Twelve-Month Clinical and Histopathological Performance of a Novel Synthetic Cornea Device in Rabbit Model

Purpose

To report the biological stability and postoperative outcomes of a second-generation, single-piece, flexible synthetic cornea in a rabbit model.

Methods

Device materials and design were amended to enhance biointegration. Optic skirt design devices were made from compact perfluoroalkoxy alkane with porous expanded polytetrafluoroethylene ingrowth surface overlying the skirt and optic wall. Sixteen devices were implanted into intrastromal pocket in rabbit eyes. Rabbits were randomly assigned to 6- and 12-month follow-up cohorts (n = 8 in each) postoperatively. Monthly examinations and optical coherence tomography assessed cornea-device integration, iridocorneal angle, optic nerve, and retina.

Results

There were no intraoperative complications. All devices were in situ at exit, with clear optics. No retroprosthetic membrane, glaucoma, cataract formation, or retinal detachment was observed. Two rabbits in the 6-month group had mild, focal anterior lamella thinning without retraction adjacent to the optic near tight sutures. Three postoperative complications occurred in the 12-month group. One rabbit diagnosed with endophthalmitis was euthanized on day 228. Mild sterile focal retraction of anterior lamella occurred in two rabbits, which were terminated on days 225 and 315. Light microscopic examination of enucleated globes demonstrated fibroplasia with new collagen deposition into the porous scaffold without significant inflammation, encapsulation, or granuloma formation.

Conclusions

Clinical evaluations, imaging, and histopathological findings indicate favorable outcomes of this synthetic corneal device in a rabbit model. Early feasibility studies in humans are being planned.

Translational Relevance

Favorable 12-month results of the device in rabbits demonstrate vision-restoring potential in corneally blind individuals at high risk of failure with donor keratoplasty.

In vivo measurement of the attenuation coefficient of the sclera and ciliary muscle

We acquired 1325 nm OCT images of the sclera and ciliary muscle of human subjects. The attenuation coefficients of the sclera and ciliary muscle were determined from a curve fit of the average intensity profile of about 100 A-lines in a region of interest after correction for the effect of beam geometry, using a single scattering model. The average scleral attenuation coefficient was 4.13 ± 1.42 mm-1 with an age-related decrease that was near the threshold for statistical significance (p = 0.053). The average ciliary muscle attenuation coefficient was 1.72 ± 0.88 mm-1, but this value may be an underestimation due to contributions from multiple scattering. Overall, the results suggest that inter-individual variations in scleral attenuation contribute to variability in the quality of transscleral OCT images of the ciliary muscle and the outcome of transscleral laser therapies.

Automated instrument designed to determine visual photosensitivity thresholds

The Ocular Photosensitivity Analyzer (OPA), a new automated instrument to quantify the visual photosensitivity thresholds (VPT) in healthy and light sensitive subjects, is described. The OPA generates light stimuli of varying intensities utilizing unequal ascending and descending steps to yield the VPT. The performance of the OPA was evaluated in healthy subjects, as well as light sensitive subjects with achromatopsia or traumatic brain injury (TBI). VPT in healthy, achromatopsia, and TBI subjects were 3.2 ± 0.6 log lux, 0.5 ± 0.5 log lux, and 0.4 ± 0.6 log lux, respectively. Light sensitive subjects manifested significantly lower VPT compared to healthy subjects. Longitudinal analysis revealed that the OPA reliably measured VPT in healthy subjects.

A new, specular reflection-based, precorneal tear film stability measurement technique in a rabbit model: viscoelastic increases tear film stability

PURPOSE

To develop a safe, noninvasive, noncontact, continuous in vivo method to measure the dehydration rate of the precorneal tear film and to compare the effectiveness of a viscoelastic agent in maintaining the precorneal tear film to that of a balanced salt solution.

METHODS

Software was designed to analyze the corneal reflection produced by the operating microscope's coaxial illumination. The software characterized the shape of the reflection, which became distorted as the precorneal tear film evaporated; characterization was accomplished by fitting an ellipse to the reflection and measuring its projected surface area. Balanced salt solution Plus (BSS+) and a 2% hydroxypropylmethylcellulose viscoelastic were used as the test agents. The tear film evaporation rate was characterized and compared over a period of 20 minutes in 20 eyes from 10 New Zealand white rabbits.

RESULTS

The ellipse axes ratio and surface area were found to decrease initially after each application of either viscoelastic or BSS+ and then to increase linearly as the tear film began to evaporate (P < 0.001) for eyes treated with BSS+ only. Eyes treated with BSS+ required 7.5 ± 2.7 applications to maintain sufficient corneal hydration during the 20-minute test period, whereas eyes treated with viscoelastic required 1.4 ± 0.5 applications. The rates of evaporation differed significantly (P < 0.043) between viscoelastic and BSS+.

CONCLUSIONS

The shape and surface area of the corneal reflection are strongly correlated with the state of the tear film. Rabbits' corneas treated with viscoelastic remained hydrated significantly longer than corneas treated with BSS+.

Local ischemia and increased expression of vascular endothelial growth factor following ocular dissemination of Mycobacterium tuberculosis

The pathogenesis of intraocular tuberculosis remains poorly understood partly due to the lack of adequate animal models that accurately simulate human disease. Using a recently developed model of ocular tuberculosis following aerosol infection of guinea pigs with Mycobacterium tuberculosis, we studied the microbiological, histological, and clinical features of intraocular tuberculosis infection. Viable tubercle bacilli were cultivated from all eyes by Day 56 after aerosol delivery of ∼200 bacilli to guinea pig lungs. Choroidal tuberculous granulomas showed reduced oxygen tension, as evidenced by staining with the hypoxia-specific probe pimonidazole, and expression of vascular endothelial growth factor (VEGF) was detected in the retinal pigment epithelium (RPE) and photoreceptors. Fundoscopic examination of M. tuberculosis-infected guinea pig eyes revealed altered vascular architecture and chorioretinal hemorrhage by Day 56 after infection. This model may be useful in further elucidating the pathogenesis of ocular tuberculosis, as well as in developing tools for diagnosis and assessment of antituberculosis treatment responses in the eye.