What's Happening Under Your Scleral Lens? A Small Fluid Reservoir Study

If you wear scleral lenses for keratoconus, you'll know the routine: fill the bowl of the lens with saline, pop it on, and it vaults over your cornea on a cushion of fluid. That fluid layer, called the fluid reservoir, is a big part of why scleral lenses can give such clear, comfortable vision on an irregular cornea. If you're new to scleral lenses, our guide to scleral lenses for keratoconus in New Zealand covers the basics.

But what actually happens in that little pool of fluid over a few hours of wear? A 2026 study from the University of Houston took a closer look.

What the researchers did

The study included 37 people: 21 with keratoconus who were regular, long-term scleral lens wearers, and 16 people with normal corneas who don't usually wear scleral lenses and wore one briefly under standardised conditions for the study.

After at least two hours of lens wear, the researchers collected the fluid from under each lens. They counted the immune cells (white blood cells) using an automated analyser and measured 19 cytokines, chemokines and growth factors. These are chemical messengers that cells use to signal to each other, including during inflammation. They also used anterior segment OCT imaging to look at the fluid layer.

This was a cross-sectional study, meaning a single snapshot in time, done at one site.

What they found

• More immune cells in keratoconus. All immune cell counts in the fluid were higher in the keratoconus group than in the normal group (p = 0.02). A p-value of 0.02 means a difference this large would be unlikely if there were truly no difference between the groups.
• A different chemical profile. Five markers were significantly higher in keratoconus: eotaxin, IL-4, IL-15, MIP-1β and TNF-α. Two, IL-7 and IFN-γ, were higher in the normal eyes.
• Some trends that didn't hold up. Other markers, such as IL-6, IL-8 and MCP-1, trended higher in keratoconus but were not significant once the researchers corrected for testing many markers at once. When you test 19 things, a few will look different by chance alone, so this correction (called false discovery rate correction) is a sensible safeguard.

The abstract doesn't give the actual cell counts or marker levels, so we can't say how large these differences were. It also doesn't report the imaging findings, comfort, fogging or any eye-health problems.

The authors describe the fluid reservoir as a "biologically active" space that may collect disease-related signals, and suggest it could become a useful place to sample the eye's surface in future research.

What this does and doesn't mean

It is tempting to read "inflammatory markers under the lens" and worry that scleral lenses are harmful. This study doesn't show that. There are two important reasons.

First, the groups differed in more than just keratoconus. The keratoconus group were long-term habitual wearers, while the normal group wore a lens briefly for the study. So we can't tell whether the differences come from keratoconus itself, years of lens wear, different lens fits, or all three.

Second, the study measured chemicals in a fluid sample, not anything patients experienced. It didn't show worse comfort, worse vision or eye damage.

What it does support is something your optometrist will already encourage: regular check-ups. Practical steps include:

• keeping your scheduled scleral lens follow-up visits, so the fit, the fluid layer and the health of your cornea can be checked;
• following your lens cleaning and handling routine, using fresh, recommended saline every time you fill the lens;
• letting your optometrist know if you notice midday fogging, redness, discomfort or a change in vision, as a fit or routine adjustment may help.

Where this fits in your care

The front door for keratoconus care is a keratoconus-focused optometrist. At Rose Optometry in Hamilton, our optometrists, including Jagrut Lallu and Jacqueline Rowe, diagnose keratoconus, document any progression with sequential corneal maps, fit and review scleral lenses, and refer to an ophthalmologist for cross-linking when it is needed. You can read more about our keratoconus and scleral lens care in Hamilton.

What the studies can't tell us

• Only the abstract was available to us. We could not read the full paper, so funding, conflicts of interest, any lens-maker involvement, unusable samples and side-effects could not be checked.
• Small and single-site. With 37 people, the study is too small to draw firm conclusions.
• Confounded comparison. Long-term wearers with keratoconus were compared with short-term wearers without it.
• No effect sizes. The abstract reports which markers differed, but not by how much.
• A snapshot. It can't tell us whether these markers change over time, with a refit, or matter for eye health.

If your scleral lenses are fogging, uncomfortable or due for a check, you can book a keratoconus assessment with our optometrists in Hamilton.

References

• Keyzer M, Guerra E, Bhattacharyya P, Walker MK. Immune cells and cytokines in the scleral lens fluid reservoir in keratoconus. Cont Lens Anterior Eye. 2026;49(5):102701. PMID: 42468385. https://doi.org/10.1016/j.clae.2026.102701