This article was originally published in a sponsored newsletter.

With the introduction of new technology for measuring scleral shape, it’s estimated that non-spherical scleral profiles are quite common, with an approximate prevalence of around 94%.¹ However, based on the consensus from practitioner survey data in 2017 regarding scleral lens prescription and management practices, the use of non-spherical landing zones in scleral lens prescriptions and management practices was relatively low, at about 36%.²

According to industry manufacturing data on 16.5mm diameter toric scleral lenses, which reviewed practitioner prescribing habits from 2018 to 2020, 78% of lenses prescribed had a magnitude of toricity of 150μm, with approximately 92% of lenses featuring a landing zone toricity between 100μm and 200μm.^3,4

A publication by Alexander and colleagues aimed to quantify the impact of landing zone toricity on scleral lens fitting characteristics, including rotation and decentration and lens flexure optics, during short-term wear.5 The scleral lenses all had a total diameter of 16.5mm, a back optic zone radius of 7.46mm, a –1.00D back vertex power, a 150μm center thickness, and various sagittal heights (4,000μm, 4,200μm, and 4,400μm). Lenses were manufactured in hexafocon A with a refractive index of 1.415.

In a randomized order, participants wore scleral lenses that had various landing zone toricities (0μm, 100μm, 150μm, and 200μm). Ten young, healthy participants (mean 24 years [SD = 7 years]) participated in the study and wore lenses for 30 minutes without changes in the other lens parameters. In this lens design, the landing zone toricity can be adjusted in increments of 25μm, from 0μm to 350μm, with the diagnostic fitting set using a landing zone toricity of 150μm.

Corneoscleral profilometry was used to quantify scleral toricity. Topography over scleral lenses was used to quantify lens flexure, rotation, and decentration during lens wear. Repeated measures analyses were performed based on landing zone toricity and residual scleral toricity (the difference between scleral and lens toricity) for eyes that had “low” scleral toricity (mean = 96μm) and “high” scleral toricity (mean = 319μm).

Compared to spherical landing zones, toric landing zones significantly reduced lens flexure by 0.37D ± 0.21D (p < 0.05) and lens rotation by 20º ± 24º (p < 0.05). Horizontal and vertical lens decentration did not vary significantly with landing zone toricity.

These trends in flexure, rotation, and decentration were also observed in eyes that had both “low” and “high” magnitudes of scleral toricity when analyzed based on residual scleral toricity.

Landing zones with 100μm to 200μm toricity significantly reduced lens flexure (by approximately 62%) and rotation (by about 77%) compared to a spherical landing zone, though they did not significantly affect horizontal or vertical lens decentration when controlling for other variables.

This study’s results show that incorporating a toric landing zone, even for eyes that have lower scleral toricity (around 100μm), may be advantageous, particularly for front-surface optical designs.

Reference(s):

1. DeNaeyer G, Sanders D, van Der Worp E, Jedlicka J, Michaud L, Morrison S. Qualitative assessment of scleral shape patterns using a new wide field ocular surface elevation topographer. J Contact Lens Res Sci. 2017 Nov 16;1:12-22.
2. Schornack MM, Fogt J, Nau A, et al. Scleral lens prescription and management practices: emerging consensus. Cont Lens Anterior Eye. 2023 Feb;46:101501.
3. Kojima R, Caroline P, Kinoshita B, Lampa M, Andre M, Fujimoto M. How toric should scleral lenses be for most patients? Poster presented at the Global Specialty Lens Symposium, Las Vegas. 2020.
4. Kojima R, Caroline P, Lampa M, et al. Scleral lens prescribing trends – 12 month lab data. Poster presented at the Global Specialty Lens Symposium, Las Vegas. 2022.
5. Alexander J, Belaineh Aweke Y, et al. The effect of landing zone toricity on scleral lens fitting characteristics and optics. Ophthalmic Physiol Opt. 2024 Jul;44:867-875.

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