Experimental Research Of Operative Time Selection After Traumatic Optic Nerve Injuries

Background:Traumatic optic neuropathy(TON) is defined as partial or total loss of visual sight resulting in temporary or permanent blindness due to traumatic injury. TON is a frequent cause of visual deformity,usually accompanied with cranio-facial compound wound.With the increase of incidence of traffic accident during recent years,TON also increases.Until now,the diagnosis and treatment of TON still lack confirmed,uniform understanding.Optic nerve decompression is the clinical metnod in common use to treat TON.But as mentioned above,TON is usually accompanied with severe cranio-facial wound,more attention is payed to salvage the patient's life in early wound stage,TON is therefor ignored and the best treatment opportunity is missed,permanent loss of visual sight is usually inevitable.Therefor,the choice of surgical opportunity for TON becomes an issue of much concern.Objective:This research is designed to study the possible mechanism of TON via prospective animal experiment.Animal model of TON is established in rabbit,aimed at systematic observation of changes of the visual evoked potentials and morphology in order to find out the relevant relations between operation opportunity and clinical effect of traumatic optic nerve injuries,and offer the theoretical foundation for the clinical surgical treatment and reference for suitable operation time limitation. Material and method:Animal models of TON and nerve decompression at different times after injury were established,followed by quantitative study of pattern reversal visual evoked potentials.At the same time,the morphological changes of optic nerve were observed under light microscope.All animals were randomly devided into normal control,decompression in 2 days,in one week,in 2 weeks and non-decompression group respectively.Results:1.Histopathological observation1.1 In normal control group,the astrocytes of optic nerve revealed cylindric form and arranged evenly on vertical section,the neural fibres arranged neatly and were even to dye.the configuration of the blood vessel was nice on the cross section.1.2 In decompression in 2 days group,the arrangement of astrocytes was basically even on vertical section,vacuoles,slight swelling of nerve,exudation around the blood vessel and a small amount of astrocytes hyperplasia were observed in the damaged area.1.3 In decompression in one week group,the arrangement of astrocytes was inordinate on vertical section.A lot of vacuoles in uniform size,demyelination of nerve, uncovered axons,obvious exudation around the blood vessel and obvious astrocytes hyperplasia were observed in most areas. v1.4 In decompression in 2 weeks group,the cylindric arrangement of astrocytes disappeared completely on vertical section.Obvious astrocytes hyperplasia of full vision field,obvious of nerve,local necrosis could be observed while exudation around the blood vessel reduced with inflammatory infiltration.1.5 In non-decompression group,necrosis in flakes,obvious nerve demyelination, serious exudation around the blood vessel and astrocytes hyperplasia were observed.2.Comparasions of P-VEP P-VEP of of each health rabbit revealed typical NPN contours,while NPN waves in injured ones being low and flat.The latent period of P wave was lengthened and the amplitude was reduced.The differences of latent period and amplitude were significant statistically.2.1 Self-comparasions of P-VEP before and after decompression(1)For decompression in 2 days group,the differences of amplitude and latent period were significant statistically.(2) For decompression in one week group,the differences of amplitude and latent period were insignificant statistically.(3) For decompression in 2 weeks group,the difference of amplitude was insignificant,and that of latent period was statistically significant.2.2.The comparisons of P-VEP every two groups at 2 weeks after decompression(1) The differences of latent period Between every two groups among decompression in 2 days,in one week,in 2 weeks group were extremely significant,those of amplitude between decompression in 48 hours,in one week,in 2 weeks group were extremely significant,while that between decompression in one week,in 2 weeks group was significant.(2) The differences of latent period and amplitude between decompression in 2 days, in one week group and non-decompression group were significant with that between decompression in 2 weeks and non-decompression group was insignificant.Conclusion:1.It is confirmed that the excessive loss of neurons due to secondary degeneration following optic nerve injuries is the most important factor for visual impairment.Therefore,it is highly crucial to prevent neurons from secondary damage for improving visual function.2.The optic nerve decompression is benefit to protection of visual function in indirect optic nerve injuries.Visual function is better improved by decompression in 2 days than in 2 weeks.In order to protect visual functions the decompression should be performed as soon as possible.