retinoblastoma is the most common intraocular malignancy in childhood , and represents about 3% of all pediatric disease . retinoblastoma , a diagnosis that affects not only vision but also survival for many individuals , is also the most common intraocular tumor of childhood . the incidence of retinoblastoma is generally the same worldwide , at 1 case per 15 000 to 20 000 live births , corresponding to about 9000 cases every year . the mortality rate of retinoblastoma in children is about 4070% in asia and african countries , and 35% in europe , canada , and the usa . early retinoblastoma damage to the visual system may include pathophysiologic changes in the retina and corneal nerve head , and orbital corneal nerve damage . therefore , we speculate that the change in or injuries of the cornea may reflect or correlate with retinoblastoma status . in this study we focused on biomarkers obtained from electroencephalography ( eeg ) recordings to reflect corneal nerve injury in retinoblastoma in the eyes - closed resting state . previous studies   have also investigated corneal nerve injury in eyes of humans and animals . several classical eeg biomarkers have recently been identified for predicting prognosis of retinoblastoma patients , including 5 different frequencies and powers . according to our clinical observations , eeg band power may be correlated with corneal nerve injury in retinoblastoma patients . thus , in this study we compared clinical eeg recordings with cornea confocal microscope results , and explored the use of eeg in retinoblastoma patients . this research was approved by the ethics committee of weifang medical university . written informed consent was obtained from parents or legal guardians for participation in the study . twenty consecutive patients who had been referred due to retinoblastoma to the department of ophthalmology , affiliated hospital of weifang medical university between 2010 and 2014 participated in this study . these 20 patients all had nonhereditary unilateral retinoblastoma presenting as intraocular tumor requiring primary enucleation . retinoblastoma in this study was diagnosed according to the method of dean et al . . the visual analysis was performed on standard bipolar montages with electrode positions according to the 10 to 20 international systems . the detailed processes of the eeg examination were performed as reported by zeng et al . . to observe the status of the subbasal never plexus , more than 3 representative images were evaluated for analysis . three masked and independent investigators evaluated the morphology of the corneal nerve and the subbasal nerve plexus , performed according to a previous report . the evaluation of the total length of nerve fibers represents the nerve density in the micrometers / frame ( 158 , 700 m ) . we designated the number of main nerves under a microscope as the main nerve trunks . we designated the number of nerve branches as the nerve branching under a microscope . using a microscope , we designated all of the nerves as the total nerves , including nerve branches and the main nerve trunks . this research was approved by the ethics committee of weifang medical university . written informed consent was obtained from parents or legal guardians for participation in the study . twenty consecutive patients who had been referred due to retinoblastoma to the department of ophthalmology , affiliated hospital of weifang medical university between 2010 and 2014 participated in this study . these 20 patients all had nonhereditary unilateral retinoblastoma presenting as intraocular tumor requiring primary enucleation . retinoblastoma in this study was diagnosed according to the method of dean et al . . the visual analysis was performed on standard bipolar montages with electrode positions according to the 10 to 20 international systems . the detailed processes of the eeg examination were performed as reported by zeng et al . . to observe the status of the subbasal never plexus , more than 3 representative images were evaluated for analysis . three masked and independent investigators evaluated the morphology of the corneal nerve and the subbasal nerve plexus , performed according to a previous report . the evaluation of the total length of nerve fibers represents the nerve density in the micrometers / frame ( 158 , 700 m ) . we designated the number of main nerves under a microscope as the main nerve trunks . we designated the number of nerve branches as the nerve branching under a microscope . using a microscope , we designated all of the nerves as the total nerves , including nerve branches and the main nerve trunks . a total of 20 patients ( 11 girls and 9 boys ) were included , with a median age of 58 months ( range , 43 to 127 months ) . according to the intraocular international retinoblastoma classification ( iirc ) , there were 0 patients with extreme low risk ( group a ) , 1 patient with low risk ( group b ) , 1 patient with intermediate risk ( group c ) , 16 patients with high risk ( group d ) , and 2 patients with extreme high risk ( group e ) . figure 1 shows the changes of the dominant power bands within delta and theta bands . the eeg pattern of the retinoblastoma patients was characterized by a distinct increase in the delta ( figure 1 , p<0.01 ) and significant decrease in the theta power ( figure 1 , p<0.05 ) . the results of cornea confocal observation showed that the corneal branch nerve fiber density was decreased significantly compared to the normal individuals . however , the density of the tumid and dendritic nerves was significantly increased compared to the normal individuals . the basal epithelium curving nerves were also significantly increased in the eyes of retinoblastoma patients ( figure 2a ) . however , the subbasal nerve plexus remained normal ( figure 2b ) . these results show that the corneal nerve was significantly damaged in eyes of retinoblastoma patients . in order to investigate the correlation between corneal nerve injury and the eeg spectra power , the results indicated that corneal nerve injury was positively correlated with the delta eeg spectra power ( figure 3a , p<0.05 ) and the corneal nerve injury was negatively correlated with the theta eeg spectra power ( figure 3b , p<0.05 ) . this suggests that the eeg spectra power changes may reflect corneal nerve injury in retinoblastoma patients . we found that the sensitivity and specificity of the increased delta power and decreased theta power in the diagnosis of retinoblastoma patients were different . in increased delta power ( delta > 3.8 ) , sensitivity and specificity were 75% and 85% , and in decreased theta power ( theta < 4.3 ) sensitivity and specificity were 80% and 80% , respectively ( table 1 ) . if compounded in parallel , the sensitivity of detecting corneal nerve injury was 75% and the specificity was 88% . if compounded in series , the sensitivity and specificity were 85% and 67% , respectively ( table 1 ) , which is appropriate for the diagnosis of corneal nerve injury in retinoblastoma patients . a total of 20 patients ( 11 girls and 9 boys ) were included , with a median age of 58 months ( range , 43 to 127 months ) . according to the intraocular international retinoblastoma classification ( iirc ) , there were 0 patients with extreme low risk ( group a ) , 1 patient with low risk ( group b ) , 1 patient with intermediate risk ( group c ) , 16 patients with high risk ( group d ) , and 2 patients with extreme high risk ( group e ) . figure 1 shows the changes of the dominant power bands within delta and theta bands . the eeg pattern of the retinoblastoma patients was characterized by a distinct increase in the delta ( figure 1 , p<0.01 ) and significant decrease in the theta power ( figure 1 , p<0.05 ) . the results of cornea confocal observation showed that the corneal branch nerve fiber density was decreased significantly compared to the normal individuals . however , the density of the tumid and dendritic nerves was significantly increased compared to the normal individuals . the basal epithelium curving nerves were also significantly increased in the eyes of retinoblastoma patients ( figure 2a ) . however , the subbasal nerve plexus remained normal ( figure 2b ) . these results show that the corneal nerve was significantly damaged in eyes of retinoblastoma patients . in order to investigate the correlation between corneal nerve injury and the eeg spectra power , spearman rank correlation analysis was performed . the results indicated that corneal nerve injury was positively correlated with the delta eeg spectra power ( figure 3a , p<0.05 ) and the corneal nerve injury was negatively correlated with the theta eeg spectra power ( figure 3b , p<0.05 ) . this suggests that the eeg spectra power changes may reflect corneal nerve injury in retinoblastoma patients . we found that the sensitivity and specificity of the increased delta power and decreased theta power in the diagnosis of retinoblastoma patients were different . in increased delta power ( delta > 3.8 ) , sensitivity and specificity were 75% and 85% , and in decreased theta power ( theta < 4.3 ) sensitivity and specificity were 80% and 80% , respectively ( table 1 ) . if compounded in parallel , the sensitivity of detecting corneal nerve injury was 75% and the specificity was 88% . if compounded in series , the sensitivity and specificity were 85% and 67% , respectively ( table 1 ) , which is appropriate for the diagnosis of corneal nerve injury in retinoblastoma patients . the eeg method of prognosis used in this study agrees with previous reports on use of the corneal nerve for disease diagnosis and prognosis [ 1315 ] . however , using eeg to