Case reports of three atypical infiltrative keratitis events with high DK soft contact lens wear

PURPOSE

We report three atypical infiltrative keratitis events in patients that had successfully worn highly oxygen permeable (Dk) soft contact lenses on an extended wear (EW) schedule for at least 15 months. These cases highlight the role of patient/practitioner education, patient compliance, examination, and appropriate referrals that are required to reduce the risk of complications during lens wear.

METHODS AND RESULTS

Each patient had been wearing high Dk soft lenses on an EW schedule with monthly replacement for at least 15 months and presented with severe pain, redness, and photophobia. The events were characterized by focal infiltrate(s) with an overlying epithelial defect in the superior periphery to mid-periphery of the cornea and extensive diffuse infiltration.

CONCLUSIONS

The signs and symptoms of each case were more severe than is typically associated with contact lens-related infiltrative keratitis. Because of the slow progression of signs and relatively fast resolution, the cases were not found to be microbial keratitis. Although high Dk soft contact lenses overcome hypoxia-associated complications associated with extended wear, patients and practitioners must be vigilant as adverse events can still occur and in rare instances can be severe. Education and patient compliance are a crucial part of successful management of patients on EW schedules. Constant reinforcement is necessary to ensure patient compliance.

Predicting extended wear complications from overnight corneal swelling

PURPOSE

To examine the hypothesis that the corneal overnight swelling response (ONSR) is a predictor of ocular complications in contact lens extended wear (EW).

METHODS

The Berkeley Contact Lens Extended Wear Study (CLEWS) was a randomized, concurrently controlled clinical trial in which more than 200 subjects in EW with rigid gas-permeable (RGP) lenses were observed for 1 year. After adapting to EW, subjects were randomized to either medium or high oxygen-permeable (Dk) RGP lenses and underwent clinical assessments, keratometry, and corneal pachometry at 3-month intervals.

RESULTS

The ONSR was directly related to lens Dk (P = 0.01) and exhibited substantial variability across subjects. The probability of remaining free of complications over time was not significantly lower for subjects with a mild ONSR compared with those with greater edema (P = 0.84). The risk of development of keratopathy was not significantly related to the ONSR (relative risk = 1.00).

CONCLUSIONS

The corneal ONSR is not a good predictor of ocular complications in 1 year of RGP EW. Lenses that cause little or no corneal edema are not necessarily safer for overnight wear.

Epithelial split associated with wear of a silicone hydrogel contact lens

PURPOSE

To describe the appearance and management of a superior epithelial arcuate lesion (SEAL) observed in association with the wear of a silicone hydrogel lens.

METHODS

We present a case of a 30-year-old male who presented with a SEAL after 4 months of wear of a silicone hydrogel lens on a 30-day extended wear schedule. Bacteriological examination of the lenses and ocular adnexa was conducted at the time of the event. The clinical presentation and management are presented and compared to a review of cases associated with hydrogel lenses.

RESULTS

The patient presented with symptoms of mild irritation. A linear splitwas noted in the superior peripheral cornea of the affected eye and was associated with limbal injection, stromal infiltrates, and fluorescein staining. Normal ocular biota was recovered from the lenses and eyelids of both eyes. Visual acuity remained unchanged and the lesion resolved following prophylactic treatment and discontinuation of lens wear for 8 days.

CONCLUSIONS

The diagnosis and management of this SEAL case in a silicone hydrogel lens wearer mirrored that of previous events associated with hydrogel lenses. The possible etiologies of SEAL in this case are discussed and include mechanical irritation and dehydration of the lens surface.

