Overnight Contact Lens Wear Research Articles

Changes in Limbal Optical Coherence Tomography Angiography Outcomes in Patients With Overnight Contact Lens Wear.

To evaluate the perilimbal vasculature of patients who wear contact lenses (CLs) overnight with optical coherence tomography angiography (OCTA) and compare the results with healthy population. Forty-two patients were included in this observational study. The OCTA imaging was performed in the temporal quadrant of the perilimbal region using a swept-source optical coherence tomography system (Triton DRI-OCT; Topcon Corporation, Tokyo, Japan). The assessments were made in two depths: starting from the conjunctival epithelium to 200 μm scleral depth and the scleral depth between 200 and 1,000 μm. The vessel density, vessel length density, vessel diameter index, and fractal dimension were the main outcomes and compared between overnight CL users and healthy population. Twenty-two patients who have been using CLs overnight for at least 3 months and 20 healthy individuals were included in the study. The vessel density at the superficial layer was significantly higher in the CL group compared with the control group (P<0.001). Vessel diameter index, vessel length density, and fractal dimension at the superficial layer did not differ between the groups (P>0.05 for all). There was no difference in the vessel density, vessel diameter index, vessel length density, and fractal dimension in the deep layer between the groups (P>0.05 for all). Patients who use CL overnight exhibit increased vessel density in the superficial layers of the perilimbal region, which may suggest new vessel formation in the conjunctiva. Anterior segment OCTA may be useful to evaluate the initial changes in limbal vasculature in CL users.

A study of contact lens compliance in a non-clinical setting

PurposeTo evaluate soft contact lens replacement, overnight (ON) wear, and contact lens case compliance in a non-clinical sample. MethodsSubjects (n = 297) were recruited at the Center for Science and Industry (COSI) in Columbus, Ohio. Adult (≥ 18 years) soft contact lens wearers completed a survey about contact lens replacement, ON contact lens wear, and contact lens case replacement habits. ResultsTwo-week replacement lenses (according to the manufacturer’s replacement schedule [MRS]) were most common (45.5%), followed by monthly (34.3%) and daily replacement (20.2%). Non-compliance with replacement schedule was reported in 38.7% of subjects. Age (p = 0.02), years of lens wear (p = 0.02), and MRS (p <0.0001) affected replacement compliance. Post-hoc analysis showed daily replacement wearers were more compliant than two-week (p <0.0001) and monthly (p <0.0001) replacement wearers with prescribed lens replacement. Non-compliance with prescribed ON wear was reported in 23.9% of subjects. Subjects who were non-compliant with lens replacement were more likely to be non-compliant with ON wear (p = 0.02) and had worn contact lenses for less time (p = 0.02). Of the subjects who used contact lens cases, 74.6% were unsure when they should replace their case. Frequency of case replacement was not associated with age (p = 0.5), gender (p = 0.5), years of contact lens wear (p = 0.7), MRS (p = 0.4), replacement compliance (p = 0.3), or ON wear compliance (p = 0.7). ConclusionsDaily replacement wearers were most likely to be compliant with contact lens replacement, but all subjects, including daily replacement wearers, had similar ON wear non-compliance. Non-compliant lens replacement was associated with non-compliant ON wear, but contact lens case replacement was not related to either compliance category. The majority of subjects had no knowledge of proper contact lens case replacement, despite compliance in other categories.

Contact Lens Induced Limbal Stem Cell Deficiency: Clinical Features in Korean Patients.

PurposeTo describe the clinical features of Korean patients with contact lens-induced limbal stem cell deficiency (CL-LSCD).MethodsMedical records of 22 patients who were diagnosed with CL-LSCD between 2014 and 2019 were reviewed retrospectively. Outcome measures included demographics, clinical presentation, treatment, clinical course, and pattern of contact lens (CL) wear.ResultsForty-two eyes of 22 patients were found to have typical changes associated with CL-LSCD. Twenty (91%) patients were women and mean age was 36 ± 12 years. All patients had myopia with mean spherical equivalent of −7.52 ± 3.2 diopter. Twenty (91%) patients had bilateral disease and the location of limbal involvement was diffuse in 20 eyes (47.6%) and partial in 22 eyes (52.4%, superior in 20 eyes and inferior in 2 eyes). Fourteen (63.6%) patients complained of decreased visual acuity. Average period of CL wear was 14 ± 9 years. Four patients used cosmetic colored CLs and four patients had a history of overnight CL wear. All 12 patients who completed follow-up (28 ± 42 weeks) showed improvement in visual acuity and ocular surface condition after cessation of CL wear and medical treatment. Of them, five (42%) patients showed full recovery while seven (58%) showed partial recovery.ConclusionsIf a patient with a history of CL wear for an extended period of time presents with decreased visual acuity, practitioners should perform detailed examinations with suspicion of CL-LSCD, including fluorescein staining. CL-LSCD is usually reversible and close follow-up with conservative treatment is recommended as the initial treatment option.

