Enucleated Porcine Eyes Research Articles

Tachykinin-1 gene products in porcine ocular tissues: Evidence for transcriptional and post-translational regulation

The tachykinin-1 gene in mammals produces structurally-related regulatory peptides, substance P (SP), neurokinin A (NKA), neuropeptide K (NPK) and neuropeptide-γ. The production of these peptides is regulated by both differential mRNA transcription and post-translational precursor processing. Such processes are known to be highly tissue- and species-specific. In this study, we have examined tachykinin-1 gene expression and precursor processing in porcine ocular tissues by employing specific tachykinin radioimmunoassays coupled with reverse phase HPLC characterization. Optic nerve, cornea, iris, ciliary body, retina, choroid and sclera were micro-dissected from freshly enucleated porcine eyes (n = 10). Following acidified ethanol extraction of tissues, dried extracts were reconstituted and subjected to two radioimmunoassays, one of which is highly specific for intact SP, the other for NKA, NKB, NPK and neuropeptide-γ. In all tissue extracts except the retina, the molar concentration of SP immunoreactivity was significantly greater than that of NKA. These data would imply expression of both α- and β-preprotachykinin-1 in these ocular tissues. Reverse phase HPLC analysis confirmed the presence of authentic SP and NKA in all tissue extracts. However, in extracts of the retina, NKA immunoreactivity co-eluted with synthetic NPK standard. These chromatographic data suggest differential processing of the β-preprotachykinin-1 precursor in the retina compared with the other ocular tissues. Thus differential mRNA transcription of the tachykinin-1 gene coupled with differential precursor processing appears to occur in porcine ocular tissues and may be a process of functional significance in the regulation of visual physiology.

In Situ Collagen Gel Mold as an Aid in Excimer Laser Superficial Keratectomy

The aim of this study is to evaluate the potential use of bovine type I collagen as an adjuvant to excimer laser keratectomy. A suspension of collagen with the capability to polymerize into a gel was applied to the anterior corneal surface of freshly enucleated porcine eyes, using 35.0 diopter (D), 45.5 D, or 52.0 D contact lenses as molds. Keratometry, photokeratoscopy, slit-lamp photography, scanning electron microscopy, and light microscopy were performed on the new surfaces. Furthermore, an irregular corneal surface was created and a suspension of collagen was applied to mask protruding irregularities, therefore creating a smooth surface that was subjected to excimer laser keratectomy. Ablation rates for both collagen and cornea were measured. Collagen suspension placed on a cornea and molded with contact lenses created a smooth-surfaced gel that conformed to the shape of the contact lens and adhered to the anterior cornea; it was optically smooth and regular as shown by photokeratoscopy, keratometry, and scanning electron microscopy. The corneal curvature was altered in accordance with the base curvature of the contact lens used. Results of keratometry showed resolution of pre-existing astigmatism without induction of new astigmatism. The ablation rate of the gel was not measurably different than that of cornea; hence, when applied to an irregular corneal surface, a smooth surface was created after excimer laser ablation. This study supports the potential value of collagen gel as an adjuvant to excimer laser keratectomy for removal of corneal irregularities as well as for correction of myopia or hyperopia with or without astigmatism.

Scanning Electron Microscopy of Corneal Incisions Using Steel, Diamond, and Sapphire Blades

In order to compare the wound morphology they produce, we used steel (Myocure), diamond (CILCO DK 121), and sapphire (Katena K2-6500) blades, to make parallel linear incisions, 500 microns deep, in 12 fresh enucleated porcine eyes. There was no discernible difference among the blades in terms of either the morphology of the collagen lamellae of the sides or the depth of the incisions produced. The major differences in the cuts produced were attributable primarily to the differences in the footplates.

Thermal Side Reactions During In Vitro Contact Cyclophotocoagulation With the Continuous Wave Nd: YAG Laser

We compared the effects of continuous wave Nd:YAG laser irradiation on the ciliary body and sclera of enucleated porcine eyes produced by two means of transmission: contact coagulations via a quartz fiber (core 600 microns), and noncontact coagulations via a focussing handpiece. Application times ranged from 10 ms to 1.5 seconds. During contact coagulations using plane fiber tips the temperature at the fiber tip, due to deposits of carbonized tissue, sometimes increased markedly, increasing the risk of perforation. Clinical application of the contact method using plain fiber tips is not recommended.

Effect of heat-treatment on the mechanical properties on one per cent. carbon steel

Accommodation may be restored to presbyopic lenses by refilling the lens capsular bag with a soft polymer. After this accommodative lens refilling prevention of capsular opacification is a requirement, since capsular opacification leads to a decreased clarity of the refilled lens. It has been hypothesized that capsular fibrosis causing the capsular opacification results in increased stiffness of the lens capsular bag, therewith contributing to a decrease in accommodative amplitude of the lens. However, the change in viscoelastic properties of refilled lenses due to capsular fibrosis has never been measured directly. In this study we examined natural lenses from enucleated porcine eyes and refilled lenses directly after refilling and after three months of culturing, when capsular fibrosis had developed, and determined their viscoelastic properties with a low load compression tester. Control refilled lenses were included in which capsular opacification was prevented by treatment with actinomycin D. We related lens stiffening to the degree of capsular opacification, as derived from the microscopic images taken with a confocal laser scanning microscope. Overall, the refilled lenses directly after refilling were softer than refilled lenses after three months of culturing, and refilled lenses treated with actinomycin D were softer compared with untreated refilled lenses. The degree of capsular opacification as assessed by microscopy corresponds to an increase in lens stiffness. This indicates that the viscoelastic properties of the refilled lens are influenced by capsular fibrosis and modulated by treatment of the lens epithelium. In conclusion, this study shows that the development of capsular fibrosis negatively affects the viscoelastic properties of isolated, cultured refilled lenses.