Unpopular opinion:

It’s a truly hot take, but is this based in reality? Let’s explore.

RIP Corneal Transplants

Procedures to halt the progression of ectatic disease, specifically corneal collagen crosslinking (CXL), have reduced the necessity for invasive procedures such as penetrating keratoplasties. [1,2] Hegem et al. found that corneal transplants for keratoconus decreased from 40% to 3% after the implementation of CXL as standard of care.[3] This shift is also evident in the Eye Bank Association of America (EBAA) data keratoconus is no longer the leading indication for penetrating keratoplasty.[4] However, it’s disingenuous to imply that all of this is due to CXL, because medical contact lenses also contribute to this trend. Koppen et al. found that 40 of 51 eyes with severe keratoconus avoided keratoplasty through the use of scleral lenses.[5] Similarly, Ling et al. reported a reduced risk for undergoing keratoplasty with rigid corneal and scleral lenses, showing hazard ratios of 0.30 and 0.19, respectively.[6] Additionally, procedures such as topography-guided photo refractive keratectomy (TGPRK) and corneal tissue addition keratoplasty (CTAK) are reducing the severity of irregular corneal shapes, thereby allowing for simpler contact lens options. Roll et al. reported that TGPRK reduced corneal asymmetry in a patient with keratoconus, enabling the successful use of soft toric lenses after struggling with multiple rigid lens options.[7] CTAK has resulted in dramatic improvements in refractive error, corneal topography, and visual acuity. Post-CTAK, uncorrected vision improved from 20/327 to 20/82. Spectacle-corrected vision improved from 20/82 to 20/43. MRSE improved from -6.25 ± 5.45 diopters (D) to -1.61 ± 3.33 D. Average keratometry changes showed that the Kmean flattened by -8.44 D, Kmax flattened by -6.91 D, and the point of maximum flattening was -16.03 D.[8] These procedures are becoming increasingly common for the management of irregular corneas.

The Soft Specialty Lens Takeover

Rigid corneal lenses are often the primary choice for managing corneal irregularities [9] but may not suit all patients due to discomfort or difficulty with handling. Additionally, practitioners find rigid corneal and scleral lenses more difficult to fit compared to custom soft lenses for keratoconus (Gelles and Barnett, Data on File Jobson Medical Information, Keratoconus Education Initiative Practitioner Survey). Thus, adoption of custom soft lenses may become more widespread. Soft lenses may offer an effective alternative, especially for those patients who are intolerant to rigid corneal lenses. A retrospective chart review revealed that 75% of keratoconus patients who were previously unsuccessful with rigid lenses were successfully re-fit with standard or custom soft lensess.[10] A case series exploring three patients with mild corneal irregularities, including corneal scars or early keratoconus, demonstrated not only success but also a superior level of acuity in standard toric soft lenses that was not previously achievable with glasses or rigid corneal lenses.[11]

The main challenge in these eyes is achieving an appropriate contact lens-to-eye relationship. This is primarily dependent on aligning the lens’ sagittal depth with that of the eye. This depth is primarily influenced by the corneal diameter, or horizontal visible iris diameter (HVID), followed by corneal curvature. As the corneal diameter increases or curvature steepens, sagittal depth increases. A soft lens that is too shallow in sagittal depth can cause excessive movement and irritation, leading to lens dropout. Conversely, a lens that is too deep may result in a tight fit, which can also result in irritation and potential discontinuation. Commercially available soft lenses are limited in their parameters, with a “one size fits most” approach, but studies indicate that there are significant variations in sagittal depth across different manufacturers, even for lenses with the same base curves.[12] The sagittal depth charts from van der Worp et al. may aid practitioners in lens selection to improve outcomes. For eyes that cannot be accommodated even with sagittal depth knowledge, custom soft lenses can address these fitting challenges by offering parameters to fit a wider range of corneal sizes and shapes. Additionally, increased soft lens center thickness can mask irregular astigmatism, and aspheric optics can be used to reduce aberrations and enhance visual clarity.

"The trend toward early detection and intervention suggests more mild disease and a growing role for custom soft lenses."

Limitations of Soft Lenses

Though custom soft lenses are poised for growth, there are limitations. Consider how they are manufactured. Both custom soft lenses and scleral lenses begin with lathe cutting a button of material, but custom soft lenses require additional steps, including a critical hydration phase. A challenge in custom soft lenses’ production is managing material expansion. Microscopic problems become larger ones as the lens expands to its final dimensions, which can lead to dimension inconsistencies that result in rejected lenses, lower yields, or inconsistent on-eye performance. Other material characteristics can pose a challenge. Most custom soft lenses are often made from hydrogel materials. Silicone hydrogel options are available in some designs, but even so, achieving a Dk/t that satisfies the Harvitt and Bonanno criteria is challenging, especially for custom soft lenses for irregular corneas that have a center thickness starting at 0.3mm. This becomes more problematic for patients who need to wear their lenses for extended periods. A significant hurdle with custom soft lenses is the associated cost. A pair of scleral lenses can last an average of two years,[13] but custom soft lenses are replaced bi-annually or quarterly and are often more expensive than commercially available soft toric lenses. Additionally, their production requires more time and produces lower yields, increasing costs for laboratories. Lens deformation is also a notable impediment to a successful soft lens fit. Their flexible and hydrophilic nature makes them prone to warping from handling, environmental factors, and regular daily wear, leading to discomfort and visual distortion.[14] Many of these limitations will be overcome by improvements in materials and manufacturing as well as by applying principles from scleral lens innovations such as wavefront-guided optics and custom posterior surfaces.

