Experimental Study On Radial Optic Neurotomy In Cats

Objectives:1. To investigate fibrous component parts and structure morphology of connectiv tissue in normal cat's laminal cribrosa and optic nerve head and demonstrate the similarity and difference between cat and humanbeing.2. To explore the anatomical changes of the laminal cribrosa and the optic nerve head in vivo cats after radial optic neurotomy.3. To explore the vascular cast changes of the optic nerve head in vivo cats after radial optic neurotomy.Methods:1. A total of 12 healthy cats 24 eyes were used in the experiment, 16 normal cat autopsy eyes were examined by histochemical staining, 8 normal cat autopsy eyes were examined by transmission electron microscope and computer assistant image analytical techniques.The normal anatomic data of the distance between limbus and pars plana, thickness of eyeball wall at the site of perioptic nerve and the diameter of optic nerve head were measured of all normal eyes.2. A total of 18 healthy cats were used in the experiment, which were divided in four operative groups. Four operative group was executed at the 1^st, 15^th, 30^th, and 90^th day after underwent RON bilaterally. The enucleated eyes of each operative group were divided in two parts: one part was cut insection routinely and enbedded in paraffin, the cross sections were stained by histochemical special staining. A cell-maceration/scanning electron microscopic method was employed to demonstrate the arrangement of the collagen fibrillar network of laminal cribrosa in another part.3. A total of 10 healthy cats 20 eyes were used in the experiment. All the animals underwent RON unilaterally, the other eyes were as control in 10. Fundus was examed and FFA was performed before and at the 1^st, 15^th, 30^th, and 90^th day after RON unilaterally. Microvascular castings of the optic nerve head were prepared by transcardial injection of liquid plastic. Scanning electron microscopic and anatomic microscopic techniques were used for investigation and analysis at 90^th day after RON unilaterally.Results:1. The distance between limbus and pars plana is 6.8 mm-8.6mm. The thickness of perioptic nerve of eyeball wall is (0.78±0.06) mm. The diameter of optic disc is (1.3±0.11) mm. The diameter of optic nerve is (2.2±0.3) mm. The lamianal cribrosa is well developed. Neuroglia, vessels, nerve fibers and connective tissue united to form the laminal cribrosa. The laminal bundles of cat contain all the three kinds of fibers of hunman: collagen fibers (I and III type), elastic fibers and reticular fibers. The three-dimensional structure of laminal cribrosa is close to that of humanity. The three layers of intraocular optic nerve sheath of cat are connected with sclera.2. After the operation, the incision came into being and local hemorrhage infiltrated into the circumambience and backside. At the 1st d, no damage of the major vesselwall was found and the incision had the surgical intervals with the subarachnoid spaces.Histological examination of the optic nerve demonstrated foci of hemorrhage, reactive gliosis and inflammatory cells. At 15 day, incision is core-like shape and hyperplastic neuroglia cells and fibroblasts aggreated at the incision. At 30 day, there was obvious proliferation at the neurotomy site. The aligned texture of collagen fibril of the laminal cribrosa near the incision moved close to each other. At the 90th day, a discret scar was noted at the site.that reached the cribriform and sclera.3. The cilioretinal arteries and choroidal arteries which come from short posterior ciliary arteries supply the optic nerve head. There is no large vessel entering the optic nerve forming central retinal vessel system. The cilioretinal arteries contribute to the surface microvascular and capillaries of the optic nerve head. No complete arterial circle around the optic nerve head was identified. The lesion of radial optic neurotomy is"V" shape. No damage of the major retinal vessels and choroidal large vessles layer were found. No neovascularization was found at site of the incision.Conclusions:1. There is little anatomical difference between cat and humanbeing in optic nerve head. Cat can be selected as an experimental animal for basal investigation of laminal cribrosa and optic nerve head.2. RON can cut scleral ring sharply and no damages of the major vessel .The insion of RON connected with subarachnoid spaces of intraocular optic nerve and became broaden gradually at the site of scleral ring.3. RON could injury the local microvasculature and capillaries of optic nerve head. The incision has no influence on Zinn-Hallers circle.