Thickness changes in the corneal epithelium and Bowman\u2019s layer after overnight wear of silicone hydrogel contact lenses

BackgroundTo investigate thickness changes in the corneal epithelium and Bowman’s layer after overnight silicone hydrogel contact lens (CL) wear by using ultra-high resolution optical coherence tomography (UHROCT).MethodsEleven subjects without CL wearing history were recruited for this study. An UHROCT was used to measure the thickness of the epithelium (ET), Bowman’s layer (BT), stroma (ST), and total cornea (CCT) at the center of both eyes. A silicone hydrogel CL was inserted in the right eye of each subject, and the fellow non-CL wearing left eye served as the control. The lens was inserted at 9:30 pm and removed at 8:00 am the next morning. The subjects were evaluated at 9:00 pm (baseline), 9:30 pm (lens insertion), 10:00 pm (before sleep), 7:00 am (waking), 7:30 am, and 8:00 am (lens removal).ResultsCompared to the lens insertion level, the ET of the lens-wearing eye increased by 5.73% at eye opening (P = 0.001). The ET of the non-CL wearing eye and the BT in both eyes did not change after overnight CL wear. Compared to baseline, the CCT of the lens-wearing eye increased by 2.87% upon waking (P = 0.003) and recovered 30 min later (P = 0.555). In contrast, compared to baseline, the CCT of the non-CL wearing eye did not increase upon waking (P = 0.105).ConclusionsBy using UHROCT, we found that overnight CL wear induced different swelling responses in the various sublayers of the cornea.Trial registrationRetrospectively registered. Registration number: ChiCTR1800015115. Registered 07 March 2018.

Changes in Tear Cytokines Following a Short Period of Daily and Overnight Silicone Hydrogel Lens Wear

Background and Objective: To investigate changes in ocular surface inflammatory markers after daily and overnight silicone hydrogel contact lens wear in healthy wearers.&#x0D; Material and Methods: Twenty-six experienced soft contact lens subjects were evaluated at baseline, after 1-day of silicone hydrogel lens wear, and after 1-night of wear. Basal tears were collected at each visit and tear cytokine concentrations were quantified using multiplex [interleukin (IL)-1β, IL-6, IL-10, IL-12(p70), IL-17A and tumor necrosis factor (TNF)-α] or ELISA (IL-8) kits. A historical control group of 27 non-contact lens wearers was used to compare absolute concentrations and diurnal variations in tear cytokine concentrations. Changes in cytokine concentrations were analyzed using linear mixed models. Linear regression with bootstrapping was used to assess whether changes in IL-1β concentrations were associated with changes in other cytokines.&#x0D; Results: IL-8 concentrations decreased after 1 day of silicone hydrogel contact lens wear and returned to baseline levels the next morning (p=0.04). This same diurnal fluctuation was seen in non-contact lens wearers (p=0.03). With daily contact lens wear, there was a significant positive correlation between the changes in IL-1β and IL-8, TNF-α, IL-10 and IL-12(p70) (all p&lt;0.03). With overnight contact lens wear, there were significant positive correlations between the changes in IL-1β and IL-6, IL-17A and TNF-α (all p&lt;0.01).&#x0D; Conclusion: A short period of daily and overnight silicone hydrogel lens wear does not significantly alter the inflammatory status in adapted soft contact lens wearers.

Risk factors for contact lens-related microbial keratitis in Singapore.

