| Background and PurposeCorneal surface disorders and opacities are complicated clinical diseases .There is no effective treatment for these diseases before the appearance of the penetrating keratoplasty. Recently phototherapeutic keratectomy (PTK) for treating all kinds of superficial corneal pathologic changes has got the good clinical effects. PTK worked by argon fluoride (ArF) excimer laser at 193nm ultraviolet light separates molecules in biological tissue, thus can perform precise corneal ablation and remove the opacities. Due to its safety, precise, effectiveness, reproduction and slight damage to the surrounding tissues, PTK is being recognized and accepted by ophthalmologists in many countries. It is being developed and widely used in the world, and also becoming an effective surgical tool for these diseases. It has made some of the patients delay or postpone corneal grafting. However, Surgical procedures ablation with PTK destroyed the mostly central corneal innervation. Some studies showed that denervation of the corneal sensory never cause descended function of corneal sensitivity, reducedmetabolic activity of cornea, decreased mitotic activity of epithelial cells and diminished healing capacity. All these above may result in haze formation, corneal transparency descent and vision reduce. Corneal wound healing and never regeneration was influenced after PTK by multiple factors. Thus it is the key to accelerated corneal tissues reparation and function recovery.Nerve growth factor (NGF) is the first growth factor to have been discovered more than 50 years before. It exerts effects by signaling through surface membrane receptors, TrkA and P75 in the neurotissue and unneurotissue. NGF can enhanced the proliferation of nerve cells and other cells.It is not easy to change the excimer laser technique, but we can do it through improving remedy and surgical technique, which is feasible and necessary for treatment after PTK. For the sake of effective medical methods for corneal tissue reparation after excimer laser, hereby we performed this experimentation.To evaluate the effect of topical application nerve growth factor on the recovery of corneal sensitivity, nerve regeneration and wound healing after excimer laser phototherapeutic keratectomy. Materials and Methods(1) Animal experiment and the model of superficial rabbit corneal scar: Thirty New Zealand healthy white rabbits without any ocular disease were used as superficial corneal scar model by burn with 8.17% sulfuric acid, and then treated with PTK in two weeks.(2) The treatment parameters of PTK: Energy density was 160-180mJ/cm2, energy 0.25//m/pulse, ablative diameter 8mm, frequency 10HZ, continual pulse, ablative depth: lOO/zm (including epithelium). In each rabbit one eye was in experimental and the other eye was in control group.(3) Experimental drug: Mouse Nerve Growth Factor for Injection: Production of Wuhan Haiter Pharmaceutical Co, Ltd(4) Treatment after surgery: Nerve growth factor was topically applied to the right eyes (experimental group), and artificial tears was applied to the left eyes (control group).(5) The examinations after surgery: The changes in time of reepithelialization and the corneal haze formation were examined by slit lamp microscope, cornealsensitivity was measured by using a Cochet-Bonnet aesthesiometer after 1, 2, 4, 8,12, and 16 weeks postoperatively, respectively. The rabbits were immediately killed respectively at 1, 2, 4, 8, 12, and 16 weeks after measured corneal sensitivity. Both corneal samples of each rabbit were removed at once and underwent the measured corneal transparency using an optimeter. After this, nerve regeneration status and the numbering of intraepithelial nerves were evaluated at 1,2,4, 8,12, and 16 weeks after PTK by gold chloride staining and underwent light microscope examination. Corneal wound healing was also evaluated by hemotoxylin and eosin (H&E) staining by light microscope examination. At 1 and 4 weeks, the cornea was bisected, half of the cornea specimen was examined by electron microscope, and endothelium cells by scanning electron microscope (SEM).(6) Statistical analysis: Paired t test and Wilcoxon signed rank test were used. Results1. Slit-lamp microscope examination(l)The model of superficial rabbit corneal scar and PTK treatment: there was no difference of corneal epithelial cell which completely covered the laser section with in 5~-7 days between NGF group and AT group (P>0.05).2. Recovery of corneal sensitivityThere was no different of corneal sensitivity preoperatively (P>0.05), and the difference between the NGF group and the control group was statistically significant (P <0.05) postoperatively. The sensitivity was higher in the NGF group than in the AT group, and the recovery of sensitivity was faster in the NGF group than in the AT group except at 2 weeks.3. Corneal transparency and absorbanceThe difference of corneal transparency and absorbance in the wavelength range 400nm to 700nm between the NGF group and the AT group was statistically significant (P <0.05) postoperatively. The transparency was higher in the NGF group than in the AT group postoperatively.4. Light microscope examination(1) Gold chloride staining: At 2, 4, 8, 12, and 16 weeks after operation, subepithelial leash nerves regeneration at the laser site in the NGF group were similarto the normal than those in the AT group .(2) The number of intraepithelial plexus were more abundant in the NGF group than in the AT group except at 2 weeks. The difference was significant between the NGF group and AT group (P <0.05).(3) H&E staining: The excessive epithelial hyperplasia, subepithelial collagen proliferation and the scar formation at the subepithelial stroma were more remarkable in the AT group during period after operation.5. Electron microscope examination1) On SEM examination: corneal epithelial cell which completely covered the laser section with in 1 week between experimental group and control group. 4 weeks after the operation, the epithelial cells similar to the normal endothelial cells, but microvill were present on surface in the control group less than experimental group.2) On SEM examination: the endothelium exhibited slight edema 1 week after the surgery. The mosaic of hexagonal endothelial cells joined tightly, and the cellular membrane integrate. A few of the endothelial cells distorted pentagor and the size variously. 4 weeks after the operation, the endothelium appeared as a regular mosaic of hexagonal cells, similar to the normal endothelial cells.Conclusions1. PTK was an effective and safe treatment for superficial corneal diseases.2. NGF ophthalmic solutions will help the recovery of corneal sensitivity, nerve regeneration, reduced scar formation, accelerate corneal transparency after PTK.3. The wound healing process tended to stabilize at fourth months after PTK in rabbit cornea. Corneal nerve regeneration and wound healing are a unified and continuous process.4. Topical applied exogenous NGF has no apparent side effects during experiment period and it is also being a simple and facility method after surgery.5. NQF ophthalmic solutions appears to be an effective medicine for corneal tissue reparation.
|
PDF Full Text Request