Conjunctival impression cytology in contact lens wearers

The upper tarsal conjunctiva is in constant friction with the surface of the contact lens. The conjunctival surfaces of 80 soft and gas-permeable contact lens wearers (40 each) and 20 controls were studied using biomicroscopy and impression cytology. A filter dissolution technique was used to process the conjunctival imprints. Biomicroscopic and cytologic grading of the conjunctivae was performed using four-tier grading systems. Impression cytology is a non-invasive, painless procedure. The altered technique of processing yielded better cellularity and excellent cellular detail. On biomicroscopy and cytology, all controls showed Grade 1 appearances. Soft lens wearers who were symptomatic were found to have a significant increase in both biomicroscopic and cytologic grades, when compared with their asymptomatic counterparts. No correlation was found between duration of lens use and biomicroscopic or cytologic grades. All changes were found to be more severe in soft lens wearers.

The Berkeley Contact Lens Extended Wear Study. Part I : Study design and conduct

OBJECTIVE

The primary aim of the Berkeley Contact Lens Extended Wear Study (CLEWS) was to test the hypotheses that extended wear of rigid gas-permeable (RGP) contact lenses with greater oxygen permeability (Dk) reduces the incidence of contact lens-associated keratopathy (CLAK) and increases the survival rate in RGP extended wear (EW). In this article we describe the clinical trial design in detail, present the results of subject recruitment and retention, and provide the baseline demographic and ocular characteristics of the CLEWS subjects, whose data will be analyzed to address the study aims in a companion article.

DESIGN

A randomized, concurrently controlled clinical trial.

INTERVENTION

Subjects were fitted with day wear (DW) high-Dk RGP lenses and then adapted to EW. Subjects who adapted to EW were then randomly assigned to either high- or medium-Dk RGP lenses for 12 months of 6-nights/week EW.

MAIN OUTCOME MEASURES

Slit-lamp assessment and grading of 17 possible keratopathies, measurement of refractive error and corneal curvature, and symptoms. Follow-up data were collected every 3 months.

RESULTS

From 545 subjects entering the DW adaptation phase, 201 adapted to EW and were randomly assigned to medium- or high-Dk lenses for 12 months of EW. The baseline characteristics of the two study groups were similar and did not differ from the 344 DW subjects who failed to adapt to EW. The distributions of oxygen transmissibility for the two study groups were disjoint, indicating that each group received distinctly different levels of hypoxia.

CONCLUSIONS

We show that CLEWS was appropriately designed to address the study hypotheses, was conducted with regard for the safety of the subjects, and adhered to rigorous protocols designed to control for bias and ensure the integrity of study data. We establish the internal validity of between-group statistical comparisons and characterize our study population to permit informed evaluation of the applicability of our results to the contact lens-wearing population in general.

The Berkeley Contact Lens Extended Wear Study. Part II : Clinical results

OBJECTIVE

To describe the principal clinical outcomes associated with 12 months use of rigid gas-permeable (RGP) extended wear contact lenses and address two primary study questions: (1) does extended wear (EW) of high oxygen transmissibility (Dk/t) RGP lenses reduce the incidence of ocular complications, and (2) does the wearing of high-Dk/t lenses reduce the rate of failure to maintain 6-night RGPEW over 12 months?

DESIGN

A randomized, concurrently controlled clinical trial.

INTERVENTION

Subjects who adapted to EW with high Dk (oxygen permeability) RGP lenses were randomized to either high Dk or medium-Dk RGP lenses for 12 months of 6-night EW.

MAIN OUTCOME MEASURES

Contact lens-associated keratopathies (CLAK), changes in refractive error and corneal curvature, and survival in EW.

RESULTS

Two hundred one subjects were randomized to medium or high-Dk lenses for 12 months of EW. Sixty-two percent of the subjects in each group completed 12 months of EW; however, the probability of failure was significantly greater for the medium-Dk group. Although the risk of complications was similar for the two groups, the number of CLAK events that led to termination were 16 versus 5 for the medium-Dk and high-Dk groups, respectively. This suggests that the type of adverse response or the inability to reverse an adverse event was different for the group being exposed to the lower oxygen dose.

