Changes in corneal biometry and the associated histology in rhesus monkeys wearing orthokeratology contact lenses.

PURPOSE: This study compared the effect of orthokeratology (OK) lens wear on corneal topography and microstructure between the 1-night and 30-night wearers to predict any adverse responses of the eyes to long-term OK lens wear. METHODS: Nine rhesus monkeys with one eye wearing an OK lens and the fellow eye wearing a rigid gas permeable (RGP) lens were used in this study. The lenses were worn for 11 hours, with the measurement of corneal curvature and thickness and axial components of the eye at 0 night (n = 9), 1 night (n = 9), and 30 nights (n = 6). Histology was performed at 1 and 30 nights of lens wear. RESULTS: Corneal surface power in the 3-mm central region was reduced in the OK eye when compared with the RGP eye (P < 0.05). Central corneal thickness was only reduced in 30 nights of OK lens wear (P < 0.05). Under light microscopy, the 1-night OK or RGP eyes showed normal morphology in all layers of the cornea. The 30-night OK eyes showed a thinned central corneal epithelium and a thickened but less stratified paracentral corneal epithelium when compared with the 30-night RGP eyes. Under electron microscopy, intercellular junctions of corneal epithelium in the 30-night OK eyes were much looser than those in the 1-night OK eyes. However, the density and morphology of hemidesmosomes were similar between the OK and RGP eyes at 30 nights of lens wear. CONCLUSIONS: Overnight OK can change the corneal curvature through anterior corneal remodeling, resulting in an effective correction of myopia. However, a decrease in intercellular junctions during long-term wear may compromise the functions of the corneal epithelium as a border mechanical barrier.

The influence of surface topography of a porous perfluoropolyether polymer on corneal epithelial tissue growth and adhesion.

Design principles for corneal implants are challenging and include permeability which inherently involves pore openings on the polymer surface. These topographical cues can be significant to a successful clinical outcome where a stratified epithelium is needed over the device surface, such as with a corneal onlay or corneal repair material. The impact of polymer surface topography on the growth and adhesion of corneal epithelial tissue was assessed using porous perfluoropolyether membranes with a range of surface topography. Surfaces were characterised by AFM and XPS, and the permeability and water content of membranes was measured. Biological testing of membranes involved a 21-day in vitro tissue assay to evaluate migration, stratification and adhesion of corneal epithelium. Similar parameters were monitored in vivo by surgically implanting membranes into feline corneas for up to 5 months. Data showed optimal growth and adhesion of epithelial tissue in vitro when polymer surface features were below a 150 nm RMS value. Normal processes of tissue growth and adhesion were disrupted when RMS values approached 300 nm. Data from the in vivo study confirmed these findings. Together, outcomes demonstrated the importance of surface topography in the design of implantable devices that depend on functional epithelial cover.

A perfluoropolyether corneal inlay for the correction of refractive error.

This study assessed the long-term biological response of a perfluoropolyether-based polymer developed as a corneal inlay to correct refractive error. The polymer formulation met chemical and physical specifications and was non-cytotoxic when tested using standard in vitro techniques. It was cast into small microporous membranes that were implanted as inlays into corneas of rabbits (n = 5) and unsighted humans (n = 5 + 1 surgical control) which were monitored for up to 23 and 48 months respectively. Overall, the inlays were well tolerated during study period with the corneas remaining clear and holding a normal tear film and with no increased vascularisation or redness recorded. Inlays in three human corneas continued past 48 months without sequelae. Inlays in two human corneas were removed early due to small, focal erosions developing 5 and 24 months post-implantation. Polymer inlays maintained their integrity and corneal position for the study duration although the optical clarity of the inlays reduced slowly with time. Inlays induced corneal curvature changes in human subjects that showed stability with time and the refractive effect was reversed when the inlay was removed. Outcomes showed the potential of a perfluoropolyether inlay as a biologically acceptable corneal implant with which to provide stable correction of refractive error.