diagnose corneal nerve injury in retinoblastoma patients has not been explored in previous studies . the 3 goals of retinoblastoma diagnosis , treatment , and improvement are saving the patient s life , eyes , and vision . in our previous study , we examined the eeg power bands and analyzed their relationship with corneal nerve injury . we observed not only increased power in the prevailing eeg power bands , but also a moderate shift of the dominant frequency peak toward faster theta and delta . this might be because retinoblastoma afflicts the corneal nerve , which is related with visual activity . our results show that the delta power was increased and theta power was decreased in retinoblastoma patients compared to normal individuals . in clinical ophthalmology , the pathogenesis of many diseases , such as herpes simplex keratitis , glaucoma , and retinoblastoma , may affect the corneal nerves [ 5,1820 ] . the cornea is the most densely innervated part of the human body , containing myelinated a and unmyelinated c fibers derived from the ophthalmic division of the trigeminal nerve . therefore , corneal confocal microscope analysis is always used in the diagnosis of corneal nerve damage . our results indicate decreased corneal branch nerve fiber density , as well as the appearance of the dendritic particles and tumid neurons , which suggests that retinoblastoma might induce corneal nerve injury . therefore , we analyzed the correlation between corneal nerve injury and the delta and theta power of eeg . the results indicated that the corneal nerve injury was positively correlated with the delta power and negatively correlated with the theta power of eeg . actually , the changes in eeg theta and delta power was very slight and short - term . our study indicated that the theta and delta power were mainly observed in the high - risk stage ( group d ) of retinoblastoma , according to the iirc classification and that the changes in eeg powers can not be obtained in many patients or at other stages . therefore , we speculate that the changes in delta and theta power are transient and are related to iirc stage for the retinoblastoma . in our study , the sensitivity of the increased delta power and decreased theta power in the diagnosis of corneal nerve injury were 75% and 80% , respectively and the specificity was 85% and 80% , respectively . if compounded in parallel , the specificity of corneal nerve injury was 88% and if compounded in series , the sensitivity was 85% , and it was obviously higher than in other groups . if this method can help determine whether the corneal nerve is already injured in retinoblastoma patients , it will provide useful a reference for follow - up , adjunctive therapy , and the prognosis of retinoblastoma patients . the changes in delta and theta of eeg appear to be associated with occurrence of corneal nerve injury . useful information can be provided for evaluating corneal nerve damage of retinoblastoma patients through analyzing eeg power bands .
backgroundin our clinical experience we discovered that eeg band power may be correlated with corneal nerve injury in retinoblastoma patients . 
 this study aimed to investigate biomarkers obtained from electroencephalography ( eeg ) recordings to reflect corneal nerve injury in retinoblastoma patients.material/methodsour study included 20 retinoblastoma patients treated at the department of ophthalmology , affiliated hospital of weifang medical university between 2010 and 2014 . 
 twenty normal individuals were included in the control group . 
 eeg activity was recorded continuously with 32 electrodes using standard eeg electrode placement for detecting eeg power . 
 a cornea confocal microscope was used to examine corneal nerve injury in retinoblastoma patients and normal individuals . 
 spearman rank correlation analysis was used to analyze the correlation between corneal nerve injury and eeg power changes . the sensitivity and specificity of changed eeg power in diagnosis of corneal nerve injury 
 were also analyzed.resultsthe predominantly slow eeg oscillations changed gradually into faster waves in retinoblastoma patients . 
 the eeg pattern in retinoblastoma patients was characterized by a distinct increase of delta ( p<0.01 ) and significant decrease of theta power p<0.05 ) . 
 corneal nerves were damaged in corneas of retinoblastoma patients . 
 corneal nerve injury was positively correlated with delta eeg spectra power and negatively correlated with theta eeg spectra power . the diagnostic sensitivity and specificity by compounding in the series were 60% and 67% , respectively.conclusionschanges in delta and theta of eeg appear to be associated with occurrence of corneal nerve injury . 
 useful information can be provided for evaluating corneal nerve damage in retinoblastoma patients through analyzing eeg power bands .