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    Question

    What is scleral lens settling?

    Your lens isn't sitting quite where it was when you put it in. Over the first few hours it sinks a little, and the fluid under it thins. Here's what studies have measured.

    By the Scleral Lens Team · Last reviewed October 2, 2026 · 8 published sources cited

    The short answer

    Settling is the gradual sinking of a scleral lens into the soft tissue covering the white of the eye after you put it in. As it sinks, the layer of saline over your cornea gets thinner. Studies have measured average thinning of roughly 60 to 150 microns over the first 4 to 8 hours, with most of it in the first 2 to 4 hours. Fitters plan for settling so the lens still clears your cornea once it has settled.

    Key points

    • Settling happens because the conjunctiva, the tissue the lens rests on, is soft and compresses.
    • Most settling happens within the first 2 to 4 hours, then levels off.
    • The amount varies between people, lens designs, and even from day to day.
    • Fitters judge the fit after settling so the lens doesn't end up touching the cornea.

    Why lenses settle

    A scleral lens doesn’t rest on bare white sclera. It rests on the conjunctiva, a thin, soft, clear tissue that covers the sclera. When the lens sits on that tissue for a while, the tissue compresses and the lens sinks slightly toward the eye. As the lens sinks, the saline layer between the lens and your cornea gets thinner. Reviews attribute this to the pliable nature of the conjunctiva.[1]

    How much, and how fast

    Studies measure settling as the loss of fluid thickness over the center of the cornea, in microns (thousandths of a millimeter). Results vary with the study, the lens, and the person:

    • Keratoconus, 8 hours. In 22 eyes of 11 people, the central fluid layer thinned by an average of about 27 microns after 1 hour, 51 microns after 4 hours, and 63 microns after 8 hours. About 80% of the settling happened in the first 4 hours. Smaller-diameter lenses settled more.[2]
    • Healthy eyes, 8 hours. In 15 young adults, central clearance fell by about 76 microns over 8 hours. Half of that happened within 45 minutes and three-quarters within 2 hours, leveling off at about 4 hours.[3]
    • Normal corneas, 6 to 8 hours. In 16 people, the fluid layer thinned by an average of 83 microns.[7]
    • Keratoconus, 6 hours. In keratoconus eyes wearing lenses of different thicknesses, the fluid layer thinned by about 80 microns after 6 hours, regardless of lens thickness.[8]
    • A larger mixed group, 4 hours. In 75 people with regular corneas, keratoconus, or corneal transplants, the central fluid layer thinned by about 149 microns over 4 hours, most rapidly in the first 2 hours, with no difference between the three groups.[5]

    A review summarizing several of these studies reports average settling over the first 8 hours ranging from about 63 to 114 microns, depending on lens design and individual factors.[1]

    Settling isn’t even across the lens, either. In healthy eyes fitted with a symmetrical lens, the fluid layer was thicker on one side than the other at first, and the different regions settled at different rates before evening out.[4] And it varies a lot from person to person: in a study of 20 people with keratoconus or similar conditions, settling differed between people, initial fits, and over time.[6]

    Why it matters

    Clearance. If a lens starts with too little vault, settling can bring it into contact with the cornea, risking irritation over time. Some authors recommend fitting with a little extra vault for progressive conditions like keratoconus.[1] See what is scleral lens vault?

    Vision. In normal corneas, the over-refraction barely changed after settling, and vision stayed the same.[7] In healthy eyes, the settling-related change in the power of the fluid layer was small, about 0.12 diopters.[3] Changes in irregular corneas haven’t been studied as directly. If your vision shifts over the day, tell your fitter. See what is an over-refraction?

    Tightness. Settling also brings the lens edge more firmly onto the conjunctiva. A lens that’s too tight may leave a red ring or pressure mark after removal. See red ring after removal.

    What it means for your visits

    Because most settling happens in the first few hours, fitters often want to see a lens that has been worn for a while before judging the fit or the prescription. If your fitter asks you to arrive having worn your lenses for a few hours, that’s why. Follow their instructions for your visits.

    Common questions

    Can I feel my lens settling?

    Most people don't notice it. If your lens feels tighter as the day goes on, or you see redness or a ring where the edge sits, mention it to your fitter, since that can be a sign the lens is pressing too firmly.

    Does settling happen every time I put my lens in?

    Yes. The lens settles each time you insert it, because you start with fresh saline and the lens sinks again into the soft tissue.