To investigate independent risk factors for contact lens-related microbial keratitis in Singapore and estimate their impact on disease load. Cases were contact lens wearers presenting to Singapore National Eye Centre with microbial keratitis between 2008 and 2010. Community contact lens wearers were recruited as controls. All wearers completed a previously validated questionnaire describing contact lens wear history, hygiene and compliance habits, and demographics. Risk factors significant in univariate analysis (P<0.2) were evaluated in a multivariate model. In all, 58 cases of microbial keratitis and 152 contemporaneous controls were identified. When controlling for other variables, Chinese had a 7 × lower risk compared with other races (95% CI: 2.3-21.3, P=0.001). Those aged between 25 and 44 years were at 3 × increased risk compared with younger wearers (95% CI: 1.1-9.6, P=0.04). Occasional overnight contact lens wear (less often than one night per week) was associated with a 4 × higher risk (95% CI: 1.2-15.4, P=0.03) compared with daily use. Not washing hands before handling was associated with a 13 × increased risk (95% CI: 1.9-84.8, P=0.008). Use of multipurpose solution A carried a 16 × higher risk compared with hydrogen peroxide (95% CI: 1.5-174.0, P=0.02). The combined PAR% for modifiable risk factors (occasional overnight wear, not washing of hands, and MPS A) was 82%. Consistent with previous findings, independent risk factors for contact lens-related microbial keratitis include poor hand hygiene, occasional overnight wear, and type of lens care solution. Prolonged overnight or extended contact lens use was infrequent in this population.

Evidence of Lipid Degradation During Overnight Contact Lens Wear: Gas Chromatography Mass Spectrometry as the Diagnostic Tool

We investigated structural differences in the fatty acid profiles of lipids extracted from ex vivo contact lenses by using gas chromatography mass spectrometry (GCMS). Two lens materials (balafilcon A or lotrafilcon A) were worn on a daily or continuous wear schedule for 30 and 7 days. Lipids from subject-worn lenses were extracted using 1:1 chloroform: methanol and transmethylated using 5% sulfuric acid in methanol. Fatty acid methyl esters (FAMEs) were collected using hexane and water, and analyzed by GCMS (Varian 3800 GC, Saturn 2000 MS). The gas chromatograms of lens extracts that were worn on a continuous wear schedule showed two predominant peaks, C16:0 and C18:0, both of which are saturated fatty acids. This was the case for balafilcon A and lotrafilcon A lenses. However, the gas chromatograms of lens extracts that were worn on a daily wear schedule showed saturated (C16:0, C18:0) and unsaturated (C16:1 and C18:1) fatty acids. Unsaturated fatty acids are degraded during sleep in contact lenses. Degradation occurred independently of lens material or subject-to-subject variability in lipid deposition. The consequences of lipid degradation are the production of oxidative products, which may be linked to contact lens discomfort.

α1‐antitrypsin and C‐reactive protein levels in tear fluid after continuous contact lens wear

BackgroundCorneal inflammation has long been associated with contact lens wear and the use of extended‐wear lenses enhances the risk of corneal injury. Elucidation of the molecular mediators of contact lens‐associated inflammation has the potential to provide injury‐identifying markers early in the inflammatory process, as well as determine potential therapeutic targets.MethodsThis cross‐over study investigated a potential correlation between overnight contact lens wear and the concentrations of two markers of inflammation, α1‐antitrypsin and C‐reactive protein, in tear fluid. To obtain baseline measurements, 17 subjects adapted to wearing silicone hydrogel contact lenses wore their prescribed eye glasses for one week, after which tears were collected and ocular health assessed by a licensed optometrist. Subjects then returned to wearing their prescribed silicone hydrogel lenses continuously for one week. A second tear sample was collected and ocular inflammation was again assessed. Enzyme‐linked immunosorbent assays were performed on all tear samples for both α1‐antitrypsin and C‐reactive protein.Resultsα1‐antitrypsin was significantly (p = 0.01) elevated after continuous contact lens wear, with increases above baseline concentrations averaging 2.48‐fold. Optometric assessment of inflammation loosely correlated with levels of this inflammatory marker. C‐reactive protein was detected in the tears of subjects at both times and levels were also slightly elevated after extended lens wear, but not significantly (p > 0.5) and not consistently in all subjects.ConclusionThe results of this study suggest that α1‐antitrypsin in tear fluid may be useful as an early marker of contact lens‐associated ocular irritation and inflammation. The presence of C‐reactive protein in the tears of contact lens wearers is a novel finding which, while not correlative with either α1‐antitrypsin concentrations or clinically observable inflammation, may warrant further study.

Consequences of lipid degradation during overnight contact lens wear

Purpose: To examine the differences in tear lipid profiles caused by degradation between daily and continuous wear contact lens modalities. Fatty acid profiles from ex vivo lens extracts were analysed using Gas Chromatography Mass Spectrometry (GCMS). A Langmuir trough was used to study the surface behaviour of extracted lipids between the two wear modalities.