Reverse geometry rigid gas permeable contact lens wear reduces high-order aberrations and the associated symptoms in post-LASIK patients.

PURPOSE: This study evaluated the efficacy of custom-made reverse geometry rigid gas permeable (RGP) contact lenses in the control of symptoms related to increased wavefront aberrations after LASIK correction of myopia. MATERIALS AND METHODS: Twenty-eight myopes treated with LASIK were assessed for post-LASIK symptoms (declined night vision, glare, halos and/or monocular diplopia) and corneal topography. A set of RGP contact lenses was selected as trial lenses based on the matching between the lens and the patient's corneal topography. If the fluorescein pattern between the trial lens and the corneal surface showed a central alignment, a mid-peripheral bearing and peripheral clearance and if the patient felt comfortable with the lens wear, a duplicated lens was ordered for the patient. Otherwise, a lens satisfied with corneal topography of the patient and clinical judgment was used. Visual acuity (VA) and wavefront aberrations were measured after the lens wear. RESULTS: The custom-made lenses well matched the host cornea with no dislodgment in all subjects. The post-LASIK eyes showed an increase of 1 Snellen line in VA (from 0.90 +/- 0.33 to 1.11 +/- 0.24) and a significant improvement in all symptoms after the lens wear. The total higher-order aberration is significantly reduced after the lens wear with at least 70% reduction in either spherical aberration, coma, third or fourth aberration but only 33% reduction in the fifth aberration. CONCLUSIONS: Reverse geometry RGP lenses with the design based on individual topographic data can improve visual performance of post-LASIK eyes by reducing higher order aberrations.

Differences between overnight and long-term wear of orthokeratology contact lenses in corneal contour, thickness, and cell density.

PURPOSE: To investigate changes in corneal topography and morphology in human eyes wearing orthokeratology (OK) lenses for overnight and over a 5-year period. MATERIALS AND METHODS: Fifty-six adults with moderate myopia were assigned to 2 groups based on age matching: 5-year lens wear (n = 26, 51 eyes) and 1-night lens wear (n = 30, 60 eyes). All subjects wore reverse-geometry OK lenses with the eyes before 1-night lens wear serving as a control to both the groups. Visual acuity, slit-lamp biomicroscopy, confocal microscopy, and corneal topography were assessed before and after lens wear. RESULTS: Visual acuity was improved satisfactorily with flattening of the central cornea in both lens wear groups. Corneal thickness increased extensively in the 1-night lens wear group but only paracentrally in the 5-year lens wear group. Central epithelial thinning with a decreased density of the basal cells was only observed in the 5-year group. Keratocyte density was reduced throughout the entire corneal thickness for the 2 groups. Endothelium was normal in density and morphology for the 2 groups. CONCLUSIONS: Short-term and long-term OK lens wear can effectively correct myopia by flattening the cornea. The flattened cornea in the short-term lens wear is mainly because of the thickening of the midperipheral cornea. In the long-term lens wear, however, this change is associated with thickening of the midperipheral cornea and thinning of the central corneal epithelium.

Carboxymethyl cellulose stimulates rabbit corneal epithelial wound healing.

