Rabbit Models of Contact Lens–Associated Corneal Hypoxia: A Review of the Literature

Ocular tear fluid biomarkers collected by contact lenses

PURPOSE

To collect tear fluid biomarkers from contact lenses (CLs) and determine the impact of CL wear duration.

METHODS

Rabbits were fitted with commercial etafilcon A CLs, which were collected after 1 min, 4 and 8 h (n = 4/time point). Tear fluid proteins and cytokines were extracted from the CLs and quantified. An exploratory comparison was performed between CLs and Schirmer Strips (SS) for a 1 min duration.

RESULTS

The concentration of MUC5AC was significantly higher after 4 h of CL wear. The expression of all investigated cytokines (IL-1α, IL-1β, IL-8, IL-17A, IL-21, Leptin, MIP-1β, MMP-9, NCAM-1, and TNF-α) was detectable after 1 min of CL wear, and over time, all showed significant variations throughout the 8-h CL wear period. Notably, IL-1α significantly increased by 8 h of CL wear, while MMP-9 decreased. Albumin and lysozyme did not show significant variations with CL wear. Differences between CLs and SS after 1 min were statistically significant for albumin, Leptin, TNF-α, IL-1α, IL-1β, and IL-8.

CONCLUSIONS

The duration of CL wear significantly affects the collection of some tear fluid biomarkers. Albumin, MUC5AC, and cytokines may have individual and synergistic diagnostic or prognostic potential. CLs and SS were similar for lysozyme and MUC5AC but differed in the collection of albumin and some cytokines. CLs are a viable tear fluid collection method for biomarker analyses and can be immediately added as a routine clinical test by being FDA-approved medical devices.

One Week Sustained In Vivo Therapeutic Release and Safety of Novel Extended-Wear Silicone Hydrogel Contact Lenses

Since the seminal work of Wichterle in 1965 describing the first soft contact lenses and their potential for ocular drug delivery, the field has yet to realize his vision. Maintaining all lens commercial properties combined with a mechanism for controlled drug release of therapeutically relevant concentrations for duration of wear is a major challenge. Here, successful in vivo week-long sustained release of a small molecular weight therapeutic in rabbits from extended-wear silicone hydrogel contact lenses meeting all commercial specifications by utilizing a novel macromolecular memory strategy is reported for the first time. Lens-treated eyes show a continuous, therapeutically relevant bromfenac tear concentration of 256.4 ± 23.1 µg mL^-1 for 8 days. Bromday (bromfenac ophthalmic solution, 0.09%, Bausch+Lomb) topical drops exhibit a quick peak concentration of 269.3 ± 85.7 µg mL^-1 and 100 min duration. Bioavailability (AUC_0-8days ) and mean residence time of lenses are 26 and 155 times higher than drops, respectively. Lenses are safe, well tolerated, and no corneal histological differences are observed. This work highlights the enormous potential of drug releasing lenses as a platform strategy, and offers a new dropless clinical strategy for post-cataract, uveitis, post-LASIK, and corneal abrasion treatment.

Dexamethasone-Eluting Contact Lens for the Prevention of Postphotorefractive Keratectomy Scar in a New Zealand White Rabbit Model

PURPOSE

To evaluate the safety and efficacy of an experimental dexamethasone-eluting contact lens (DCL) for the prevention of postphotorefractive keratectomy (PRK) corneal haze in a New Zealand White (NZW) rabbit model.

METHODS

Both eyes of 29 NZW rabbits underwent PRK. The rabbits were randomized to one of the 5 study arms for 4 weeks: tarsorrhaphy only, tarsorrhaphy and bandage contact lens (BCL) replaced weekly, tarsorrhaphy and BCL for 1 week plus topical 0.1% dexamethasone ophthalmic solution (drops) for 4 weeks, tarsorrhaphy and BCL replaced weekly plus topical dexamethasone for 4 weeks, and tarsorrhaphy and DCL changed weekly for 4 weeks. Each week for 4 consecutive weeks postoperatively, the tarsorrhaphies were opened, the eyes underwent evaluation and imaging, and the tarsorrhaphies were replaced. Contact lenses were cultured on removal. Central corneal haze was assessed weekly with corneal densitometry. After 4 weeks, the animals were killed, and the eyes were enucleated for histopathologic analysis.

