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    Wearing guide

    Filling solution and air bubbles

    What goes in the bowl of a scleral lens, how full to fill it, and what to do when an air bubble gets trapped under the lens.

    By the Scleral Lens Team · Updated October 2, 2026 · 4 published sources cited

    The short answer

    Fill the lens with preservative-free saline from a fresh single-use vial until it domes slightly above the rim, and keep your face parallel to the floor as it goes in. If you see a bubble, take the lens out, refill it, and put it back in. Don't wait it out.

    Before you start

    Time: A minute or two to check, and a fresh insertion if there's a bubble.

    • Preservative-free saline in single-use vials
    • Your inserter and removal plunger
    • A flat mirror
    • A flashlight or your phone's light

    Step by step

    1. Open a fresh vial

      Use preservative-free saline, and a new single-use vial for each insertion.

    2. Fill until it domes

      With the lens on the inserter, hollow side up, add saline until it rises slightly above the rim. Overfilling a little is fine; underfilling is what lets air in.

    3. Keep your face parallel to the floor

      Look straight down into the mirror. If your head tilts, the saline spills and air takes its place.

    4. Insert in one smooth motion

      Bring the lens straight up until it settles, then pull the inserter straight back.

    5. Shine a light and look

      Hold a light to the side of your eye and look in the mirror. A bubble shows up as a bright, round pocket under the lens.

    6. Check your vision and comfort

      Cover the other eye and look around: vision should be clear and undistorted. Haze or discomfort right after insertion can also mean a bubble.

    7. If there's a bubble, start over

      Remove the lens, refill it to the brim, and insert again. Don't try to blink or massage a bubble out.

    These are general steps. If your fitter taught you differently, follow your fitter: your lens and eyes are theirs to know. Print the mirror cards to keep by your sink.

    Why the filling solution matters

    When a scleral lens is in, the saline you filled it with sits against your cornea all day. It’s what smooths an irregular cornea and keeps a dry one wet, so it has to be gentle and clean.

    • Preservative-free. Preservatives such as benzalkonium chloride, common in multi-use eye products, can damage the cells on the surface of the cornea and conjunctiva.[1]
    • Sterile and single-use. In an international survey of scleral lens practitioners, 67% of patients used single-use vials of non-preserved saline.[2] In a report of corneal infections in scleral lens wearers, the authors recommended sterile, preferably single-use saline.[3]
    • Never water. The FDA advises never using tap, distilled, or homemade saline with contact lenses. Tap and distilled water have been linked to Acanthamoeba keratitis, a hard-to-treat corneal infection.[4]

    Buffered or non-buffered

    Most wearers fill with non-buffered saline: plain 0.9% sodium chloride. Buffered saline is adjusted to match the pH of natural tears, and some people with sensitive or dry eyes find it more comfortable. Which one you use is your fitter’s call. If one stings or feels uncomfortable, mention it rather than switching on your own.

    Where bubbles come from

    Almost always from an underfilled lens. If the saline is level with the rim, or below it, there’s air sitting on top. As the lens meets your eye, that air can be trapped between the lens and the cornea. Tilting your head on the way up does the same thing, by spilling saline and letting air in.

    That’s why the fix is the same two habits every time: fill until it domes, and keep your face parallel to the floor.

    What a bubble does

    • It blurs your vision where it sits, because light bends differently through air than through saline.
    • It can leave a dry patch. The cornea under a bubble isn’t bathed in saline, so a patch can dry out and feel sore by the end of the day.

    A bubble isn’t something to wear through. Take the lens out, refill it, and put it back in.

    If bubbles keep coming back

    Persistent bubbles, even with good technique, can point to the way the lens fits your eye. Tell your fitter: they can change the design of the next lens. In the meantime, keep checking after every insertion.

    Common mistakes

    • Filling to the rim but not above it.
    • Filling with multipurpose solution or saline from a multi-use bottle.
    • Reusing an opened vial later in the day, or the next day.
    • Tilting your head as the lens comes up.
    • Leaving a bubble in and hoping it goes away.

    Common questions

    Can I use the rest of a saline vial later?

    No. Single-use vials have no preservative, so once opened they're no longer sterile. Open a fresh one each time you fill a lens.

    Is a tiny bubble at the edge okay?

    Ask your fitter what they want you to do. As a rule, if you can see a bubble or your vision is hazy, take the lens out and refill it.

    What's the difference between buffered and non-buffered saline?

    Non-buffered is plain 0.9% sodium chloride, the most common choice. Buffered saline is adjusted to match the natural pH of tears, and some people with sensitive or dry eyes find it more comfortable. Your fitter can tell you which suits you.

    I keep getting bubbles even when I fill to the brim. What's wrong?

    First check your technique: a level face and one smooth motion. If bubbles keep coming back anyway, it can point to the fit of the lens, which your fitter can adjust on the next lens.

    Can I fill my lens with eye drops?

    Don't add drops or anything else to the saline unless your fitter has told you to. Fill with the preservative-free saline they recommended.

    Keep going

    Guide

    How to insert a scleral lens

    Fill the lens to the brim with preservative-free saline, look straight down with your face parallel to the floor, hold both lids wide at the lashes, and bring the lens straight up to your eye in one smooth motion. Then check for bubbles every time.

    Guide

    How to remove a scleral lens

    Put a drop or two of artificial tears in your eye first. Then press the small removal plunger onto the lower third of the lens, never the center, until it grips, and pull outward. Do it over a towel, and clean the lens right away.

     Common worry

    Are scleral lenses hard to put in?

    At first, usually yes. It's a learned skill, and the first tries can take a long time. But in a year-long study, most wearers got noticeably faster and needed fewer attempts as the months went on. Give yourself two to three weeks before deciding you can't do it.

    Sources

    1. Goldstein MH, Silva FQ, Blender N, Tran T, Vantipalli S. Ocular benzalkonium chloride exposure: problems and solutions. Eye (Lond). 2022;36(2):361-368. doi:10.1038/s41433-021-01668-x pubmed.ncbi.nlm.nih.gov
    2. Schornack MM, Fogt J, Nau A, et al. Scleral lens prescription and management practices: emerging consensus. Cont Lens Anterior Eye. 2023;46(1):101501. doi:10.1016/j.clae.2021.101501 pubmed.ncbi.nlm.nih.gov
    3. Sticca MP, Carrijo-Carvalho LC, Silva IMB, et al. Acanthamoeba keratitis in patients wearing scleral contact lenses. Cont Lens Anterior Eye. 2018;41(3):307-310. doi:10.1016/j.clae.2017.12.004 pubmed.ncbi.nlm.nih.gov
    4. U.S. Food and Drug Administration. Contact Lens Risks. Content current as of September 4, 2018. fda.gov

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