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

Corneal Oxygen Uptake Associated With Piggyback Contact Lens Systems

PURPOSE

The purpose of this study was to determine the effects of static (without blinking) and dynamic (with blinking once every 5 seconds) wear of piggyback contact lens systems on corneal oxygen uptake.

METHODS

Corneal oxygen uptake rates were measured on the right eyes of 11 human subjects by using a polarographic electrode. Measurements were made for the normal open eye and after 5 minutes of wear of 4 rigid lens materials (Dk/t 0-82.5), 4 soft lens materials (Dk/t 13-122), and 16 combinations of rigid and soft lens materials. The piggyback systems were worn under both static and dynamic conditions. Repeated-measures analysis of variance was used to compare oxygen uptake rates associated with the wear of the rigid lens components, soft lens components, piggyback systems, and static versus dynamic wearing conditions. Spearman correlation coefficients and regression analyses were used to examine relationships between corneal oxygen uptake rates.

RESULTS

Measurable differences were found among oxygen uptake rates associated with the rigid lens components, soft lens components, and piggyback systems. Blinking resulted in no reduction in corneal oxygen uptake with the piggyback systems. Corneal oxygen uptake associated with the wear of the piggyback systems could not be predicted from those associated with the rigid and soft lens components of the systems.

CONCLUSIONS

Piggyback combinations of rigid and soft lens components with the highest transmissibilities resulted in the least increase in corneal oxygen uptake beyond that of the normal open eye.

Scalloped Channels Enhance Tear Mixing Under Hydrogel Contact Lenses

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.

Infectious Keratitis After Overnight Orthokeratology in Canada

PURPOSE

To report 3 cases of infectious keratitis related to overnight orthokeratology use.

METHODS

Retrospective case observation.

RESULTS

All 3 patients were using overnight orthokeratology lenses when they presented with unilateral corneal ulcers. The organisms isolated were Acanthamoeba, Pseudomonas aeruginosa, and Serratia marcescens. The clinical presentation and treatment of each case is presented.

CONCLUSIONS

Overnight orthokeratology use may be associated with infectious keratitis despite the use of more oxygen-permeable materials and improved lens design. Patient education with informed consent, appropriate lens care, and meticulous follow-up is important. Because this complication is potentially sight threatening, orthokeratology requires further analysis and evaluation to establish its safety. The cases here are the first few reported cases in North America.

A 1-year prospective clinical trial of menicon Z (tisilfocon A) rigid gas-permeable contact lenses worn on a 30-day continuous wear schedule

PURPOSE

To establish the safety and efficacy of clinical performance of a novel hyper-O2-transmitting rigid gas-permeable (RGP) lens (tisilfocon A) worn continuously for 30 days (29 nights) equivalent to a conventional control hydrogel lens (etafilcon A) worn for 7 days (6 nights).

METHODS

The study was a prospective, open-label, 24-center, concurrent cohort-controlled clinical trial.

OUTCOME MEASURES

Outcome measures included rates of adverse events, slitlamp findings, length of wear achieved, lens-corrected visual acuity, corneal refractive changes, dryness, and lens deposits.

RESULTS

The RGP lens wear test was equivalent or superior to the hydrogel control performance in all categories. Two-thirds (66.5%) of patients wearing the RGP lens achieved continuous wear periods greater than 22 nights; and 60.4% achieved more than 28 nights of continuous use. There was a statistically significant lower rate of adverse events, considered definitely related to lens wear, for the RGP test lens versus the hydrogel control (none vs. 2.2%; P = 0.007, Fisher's exact two-sided test).

CONCLUSIONS

Continuous wear of the tisilfocon A (Menicon Z, Menicon Co., Ltd., Nagoya, Japan) RGP lens for up to 30 nights is a safe and equivalent alternative to 7-day (6-night) hydrogel wear.