RESULTS

The tarsorrhaphy only group displayed more haze with a greater change in optical densitometry from pre-op compared with the other treatment groups. There was no difference between the DCL group and the groups receiving a BCL and dexamethasone drops in densitometry or histopathology. No NZW rabbits developed clinical signs of infection, and cultures from DCLs and BCLs grew similar organisms.

CONCLUSIONS

In the post-PRK rabbit model, DCLs worn weekly for 4 weeks were safe and as effective at preventing corneal haze as 0.1% dexamethasone drops applied 4 times a day for 4 weeks.

Steroid-eluting contact lenses for corneal and intraocular inflammation

Ocular inflammation is one of the leading causes of blindness worldwide, and steroids in topical ophthalmic solutions (e.g. dexamethasone eye drops) are the mainstay of therapy for ocular inflammation. For many non-infectious ocular inflammatory diseases, such as uveitis, eye drops are administered as often as once every hour. The high frequency of administration coupled with the side effects of eye drops leads to poor adherence for patients. Drug-eluting contact lenses have long been sought as a potentially superior alternative for sustained ocular drug delivery; but loading sufficient drug into contact lenses and control the release of the drug is still a challenge. A dexamethasone releasing contact lens (Dex-Lens) was previously developed by encapsulating a dexamethasone-polymer film within the periphery of a hydrogel-based contact lens. Here, we demonstrate safety and efficacy of the Dex-Lens in rabbit models in the treatment of anterior ocular inflammation. The Dex-Lens delivered drug for 7 days in vivo (rabbit model). In an ocular irritation study (Draize test) with Dex-Lens extracts, no adverse events were observed in normal rabbit eyes. Dex-Lenses effectively inhibited suture-induced corneal neovascularization and inflammation for 7 days and lipopolysaccharide-induced anterior uveitis for 5 days. The efficacy of Dex-Lenses was similar to that of hourly-administered dexamethasone eye drops. In the corneal neovascularization study, substantial corneal edema was observed in rabbit eyes that received no treatment and those that wore a vehicle lens as compared to rabbit eyes that wore the Dex-Lens. Throughout these studies, Dex-Lenses were well tolerated and did not exhibit signs of toxicity. Dexamethasone-eluting contact lenses may be an option for the treatment of ocular inflammation and a platform for ocular drug delivery. STATEMENT OF SIGNIFICANCE: Inflammation of the eye can happen either on the ocular surface (i.e. the cornea) or inside the eye, both of which can result in loss of vision or even blindness. Ocular inflammation is normally treated by steroid eye drops. Depending on the type and severity of inflammation, patients may have to take drops every hour for days at a time. Such severe dosing regimen can lead to patients missing doses. Also, more than 95% drug in an eye drop never goes inside the eye. Here we present a contact lens that release a steroid (dexamethasone) for seven days at a time. It is much more efficient than eye drops and a significant improvement since once worn, the patient will avoid missing doses.

Gas-Permeable, Irritation-Free, Transparent Hydrogel Contact Lens Devices with Metal-Coated Nanofiber Mesh for Eye Interfacing

An electronic "smart" contact lens device with high gas permeability and optical transparency, as well as mechanical compliance and robustness, offers daily wear capability in eye interfacing and can have broad applications ranging from ocular diagnosis to augmented reality. Most existing contact lens electronics utilize gas-impermeable substrates, electronic components, and interfacial adhesion layers, which impedes them from applications requiring continuous daily wear. Here we report on the design and fabrication of an eye interfacing device with a commercial ocular contact lens as the substrate, metal-coated nanofiber mesh as the conductor, and in situ electrochemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) /poly(styrene sulfonate) (PSS) as the adhesion material. This hydrogel contact lens device shows high gas permeability, wettability, and level of hydration, in addition to excellent optical transparency, mechanical compliance, and robustness. Using a rabbit model, we found that the animals wearing these hydrogel contact lens devices continuously for 12 hours showed a level of corneal fluorescein staining comparable to those wearing pure hydrogel contact lenses for same period of time, with no obvious corneal abrasion or irritation, indicating their high level of safety for continuous daily wear. Finally, full-field electroretinogram (ERG) recordings on rabbits were carried out to demonstrate the functionality of this device. We believe that the strategy of integrating nanofiber mesh-based electronic components demonstrated here can offer a general platform for hydrogel electronics with the advantages of preserving the physiological and mechanical properties of the hydrogel, thus enabling seamless integration with biological tissues and providing various wearable or implantable sensors with improved biocompatibility for health monitoring or medical treatment.

