This article was originally published in a sponsored newsletter.

Even though contemporary scleral lenses are manufactured with highly oxygen-permeable materials, corneal edema may be induced in sealed lens designs by the lens thickness, fluid reservoir, and minimal tear exchange.¹ This is especially the case in eyes that have a diminished corneal endothelial cell count such as with Fuchs’ endothelial dystrophy, bullous keratopathy, and penetrating keratoplasty.^2-5 These conditions, including corneal edema, may preclude scleral lens wear altogether.⁶

A novel study assessed and quantified the response to scleral lens wear in the periphery of the cornea, an important anatomical location that regulates corneal homeostasis.⁷ Maintaining ocular surface homeostasis is imperative for contact lens wearers, eyecare practitioners, and lens manufacturers who manufacture these lenses.⁸

The study examined and quantified the amount of corneal edema induced by scleral lenses in 10 healthy individuals who wore scleral lenses with different fitting characteristics. Individuals were fit with low (mean 141μm), medium (482μm), and high (718μm) central post-lens fluid reservoir thicknesses over three unique study visits.

The experimental results were equated with corneal edema theoretical models, accounting for scenarios containing and deprived of limbal metabolic support, which includes the lateral metabolite movement and limbal vasculature functionality.

Optical coherence tomography was employed to evaluate stromal corneal edema, thickness of the scleral lens, and thickness of the fluid reservoir. Stromal corneal edema was quantified within the central (0mm to 2.5mm from the apex of the cornea) and peripheral (1.25mm to 3mm from the corneal scleral spur). Data from the clinical experiment were likened with theoretical model publications of corneal edema from the center and periphery of the cornea.

The amount of stromal edema differed with the thickness of the post-lens fluid reservoir (p < 0.001) for both the center and periphery of the cornea. Compared to a small post-lens fluid reservoir thickness (1.00 (1.01)%) (p ≤ 0.01), the mean (standard deviation) edema of the stroma was larger for the medium (2.08 (1.21)%) and high (2.22 (1.31)%) conditions of the post-lens fluid reservoir thickness. The amount of stromal edema steadily expanded from center of the cornea to the peripheral cornea by approximately 0.3%, which is a relative upsurge of 18%. However, this difference was not statistically significant.

The amount of stromal edema in the periphery produced by scleral lenses was significantly greater for scleral lenses with medium and high post-lens fluid reservoir thickness levels, which is consistent with prior publications of the response of the central corneal. Increasing corneal edema toward the limbus is aligned with theoretical models of edema from the periphery absent of metabolic aid from the limbus.

Both the center and periphery of the cornea exhibited comparable levels of edema, displaying an increase in edema for post-lens fluid reservoir thicknesses with medium and high thicknesses. The gradual rise in edema toward the limbus aligns with a theoretical model lacking limbal metabolic aid to control peripheral corneal swelling. In order to alleviate corneal hypoxic stress, central and peripheral fluid reservoir thickness should be minimized as much as practically possible, while avoiding potential mechanical or suction-related fitting complications.

Reference(s):

1. Barnett M, Courey C, Fadel D, et al. CLEAR - Scleral lenses. Cont Lens Anterior Eye. 2021 Apr;44:270-288.
2. Kumar M, Shetty R, Lalgudi VG, Vincent SJ. Scleral lens wear following penetrating keratoplasty: changes in corneal curvature and optics. Ophthalmic Physiol Opt. 2020 Jul;40:502-509.
3. Kumar M, Shetty R, Khamar P, Vincent SJ. Scleral lens–induced corneal edema after penetrating keratoplasty. Optom Vis Sci. 2020 Sep;97:697-702.
4. Guillon Nc, Godfrey A, Hammond DS. Corneal oedema in a unilateral corneal graft patient induced by high Dk mini-scleral contact lens. Contact Lens Anterior Eye. 2018 Oct;41:458-462.
5. Nguyen LT, Yang D, Vien L. Case series: corneal epithelial macrocysts in scleral contact lenses post–penetrating keratoplasty. Optom Vis Sci. 2018 Jul;95:616-620.
6. Fadel D, Kramer E. Potential contraindications to scleral lens wear. Cont Lens Anterior Eye. 2019 Feb;42:92-103.
7. Iqbal A, Fisher D, Alonso-Caneiro D, Collins MJ, Vincent SJ. Central and peripheral scleral lens-induced corneal oedema. Ophthalmic Physiol Opt. 2024 Jun;44:792-800.
8. VanDerMeid KR, Byrnes MG, Millard K, Scheuer CA, Phatak NR, Reindel W. Comparative Analysis of the Osmoprotective Effects of Daily Disposable Contact Lens Packaging Solutions on Human Corneal Epithelial Cells. Clin Ophthalmol. 2024 Jan 25;18:247-258.

Melissa Barnett, OD, FAAO, FSLS is the director of optometry at the University of California, Davis. She has received remuneration from ABB, Acculens, Abbvie, Azura, Bausch + Lomb, BCLA, Bruder, Bruno Vision Care, CooperVision, Dompé, Epion, JJVC Vistakon, Lentechs, Ocusoft, Orasis, RVL Pharmaceuticals, Sight Sciences, Science Based Health, STAPLE Program, Sun Pharma, Taursus, and Visus.