A Study On The Mechanism Of Traumatic Optic Neuropathy Without Optic Canal Fracture And Its Surgical Treatment

Objectives:Traumatic optic neuropathy(TON)is an important cause to the low visual and blindness.Although the steroids,or optic canal decompression,or observation,or combination of them were used,its treatments remain in debate.Clinicians and we found that optic nerve sheath decompression(ONSD)could effectively treat some type of TON.However,there is no large scale clinic study on the effect of ONSD to TON,and the mechanisms of ONSD to treat TON is unclear.It is speculated that sub-sheath(or sub-arachnoid)hemorrhage or meningocele,or optic nerve sheath compartment syndrome,or optic nerve edema or combination of them can raise the intra-sheath pressure and cause the damage to the optic nerve.After ONSD,the intra-sheath pressure is released with the vision improved.But there is no animal model of intra-sheath hypertension and experiments on the above hypothesis.So the first objective of this study is to investigate the effect and safety of ONSD to treat TON without the optic canal fracture.Regarding the compression to the optic nerve,two types can be classified.One is the external compression to the optic nerve,which includes the canal fractures and epidural(or extra-sheath)hematoma.The other is the internal compression,which includes subdural(or intra-sheath,or sub-arachnoid)hematoma,meningocele,optic nerve sheath compartment syndrome,optic nerve edema,or intra-nerve bleeding.there is no animal model to study the internal compression.So the second objective is to simulate the internal compression to the optic nerve by establishing an animal model with intra-sheath hypertension.It will provide the theoretic and experimental base for the treatment to TON by ONSD.To realize the above goals,a sensitive and stable intra-sheath pressure monitor,by which the intra-sheath/cranial pressure can be measured,have to be made firstly.So the third one is to make an intra-sheath pressure monitor,and to investigate the pressure difference between the intra-sheath and intracranial spaces.Methods:1)A novel intra-sheath pressure monitor was made to measure the intra-sheath and intracranial pressures under different conditions.2)An animal model of intra-sheath hypertension by injection of hyaluronate sodium was made.F-VEP and histological sections were performed to evaluate optic function and histological change from the intra-sheath compression.The mechanisms of the optic nerve damage from the intra-sheath compression were studied by TUNEL assay and immunohistochemistry for Caspase-3/P53/Bax.Also the axoplasmic flow was detected by Horseradish Peroxidase injection.3)ONSD was performed on TON without the optic canal fracture.A retrospective study was carried out to investigate the effect and safety of ONSD on TON.Results:1)An intra-sheath pressure monitor was successfully made.The intra-sheath pressure and the intracranial pressure were measured respectively in normal rabbits,rabbits with intracranial hypertension,and rabbits with a decompressed intracranial hypertension.Although the intra-sheath space is communicated with the intracranial one,there are pressure differences between the intra-sheath and intracranial spaces,and the intra-sheath pressure can be higher than the intracranial one.2)An animal model of intra-sheath hypertension was successfully made by the injection of hyaluronate sodium.The histological and functional damage to the optic nerve was found with the apoptosis and impaired axoplasmic flow.3)In 32 TON without the optic canal fracture,the postoperative vision improved in 14 patients with a rate of 43.75%.In 18 patients with a vision above light perception,the postoperative vision improved in 13 in two weeks with a rate of 72.22%.The results are comparable to the reported data treated by steroids,optic canal decompression or the combinations.The complications of ONSD to treat TON are mild and transient.Conclusions:1)The pressure differences between the intra-sheath and intracranial spaces is found.Under circumstances the intra-sheath pressure can be higher than the intracranial one.2)An animal model with intra-sheath compression is established,which provides a new model for investigating the optic nerve injury.The damaged axoplasmic flow and apoptosis are found to play roles in the model.3)The performance of ONSD in TON without the optic canal fracture is safe.It might be helpful to the TON with a vision above the light perception,but helpless to those with no light perception.Regarding the ration of risk to beneficial,ONSD is a good alternative to TON patients with a vision above light perception.Removing the treatable risk factors such as intra-sheath/sub-arachnoid hematoma,meningocele,optic nerve sheath compartment syndrome,or inflammatory factors through ONSD is valuable to improve or restore patients’ visual function.