Tear lipid degradation during overnight contact lens wear

Purpose: To examine the differences in lipids deposits from worn silicone hydrogel materials (Balafilcon A and Lotrafilcon A) worn daily vs overnight. The deposits were analysed using Gas Chromatography Mass Spectrometry (GCMS). Method: Single lenses were extracted in chloroform: methanol (1:1) and transmethylated prior to analysis by GCMS. The lenses used were collected from a clinically controlled study (n=30) where lenses were worn daily or continuously for 30 days. Results: Lotrafilcon A lenses (16:0 average peak height 112 Kcounts) accumulated much less lipid than Balafilcon A (16:0 average peak height 1213 Kcounts). Results also showed a significant difference in lipid profile from lenses worn on a daily wear basis compared to those worn on a continuous wear basis and this was shown to be irrespective of lens material. The lenses that were worn daily for a month accumulated more unsaturated lipid such as C16:1 and C18:1. The lenses which had been worn continuously for the same period of time had little to no unsaturated fatty acids. Conclusions: Although atmospheric oxidation of lipids occurs during daily wear of contact lenses, oxidation of lens-immobilised lipids during successive periods of overnight wear is even more dramatic. The fact that lenses worn on an overnight basis for 30 days yielded predominately saturated lipids suggests that unsaturated lipids are oxidised during eye closure. This correlates with the known increase in inflammatory mediators in the overnight tear film and indicates a marked increase in free radical production leading to the degradation of unsaturated lipids.

A Re-evaluation of the Risk of Microbial Keratitis From Overnight Contact Lens Wear Compared With Other Life Risks

In 1995, Myers and Weiss published an article comparing the risk of ulcerative keratitis related to low oxygen permeability (Dk) extended contact lens wear to other life risks. This article updates the risks associated with silicone hydrogel (SH) extended wear contact lens use and some comparative life risks, to provide a current perspective within the hierarchy of life risks. A comparative ratio was defined as the incidence of microbial keratitis in a population of SH extended wear contact lens users divided by the incidence of other disease or occurrence in a given population at risk. The risk of SH lens-related microbial keratitis is about 1.5 to 16 times less risky than certain nonfatal disruptive occurrences in the general population, and about the same as the risk of developing breast cancer. Compared with other ocular conditions, the risk of microbial keratitis with SH lenses is about the same as developing late-stage age-related macular degeneration or retinal detachment after cataract extraction on an annual basis; it is over 200 times greater than developing eye or orbit cancer; it is about 7, 20, or more than 30 times less than proceeding to penetrating keratoplasty in keratoconus, developing nuclear cataract, or experiencing a corneal inflammatory event during low-Dk extended wear, respectively. Although the risk of microbial keratitis with modern day SH contact lens extended wear has not changed since the 1980s, when put in perspective with other life risks, it is a relatively rare occurrence.

Hypoxia, Overnight Wear, and Tear Stagnation Effects on the Corneal Epithelium: Data and Proposed Model

: To explore the possible mechanisms that may lead to overnight contact lens-associated corneal morbidity by examining data from several corneal epithelial permeability experiments obtained under different environmental and lens fitting paradigms. : Epithelial permeability was assessed by using fluorometry to determine the fluorescein penetration rate from the tear film into the corneal stroma. Changes in this rate provide an index of the corneal epithelial status; increased permeability leads to decreased barrier function. : Hypoxia and tear stagnation during overnight lens wear play a significant role in altering the corneal epithelial barrier function (P<0.05). However, eliminating lens-induced hypoxia alone does not ameliorate changes in epithelial status (P<0.05). : Based on data from these experiments, it is suggested that hypoxia and tear stagnation should be eliminated to minimize alteration of the corneal epithelium associated with overnight contact lens wear.