PURPOSE: Previously, we reported carboxymethyl cellulose (CMC) binding to human corneal epithelial cells and promoting corneal epithelial wound closure in vitro. Using an animal model, the efficacy of CMC in promoting corneal wound healing was examined. MATERIALS AND METHODS: Following corneal epithelial wounding of NZ white rabbits, CMC (0.2% or 1.0%) or control vehicle (PBS) was administered topically (4 times daily for 3 days) to wounded and unwounded eyes with or without contact lens wear. Wound healing in response to the treatments was measured as percentage reduction of fluorescein-stained wound area 0 to 72 hr post-wounding. Corneas were examined histologically and expression of zonula occludens-1 (ZO-1) tight-junction was detected by immunohistochemistry. RESULTS: Percentage wound reduction in CMC-treated groups was significantly greater than controls (p < 0.05) at 24 and 32 hr. Complete wound closure was observed by 48 hr in 100% of CMC-treated eyes compared to 45% of vehicle-treated eyes. CMC also promoted wound closure dose-dependently. Epithelial cells formed an intact layer following CMC-treatment whereas vehicle-treated cells were less ordered. Strong ZO-1 expression in corneal epithelia of CMC-treated eyes was observed at 72 hr. Contact lens wear appeared to delay wound closure compared to without lens wear during CMC-treatment (p = 0.001). CONCLUSIONS: CMC promoted dose-dependent corneal epithelial wound healing. CMC stimulated ZO-1 expression, indicating accelerated corneal epithelial resistance barrier regeneration.

Synthetic corneal inlays.

This review is based on the activities of the Vision Cooperative Research Centre (previously Cooperative Research Centre for Eye Research and Technology) Corneal Implant team from 1991 to 2007. The development of a synthetic polymer of perfluoropolyether (PFPE), meeting essential physical and biological requirements, for use as a corneal inlay is presented. Each inlay was placed in a corneal flap created with a microkeratome and monitored over a two-year period in a rabbit model. The results indicate that the PFPE implant shows excellent biocompatibility and biostability. As a result, a Phase 1 clinical trial is being conducted. Three years post-implantation, the PFPE inlays are exhibiting continued excellent biocompatibility. Corneal inlays made from PFPE are biocompatible with corneal tissue in the long term and offer a safe and biologically-acceptable alternative to other forms of refractive surgery.

[A comparison of Chinese reading parameters among rapid serial visual presentation, full screen and printed displays].

OBJECTIVE: This study investigated reading speed of Chinese in rapid serial visual presentation (RSVP), full screen and printed display among young adults with normal vision. The critical font size and critical acuity reserve in RSVP were also evaluated. METHODS: Thirty university students with a visual acuity of at least 20/20 in both eyes (uncorrected or corrected) were recruited in this study. The visual acuity threshold (VAT) (3 m distance) was evaluated for all subjects using a self-designed visual acuity chart presented on a computer screen. The reading speed for Chinese was measured under RSVP (10 font sizes from 4 to 33 pt), full screen and printed display (2 font sizes: 10 and 13 pt). The reading speed (wpm) was expressed as the percentage of words read correctly x 60 x total number of words/time used (second). The acuity reserve (RA) was expressed as RA = SP/ST, where SP was the font size of the reading material for the reader and ST was the acuity threshold expressed as a font size. RESULTS: The visual acuity threshold (VAT) at a distance of 40 cm in these 30 subjects was (2.2 +/- 0.3) pt (mean +/- SD). The reading speed increased significantly with the increasing font sizes until the font size reached (7.8 +/- 0.4) pt where the maximum reading speed (258.0 +/- 34.4 wpm) was achieved. The reading speed remained at a constant value in font sizes ranging from 7.8 to 33 pt. The reading speed increased with the increasing R(A) until the R(A) reached 3.5:1 and then remained unchanged. There was no significant difference in reading speed between full screen and printed displays (P > 0.05). The reading speed in full screen or printed display was significantly faster than in RSVP (10 pt: full screen display versus RSVP: t = -10.15, P < 0.01; printed display versus RSVP: t = -8.77, P < 0.01. 13 pt: full screen display versus RSVP: t = -11.64, P < 0.01; printed display versus RSVP: t = -10.79, P < 0.01). CONCLUSIONS: Young readers who use the computer as a reading tool can achieve a maximum reading speed for Chinese when the font size of the reading text is larger than 7.8 pt. A font size of at least 3.5 times the acuity threshold can attain a maximum reading speed for RSVP.

Two-year preclinical testing of perfluoropolyether polymer as a corneal inlay.