Famous Last Words

So, are corneal transplants and rigid lenses dead? No way! Not all patients with keratoconus or ectasia will be diagnosed and treated early for a variety of reasons, such as delayed care, limited diagnostic instruments, cost of care, etc. Irregular corneal astigmatism will still occur due to disease, trauma, surgery, and iatrogenic causes. For more severe corneal irregularities, these options will remain the mainstay. However, the trend toward early detection and intervention suggests more mild disease and a growing role for custom soft lenses. Their ability to fit a variety of ocular geometries and prescriptions positions them comfortably and effectively as a growing and key component of the future of care.
References

1. Abdelaziz L, Barbara R. History of the Development of the Treatment of Keratoconus. Int J Kerat Ect Cor Dis 20132(1):31-33.

2. Godefrooij, D. A., Gans, R., Imhof, S. M., & Wisse, R. P. (2016). Nationwide reduction in the number of corneal transplantations for keratoconus following the implementation of cross-linking. Acta ophthalmologica, 94(7), 675–678. https://doi.org/10.1111/aos.13095

3. Hagem, A. M., Thorsrud, A., Sæthre, M., Sandvik, G., Kristianslund, O., & Drolsum, L. (2023). Dramatic Reduction in Corneal Transplants for Keratoconus 15 Years After the Introduction of Corneal Collagen Crosslinking. Cornea, 10.1097/ICO.0000000000003401. Advance online publication. https://doi.org/10.1097/ICO.0000000000003401

4. Mathews, Priya Benbow, Amber Corcoran, Kevin DeMatteo, Jennifer Philippy, Brian Van Meter, Woodford . 2022 Eye Banking Statistical Report—Executive Summary. Eye Banking and Corneal Transplantation 2(3):p e0008-12, September 2023. | DOI: 10.1097/ebct.0000000000000008

5. Koppen, C., Kreps, E. O., Anthonissen, L., Van Hoey, M., Dhubhghaill, S. N., & Vermeulen, L. (2018). Scleral Lenses Reduce the Need for Corneal Transplants in Severe Keratoconus. American journal of ophthalmology, 185, 43–47. https://doi.org/10.1016/j.ajo.2017.10.022

6. Ling JJ, Mian SI, Stein JD, Rahman M, Poliskey J, Woodward MA. Impact of Scleral Contact Lens Use on the Rate of Corneal Transplantation for Keratoconus. Cornea. 202140(1):39-42. doi:10.1097/ICO.0000000000002388

7. Roll, E. H., GP, J. D., Hersh, P. S., Yu, A. S., Su, B., & Greenstein, S. A. (2023). Less Complex Contact Lens Required for a Patient With Keratoconus After Topography-Guided Photorefractive Keratectomy. Eye & contact lens, 49(11), 505–507. https://doi.org/10.1097/ICL.0000000000001023

8. Greenstein SA, Yu AS, Gelles JD, Eshraghi H, Hersh PS. Corneal tissue addition keratoplasty: new intrastromal inlay procedure for keratoconus using femtosecond laser-shaped preserved corneal tissue. J Cataract Refract Surg. 2023 Jul 149(7):740-746. doi: 10.1097/j.jcrs.0000000000001187. PMID: 36943309.

9. Shorter, E., Harthan, J., Nau, C. B., Nau, A., Barr, J. T., Hodge, D. O., & Schornack, M. M. (2018). Scleral Lenses in the Management of Corneal Irregularity and Ocular Surface Disease. Eye & contact lens, 44(6), 372–378. https://doi.org/10.1097/ICL.0000000000000436

10. Su, B., Yu, A., Chung, D., Greenstein, SA., Gelles, JD. (2023). Success with Soft Contact Lenses after Failure of Rigid Contact Lenses in Keratoconus. Investigative Ophthalmology & Visual Science, 64 (8), 3539-3539.

11. Krisa, S. (2023). Your Weapon of Choice in Early Keratoconus and Mild Corneal Scars: Soft Toric Lenses. Global Specialty Lens Symposium Poster Session.

12. van der Worp, E., Lampa, M., Kinoshita, B., Fujimoto, M. J., Coldrick, B. J., & Caroline, P. (2021). Variation in sag values in daily disposable, reusable and toric soft contact lenses. Contact lens & anterior eye : the journal of the British Contact Lens Association, 44(6), 101386. https://doi.org/10.1016/j.clae.2020.11.006

13. Pritikin, E., Rodman, J., & Chiu, G. B. (2023). Average Scleral Lens Replacement Period at a Tertiary Care Hospital. Eye & contact lens, 49(10), 422–427.

14. Young G. Exploring the relationship between materials and ocular health and comfort. CL Spectrum. 2007.

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