    Can settling make my lens touch my cornea?

    It can if the lens starts with too little clearance. That's why fitters assess the fit after the lens has settled, and sometimes design in a little extra clearance at the start. Your fitter checks this at follow-up visits.

    Keep reading

    What is scleral lens vault, or clearance?

    Vault, also called clearance, is the gap between the back of a scleral lens and the front of your cornea, filled with saline. Too little and the lens can touch the cornea as it settles; too much and less oxygen reaches the cornea and vision can be affected. Published reviews cite targets of roughly 100 to 200 or 100 to 300 microns after the lens settles, but they also stress that the right vault is whatever keeps your vision clear, your eye comfortable, and your cornea healthy.

    What is an over-refraction?

    An over-refraction is a vision test done while you wear your scleral lens. Your fitter places trial lenses in front of your eye to find any remaining prescription, then builds that correction into your next lens. Because the lens settles over the first hours of wear and can flex or tilt on the eye, fitters often check the over-refraction after the lens has been on for a while. Small changes in fit can shift the result.

    What are mini-scleral lenses?

    A mini-scleral lens is a scleral lens that extends only a little past the edge of your cornea. In the classification most often cited, a mini-scleral lens is up to 6 mm wider than the visible colored part of your eye, and a large scleral lens is more than 6 mm wider. Both vault over the cornea and rest on the white of the eye; they just differ in how far they reach. Your fitter picks the size that suits your eye's shape and your condition.

    Do scleral lenses change the shape of your cornea?

    Scleral lenses are designed to vault over the cornea rather than press on it, so they aren't meant to reshape it. Studies find small, temporary changes: slight corneal swelling while the lens is on, and minor curvature changes that mostly return to baseline after the lens comes out. Eyes with a weakened inner corneal layer, such as after a transplant, can swell much more, so they need closer monitoring. Scleral lenses are not a treatment to stop keratoconus from progressing.

    Sources

    1. Macedo-de-Araújo RJ, Fadel D, Barnett M. How can we best measure the performance of scleral lenses? Current insights. Clin Optom (Auckl). 2022;14:47-65. doi:10.2147/OPTO.S284632 pubmed.ncbi.nlm.nih.gov
    2. Esen F, Toker E. Influence of apical clearance on mini-scleral lens settling, clinical performance, and corneal thickness changes. Eye Contact Lens. 2017;43(4):230-235. doi:10.1097/ICL.0000000000000266 pubmed.ncbi.nlm.nih.gov
    3. Vincent SJ, Alonso-Caneiro D, Collins MJ. The temporal dynamics of miniscleral contact lenses: central corneal clearance and centration. Cont Lens Anterior Eye. 2018;41(2):162-168. doi:10.1016/j.clae.2017.07.002 pubmed.ncbi.nlm.nih.gov
    4. Vincent SJ, Alonso-Caneiro D, Collins MJ. Regional variations in postlens tear layer thickness during scleral lens wear. Eye Contact Lens. 2020;46(6):368-374. doi:10.1097/ICL.0000000000000676 pubmed.ncbi.nlm.nih.gov
    5. Wang F, Vincent SJ, Cho P, et al. Wide-angle fluid reservoir thickness changes during short-term scleral lens wear. Eye Vis (Lond). 2025;12(1):27. doi:10.1186/s40662-025-00443-3 pubmed.ncbi.nlm.nih.gov
    6. Otchere H, Jones LW, Sorbara L. Effect of time on scleral lens settling and change in corneal clearance. Optom Vis Sci. 2017;94(9):908-913. doi:10.1097/OPX.0000000000001111 pubmed.ncbi.nlm.nih.gov
    7. Bray C, Britton S, Yeung D, Haines L, Sorbara L. Change in over-refraction after scleral lens settling on average corneas. Ophthalmic Physiol Opt. 2017;37(4):467-472. doi:10.1111/opo.12380 pubmed.ncbi.nlm.nih.gov
    8. Iqbal A, Thomas R, Mahadevan R. The effect of different thickness scleral lens on corneal parameters in eyes with keratoconus. Indian J Ophthalmol. 2022;70(12):4251-4256. doi:10.4103/ijo.ijo_1309_22 pubmed.ncbi.nlm.nih.gov

    Last updated October 2, 2026. Found an error or a newer study? Let us know and we'll correct the page.