CONCLUSIONS

The level of oxygen available to the cornea has a significant impact on maintaining successful RGP extended contact lens wear, but not on the initial onset of CLAK. The number of clinical events leading to termination was substantially higher for the medium Dk group, which suggests that corneal hypoxia is an important factor in the development of CLAK. Although overnight contact lens wear should be recommended with caution and carefully monitored for early detection of ocular complications, it appears that high-Dk RGP lenses can be a safe and effective treatment for correction of refractive error for most individuals who can adapt to EW.

Microcysts: clinical significance and differential diagnosis

BACKGROUND

Microcysts are the most-distinctive and easily detectable indicator of contact lens-induced hypoxia. They should not be confused with cyst-like inclusions that occur in conditions such as Meesmann's dystrophy, bullous keratopathy, and Cogan's microcystic dystrophy, or with mucin balls, vacuoles, microcystic edema, and infiltrates.

METHODS

Data from published literature and recent data from The Cornea and Contact Lens Research Unit (CCLRU) clinical trials involving low Dk and prototype high Dk soft contact lenses (SCLs) were examined.

RESULTS

Extended wear with low Dk SCLs induces significant numbers of microcysts, whereas extended wear with high Dk SCLs does not. Subjects who transfer from low Dk to high Dk lenses have an initial increase in the number of microcysts after seven days that declines to normal levels over 1 to 3 months. Microcysts can be differentiated from other ocular conditions as they show reversed illumination, are 10- to 50-microm irregularly shaped dots, and are often associated with lens-induced hypoxia.

CONCLUSIONS

Microcysts are easily observed and differentiated from other conditions in clinical practice. On average, fewer than ten microcysts per eye occur in nonhypoxic lens wear and, on average, more than 20 microcysts per eye are an indication of chronic hypoxia. The increase in microcyst numbers after transfer from low to high Dk lens wear is transitory and does not necessitate a period of no lens wear.

Association of acinetobacter species with contact lens-induced adverse responses

PURPOSE

To determine the levels of Acinetobacter species associated with normal soft contact lens wear and to determine whether Acinetobacter species are involved in adverse reactions that occur during contact lens wear.

METHODS

Patients wore soft contact lenses on an extended-wear basis. The bacteria on lenses and ocular swabs during asymptomatic and symptomatic lens wear were identified using standard microbiologic methods.

RESULTS

Acinetobacter species were isolated and identified from 16 (13%) of 126 patient samples. Greater numbers of Acinetobacter species were isolated from lenses of patients experiencing adverse responses than from asymptomatic patients. Acinetobacter species were isolated from patients experiencing symptomatic adverse responses in 4 (13%) of 32 cases.

CONCLUSION

It appeared that Acinetobacter species colonized the eye of extended contact lens wearers at a time when the normal functioning of the eye was compromised by contact lens wear. When Acinetobacter species were in high numbers on a contact lens, an adverse response occurred. This may implicate Acinetobacter species as a contributing factor to adverse responses associated with contact lens wear.

Seven-day extended wear and 30-day continuous wear of high oxygen transmissibility soft silicone hydrogel contact lenses: a randomized 1-year study of 504 patients

PURPOSE

To compare the performance and complication rates of PureVision (Bausch & Lomb, Inc.) high Dk/t silicone hydrogel lenses in 30-day continuous wear and 7-day extended wear.

METHODS

Five-hundred four (504) patients were randomized to 30-day continuous wear (353 patients) or to 7-day extended wear (151 patients) and followed for 12 months.

