The following factors were not found to have a significant effect on corneal staining: patient age, gender, average wearing time, wearing time at the examination, oral contraceptive use in females, use of oral antihistamines, use of oral antihypertensives, type of wear (extended, flexible, or daily), spherical vs. toric lens type, contact lens water content, total time of lens wear, type of care system, use of enzyme, and removal of contact lenses by pinching directly off the cornea.
Results from the multivariable logistic regression analyses for any staining and moderate-to-severe staining are shown in Table 6. Patients who reported compliance with their care system were 54% less likely to show any staining and 58% less likely to show moderate-to-severe staining than patients who did not comply. Reported replacement schedule was also significantly related to the presence of staining. Patients who replaced their lens daily were 11 (1/0.09) times less likely to show staining than patients on a conventional replacement schedule. Similarly, patients who replaced their lens every 3 to 6 months were 66% less likely to show staining than patients on a conventional replacement schedule. Due to the small sample size in the moderate-to-severe staining group, conventional lens wear was compared with all other more frequent lens replacement schedules combined. Replacing lenses more frequently than a conventional lens replacement was associated with a 60% reduction in the odds of moderate-to-severe staining.
The use of rewetting drops was associated with a 2-fold increase in the odds of any staining. Rewetting drop use was not significantly associated with moderate-to-severe corneal staining. In contrast, lenspower was not associated with some degree of staining; however, it was significantly related to moderate-to-severe staining. Both moderate-to-high myopia (−3.12 D and more minus contact lens power) and hyperopia (plano and plus contact lens power) were associated with an increased odds of moderate-to-severe staining (aOR = 3.57 and aOR = 1.05, respectively) compared with low myopia. Neither lens design (toric or spherical) nor water content of lens was found to be significantly related to the presence of any staining or moderate-to-severe staining.
Descriptive statistics for each clinical site are shown in Table 7. The mean total staining scores ranged from 0.10 (N = 5 patients) to 3.60 (N = 5 patients). The minimum staining score was 0.0, and the maximum reported total score was 10.0.
With our sample size, we could detect a 25% increase in the prevalence of any staining with 80% power for each of the following: gender, water content, lens power, replacement schedule, care system, use of enzyme, compliance with care system, and patient pinches lens from cornea. Unfortunately, the low overall prevalence of moderate-to-severe staining demands a much larger sample size for adequate power. In the case of moderate-to-severe staining, our sample size allowed us to detect a 50% increase in prevalence for only gender, lens power, and patient pinches lens directly from cornea. Thus, we cannot be sure that some of the factors for which we did not obtain statistically significant results are truly not associated with corneal staining.
Prevalence of Staining After Lens Removal
It has been reported that some degree of corneal staining occurs with contact lens wear. 6,9,10,14,16,17,19,27–30 In addition, although variable, the prevalence of corneal fluorescein staining is reported to be 4 to 79% in normal, non-contact lens wearing patients. 1,4–8 Fluorescein staining was observed in at least one eye in 55.7% of the hydrogel lens wearers examined in this study. Moderate-to-severe staining was documented in 8.0% of consecutive contact lens patients in this study. Methodological differences in describing staining frequency and severity in both contact lens wears and non-contact lens wearers have led to varying reports of the prevalence of corneal staining. In many studies of contact lenses, corneal staining (superficial punctate keratitis) is considered a complication of lens wear. As such, the presence/absence of corneal staining is reported without reference to the degree of corneal staining, and the protocol used to describe the amount of staining as a “complication” is often not reported. Therefore, comparing the prevalence of corneal staining between studies is difficult.
In a study of the complications associated with conventional extended-wear and disposable extended-wear, superficial punctate keratitis was reported as a complication in 45.9% (28/61) of conventional extended-wear patients and 16.9% (11/65) of disposable extended-wear patients. 28 In comparing disposable daily-wear and conventional daily-wear, the estimated site-adjusted prevalence of superficial punctate keratitis (reported as a complication) was 1.2% for disposable wear and 2.6% for conventional wear. 9 In both of these studies, there is no description of how severe the staining was to be classified as a complication. Cases of any degree of staining would have gone undetected in these studies if the investigators thought the staining was present yet not clinically significant. Our study quantifies the amount of any staining present in consecutive contact lens patients presenting for eye care. Similarly, in a randomized cross-over study of daily disposable lenses vs. extended-wear by Nichols et al., 31 54.2% of patients had some degree of staining (any staining) after daily disposable wear, and 79.2% showed staining after extended-wear.