The Current State of Corneal Reshaping

The application of contact lenses to alter the shape of the cornea and temporarily reduce or eliminate myopia is known as orthokeratology, corneal refractive therapy, or corneal reshaping. It was first introduced in the 1960s, but high oxygen permeable materials and more sophisticated designs allow patients to wear contact lenses only during sleep, while dramatically improving the predictability and rate of myopia reduction. Many studies have shown that most corneal reshaping patients achieve uncorrected visual acuity of 20/25 or better that lasts all day long in one to two weeks of nighttime wear. Treatment is primarily effective through central epithelial thinning and midperipheral epithelial and stromal thickening. Much remains to be learned about corneal reshaping contact lenses and their effects on the cornea. The authors reviewed existing knowledge and determined what needs to be learned in order to provide patients with appropriate informed consent prior to corneal reshaping contact lens wear. While corneal reshaping contact lenses are effective at temporarily reducing or eliminating myopia, claims about the progress of myopia being controlled with corneal reshaping contact lenses should not be made until further studies are published in peer-reviewed literature. The incidence and prevalence of microbial keratitis related to corneal reshaping contact lens wear is not known. Any overnight wear of contact lenses increases the risk of infection, but it is not known whether the risks of microbial keratitis are greater for corneal reshaping overnight contact lens wearers than other form of overnight contact lens wear. It is also not known whether the risk of microbial keratitis is greater for children than adults, but we must determine if children are at greater risk than adults because many children are wearing corneal reshaping contact lenses. Finally, it is recommended that ongoing education be provided to practitioners and staff regarding safety, informed consent, and prevention of potential problems, with special emphasis on the critical need to properly and thoroughly disinfect lenses that will be worn overnight.

Extended wear contact lenses

Extended wear and continuous wear are synonymous terms that describe a modality of overnight contact lens wear, usually for a period of 1 to 4 weeks. Extended wear of soft contact lenses was first advocated by de Carle in the late 1970s. The first contact lenses approved by the US Food and Drug Administration (FDA) for extended wear were for therapeutic indications [1]. Subsequently, the Permalens (CooperVision, San Jose, California) received approval for extended wear in patients with aphakia in 1978 and the Hydrocuve II-55 in 1980 for cosmetic extended wear [2].

Altered conjunctival response after contact lens-related corneal inflammation.

Corneal inflammation in overnight contact lens (CL) wear is not fully understood. We designed a masked study to examine the impact of overnight CL wear on clinical variables in subjects who had previously experienced corneal inflammatory disease. Forty-four subjects were entered into the study: Nine subjects who had previously experienced CL-associated acute red eye (CLARE) and nine controls; 13 subjects who had previously experienced CL-induced peripheral ulceration (CLPU) and 13 controls, respectively. Controls were matched for age, gender, CL wear experience, and refractive error. Subjects wore bilateral disposable CLs (-3.00 DS). Corneal, conjunctival, and CL fitting variables were assessed prior to sleep, after a single night of CL wear, at 1, 2, and 4 hours after waking by clinicians who were masked to group membership. Retrospective analysis of prewear corneal and conjunctival variables for CLARE subjects and their respective controls was also performed. Contact lens-associated acute red eye subjects consistently showed higher limbal redness (p < 0.05), bulbar redness (p < 0.05), and conjunctival staining (p < 0.005) compared with controls. Lens fitting and corneal variables were not significantly different at any time point for CLARE subjects. Contact lens-induced peripheral ulceration subjects were not different from matched controls for any variable at any time point. Limbal redness varied significantly over time among controls, with highest values measured at eye opening (p < 0.05). Retrospective analysis of prewear variables showed no significant differences between CLARE and control subjects. Wearers who previously experienced CLARE had a greater conjunctival response to CL wear compared with wearers who had no previous inflammatory disease. Clinical observations, however, were not helpful in predicting wearers who were predisposed to CLARE.

Evasion of cellular ocular defenses by contact lens isolates of Serratia marcescens.

Contact lens contamination by Serratia marcescens can lead to the development of microbial keratitis and contact lens-induced acute red eye, particularly during overnight contact lens wear. The aim of this study was to investigate the interaction of S. marcescens with polymorphonuclear leukocytes (PMNs), which occur in closed-eye tears. The respiratory burst of PMNs, when incubated with S. marcescens, was measured using chemiluminescence. Phagocytosis of planktonic and biofilm-grown bacteria by PMNs was also determined. Some strains of S. marcescens did not induce a respiratory burst from PMNs and resisted phagocytosis regardless of opsonization. Phagocytic resistance and growth in the presence of PMNs was markedly increased when bacteria were grown as a biofilm on a contact lens. The ability of S. marcescens to resist phagocytosis and grow to high levels in the presence of PMNs, particularly when grown as a biofilm on contact lenses, may be a mechanism by which this bacterium can survive the ocular host defense system, grow, and cause keratitis or other adverse responses.

