What fogging is
Midday fogging is a gradual haze that builds a few hours after you put your lenses in. Vision starts out sharp, then turns cloudy, milky, or smoky. It’s one of the most common problems scleral lens wearers report. In a survey in which practitioners described their most recent established scleral lens patient, 25.8% of those patients reported midday fogging.[1] In a study of 120 veterans fitted with scleral lenses, 15.8% had trouble with midday fogging or bubbles.[8]
Fogging is different from blur right after insertion, which is usually a bubble or a dirty lens (see blurry right after insertion). It’s also different from vision that shifts during the day without looking hazy, which has other causes (see vision changes during the day).
Front of the lens or behind it?
The fog can come from two places, and the fixes are different.
| What you notice | Where it probably is | What usually helps |
|---|---|---|
| Blinking or a rewetting drop clears it for a few seconds | On the front surface of the lens | Cleaning, a surface coating, treating dry eye |
| Blinking does nothing; vision looks milky or smoky | In the saline behind the lens | Removing, rinsing, and refilling; fit changes |
On the front. Your tears are meant to spread smoothly over the front of the lens. If the tear film is uneven, often because of dry eye or meibomian gland problems (the oil glands in your eyelids), the surface scatters light and vision looks smeary. In a study of 48 habitual scleral lens wearers, 58% (28 of 48) reported fogging. Their fitters found no difference in fit between those with and without fogging, but poor front-surface wetting and a diffuse haze in the reservoir were both more common in the eyes that fogged.[3]
Behind the lens. The saline under a scleral lens sits against your eye all day. Over hours it can collect particles, and once there are enough of them, light scatters on the way through. Wearers usually notice blur and some discomfort and end up removing the lens to clean, refill, and reinsert.[2]
Why it happens to some people and not others
Researchers are still working this out, and the answer seems to differ from person to person.
- Dry eye and inflammation. In a study of 48 wearers, those with fogging had dry eye symptom scores in the severe range, while those without fogging scored in the normal range.[4] A review of the research describes a growing view that fogging may ultimately be related to inflammation, which can come from different sources in different people.[2] In the practitioner survey, patients with fogging were more likely to also report redness or irritation with their lenses.[1]
- Not one product or design. In that same survey, fogging wasn’t linked to lens diameter, daily cleaner, storage solution, or filling solution.[1] In the 48-wearer study, no single lens or solution factor made a significant difference on its own.[4]
- How tears move behind the lens. In one study of established wearers, eyes where tears flowed in under the lens very quickly were more likely to belong to people who reported fogging.[5] Yet in a short study of 20 healthy adults, lenses with three small holes near the edge (fenestrations) collected less debris over three hours than the same lenses without holes, between 2 and 4.8 times less depending on the measure. The authors noted that longer studies in people with eye disease are still needed.[6]
Those findings pull in different directions, which is why there’s no universal fix. Your fitter looks at your eye, your fit, and your tear film, then changes one thing at a time.
What your fitter can change
- The fit. If the lens edge or landing zone is letting debris in, the fitter can reshape it so the lens seals differently on the white of your eye. For some eyes, a different design (including a fenestrated one) may be worth trying.
- A surface coating. Some lenses can be given a coating that helps tears spread over the front. In a small double-masked trial, 21 scleral lens wearers with dry eye wore coated and uncoated versions of the same lens for 30 days each. With the coated lens, comfort was better, comfortable wearing time was longer, and foggy vision was less frequent.[7]
- Treating dry eye and lid disease. If your tear film or eyelid glands are part of the problem, treating them can help the lens as much as the eye. See dry eyes while wearing scleral lenses.
- A planned midday refill. For some people, a scheduled lens removal, rinse, and refill around lunchtime simply becomes part of the routine.
Doing a midday refill safely
Treat it like a full insertion. Wash and dry your hands, remove the lens with your plunger, rinse it with preservative-free saline, fill it to the brim from a new vial, and reinsert. Don’t top up a half-used vial, and never use tap water or saliva on the lens.[9] Keep a small kit at work or in your bag so you’re not tempted to cut corners.
Common mistakes
- Topping up or reusing saline from a vial you opened earlier.
- Using preserved eye drops or multi-purpose solution to fill the lens.
- Assuming fogging is just something you have to live with, and not mentioning it.
- Rubbing your eye through the lid to try to clear it.
Common questions
How common is midday fogging?
Common enough that researchers study it closely. In a survey in which practitioners described their most recent established scleral lens patient, about a quarter of those patients reported midday fogging. In a smaller clinic study of 48 habitual wearers, more than half did.
Is it safe to take my lens out and put it back in during the day?
Many fitters build a planned midday refill into the routine. Use clean hands, fresh preservative-free saline from a new vial, and your usual tools, and ask your fitter whether it suits you.
Will a different saline fix it?
Sometimes, but there's no single product that reliably prevents fogging. In one study, no specific lens design or care product was linked to fogging. Ask your fitter before you switch anything.
Can fogging be a sign of something more serious?
Fog on its own usually isn't. But blur that doesn't clear when the lens is out, or blur with pain, redness, discharge, or light sensitivity, is a reason to take the lens out and call your eye doctor today.
Do lenses with small holes in them help?
Some lenses have tiny holes, called fenestrations. In a short study of healthy eyes, they collected less debris behind the lens over three hours. It's early research, and your fitter will decide whether that design suits your eye.