Our prevalence of staining, although higher than the prevalence of the reported complication superficial punctate keratitis and similar to the report of Nichols and coworkers, 31 is lower than reports of any staining in non-contact lens wearing patients (79.0%). 8 Although the grading scale was the same (any staining ≥0.5 in at least one region), we cannot explain why more non-contact lens wearers have staining. In a preview of their work, Korb and Korb 5 noted that there appeared to be a “trend toward a lower incidence of corneal staining” than the staining found before lens fitting in the first 71 of 300 soft contact lens patients enrolled in their study. The results of this study were never published.
Lens Care Systems
Patients who admitted noncompliance with their lens care system had a significantly greater amount of corneal staining. This finding is intuitive in that a clinician would expect that a higher degree of compliance would yield cleaner, more deposit-free lenses and therefore less corneal staining. In this study, patients described the lens care routine to the examining doctor, and compliance was determined based on the manufacturer-recommended guidelines for the lens care system. In this study, ReNu was the most frequently used lens care system. In the case of noncompliance with a chemical system, patients would often report eliminating the mechanical rubbing step of the contact lens cleaning/disinfection process. Skipping this step could increase the deposition of debris including protein on the lens surface. In addition, chemical care systems have been shown to be more toxic to rabbit epithelium and human corneal epithelium 20,21 and have also been associated with more corneal staining than hydrogen peroxide systems. 32
In the late 1970s and 1980s, adverse reactions to common chemical disinfection solutions were reported. 33–36 New-generation preservatives have replaced many of the preservatives used in the disinfection process at that time. Anecdotal reports of current cases of chemical care system sensitivity have been discussed clinically; however, research in the area of current contact lens solution sensitivity (at a mild to moderate level) is limited. 32 In this study, the type of care system used was not associated with corneal staining. Enzyme use also had no apparent affect on corneal staining. Clinically, patients who are on frequent lens replacement schedules are thought to have less corneal staining, and most patients wearing disposable contact lenses generally do not use enzyme cleaning.
Patients using rewetting drops demonstrated significantly more corneal staining than patients reporting no use of rewetting drops. It is possible that patients who select to use rewetting drops do so to alleviate ocular discomfort associated with contact lens wear. These patients may be marginal dry eye patients or patients with subclinical anterior segment disorders and may warrant closer evaluation by their contact lens practitioner, especially in the event of noncompliance with the contact lens care system. Sensitivity to preservatives in the contact lens care systems or in the rewetting drops could also play a role in corneal staining and contact lens comfort. Our data demonstrate that noncompliance with any care system is associated with corneal staining. Contact lens practitioners may want to consider reviewing care system compliance, including the use of nonpreserved lubricating eye drops in patients with corneal staining.
Wearing and Replacement Schedules and Lens Age
In this sample, we were unable to find a significant difference between corneal staining in extended-wear vs. daily-wear patients. Superficial punctate corneal staining associated with extended-wear is often though of as a complication of extended-wear and has been described in the literature. 9,10,29,37–39 Similar to our findings, Poggio and Abelson 10 compared the complications associated with extended-wear (disposable and conventional) vs. conventional soft daily-wear, and found no significant differences in the frequency of superficial punctate keratitis between patients wearing either type of extended-wear lenses and conventional lenses, although more patients in conventional extended-wear demonstrated corneal staining. In a 3-year study by Poggio and Abelson, 9 disposable extended-wear patients had significantly less corneal staining than conventional extended-wear patients. Their study also showed fewer complications of any kind (including staining) in the second and third years of the study, which is consistent with previous studies. 29,37 This was attributed to discontinuation of extended-wear in patients experiencing complications with the extended-wear modality. Watanabe and Hamano 11 reported that a total of 3.6% (197/5478 eyes) of patients wearing disposable extended-wear lenses were observed to have a corneal epithelial “complication” on at least one examination during the entire follow-up period, and in patients with staining, a much higher noncompliance rate was noted. In contrast, a recent study by Nichols et al. 31 found that soft disposable extended-wear patients demonstrated more corneal staining than patients in a daily disposable lens modality.
