also have fixed sagittal heights that vary across conventional designs.[11,12] Specialty lens modalities such as post-refractive corneal or scleral rigid GP lenses incorporate oblate designs to better contour this corneal shape however, these options may require more adaptation to handling and comfort.

Novel Lens Design

A novel custom soft contact lens design was augmented with a flatter central BC and a steeper peripheral BC to provide a more optimal fit for individuals with post-refractive corneal shapes while remaining in a more common contact lens modality. The lens is manufactured in a latheable silicone hydrogel (SiHy) material the ability to lathe cut the lenses, similar to GP lenses, allows for advanced customization. Sagittal height of the lenses was predicted using a comparison and average of digital data generated by profilometry biosphere elevation sagittal height measurement (left) and Placido disc ring extrapolation (right), both at chords of 15.0mm (Figure 1).

Figure 1. Data acquisition using profilometry and placido ring topography to obtain sagittal height of the eye at a chord of 15.0mm for custom soft lens design.

Selected Case Series and Results

All patients were unable to wear conventional soft lenses at BC 8.4, 8.6, or 9.0 due to instability of vision. Patients also declined rigid specialty lens modalities and requested soft lenses for perceived handling ease. Optical zone (OZ) started at 8.0mm for all lenses (most post-surgical corneas have a central ablation area of approximately 8.0mm, which therefore is a good starting point for the OZ). Left eyes (OS) are shown for all cases in figure 2.

Figure 2. Case series summary of best-fit lens parameters for post-refractive corneal shape

Comparison of Conventional to Dual-Base-Curve Lenses

Figure 3 shows a case example in patient A for a lens fit using commercially available lenses with single BCs (8.5 and 9.0) compared to the dual-BC (9.0 center/8.5 periphery) soft contact lens. The latter showed the best centration, movement and clear vision.

Figure 3: Case example in patient A using commercially available lenses with single-BC compared to a dual-BC soft contact lens.

What Does This Case Series Tell Us?

The innovation of this dual-BC SCL design demonstrates the possibility to fit the oblate-shaped cornea without excessive central clearance and to land adequately in the periphery for acceptable lens movement. Consequently, the device may provide more optimal fits that result in stable vision correction and all-day comfort. Fully digital design is becoming more possible than ever using many tools on the market that are capable of comprehensively imaging the anterior eye. The Pacific University Scleral Sag Study highlights the diversity in sagittal height of standard soft contact lenses and highlights the importance of matching appropriate sagittal height of SCLs to the anterior eye for the best comfort and performance.[11,12] Multifocal and toric options will be needed to further explore the clinical use of dual-BC soft contact lenses, as these may be less forgiving than single-vision powers with lens flexure. Nonetheless, possibilities for soft lens customization are expanding with improved lathing and materials, as rigid GP lenses have.

Conclusions

Many patients undergo refractive surgery procedures to achieve freedom from spectacles postoperative vision challenges cannot be overlooked. Specialty contact lenses can provide improved fit, comfort, and vision compared to conventional contact lenses. Understanding a patient's corneal shape and how to customize soft contacts to better contour a unique eye can achieve an optimized contact lens fit. A novel custom soft, oblate, dual-BC lens design was effective for several post-refractive contact lens fittings. Further study will be needed to elucidate the impact of other lens fitting parameters used in conjunction with custom-soft dual-BC SCLs. Applications for this design may also include other post-refractive oblate-shaped corneas such as keratoprosthesis (KPro) or penetrating keratoplasty (PKP). Offering a more personalized contact lens option can help satisfy the needs of our patients and enhance their quality of life.

Acknowledgements: Mission Eye Care Contact Lens Team: Alia Cappellani, Andrea Lasby, Vanessa Lin, Riaz Ahmed Art Optical: Bethany Peebles, Eric Marshall

References

1. Nichols KK, Redfern RL, Jacob JT, Nelson JD, Fonn D, Forstot SL, Huang JF, Holden BA, Nichols JJ. The TFOS International Workshop on Contact Lens Discomfort: Report of the Definition and Classification Subcommittee. Invest Ophthalmol Vis Sci 2013 Oct 1854(11):TFOS14-9
2. Nichols JJ, Willcox MD, Bron AJ, Belmonte C, Ciolino JB, Craig JP, Dogru M, Foulks GN, Jones L, Nelson JD, Nichols KK, Purslow C, Schaumberg DA, Stapleton F, Sullivan DA members of the TFOS International Workshop on Contact Lens Discomfort. The TFOS International Workshop on Contact Lens Discomfort: executive summary. Invest Ophthalmol Vis Sci. 2013 Oct 1854(11):TFOS7-TFOS13
3. Jones L, Brennan NA, Gonzalez-Meijome J, et al. The TFOS International Workshop on Contact Lens Discomfort: report of the contact lens materials, design, and care subcommittee. Invest Ophthalmol Vis Sci. 201354:TFOS37–70
4. Pucker AD, Tichenor AA. A Review of Contact Lens Dropout. Clin Optom (Auckl). 2020 Jun 2512:85-94. doi: 10.2147/OPTO.S198637. PMID: 32612404 PMCID: PMC7323801
5. Ritzman M, Caroline P, Borret R, Korszen E. An analysis of anterior scleral shape and its role in the design and fitting of scleral contact lenses. Cont Lens Anterior Eye. 2018 41(2) 205-213.
6. Rojas Viñuela J, Piñero DP, Martínez MB. Comparing sagittal heights calculated using corneal parameters and those measured with profilometry. Cont Lens Anterior Eye. 2023 46(2):101747
7. Consejo A, Rojas-Viñuela J, Sebastian-Carmona J, Ezpeleta J, Piñero DP. Corneoscleral junction angle in healthy eyes assessed objectively. Cont Lens Anterior Eye. 2023 Jun46(3):101815
8. González-Méijome JM, López-Alemany A, Almeida JB. Correlations between central and peripheral changes in anterior corneal topography after myopic LASIK and their implications in postsurgical contact lens fitting. Eye & Contact Lens. 200632(4):197-202.
9. Steele C, Davidson J. Contact lens fitting post-laser-in situ keratomileusis. Contact Lens & Anterior Eye. 200730:84-93.
10. Zadnik K. Contact lens management of patients who have had unsuccessful refractive surgery. Curr Opin Ophthalmol. 199910:260-263.
11. van der Worp E, Mertz C. Sagittal height differences of frequent replacement silicone hydrogel contact lenses. CLAE. 201538:157-162.
12. 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 Dec44(6):101386. doi: 10.1016/j.clae.2020.11.006. Epub 2021 Jan 8. PMID: 33423977 1.

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