SIGNIFICANCE:Optometry is desperately needed to combat the increasing rate of avoidable visual impairment that goes undiagnosed largely owing to the lack of integration of eye care services with primary care medicine. Government leaders are actively discussing substantive changes to health care legislation that will impact optometrists and their patients. The importance of a regular eye examination for disease prevention has long been undervalued in the setting of primary care. Consequently, many serious and potentially treatable ocular and systemic diseases go undiagnosed. Despite clear indicators that vision impairment increases the risk of morbidity and mortality from chronic systemic disease and decreases quality of life, vision health remains among the greatest unmet health care needs in the United States. To improve vision care services for all Americans, we must focus our attention on two central themes. First, we must educate the public, health care professionals, and policymakers on the importance of routine eye care as a preventive measure in the setting of primary care. Next, we need to recognize that optometrists, through their geographic distribution and advanced training, are in a strategic position to deliver integrated, comprehensive, cost-effective eye care services for individuals most in need. In this perspective, we discuss a model for integrating optometric services with the practice of primary care medicine to facilitate early detection of both eye and systemic disease while reducing serious and preventable health-related consequences.

Purpose

: 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.

Methods

: 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.

Results

: 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).

Conclusions

: 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.

A panel of experts was invited to discuss the following questions: Why does the prevalence of dry eye disease (DED) appear to be increasing? Are you satisfied with the current definition and classification of DED-aqueous deficiency versus evaporative dry eye? Beyond the innate human factors (e.g., genetics), what external factors might contribute to DED? What areas related to DED need to be more fully understood? In examining a patient complaining of dry eye, what is your strategy (e.g., tests, questionnaire)? What is your strategy in unraveling the root cause of a patient's dry eye symptoms that may be shared by many anterior segment diseases? What are the two or three most common errors made by clinicians in diagnosing DED? Why do contact lens (CL) patients complain of dry eye while wearing lenses but not when not wearing lenses? What areas related to CL discomfort need to be more fully understood? What is your most effective strategy for minimizing CL discomfort? With current advances in biotechnology in dry eye diagnostics and management tools, do you think our clinicians are better prepared to diagnose and treat this chronic condition than they were 5 or 10 years ago? Do you foresee any of these new point-of-care tests becoming standard clinical tests in ocular surface evaluation? What treatments are effective for obstructed Meibomian glands secondary to lid margin keratinization? What level of DED would prevent you from recommending an elected ophthalmic surgery? What strategy do you use to help your patients comply with the recommended home therapies? How do you best manage patients whose severity of dry eye symptoms does not necessarily match clinical test results, especially in cases of ocular surface neuropathy? Where do you see dry eye diagnosis and treatment in 10 years or more?

Purpose

To assess the effects of soft contact lens base curve radius (BCR), sex, ethnicity, central corneal curvatures, and vertical palpebral aperture size (PAS) on the postlens tear thickness (PLTT).

Methods

The PLTT was measured using optical pachometry on 114 experienced lens wearers who were fitted with lathe-cut soft lenses (Alden 47, polymacon, 35.5% H2O, -2.00 diopter, and 14.0 mm). Each subject was randomly allocated to one lens group receiving a BCR of 7.9, 8.3, or 8.7 mm. Pachometry measurements were taken at 30 min after lens insertion. Vertical PAS and keratometry readings were measured for 94 of the 114 subjects.

Results

The mean (95% confidence interval) PLTT was 15.7 microm (13.2-18.0 microm), 12.8 microm (10.9-14.7 microm), and 12.1 microm (10.2-14.0 microm) for the 7.9-mm, 8.3-mm, and 8.7-mm BCR groups, respectively. The differences in PLTT among the three BCR groups was significant (analysis of variance F-test; P=0.039). Post hoc testing using the Tukey honestly significant difference statistic showed that only the two extreme BCR groups (7.9 mm and 8.7 mm) were significantly different. Sex had no effect on the PLTT; however, the PLTT was significantly thinner for the Asian compared with non-Asian eyes (P=0.0001). The Asian PLTT did not vary with different soft lens BCRs. The non-Asian PLTT was thicker with lenses of the steep BCR compared with the flat BCR.

Conclusion

These results show that the base curve radius of a soft contact lens and several ocular characteristics can affect the thickness of the postlens tear film.

Purpose

To measure the effect of hypoxia and eye closure on epithelial permeability to fluorescein (P(dc)) during rigid lens extended wear (EW).

Methods

Central corneal thickness (CT) and P(dc) were measured in 42 subjects with an optical pachometer and automated scanning fluorophotometer, respectively. All subjects had been successfully wearing rigid gas-permeable (RGP) lenses on a 6-night EW regimen, and each individual was randomized to wear either medium- or high-oxygen-permeable (Dk) RGP lenses (two types of siloxane-fluorocarbon polymer lenses with Dk of 49 and 92). CT and P(dc) measurements were performed at an afternoon visit (baseline) and were repeated in the morning after 8 hours of overnight wear. Subjects slept with a patch over the right eye. The patch was not removed until immediately before the morning measurement.

Results

The mean overnight swelling response for subjects in the medium-Dk group was greater than that in the high-Dk group. Results of a paired t-test indicate that the eye wearing the medium-Dk lens with a patch overnight had a significant increase in epithelial permeability. Results of mixed-effect models suggest that eye closure and lens-induced hypoxia are significant factors in altering P(dc).

Conclusions

The results indicate that corneal epithelial permeability increases with hypoxic dose and that epithelial barrier function is impaired by overnight rigid lens wear.

Contact lens extended wear increases the permeability of epithelium to sodium fluorescein (P(dc)). The exact mechanism is not known. However, changes in P(dc) likely result from either corneal hypoxia or mechanical trauma, or both. We explored the effects of one-night continuous wear with either high- or low-Dk/t soft lenses on P(dc). The results show that corneal epithelial barrier function decreases significantly with both lens groups. We also observed that Asian eyes had higher P(dc) after overnight wear compared to non-Asian and that for both Asian and non-Asian eyes, the elimination of corneal hypoxia did not prevent changes in epithelial permeability.

Purpose

Tear exchange under a soft contact lens is directly related to the amount of lateral and transverse lens motion. Hydrodynamic modeling suggests that channels placed on the back surface of a soft lens will reduce fluid resistance and increase transverse lens movement. This study measured the effect of posterior lens surface scalloped channels on tear exchange.

Methods

Tear exchange in the postlens tear film (PoLTF) was estimated using a fluorometer to measure the exponential depletion of high-MW fluorescein under the lens expressed as the time to deplete 95% of dye (T95). A total of 32 subjects wore two pairs of identical lenses except that the experimental lens had 12 scalloped channels placed radially in the midperiphery of the posterior lens surface, whereas lenses without channels served as controls.

Results

The mean +/- standard error T95 values for the channel lenses was 28 +/- 2 minutes compared with 32 +/- 2 minutes for the control lenses (p = 0.107). There was a marginally significant difference in T95 between two lens groups in Asian eyes (p = 0.054).

Conclusion

Placing scallop-shaped channels on high-H2O content soft lenses improved the postlens tear pumping in Asian eyes.

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.

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.