This article was originally published in a sponsored newsletter.

It is well-established that scleral elevation is not spherical and is generally toric or asymmetric.¹ When evaluating sagittal height, the sclera nasally is typically higher/flatter and the sclera temporally is generally lower/steeper.^1,2 Asymmetry of the sclera is increasingly evident as the radial distance moves further from the corneal apex.

Corneoscleral shape varies among individuals. It may be considered rotationally symmetric with profiles described as spherical, aspherical and toric, and rotationally asymmetric with profiles described as regular and irregular.³ Each shape of the eye requires a customized landing zone to obtain an ideal fit. Corneoscleral shape has scleral lens fit implications, such as unequal weight distribution on the landing zone. The landing zone alignment can impact both the optical qualities and fit of a scleral lens on the underlying ocular surface.

A study evaluated scleral lenses with varying toricities of the landing zone (0μm, 100μm, 150μm, and 200μm).⁴ The purpose of this study was to quantify the impact of landing zone toricity on scleral lens fit rotation and decentration and optical lens flexure during short-term scleral lens wear. Lenses were worn in a random order by 10 individuals with healthy corneas with a mean age of 24 years. The left eye of each individual was evaluated. Scleral profilometry using a corneoscleral profilometer and central corneal topography was performed.

Improved optical performance and the amount of lens flexure was decreased with 100μm to 200μm toric landing zones compared to spherical landing zones. Toric lenses exhibited 62% less lens flexure of the anterior lens surface. Additionally, the amount of lens rotation was reduced by 77% with toric landing zones compared to spherical landing zones. Lens decentration was similar in both vertical and horizontal meridians with different landing zone toricities.

Inferotemporal lens decentration was present in all lens designs. The amount of lens clearance was associated lens decentration. To decrease lens decentration, minimizing corneal clearance is an option.

Integrating a landing zone with toric attributes may prove advantageous even in eyes with lower levels of corneoscleral toricity. This may be especially helpful for advanced optical designs, such as toric and multifocal lens designs.

Additional research is needed on the influence of corneoscleral shape on customized scleral landing zones.

Reference(s):

1. Consejo A, Llorens-Quintana C, Bartuzel MM, Iskander DR, Rozema JJ. Rotation asymmetry of the human sclera. Acta Ophthalmol. 2019 Mar;97:e266-e270.
2. Macedo-de-Araújo RJ, van der Worp E, González-Méijome JM. In vivo assessment of the anterior scleral contour assisted by automatic profilometry and changes in conjunctival shape after miniscleral contact lens fitting. J Optom. 2019 Apr-Jun;12:131-140.
3. Fadel D. The influence of limbal and scleral shape on scleral lens design. Cont Lens Anterior Eye. 2018 Aug;41:321-328.
4. Alexander J, Aweke YB, Bhebhe Z, 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, 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.