RESULTS

Eighty percent of patients did not report any symptoms/complaints at the follow-up exams. There were no cases of microbial keratitis. The annual incidence of the four most common clinically significant positive slit lamp findings related to lens wear for the 30-day and the 7-day groups, respectively, were as follows: corneal staining, 10.5% and 10.6%; corneal infiltrates, 4.6% and 2.3%; slight epithelial edema, 2.0% and 3.6%; and tarsal conjunctival abnormalities, 1.6% and 3.0%. There was no significant difference in complication rates between the groups. For reasons related to lens wear, 7.6% in the 30-day group and 13.2% in the 7-day group were dropped from the study. The patients' subjective judgment of comfort, visual quality, freedom from dryness, and lens handling varied from 89 to 95 on a scale of 0 to 100. The success rate was 82.9%, slightly better for the 30-day group (84.4%) than for the 7-day group (79.5%).

CONCLUSION

The complication rate was low. Sight-threatening events, such as bacterial keratitis did not occur. Inflammatory changes were seen, although at a low rate. Anterior segment changes related to hypoxia were minimal. Limbal and bulbar hyperemiadecreased significantly after switching patients to PureVision lenses. There was no significant difference in complication rates between the 30-day group and the 7-day group.

Acanthamoeba keratitis associated with fungal keratitis

PURPOSE

To report fungal infection complicating Acanthamoeba keratitis.

METHODS

Case report. A 45-year-old woman with contact lens-related bilateral Acanthamoeba keratitis developed corneal ulcer, corneal perforation, and mature cataract in the left eye, which was managed by penetrating keratoplasty, lensectomy, and vitrectomy.

RESULTS

Histopathologic examination of the keratoplasty specimen from the left eye revealed extensive lamellar stromal necrosis with the coexistence of both empty cysts and branching hyphae. Cultures from the keratoplasty specimen grew Scedosporium apiospermum.

CONCLUSION

Keratomycosis caused by S. apiospermum may complicate protracted Acanthamoeba keratitis.

Vascular response to extended wear of hydrogel lenses with high and low oxygen permeability

PURPOSE

The purpose of this study was to determine the impact of extended wear of high and low oxygen permeability (Dk) lenses on the development or resolution of limbal hyperemia and corneal neovascularization in a randomized prospective clinical trial.

METHODS

Adapted daily-wear contact lens wearers were randomly assigned to one of two groups. The low-Dk group (N = 23) wore etafilcon A lenses (Dk/t = 40) for up to 7 days and 6 nights, and the high-Dk group (N = 39) wore lotrafilcon A lenses (Dk/t = 175) for up to 30 days and nights. Limbal hyperemia and neovascularization were assessed and graded during 9 months of extended wear. A stratified analysis to determine how change in ocular redness depended on initial presentation was also conducted.

RESULTS

On a 0 to 100 scale, extended wear of low-Dk lenses resulted in a 16-point increase in limbal hyperemia (p < 0.0001); no significant change occurred with the high-Dk lenses. The difference was greatest for low-Dk participants who initially presented with lower levels of hyperemia (N = 18). There was a slight resolution of redness in participants who initially presented with higher levels of hyperemia (N = 10) after wearing the high-Dk lenses. Neovascularization increased by an average of 0.5 on a scale of 0 to 4 in low-Dk lens wearers (p < 0.0001) but remained unchanged in the high-Dk lens wearers. The increase was most marked for the low-Dk group with lower levels of neovascularization at baseline.

CONCLUSIONS

Subjects who wore lenses with higher oxygen permeability for 9 months of extended wear exhibited a lower vascular response of the ocular surface compared with subjects who wore lenses of lower oxygen permeability for the same period. This result was found both for the surface limbal vessels and in the deeper neovascular stromal vessels. Moderate neovascularization also developed after 3 months of extended wear of low-Dk hydrogels, whereas high-Dk lenses caused no neovascularization.

[Topographic and pachymetric changes caused by prolonged use contact lenses]

PURPOSE

To evaluate the topographic and pachymetric alterations caused by soft contact lenses for prolonged use and DK/t >100 after wearing them continuously for 3 weeks.

