Hideji Ichijima

Confocal microscopic studies of living rabbit cornea treated with benzalkonium chloride.

&NA; The effects of benzalkonium chloride (BAK) on the living rabbit cornea were studied by in vivo Tandem scanning confocal microscopy (TSCM) and confirmed by conventional scanning electron microscopy (SEM). Two drops of saline or phosphate‐buffered saline (PBS) containing BAK in concentrations of 0.02, 0.01, and 0.005% was applied to rabbit eyes 15 times at 5‐min intervals. The solutions were pH 5.5‐5.9 (saline) and pH 7.5 (PBS), and osmolarity was 275‐280 (saline) and 300‐307 mOsm (PBS). Immediately after application of 0.02 and 0.01% BAK, no normal corneal superficial epithelial cells could be imaged by in vivo TSCM. No swelling of the superficial epithelial cells was observed for the control solution without BAK; however, there was a small amount of desquamation. Application of as little as 0.005% BAK caused the superficial epithelial cells to swell and desquamate. The observed desquamation of corneal superficial epithelial cells increased with higher BAK concentrations applied to the eye. One hour after final drug application, inflammatory cells appeared on the surface of the cornea treated with 0.02% BAK. These findings were correlated with SEM observations. Based on the results of this study, we believe that BAK used frequently can produce clinical corneal toxicity and that the cytotoxicity of any topical ophthalmic solutions can be evaluated by in vivo TSCM.

In vitro evaluation of lipids adsorbed on silicone hydrogel contact lenses using a new gas chromatography/mass spectrometry analytical method.

Purpose. To establish a new analytical method using gas chromatography/mass spectrometry (GC/MS) for evaluating the lipids adsorbed on silicone hydrogel (SH) contact lenses: cholesterol, cholesterol ester, wax, and squalene. Methods. A novel GC/MS method was developed and validated for the repeatability, specificity, linearity, detection and quantitation limits, and percentage recovery. The lipids in an artificial tear solution were adsorbed on 5 SH lenses (asmofilcon A, balafilcon A, galyfilcon A, lotrafilcon A, and lotrafilcon B) and 1 conventional hydrogel lens (etafilcon A) in vitro. The lipids adsorbed were then extracted and analyzed by the GC/MS method. Results. Repeatability of this analytical method was less than 2.2% deviation for all test lipids; however, the analytes were completely discriminated with sharp peak shapes, and identified specifically. The correlation coefficient showing linearity was at least 0.991 under 50 &mgr;g/mL of lipid concentration. Detection and quantitation limits were statistically 0.5 to 0.8 &mgr;g/mL and 1.4 to 2.5 &mgr;g/mL, respectively, for all analytes. Percentage recovery was estimated as approximately 80% for 3 &mgr;g/lens, 90% for 5 &mgr;g/lens, and almost 100% for larger amounts of lipids. Quantitatively, the lipids absorbed on contact lenses were lotrafilcon A = (near equal) lotrafilcon B = (near equal) etafilcon A < asmofilcon A < galyfilcon A = (near equal) balafilcon A with the value of 0.4 to 7.6 &mgr;g/lens. Lipid adsorption on SH lenses varied depending on the lipid components and lens surface properties. Conclusions. The GC/MS method established in this study is excellent for the repeatability, specificity, linearity, detection and quantitation limits, and percentage recovery, and provides a novel highly sensitive and useful tool for evaluating lipids adsorbed on SH lenses.

Effects of increasing Dk with rigid contact lens extended wear on rabbit corneal epithelium using confocal microscopy.

The effects of 24-h wear of various Dk-rigid gaspermeable (RGP) contact lenses on the rabbit corneal epithelium were studied by in vivo tandem scanning confocal microscopy (TSCM), and confirmed by scanning electron microscopy (SEM). Lenses used were polymethylmethacrylate (PMMA) (Dk/L=0), RGP experimental A lens (siloxanylmethacrylate-fluoromethacrylate- methylmethacrylate, 33), experimental B (siloxanylmethacrylate- fluoromethacrylate, 56), and experimental C (siloxanylstyrene-fluoromethacrylate copolymer, 64 x 10-9) (cm/s) (ml O2/ml mm Hg) with 0.15-mm thickness (Dk/L measured by polarograph including boundary layer effect). After 24-h PMMA lens wear, TSCM showed no superficial epithelial cells but only exposed, underlying wing cells. The cornea with experimental A showed partial superficial epithelial desquamation. With experimental B wear, slight superficial epithelial cell swelling and desquamation were observed on the surface of the cornea. No changes were observed for the eye with experimental C and control. The observed severity of desquamation of superficial epithelial cells was dependent on the oxygen transmissibility (Dk/L) of RGP lenses worn. All in vivo findings were confirmed by SEM observations. Based on the results of this study, we conclude that (a) although Dk/L=56 lens B shows no residual overnight corneal swelling, surface damage is still produced; (b) Dk/L=64 lens C is best for epithelium showing the same corneal images as control; and (c) TSCM is a good way to evaluate the contact lens safety and efficacy in vivo at the cellular level noninvasively.