The Evaluation of Ophthalmic Findings in Women Patients With Iron and Vitamin B12 Deficiency Anemia

Purpose

To determine whether there are differences in the central corneal thickness (CCT), retinal nerve fiber layer (RNFL), and ganglion cell-inner plexiform layer (GC-IPL) in women with iron deficiency anemia (IDA) and vitamin B12 deficiency anemia (B12DA).

Methods

The patients were divided and evaluated in three groups as IDA (group 1), combined IDA-B12DA (group 2), and healthy females (group 3). Each group constituted 35 subjects. CCT, endothelial cell density (CD), the coefficient of variation (CV), and hexagonality (HEX) values were evaluated. Superior, nasal, inferior, and temporal retinal nerve fiber analysis were done, and mean thickness of GC-IPL complex was also evaluated.

Results

CCT was found to be less (thin CCT) in group 2 as compared to group 1 and group 3 (P = 0.016 and P = 0.013, respectively). While CD measurements did not vary significantly between the groups, CV value was found to be lower in the control group as compared to that in the other groups (P = 0.001 and P = 0.002, respectively). HEX and the thicknesses of all RNFL and GC-IPL were lower in both the anemic groups as compared to the control group (P = 0.012 and P = 0.013, respectively); however, no significant difference was determined between the anemia groups.

Conclusions

It should be noted that anemia is a common clinical picture particularly seen in women, and there may be a tendency toward corneal and retinal disorders in these patients. The present study found that presence in the patients with IDA and with combined IDA-B12DA may have influenced endothelial functions; also the patients with anemia had significantly thinner CCT than healthy controls.

Translational Relevance

Optical coherence tomography and specular microscopy measurements may provide important data for early diagnosis and treatment of both corneal and retinal diseases according to the type of anemia in anemic women.

Nictitating membrane fixation improves stability of the contact lens on the animal corneal surface

We evaluated the feasibility and safety of nictitating membrane fixation to address reduced contact lens stability by the nictitating membrane in a rabbit model. Under general anesthesia, twelve animals received a horizontal mattress suture between the nictitating membrane and the upper eyelid of one eye. To assess the effects of this technique and secondary side effects, contact lens stability test, Schirmer tear test, tear break-up time measurement, eye tissue pathology and morphology were evaluated. Contact lens stability was increased after nictitating membrane fixation. The percentage of contact lens retention in the nictitating membrane fixed rabbit after 4 hours was 90% whereas that in the untreated rabbit was 42.5%. In addition, there were no significant differences in tear quantity and quality between the fixed and untreated eyes. Furthermore, no remarkable pathological lesions were found in gross observation during the 1-month time period or the following pathological examination. In this study, we demonstrated that nictitating membrane fixation increases contact lens stability without specific side effects using a rabbit model. This minimally invasive procedure could be useful when designing animal models for testing new contact lenses and has potential to apply to other biomaterial research on the ocular surface.

Diquafosol Ophthalmic Solution Increases Pre- and Postlens Tear Film During Contact Lens Wear in Rabbit Eyes

OBJECTIVES

To investigate the behavior of prelens tear film (PLTF) and postlens tear film (PoLTF) after the instillation of diquafosol using an experimental rabbit model of eyes with contact lens.