METHODS

Our study included 24 eyes of 12 patients aged between 19 and 32 years who were given the new Night & Day contact lens to wear. Various topographic parameters -central corneal power, corneal radii at 3, 5 and 7 mm and simulated keratometry- were analyzed together with pachymetry before the lenses were put in and the 1st and 21st day after insertion. Wilcoxon's test for matched-pairs is used for the comparison, and vectorial analysis to evaluate the sphere, cylinder and axis of the astigmatism caused by the lens.

RESULTS

The mean refraction of the patient was of -3.28 D. The initial mean central corneal power was 42.5 D. There were no significant differences in central corneal power and radii after 21 days of use of the lens. The initial mean pachymetry was of 541.46 micrometer and 557.64 micrometer after 24 h of use. There were significant differences in the pachymetry after the use of the lens.

CONCLUSIONS

No significant topographic alterations were produced following prolonged use of the contact lenses (21 days). The corneal thickness after wearing the lens was <5% in all cases.

Microcyst response to high Dk/t silicone hydrogel contact lenses

PURPOSE

To investigate the microcyst response to extended wear (EW) with high oxygen transmissible (Dk/t) silicone hydrogel lenses.

METHODS

Microcysts were monitored for 12 months in subjects wearing low Dk/t hydrogel lenses on a 6-night EW schedule or high Dk/t hydrogel lenses on a 30-night EW schedule. Subjects wearing low Dk/t lenses transferred to the high Dk/t EW lenses and schedule after 12 months and were monitored for a further 6 months.

RESULTS

The mean number of microcysts did not deviate from baseline in the high Dk/t group. Microcysts in the low Dk/t group increased over 12 months, and more microcysts were observed in low Dk/t lens wearers compared with high Dk/t lens wearers after 3 months. Microcysts increased in 50% of subjects 1 week after transfer to high Dk/t lenses and returned to baseline levels seen with high Dk/t lens wear within 3 months.

CONCLUSIONS

EW with high Dk/t silicone hydrogel lenses did not cause an increase in microcyst numbers. It is not necessary to discontinue lens wear with patients who transfer from low to high Dk/t lenses because the increase in microcysts is transitory. This result has implications for practitioners when fitting and assessing the success of high Dk/t hydrogel lenses.

Infiltrative keratitis associated with extended wear of hydrogel lenses and Abiotrophia defectiva

PURPOSE

Infiltrative keratitis is a common complication associated with extended wear of hydrogel lenses. Causative bacteria are often isolated from the lens at the time of an event. We report a case where three repeated occurrences of infiltrative keratitis were associated with contamination of the contact lenses by Abiotrophia defectiva.

METHODS

A 34-year-old man participating in a clinical trial of extended wear hydrogel contact lenses experienced three episodes of infiltrative keratitis. The clinical presentation was observed using a biomicroscope. At the time of each event, the contact lenses were removed aseptically and ocular swabs were taken for bacterial identification and enumeration. The condition was monitored until full resolution.

RESULTS

The condition was characterized by irritation, marked bulbar and limbal injection, and multiple focal subepithelial infiltrates. Many of the infiltrates also showed overlying staining with fluorescein. In each of the three events of infiltrative keratitis, A. defectiva was cultured from the contact lens and ocular swabs.

CONCLUSION

This is the first reported occurrence of infiltrative keratitis associated with A. defectiva contamination of contact lenses.

Clinical characterization of spherical post-lens debris associated with lotrafilcon high-Dk silicone lenses

PURPOSE

Experience with high Dk silicone hydrogel lenses has revealed post-lens debris, which is characterized by the appearance of spherical, translucent particles referred to as "mucin balls." The objectives of this analysis were to characterize the presence of mucin balls, determine whether any ocular characteristic predicts the development of mucin ball debris, and determine whether there is any association between mucin balls and the ocular response to contact lens wear.

METHODS

Ninety-two subjects wore lotrafilcon A lenses on an extended wear basis for up to 30 nights and were followed for 6 months. Mucin balls were graded on a 0 to 4 scale at three visits. Subjective ratings and biomicroscopic appearance were recorded at all visits.