In our study, extended-wear patients (both conventional and disposable) were compared with all patients removing lenses daily. We did not evaluate differences between conventional and disposable extended-wear due to the small sample size of conventional extended-wear patients (N = 2). The majority of extended-wear patients in this sample wear disposable lenses, and therefore may have less corneal staining than a sample with more conventional extended-wear patients. This sample might also represent “successful” extended-wear patients, in which patients with previous extended-wear complications have discontinued extended-wear. In addition, the group of patients reporting daily wear includes patients in the disposable lens modality and the conventional lens replacement schedule. The conventional lens replacement group demonstrated more staining than the other replacement schedules, which could also partially explain why no difference was seen between the extended-wear and daily-wear groups.
In agreement with our findings, Hamano et al. 40 have shown that patients wearing conventional lenses have more complications (including superficial punctate keratitis) than patients using more frequent replacement schedules. Although our sample of daily disposable lens wearers was small, our findings are consistent with other reports of less corneal staining in patients wearing daily disposable lenses. 9,40 Additional studies suggest no apparent difference in corneal staining between daily and biweekly replacement of (the same) soft hydrogel lenses. 41 Average wearing time and wearing time on the day of corneal staining assessment also had no significant effect on corneal staining. Our findings suggest that patients with more frequent replacement schedules demonstrate less corneal staining; therefore, patients should be considered for a frequent replacement program of at least every 6 months.
The Influence of Lens Characteristics on Corneal Staining
Hydrogel lens wearers showed a statistical difference in moderate-to-severe staining, with a lower frequency of staining observed in patients wearing lenses in the power range (spherical equivalent) of −1.62 to −3.00 D compared with −3.12 D and more minus lens powers. Hyperopes demonstrated equivalent odds of moderate-to-severe staining as moderate-to-high myopes. This is in contrast to previous studies that have shown that patients fit in high plus hydrogel lenses demonstrate significantly more staining (after 5 hours) than when wearing regular and thin minus lenses. 30 In a study by Guillon et al., 18 varying center thickness while maintaining water content and power (−3.00 D) demonstrated no effect on corneal staining. However, other studies have shown that thin, high water content lenses have a detrimental effect on corneal staining. 17,42 Most patients in our study were wearing disposable lenses, many of which are thin, high water content lenses. In addition, the hyperopes in the study were in the low-to-moderate range and were not wearing thick high plus (or aphakic) lenses.
The assessment of “acceptable fit” was not significant in predicting the odds of staining in the logistic model, although more patients with an “unacceptable fit” demonstrated moderate-to-severe corneal staining. In this study, the fit was assessed before the evaluation of corneal staining to reduce potential clinician bias. This supports the findings of Guillon et al. 18 and Orsborn and Zantos 17 showing that mechanical factors do not play a role in corneal staining. Staining in toric vs. spherical hydrogel lenses had an equivocal result, with the difference in staining being greater for toric lens wearers than spherical lens wearers, but without statistical significance.
Our data suggest that there are no statistically significant differences in corneal staining between right and left eyes or between males and females. Staining was greater for female patients using oral contraceptives, but failed to achieve statistical significance. Although the use of oral contraceptives is often clinically associated with symptoms of dry eye, any specific effect of oral contraceptive use on the ocular surface is unknown. Patients between the ages of 20 to 29 years exhibited the greatest staining; however, this was not statistically significant.
Staining Scales, Methods, and Between-Observer Variability
Although many published and unpublished grading scales exist to assess staining of the cornea and conjunctiva, no single grading scale is widely accepted by the cornea and contact lens community. Grading scales have been developed to assess disease-related corneal and conjunctival staining, as well as additional anterior segment complications. Photographic grading scales (CCLRU 24 and Vistakon 43), pictorial (Efron 44 and Oxford 45) and descriptive (van Bijsterveld 46 and Lemp 47) grading scales of corneal and conjunctival staining are gaining popularity in clinical research in an effort to minimize investigator bias. Both the Oxford 45 and van Bijsterveld 46 grading scales were developed to assess both corneal and conjunctival staining and utilize a summed score over the anterior ocular surface. Although developed to assess rose bengal staining, the grading scheme of the van Bijsterveld scale (0 to 3 in each region) has been applied to the cornea to assess fluorescein staining. 47 In our study, most of the participants with staining could be classified as mild, with only 8.0% demonstrating more severe corneal staining. Staining scales with more increments (0.5-unit steps) may yield more information than 0 to 3 scales when classifying mild staining.