Effects of rigid lens extended wear on lactate dehydrogenase activity and isozymes in rabbit tears

Effects of and recovery from continuous wear of four rigid gas permeable (RGP) contact lenses was assessed by noninvasive measurement of lactate dehydrogenase (LDH) activity and isozyme pattern in rabbit tears. Oxygen transmissibility (Dk/L) of lenses used was 27, 44, 84, and 97 x 10-9 (cm/s)(ml O2/ml mm Hg); lens thickness (0.15 mm) and diameter (14.0 mm) were standardized. Lenses were worn continuously for 90 days; recovery was assessed 30 days after cessation of lens wear. LDH activity was measured by UV rate assay; isozyme subtypes were determined by agarose gel electrophoresis. Light and scanning electron microscopy (LM, SEM) were used with the determination of total protein as additional measures of lens effects. LDH levels were inversely correlated with lens Dk/L values; low Dk/L values increased the anaerobic (LDH4, 5)/aerobic (LDH1,2,3) subtype,, ratio indicating in vivo metabolic shift. SEM observations were consistent with these results. There was no significant difference in the total cell content of tears or total tear protein levels between control and RGP test-wear groups. Measurement of tear LDH activity and isozyme ratios appears to provide a sensitive, noninvasive assessment of the effects of RGP lens-induced hypoxia over time on the corneal surface. A level of Dk/L of ≥84appears best for maintaining corneal physiology during extended wear. Recovery from chronic lens-induced hypoxia is characterized by a return to normal tear LDH levels and isozyme subtypes.

Laser and tandem scanning confocal microscopic studies of rabbit corneal wound healing.

The process of corneal endothelial wound healing was studied using laser and tandem scanning confocal microscopy (LSCM and TSCM). Following transcorneal freeze (TCF) injury, rabbit corneas were observed using ex vivo LSCM and in vivo TSCM. LSCM revealed the intracellular actin filament organization which, stained with phalloidin-FITC, in migrating endothelial cells, transformed fibroblast-like cells, stroma keratocytes, and epithelial cells during wound healing in corneal tissue. The TSCM provided sequential spatial observation of morphologic changes from endothelium to epithelium of the cornea during in vivo cellular repair of wound healing noninvasively on the same cornea without animal sacrifice. Ex vivo LSCM supported the morphologic analysis of the in vivo TSCM observations.

Postmarket surveillance of Menicon Z rigid gas-permeable contact lenses for up to 30 days continuous wear in the United States.

Objectives: To evaluate the incidence of microbial keratitis associated with the use of the Menicon Z rigid gas-permeable (RGP) contact lenses (CLs) for up to 30 days continuous wear (CW). For this study, CW was defined as wearing CLs in an extended-wear modality with an average wearing time of 22 days or more. Microbial keratitis was the sole endpoint of the study safety evaluation. Methods: Subjects who were interested in RGP lens CW were recruited for the study through 33 investigational practices. To be eligible for the study, subjects must have worn the Menicon Z lens for CW for at least 1.5 months with an average CW time of 22 days or more. Eligible wearers were then contacted at 6-month intervals for up to 24 months after enrollment to determine their typical wearing schedules and continuance of wear and to detect any problems that would be indicative of microbial keratitis. Discontinuation from the study was defined as a discontinuation of contact with or CL wear by the study participants. Study volunteers could be discontinued from the study at 6, 12, 18, or 24 months if they could not be contacted (lost to follow-up); if they were not wearing their CL for CW; or at their own request. Wearing time data collected for individuals discontinued from the study was included in the wearing time analysis. Results: The study population included 507 participants, of whom 173 had discontinued by the end of study at 24 months. Lack of 22 days or more of CW was the most frequently cited reason for discontinuation and accounted for 121 of the 173 subject discontinuations. Lost to follow-up, study participant choice, and other reasons accounted for the remaining 52 subject discontinuations. Of the reported wearing times over the duration of the study, 1,275 of the 1,527 contacts resulted in reported wearing times of 22 days or more of CW. There were no findings of microbial keratitis during the study. Overall, there was a low reported rate of complications for the enrolled study participants. Conclusions: On the basis of this study, CW of the Menicon Z hyper–Dk/t RGP lens provides a safe and full-time vision correction alternative for patients who can adapt to RGP lens wear.