RESULTS

Mucin balls were observed in 70% of subjects at one or more visits, and 29% of subjects at all three visits. There was no change in the mean grade of mucin balls over time. Mucin balls were graded > 1 in 20% of eyes, > 2 in 6% of eyes, and > 3 in 2% of eyes. Subjects who exhibited mucin balls at each clinical visit had significantly steeper keratometry readings along the flatter meridian (44.3 D) than those who never exhibited mucin balls (42.9 D, P < 0.0001). The percentage of subjects who "never" use lubricating drops was higher in the subjects with mucin balls (P = 0.0014). No association was found between mucin ball observation and biomicroscopic appearance, inflammatory responses, or subjective responses.

CONCLUSIONS

The presence of mucin balls does not appear to be detrimental to contact lens wear. Eyes with steeper corneal curvature were significantly more likely to present with mucin ball debris, indicating they may be a function of lens fit. Clinical factors that may be modified in order to manage the more severe presentation of mucin balls are the use of lubricating drops and the number of nights extended wear schedule.

A comparison of contact lens-related complications in various daily wear modalities

PURPOSE

To determine the incidence of contact lens-related complications in various daily wear contact lens modalities.

METHODS

The charts of 138 daily wear contact lens patients (35 daily disposable, 34 two week replacement, 34 frequent replacement, and 35 conventional daily wear lens users) were reviewed for subjective and objective contact lens problems. We also looked at two subgroups: first time lens wearers and patients with previous lens-related problems. The rate of lens related complications were calculated as events per person per year (E/P/Y) of lens wear for each year and for the total 3-year study. The percentage of patients in each group who experienced any complication was calculated. We also compared the complication rate for the groups in our current study to the rates calculated for disposable extended wear and conventional extended wear patients from our previous study.

RESULTS

We found that the E/P/Y were significantly lower for daily disposable lens wearers, but no significant differences were noted for all other lens wear modalities. There was a trend in most groups toward decreased numbers of complications in the second and third years of lens wear. Of the 23 individual signs and symptoms that were analyzed, three occurred most frequently among daily disposable lens wearers, two were most common in the 2-week replacement group, four occurred most often in frequent replacement patients, and eight were most frequent in conventional daily lens wearers. (In three categories, there were two groups with ties for the highest rate of occurrence, and two categories with zero rates for all groups.) Most of the observed differences in complication rates for individual signs and symptoms did not reach the level of statistical significance.

CONCLUSIONS

Daily disposable lens wearers had the lowest overall complication rate.

Corneal sensitivity changes in long-term wearing of hard polymethylmethacrylate contact lenses

The effect on corneal sensitivity of years of wearing hard contact lenses was evaluated in 20 subjects who had worn polymethylmethacrylate (PMMA) lenses for up to 20 years. An age- and sex-matched group of 20 eyes was used as the control group. It was found that corneal sensitivity diminished significantly in wearers of PMMA contact lenses. This reduction of corneal sensitivity was found to be most prominent centrally and was markedly related with the duration of PMMA contact lens use. The loss of corneal sensitivity due to wearing contact lenses increases the risk of a silent infection.

Continuous wear contact lenses: have we been here before?

New developments in contact lens materials have led to the introduction of new lenses designed for up to 30 days of continuous wear. Will these lenses lead to safer and healthier overnight use of lenses?

Staphylococcus aureus causes acute inflammatory episodes in the cornea during contact lens wear

The aim of this investigation was to determine the ability of Staphylococcus aureus to cause keratitis during contact lens wear in the rabbit. Rabbits were fitted with hydrogel lenses and wore them on an extended wear schedule for 7 weeks. At the end of each week of wear, one drop of S. aureus was added to the eyes, and the eyes were monitored using slit lamp bio-microscopy, with subsequent microbial and histological studies of the cornea. In the presence of S. aureus, keratitis occurred after 3 weeks of lens wear, a condition that was characterized by diffuse infiltration of the peripheral cornea and limbal redness. In the absence of bacteria, there was no infiltration until week 6. Contact lens wear also prolonged the retention of bacteria in the eye. Extended contact lens wear and S. aureus caused non-ulcerative keratitis in a rabbit model, and disturbances in the ability of the eye to remove bacteria.