METHODS

Cross-sectional, anterior segment optical coherence tomographic images of the inferior midperipheral cornea were obtained at baseline and at 5, 15, 30, 60, 90, and 120 min after the instillation of 3% diquafosol ophthalmic solution in 10 Japanese white rabbits wearing contact lenses. From the obtained images, the areas of the PLTF and PoLTF were calculated. Both artificial tear solution and 0.1% sodium hyaluronate ophthalmic solution were used for comparison.

RESULTS

Significant fluid accumulation in both the PLTF and PoLTF was observed after diquafosol instillation, whereas no fluid accumulation was visible after the instillation of artificial tear or sodium hyaluronate. The increase in PLTF area after diquafosol instillation was significantly higher (P<0.01) at 15 and 30 min than that after the instillation of artificial tear or sodium hyaluronate. The increase in PoLTF area up to 60 min after the instillation of diquafosol was significantly higher (P<0.01) than that after the instillation of either of the other two drugs.

CONCLUSIONS

Instillation of 3% diquafosol ophthalmic solution increases PLTF and PoLTF in rabbit eyes with contact lenses. Diquafosol has potential as a treatment option for contact lens-related dry eye.

Pseudomonas aeruginosa infectious keratitis in a high oxygen transmissible rigid contact lens rabbit model

PURPOSE

To establish a rabbit model of infectious Pseudomonas aeruginosa keratitis using ultrahigh oxygen transmissible rigid lenses and characterize the frequency and severity of infection when compared to a non-oxygen transmissible lens material.

METHODS

Rabbits were fit with rigid lenses composed of ultrahigh and non-oxygen transmissible materials. Prior to wear, lenses were inoculated with an invasive corneal isolate of P. aeruginosa stably conjugated to green fluorescent protein (GFP). Corneas were examined before and after lens wear using a modified Heidelberg Rostock Tomograph in vivo confocal microscope. Viable bacteria adherent to unworn and worn lenses were assessed by standard plate counts. The presence of P. aeruginosa-GFP and myeloperoxidase-labeled neutrophils in infected corneal tissue was evaluated using laser scanning confocal microscopy.

RESULTS

The frequency and severity of infectious keratitis was significantly greater with inoculated ultrahigh oxygen transmissible lenses. Infection severity was associated with increasing neutrophil infiltration and in severe cases, corneal melting. In vivo confocal microscopic analysis of control corneas following lens wear confirmed that hypoxic lens wear was associated with mechanical surface damage, whereas no ocular surface damage was evident in the high-oxygen lens group.

CONCLUSIONS

These data indicate that in the absence of adequate tear clearance, the presence of P. aeruginosa trapped under the lens overrides the protective effects of oxygen on surface epithelial cells. These findings also suggest that alternative pathophysiological mechanisms exist whereby changes under the lens in the absence of frank hypoxic damage result in P. aeruginosa infection in the otherwise healthy corneal epithelium.

Sustained in vivo release from imprinted therapeutic contact lenses

In this paper, we demonstrate the successful in vivo extended release of a small molecular weight therapeutic, ketotifen fumarate (MW=425), from molecularly imprinted, therapeutic contact lenses. This is the first time that a steady, effective concentration of drug is maintained in the tear film from a contact lens for an extended period of time for the entire duration of lens wear. Poly(HEMA-co-AA-co-AM-co-NVP-co-PEG200DMA) soft contact lenses were prepared (100±5 μm thickness, diameter 11.8 mm, power zero), and a constant tear film concentration of 170±30 μg/mL was measured for up to 26 hrs in a New Zealand white rabbit model. The results showed a dramatic increase in ketotifen mean residence time (MRT) and bioavailability compared to topical drop therapy and drug soaked lenses. The MRT for imprinted lenses was 12.47±3.99 hrs, ~4 and 50 fold greater than non-imprinted lenses and 0.035% eye drops (Zaditor®), respectively. Furthermore, AUC(0-26 hrs) was 9 and 94 fold greater for imprinted lenses than non-imprinted lenses and eye drops, respectively. The results indicate that molecular imprinting provides an exciting rational engineering strategy for sustained release. It is clear that imprinted lenses are very promising combination devices and are much more effective and efficient delivery devices than eye drops.