Corneal epithelial homeostasis following daily and overnight contact lens wear

This report reviews and integrates our recent clinical and laboratory findings of the effects of daily (DW)/overnight (EW) contact lens wear on corneal epithelial homeostasis. In a prospective, double-masked human clinical study, three lens types (high and hyper Dk/t soft; hyper Dk/t RGP) were used to assess the effects of daily and overnight lens wear on corneal epithelial thickness, cell surface size, Pseudomonas aeruginosa (PA) binding to exfoliated epithelial cells and exfoliation rates. Concomitantly, we studied in a rabbit model, the effects of overnight lens wear on corneal epithelial surface cell viability (live/dead assay, TUNEL-labeling, Annexin-V staining, Bcl-2 expression), basal cell proliferation and migration patterns. The comprehensive results obtained yield important new insights on both the normal homeostasis of the corneal epithelium and the biological changes induced by contact lens wear.

Effect of eyelid closure and overnight contact lens wear on viability of surface epithelial cells in rabbit cornea.

To determine the effects of open, closed eye, and overnight contact lens wear on homeostatic epithelial surface cell death in the rabbit cornea. One eye of each rabbit was either closed by eyelid suture or fitted with one of the following test contact lenses: (1) low Dk/t rigid gas permeable (RGP) lens, (2) hyper Dk/t RGP lens, (3) hyper Dk/t soft lens. The other eye served as a control. After 24 hours, whole corneas were carefully excised and immediately stained with a calcein-acetoxymethyl ester-ethidium homodimer viability assay to quantify the number of nonviable surface epithelial cells. In addition, exfoliated corneal epithelial cells were collected with an eye irrigation chamber to determine cell viability. In the normal cornea, open-eye conditions showed significantly more nonviable surface cells in the central cornea than in the periphery (p < 0.05). Overnight wear of all test lenses and eyelid closure induced significant decreases in the number of nonviable cells on the central corneal surface compared with controls (p < 0.05). All exfoliated corneal epithelial cells collected by eye irrigation were nonviable. In the rabbit model, overnight contact lens wear significantly downregulated spontaneous epithelial surface cell death independent of lens rigidity or material oxygen transmissibility. These effects were similar to eyelid closure without lens wear. Taken together, these results suggest that eyelid closure and the physical presence of the contact lens may protect against the shear stress forces exerted by eyelid blinking, which are believed to cause central surface cell death and subsequent exfoliation.

Ocular microbiota and polymorphonuclear leucocyte recruitment during overnight contact lens wear.

Bacterial colonization of the ocular surface and contact lens (CL) and recruitment of polymorphonuclear leucocytes (PMN) during overnight CL wear was examined in 11 asymptomatic wearers. The ocular surface was more frequently colonized than the CL, with commensal bacteria (P < 0.05). Following sleep, more bacteria were recovered from the CL compared with daily use (P < 0.05), and fewer PMN were recruited compared to sleep without CL wear (P < 0.05). Overnight CL wear may inhibit physiological PMN recruitment to the cornea by preventing their access, by modifying the chemotactic signal or by altering the activation state of the recruited cells.

Corneal stress test for extended wear: Solomon OD: CLAO J 1996;22(1):75–78

The relationship between overnight contact lens wear and infectious corneal ulcers has been widely reported. Corneal hypoxia during sleep with contact lenses is believed to be an important predisposing factor for infectious corneal ulcers. We designed a provocative test to identify corneas at risk for significant oxygen deprivation during extended wear.We measured the baseline corneal thickness of 161 eyes (82 patients). Extended wear soft lenses were then fit and pachymetry was repeated after 1 night of extended wear. Patients were instructed to continue extended wear for 6 additional nights.Seventeen of 161 eyes could not continue extended wear for the full 7 nights. All failures were due to corneal decompensation. There were no failures in the group of 133 eyes with corneal swelling of 5% or less after 1 day of extended wear. All four eyes with swelling greater than 13% failed, while the failure rates for the 24 eyes with swelling between 6-13% was about 50%. The thicker hyperopic lenses produced the majority of failures.Measuring corneal swelling after 1 night of extended wear may identify those corneas at risk for significant oxygen deprivation during overnight contact lens wear. Corneal swelling of 5% or less seems to indicate that the cornea can tolerate 7 nights of extended wear (significant to P < 0.001).