In addition, the amount and concentration of fluorescein used may have an impact on corneal staining. As with grading scales, a variety of protocols have been reported for the application of fluorescein to the corneal surface. Fluorescein strips, although convenient, may not consistently deliver a uniform volume and concentration of fluorescein. A newer strip has been developed to administer 1 μl of fluorescein (Dry Eye Test, Akorn Inc., Buffalo Grove, IL). Liquid fluorescein, although available unpreserved through a pharmacy, is not available commercially for topical application to the eye in the United States. In solution, 1 to 2% fluorescein is preferred. 47 A fluorescein strip wetted with one drop of saline (with the excess gently shaken off) is the technique recommended by Bron 45 and Lemp. 47
We admit that some degree of between-observer variability will exist even with training and the use of descriptive and photographic guides. In their work on the reliability and validity of four grading scales of contact lens complications, Efron and coworkers 48 report that the 95% confidence limits of all four systems were within ±1.38 (points) for corneal staining, which may be attributable to practitioner experience with the grading system. We have no way of knowing whether the variation in the range of reported scores between sites (Table 7) was a result of clinic population, investigator bias, or both. Utilizing the photographic and descriptive scale may have minimized investigator bias, but certainly did not eliminate variability. The variability in the distribution of scores between clinics is not easily explained. In addition, some of the centers with the highest median scores also recruited the fewest participants. Without visiting the sites or documenting the participant pool from each site, we were unable to determine the impact these sites had on the overall study. It is possible that differences in scaling between sites could confound the results. Further studies on methodology (including recruitment, site selection/training, and fluorescein amount and concentration), documentation (photographic and written), and use of grading scales in the evaluation of fluorescein corneal staining are warranted.
The purpose of this study was to determine the factors that contribute to corneal staining in hydrogel lens wearers by evaluating the following variables: type of soft lens worn, wearing time and lens replacement schedule, lens care systems, and individual patient factors. Factors that were shown to have a statistically significant effect on corneal staining in this study were as follows: patient-reported compliance with their contact lens care system, use of rewetting drops, and lens replacement schedule. Because compromise to the corneal epithelium may place contact lens wearers at a higher risk for complications, factors associated with staining should be carefully considered when prescribing and monitoring contact lenses. Over half of the contact lens wearers in this study had some degree of corneal staining, although only 8% had moderate-to-severe staining. Variability in the grading of staining occurs between examiners; therefore training is critical for clinical studies. To provide the highest quality of care to patients, it is essential that eye care practitioners prescribing contact lenses recognize and understand the many factors that can cause corneal staining.
We thank the following examining doctors (N = 21; N = 20 geographical locations) for their generous participation in this study: Audrey Brodie, OD, Tahlequah, Oklahoma; Susan Brunnett-Munson, OD, Highlands Ranch, Colorado; Arthur B. Corish, OD, Irvine, California; Wiley F. Curtis, OD, Arlington, Texas; Larry M. DeDonato, OD, Delano, California; Jeffrey Dougal, OD, Placentia, California; Michael Goldsmid, OD, San Diego, California; Steve Grant, OD, Costa Mesa, California; Mark Jensen, OD, Issaquah, Washington; Everett King, OD, Laramie, Wyoming; Jeffrey C. Krohn, OD, Fresno, California; Brian Linde, OD, Billings, Montana; Leon Miller, OD, Englewood, Colorado; Dena Mintz, OD, Corona, California; Kelly K. Nichols, OD, Columbus, Ohio; Kathy Osborn, OD, Columbus, Ohio; Charles Roberts, OD, San Juan Capistrano, California; Glenda Secor, OD, Huntington Beach, California; Robert Silverman, OD, Albany, New York; Evan Thomas, OD, Newport Beach, California; Paul Woolf, OD, Mesa, Arizona.
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Keywords:© 2002 American Academy of Optometry
fluorescein; staining; cornea; contact lens; hydrogel; dessication