PURPOSE: To assess the long-term biocompatibility and optical clarity of a perfluoropolyether (PFPE) polymer as a corneal inlay. METHODS: A 4-mm-diameter PFPE inlay was implanted under a microkeratome flap in the corneas of rabbits (n = 16) and maintained for predetermined time points of 6, 12, or 24 months. These were compared with normal (n = 3) and time-matched sham-wounded rabbit corneas (n = 8). All corneas were monitored clinically with a slit lamp. Histology was performed on all eyes on termination to assess the tissue response. RESULTS: Some sham and implanted animals were discontinued from study 1 to 2 days after surgery because of flap dislodgement. Ten animals with PFPE inlays remained in the study, and 7 of these were maintained to their predetermined time point for up to 2 years (3 were discontinued because of peripheral corneal defects). The corneas of these 7 animals remained clear and healthy, tear film remained normal, and there were no signs of inflammation, neovascularization, or increased conjunctival redness. All inlays remained centered and optically clear (clarity 85% or greater). Histology showed PFPE was biostable. The epithelia of operated corneas were stratified but slightly thinned compared with those of normal corneas. Stromal tissue anterior and posterior to each inlay appeared normal. Keratocytes in the vicinity of the inlay were normal in distribution but showed increased vacuolation, indicating tissue repair after the surgery. CONCLUSIONS: The PFPE polymer maintained a high level of optical clarity and showed long-term biocompatibility for up to 2 years when implanted as an inlay in the rabbit cornea.

[Expression of muscarinic acetylcholine receptor-1 in human retinal pigment epithelium].

OBJECTIVE: The aim of this study was to identify the presence of muscarinic acetylcholine receptors-I (M1 receptor) in human retinal pigment epithelium (RPE) in order to determine the role of M1 receptor in the maintenance of function of RPE and its role in the occurrence and development of myopia. METHODS: The 3rd-5th passages of RPE cells established in our laboratory were used in the present study. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect mRNA expression of M1 receptor in cultured RPE. Immunocytochemistry was used to detect M1 receptor protein in the RPE cells. RESULTS: Cultured RPE demonstrated mRNA expression of M1 receptor in RT-PCR. Protein of M1 receptor was presented in the RPE under immunocytochemistry. CONCLUSIONS: This study demonstrated the presence of M1 receptor in human RPE at both mRNA and protein levels. M1 receptor plays an important role in the maintenance of function of RPE. Injection of M1 receptor antagonist into the vitreous can delay the occurrence and inhibit the development of myopia, which is possibly related to the inhibition of RPE cells function.

[Expression of muscarinic acetylcholine receptor-1 in human scleral fibroblasts].

OBJECTIVE: The aim of this study was to identify the presence of muscarinic acetylcholine receptors-1 (mAChRs-1) in human sclera in order to determine whether the sclera is a potential site of action for mAChR antagonists. METHODS: Cell lines of human scleral fibroblasts were cultured in Dulbecco Modified Eagle's Medium. Reverse Transcription-Polymerase Chain Reaction (RT-PCR) was used to detect mRNA expression of M1 receptors in the fibroblasts. Immunocytochemistry was used to detect proteins of mAChRs in the cell lines. Immunohistochemical study was used to further detect the presence of M1 receptor in the frozen scleral sections. RESULTS: The cultured fibroblasts demonstrated mRNA expression of M1 receptor in RT-PCR. Protein of the M1 was present in the fibroblasts by examination of immunocytochemistry and immunohistochemistry staining. CONCLUSION: This study demonstrated the presence of M1 receptor in human scleral fibroblasts at both mRNA and protein levels. This finding indicates that the sclera is a potential site of action for the currently used mAChR antagonists in prevention of human myopia.

A comparison of biological coatings for the promotion of corneal epithelialization of synthetic surface in vivo.

