A sensory nerve supply is crucial for optimal function of the cornea. However, the mechanisms for successful innervation and the signalling pathways between nerves and their target tissue are not fully understood. Engineered tissue substitutes can provide controllable environments in which to study tissue innervation. I have therefore engineered human corneal substitutes that promote nerve in-growth in a pattern similar to in vivo re-innervation. The methodology developed for the fabrication of such an innervated model cornea and for subsequent investigation of the function of these nerves is discussed in this thesis. Briefly, nerve in-growth into the tissue-engineered cornea is enhanced by the addition of laminin and nerve growth factor, but not retinoic acid. I demonstrated that these nerves are morphologically equivalent to natural corneal nerves and make appropriate contact with their target cells, which consequently, were found to be required for their survival. The nerves had functional sodium channels and generated action potentials similar to those of native nerve endings. I also demonstrated that the nerves could respond appropriately to chemical and physical stimuli and play an important role in the overall functioning of the bioengineered tissue. The presence of nerves conferred some protection to the epithelium from chemical insult and differential retention of sodium was observed within the nerve fibres themselves. As such, this model could be further developed for use as an in vitro alternative to animals for safety and efficacy testing of chemicals and drugs. Based on the concepts developed for these in vitro innervated corneas, hybrid biosynthetic matrices with the proper dimensions, transparency and biomechanical properties for use as corneal replacements in transplantation were also developed. These matrices were successfully implanted into corneas of pigs. Regeneration of corneal tissue and nerves was observed, along with restoration of sensory function. The basic model developed therefore can be used for studying corneal wound healing, nerve-corneal cell interactions and provides a basis for developing corneal replacements for transplantation.

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The effect of unilateral optic nerve section (UONS) on the susceptibility rat rod photoreceptors to damage by visible light was studied. The optic nerve was cut intracranially by a ventral approach so as not to interfere with structures in the orbit of the eye, the brain or the blood supply to the eye. It was found that retinas with optic nerves cut (ONS) suffered substantially less damage from light than did those with intact optic nerves (ONI) in the same animals or in sham operated animals. The effect occurred in pigmented and albino rats and with varying light damage conditions. / One possible explanation for these results is that fewer photons are being absorbed by the ONS retina because fewer are reaching it or because of changes in retinal photochemistry. Monitoring the behavior of UONS rats during bright light exposure indicated that, if anything, rats tend to allow more light into their ONS eye. By measuring steady state bleach, whole retina dark adapted rhodopsin, and regeneration rate it was found that the same amount of light is absorbed by both retinas of a UONS rat. Parameters which control rhodopsin content were measured in the superior half of the vertical meridian of the retina. These include rod outer segment length, photoreceptor cell density, and rhodopsin packing density. There were no significant differences between the ONS and ONI eyes. So, even in the region of the retina used to assay light damage susceptibility, visual pigment content cannot explain the protective effect of ONS. / Correlations of light damage protection with other changes occurring in the retina after ONS are discussed and a possible neurochemical explanation is presented. / Source: Dissertation Abstracts International, Volume: 49-08, Section: B, page: 2964. / Major Professor: Theodore P. Williams. / Thesis (Ph.D.)--The Florida State University, 1988.

The optical properties of Fresnel reflections from the human ocular surfaces, called Purkinje reflections, are examined. Extensive modeling of the behavior of the reflection of sources from the front of the cornea and the front of the crystalline lens with real rays in lens design software is presented. The modeling looks at the effects of various conic constant values on the ocular surfaces and rotation of the eye in particular. First and third Purkinje images were collected from 14 subjects for varying fixation positions to compare with modeling. The results showed a decrease in third Purkinje image height as the eye rotated from gazing at a point near the light sources to a point near the optical axis of the imaging camera. This matched the predictions from modeling and indicates that fixation position is an important factor in the accuracy and repeatability of comparison phakometry results. Schematic eye models were set up for each subject and the anterior lens radius of curvature and conic constant were optimized to match the collected Purkinje image height data. The mean conic constant estimate from optimization was -3.82 with a standard deviation of 1.51. The schematic eye models did not include crystalline lens tilt or individual corneal conic constant values, each of which is estimated to contribute an uncertainty of ± 0.5 in the anterior lens conic constant value. This is the first use of Purkinje images to assess anterior lens conic constant values.

The delivery of drugs plays an important role in the treatment of ocular diseases. In this thesis, biocompatible, biodegradable materials such as poly(propylene fumarate) (PPF) and poly(lactic-co-glycolic) (PLGA) were used to prepare delivery systems. PPF together with N-vinyl pyrrolidone (NVP) was photo-crosslinked to generate monolithic polymer rods, which were loaded with either acetazolamide (AZ), dichlorphenamide (DP) or timolol maleate (TM). The release kinetics and structural properties were determined as well as the in vivo degradation. Further studies were performed to examine the influence of PPF molecular weight and the ratio of PPF/PNVP on the release kinetics. In addition, a coaxial electrospinning setup was developed to fabricate PLGA fiber networks as a delivery system. We found that prefabricated, photo-crosslinked PPF/PNVP matrices represent suitable, controllable release systems for different drugs. Furthermore, coaxial electrospinning is a promising technique to generate scaffolds for drug delivery.