The overall picture
The most detailed rate data come from a retrospective keratoconus series of 157 eyes, limited to eyes successfully fit for at least a year (so not a dropout cohort).[1]
- Physiological adverse events: 9.6% of eyes. Microbial keratitis 0.6%, phlyctenulosis 0.6%, corneal abrasion 1.3%, contact lens-induced acute red eye 1.3%, corneal infiltrative events 1.3%, pingueculitis 1.3%, and hydrops 3.2%.[1]
- Lens-related events: 55.4% of eyes. Broken lenses 26.1%, deposits 8.9%, intolerance 7.6%, reservoir fogging 7.0%, handling problems 3.8%, and poor wetting 1.9%.[1]
- Management was mostly a refit (54.0% of interventions) or patient re-education (29.5%); surgical referral accounted for 6.8%.[1]
In a veteran cohort with a broader mix of diagnoses, 55.0% of patients reported difficulty with wear, most often irritation (20.0%) or mid-day fogging or bubbles (15.8%).[2]
A 2016 review concluded that infections are reported mainly in severely compromised corneas, that hypoxic and inflammatory complications are rarely reported, and that conjunctival prolapse, epithelial bogging, midday fogging, and limbal bearing appear to be unique to scleral lens wear.[3]
Midday fogging
What you see: the patient reports vision that clouds after hours of wear and clears when the lens is removed and refilled. At the slit lamp, look for particulate debris or haze in the reservoir and for nonwetting on the front surface.
Evidence: in a five-site study of 48 habitual wearers, 58% reported fogging. Fit characteristics did not differ between eyes with and without fogging; front-surface nonwetting and diffuse reservoir haze were significantly more common in eyes with fogging.[4] In a three-site study, reservoir depth was not related to fogging from debris behind the lens.[5] Patients with surface disease or incomplete lid closure are at increased risk.[15]
Response: not urgent. Treat lid disease, and send the patient back to the fitter, who can adjust the landing zone, filling solution, surface treatment, or midday refill routine.
Conjunctival and limbal findings
What you see: blanching of conjunctival vessels at the landing zone, a pronounced impression ring or rebound hyperemia after removal, conjunctival staining in one quadrant, tissue drawn under the lens edge (prolapse), or limbal staining from bearing.
Evidence: these are recognized fitting sequelae.[3] A 2026 case series of poorly fitted lenses showed that design changes can allow patients to resume wear, and advised reassessing both fit and underlying disease at scheduled intervals.[13] A case report described intracorneal hemorrhage within 4 hours of application and removal training on the first day of wear, in a patient with long-standing keratoconjunctivitis and keratoconus; the authors frame it as a mechanical complication, a category that includes suction between lens and ocular surface.[14]
Response: route to the fitter. Pingueculitis (1.3% in the keratoconus series) can be treated by you and flagged to the fitter.[1]
Corneal edema and hypoxia
What you see: epithelial microcysts, stromal haze, striae, or a rise in pachymetry after wear.
Evidence in healthy corneas: a meta-analysis of 22 studies (830 eyes) found central corneal thickness increased by 7.93 microns with the lens in place and showed no significant change after removal. Corneal or stromal swelling averaged 0.88%. The authors judged daytime wear of modern high-Dk lenses physiologically safe, with selective monitoring advisable in high-risk patients.[6]
In grafts: post-PK eyes showed about 3% central edema after roughly 6 hours of high-Dk lens wear, greater than healthy corneas and regionally variable.[7] See scleral lenses and corneal transplants.
Response: notify the fitter promptly. For a graft, also notify the corneal surgeon, since edema may reflect endothelial failure or rejection rather than the lens.
Hydrops
Hydrops occurred in 3.2% of eyes in the keratoconus series.[1] A case series described three wearers with PKs for keratoconus more than 30 years old and recurrent ectasia who presented with acute painful focal edema suggestive of hydrops; two of the events followed a scleral lens refit closely enough that the authors suggested some association.[8]
Response: same day. Acute pain with sudden corneal edema needs urgent evaluation.
Microbial keratitis
Rates in published cohorts: 0.6% of eyes in the keratoconus series,[1] and 6% of eyes over up to nine years in a post-PK series.[11]
Risk factors from case series: all three post-PK scleral wearers with MK in one series had concurrent surface disease (keratoconjunctivitis sicca and exposure) and topical or systemic immunosuppression.[9] A series of three Acanthamoeba keratitis cases in keratoconus scleral wearers pointed to large saline volumes, overnight storage in saline, hypoxia, and not rubbing the lens.[10]
Response: same day. Ask about filling solution, storage, tap water exposure, and lens case hygiene, and consider Acanthamoeba in the differential.
Lid disease
In 49 habitual scleral wearers, upper lid wiper epitheliopathy was present in 43% of eyes and lower in 31%. Eyes with surface disease had more meibomian gland obstruction (39% vs 11% with no expressible meibum) and lid margin telangiectasia (61% vs 19%) than eyes with corneal irregularity.[12]
Response: treat as you would in any patient; tell the fitter, since lid disease affects wetting and fogging.
Triage at a glance
| Finding | Urgency | First call |
|---|---|---|
| Infiltrate, epithelial defect with pain, or discharge | Same day | You or a cornea service; notify fitter |
| Acute corneal edema with pain (possible hydrops) | Same day | You or a cornea service; notify fitter |
| Signs of graft rejection | Same day | Corneal surgeon; notify fitter |
| Edema or rising pachymetry without pain | Prompt | Fitter; surgeon if graft |
| Conjunctival blanching, prolapse, or quadrant staining | Routine | Fitter |
| Midday fogging, poor wetting, deposits | Routine | Fitter; treat lids |
| Broken or lost lens | Routine | Fitter (send parameters if you have them) |
For the routine division of work between you and the fitter, see co-managing scleral lens patients.
Common questions
Is midday fogging a sign the lens fits badly?
Not necessarily. In a study of 48 habitual wearers, fit characteristics did not differ between eyes with and without fogging; front-surface nonwetting and diffuse reservoir haze did. Fogging was also unrelated to reservoir depth in a separate three-site study. Refer it back to the fitter as a comfort and vision issue, not an emergency.
How common is microbial keratitis in scleral lens wearers?
Published rates come from small cohorts: 0.6% of eyes in a keratoconus series and 6% in a post-keratoplasty series. There is no population-based incidence estimate, and risk depends heavily on the underlying eye and care habits.
Can a scleral lens cause hydrops?
Hydrops occurred in 3.2% of eyes in a keratoconus scleral lens series, and acute hydrops-like episodes have been reported in old PK grafts soon after a refit. Hydrops is also part of the natural history of keratoconus, so these reports don't establish causation.
What is conjunctival prolapse?
Conjunctival tissue drawn into the space under the lens, typically near the limbus. A 2016 review lists it, with epithelial bogging, midday fogging, and limbal bearing, among findings that appear unique to scleral lens wear. It is a fit issue for the fitter.