PURPOSE: To investigate the effect of a range of biological coatings on corneal epithelialization of a synthetic polymer surface in vivo. METHODS: Eight diverse biological factors (collagen I, collagen III, collagen IV, laminin, fibronectin, endothelial extracellular matrix, hyaluronic acid, and chondroitin sulfate) were coated individually onto the surface of polycarbonate membranes with a pore size of 0.1 micro m. The coated membranes were implanted on the anterior cornea of adult cats and were clinically assessed for rapidity and extent of and persistence of epithelial overgrowth. The membranes with persistent epithelial attachment were examined histologically by immunohistochemistry and routine light and electron microscopy. RESULTS: Collagen I, collagen IV, and laminin consistently enhanced migration and attachment of corneal epithelial cells in vivo. Multiple-layered epithelium over the collagen I-, collagen IV-, and laminin-coated membranes was demonstrated histologically. The collagen I-coated membranes performed best, in that they showed greater stratification and differentiation of the epithelium. Formation of basement membrane and adhesion complexes over the collagen I-coated membranes was detected by immunohistochemistry and electron microscopy up to 9 weeks after implantation. Membranes coated by fibronectin, endothelial extracellular matrix, hyaluronic acid, and chondroitin sulfate did not support persistent epithelial overgrowth. Compromised biostability of these coatings was mostly likely associated with postsurgical reactions of the host corneal tissue. CONCLUSIONS: A biologically modified polymer can support migration and adhesion of corneal epithelial cells in vivo. The collagen I-modified surface exhibited the most promising performance, both clinically and histologically.

Progress in the development of a synthetic corneal onlay.

PURPOSE: This study evaluated an improved perfluoropolyether polymer formulation designed for use as a corneal onlay to correct refractive error. METHODS: Collagen I coated perfluoropolyether lenticules were implanted in feline corneas exposing a 6-mm diameter area of lenticule surface for epithelial growth. A parallel series of sham-wounded corneas were also studied. All corneas were monitored clinically for 4 or 8 weeks after surgery when animals were terminated and corneas used for histology with light and electron microscopy. RESULTS: Postoperative epithelial growth began on days 1 and 2. Lenticule surfaces were fully epithelialized by days 5 to 11. Corneas remained clear, and the lenticules maintained epithelial cover until the designated time points. Histology of the implanted corneas showed that the lenticules were well tolerated by the cornea. Each lenticule was fully covered by a multilayered epithelium with microvilli, desmosomes, and a differentiated basal cell layer. Epithelial adhesive structures (basal lamina, hemidesmosomes, and anchoring fibrils) had assembled at the tissue-lenticule interface. CONCLUSIONS: Collagen coated perfluoropolyether lenticules implanted in the feline cornea supported the growth of a stable stratified squamous epithelium. These encouraging results are a step further in the development of a corneal onlay for correction of refractive error.

The use of corneal organ culture in biocompatibility studies.

This study investigated the potential of a corneal organ culture system in the evaluation of polymers for ophthalmic devices that require epithelialisation. Two different polymers were tested in lenticule form to explore the sensitivity of this in vitro assay. Polycarbonate and perfluoropolyether-based lenticules were surgically implanted into bovine corneas and compared with a parallel series of sham-wounded corneas. Following surgery, all corneas were maintained in an air/liquid organ culture system for up to 8 days during which time they were evaluated clinically to monitor the rate of epithelial growth across the lenticule surface (implanted) or wound bed (sham). Data showed differences in the kinetics of epithelial migration according to the underlying surface with full epithelialisation of the sham series occurring on day 5+/-0.5, the perfluoropolyether lenticules on day 6+0.5 and polycarbonate lenticules on day 8+/-0.5. Histology revealed differences in the structure and morphology of the migrating and stable epithelium in each series of corneas. The differential response of the corneal epithelium was related to the physiochemical characteristics of the natural (sham) or synthetic (perfluoropolyether or polycarbonate) substrata which the epithelium could detect when maintained in organ culture. This assay system has utility for screening candidate polymers for certain ophthalmic applications.