How rigid gas-permeable lenses supply more oxygen to the cornea than silicone hydrogels: A new model

Purpose. To show the superiority of hyper-Dk rigid gas-permeable (RGP) lenses to silicone hydrogels from the viewpoint of total oxygen supply to the entire cornea. Methods. The simple model of fitting the cornea with a contact lens was divided into 1-mm steps from the center to the limbus, and the area of concentric ring zones was calculated. Precorneal oxygen tension (PO2) for each zone was calculated using the Brennan oxygen calculator, and by taking into account the area uncovered by the RGP lens and the lens thickness, the average precorneal PO2 was mathematically compared for wear of silicone hydrogel and RGP lenses. Results. The average precorneal PO2 of the RGP lens was superior to that of the silicone hydrogel lens under open- and closed-eye conditions because the precorneal PO2 in the uncovered areas of the cornea can supply large contributions. The PO2 of a silicone hydrogel lens with 125 × 10–9 of oxygen transmissibility at center thickness (Dk/tc) was estimated as 45 mm Hg under closed-eye conditions. At the same value, the Dk/tc of an RGP lens with a diameter of 11.0 mm was estimated to be 90 × 10–9. Conclusions. To minimize hypoxia in extended wear, clinicians should consider that an RGP lens with a Dk/tc value of only 90 × 10–9 is equivalent to a silicone hydrogel lens with a Dk/tc value of 125 × 10–9, and even high Dk/tc values for RGP lenses will provide more total oxygen to the entire cornea than their hybrid silicone hydrogel counterparts.

Compliance study of contact lens wearers in Japan, part 1: internet survey of actual circumstances of lens use.

Purpose: To conduct a survey of contact lens (CL) wearers who use their CLs with satisfaction in Japan and to establish the actual circumstances of CL use. Method: An Internet survey was conducted in 1,000 CL wearers in Japan with questionnaires concerning CL purchase/change, compliance with the duration of wear, and occurrence of complications of CL use. Results: Replies from 636 women (63.6%) and 364 men (36.4%) were received. The largest source of CL purchase was CL specialty stores (eyeglass chains, 41.3%). The most frequent CL types were 2-week frequent replacement (2WFR) soft CLs (SCLs) (32.1%), daily disposable (DD) (31.0%), and other lenses. The main determining factors of purchase were “price” (38.0%), “recommendation of a doctor/staff” (37.6%), and “comfort” (34.1%). The number of wearers who changed their CLs was 372 (37.2%), and the main reasons for change were “inexpensive” (34.9%) and “recommendation of a doctor/staff” (31.2%). In DD and 2WFR/planed replacement SCLs, 270 (42.7%) of 632 wearers were compliant with the recommended duration of use, and the remainder were self-identified as noncompliant. The main reason given for noncompliant behavior was “no harm in extending the duration of use” (60.3%). The number of wearers with eye complications related to lens was 373 (37.3%). Conclusions: The choice of CLs by wearers seems to be price driven rather than being safety focused. Despite being aware of noncompliant behaviors regarding CL use, there were many noncompliant wearers. Clearly, ophthalmologists, optometrists, CL manufacturers, and other CL-related practitioners should cooperate and better educate patients to promote the importance of compliance with safe lens use.

In vivo osmotic pertubation of intercellular fluid channels in the rabbit corneal endothelium

An in vivo rabbit corneal model was used to evaluate morphological changes in the corneal endothelium associated with osmotically increasing fluid movement from the anterior chamber into the stroma. When the corneal stroma is rendered more hypertonic than normal by immersing the scraped epithelial side of the cornea in a hypertonic sucrose solution, intercellular channels and apical pores at the Y-junctions between endothelial cells become greatly enlarged. The foregoing changes are reversible and do not appear to result in damage to the corneal endothelium. These observations suggest that specific intercellular channels in the corneal endothelium may provide pathways for the movement of fluid from the aqueous humor into the stroma.

Compliance study of contact lens wearers in Japan--part 2: evaluation of a subscribed membership system.

Objective: To examine the hypothesis that membership in a contact lens (CL) supply system is associated with better compliance for regular wearers (members) who belong to the subscription membership system. Methods: Subjects were 104 members and 100 nonmember wearers of 2-week frequent replacement silicone hydrogel CLs whose clinical information was retrospectively available for 1.5 to 2 years in the interval between September 2010 and August 2012. The average duration of use of a single lens was calculated from the number of lenses supplied during the observation period and surveyed using questionnaires. Subjective symptoms and eye complications were also documented and compared. Results: The average duration of use of a lens was significantly longer in nonmembers (17.8±5.6 days/lens; n=91) than in members (14.2±3.5 days/lens; n=98) (P<0.001, Mann-Whitney U test). The number of wearers who replaced their lenses within 15.4 days per lens wear was significantly higher in members (74.5%) as compared with nonmembers (45.1%) (P<0.001, Fisher exact test). Levels of compliance reported by wearers did not match with those indicated in clinical records. In recorded eye complications, the rate of incidence of allergic and giant papillary conjunctivitis tended to be higher in nonmembers as compared with members. Conclusions: The hypothesis that a membership system could be associated with better compliance was found to be supported by clinical records. It is suggested that a membership system is useful for identifying wearers who want to be more compliant and that better compliance may reduce long-term complications of lens wear.