Epithelial inclusions in association with mucin ball development in high-oxygen permeability hydrogel lenses

Debris trapped behind contact lenses may be associated with adverse reactions in extended wear. Although streaks and clumps of cellular material have been reported after overnight wear of conventional materials, recent experience with several high-oxygen permeability (Dk), silicone-containing hydrogel lenses indicates that certain participants are prone to the development of a unique back surface debris. This debris forms as spherical, translucent entities and results in depressions within the ocular surface after lens removal. Little information is known about these spherical bodies, particularly with respect to their composition and development. In this report, we provide photographic evidence of this debris (sometimes termed "mucin balls" or "lipid plugs"), discuss its differential diagnosis and describe a case in which material seems to be embedded in the epithelium as a direct consequence of their presence.

Effects of RGP lens extended wear on glucose-lactate metabolism and stromal swelling in the rabbit cornea

PURPOSE

To assess the chronic effects of rigid gas-permeable (RGP) contact lenses on corneal swelling and glucose-lactate metabolism in the rabbit cornea during 1 month of continuous extended wear and to establish the relationship between these effects and the oxygen transmissibility (Dk/L) of the test lens polymer.

METHODS

Four RGP lenses of varying Dk/L were tested in 8 rabbits per test group (left eyes served as controls). After 7 days and 1 month extended wear, the concentrations of lactate and glucose in the corneal epithelium, stroma and aqueous humor were determined by enzyme assay; and epithelial and stromal ATP concentrations were separately measured by bioluminescence techniques. Corneal thickness was measured at a standard morning time by ultrasonic pachymetry before and after 1, 7, 15 days and 1 month extended wear.

RESULTS

After 7 days and 1 month extended wear, generalized decreases were found in aqueous humor lactate levels for all test lenses, while concomitant increased aqueous glucose concentrations were observed. Total epithelial lactate levels correlated inversely with decreasing Dk/L levels for lower oxygen transmissible lenses (R = 0.951, P = 0.0051); and remained unchanged after extended wear of the hyper-oxygen transmissible Dk/L 125 test lens. By contrast, stromal lactate levels consistently decreased at all time points measured forextended wear of all test lenses. As expected, both epithelial and stromal ATP concentrations simultaneously decreased in extended wear. Overnight corneal swelling values after 24 hours wear of Dk/L = 27, 43, 70 and 125 test lenses were increased by 9.8, 7.1, 5.5, and 5.2% while persistent (residual) stromal swelling after one month extended wear was 16.8, 10.1, 8.6, and 5.6% respectively, in excess of baseline values.

CONCLUSIONS

Chronic RGP contact-lens induced hypoxia is associated with altered glucose-lactate metabolism in the cornea and aqueous humor with excess production of increased levels of lactate in the epithelium for lower Dk/L test lenses, but decreased lactate concentration in the stroma and aqueous humor. Extended wear of the hyper-oxygen transmissible test lens (Dk/L = 125) however, produced no increase in epithelial lactate levels. Expected lens-induced decreases in epithelial and stromal ATP were not dependent on lens-oxygen transmissibility. Despite the persistence of lower than normal stromal levels of lactate during 1 month of extended wear for all test lenses, residual corneal swelling values remained consistently elevated above baseline values. Taken together, these data establish that increased stromal lactate accumulation cannot account for persistent stromal edema in chronic extended wear of RGP lenses; and that this effect appears to be independent of lens-oxygen transmissibility and may thus represent the prolonged mechanical effect of lens wear itself.