Normative Measurements Of Children Orbital Structures By Low-Dose Spiral CT

Objective:The eyeball is an important visual organ. The extraocularmuscles as eye appendage maintain normal position and sports of the eyeball.Orbital disease can cause the change of the eyeball or extraocular muscles,such as the refractive error inducing antero-posterior diameter and transversediameter changes, the eye extrinsic inflammation or Graves'orbitopathyresulting in muscles and optic nerve thickened. Understanding the normalvalue of orbital structures can provide the basis for the diagnosis of diseaseand the reference for determining the treatment options. Children as a specialpopulation, the orbital diseases have characteristics of their own. So biologicalmeasurements of children orbital structures are necessary and important. In themodern imaging technologies, the accuracy of orbital measurement by CT hasconfirmed. There are many scholars carrying researches on the eyeball andextraocular muscles, mostly for the adult, but rarely for children. Because theradiation of CT is harmful to human body and the lens is very sensitive organ,especially for children, we use the low dose when scaning. At the point ofview, we research the diameter of eyeball and extraocular muscles of childrenwith low dose CT to obtain the development pattern of eyeball and extraocularmuscles and provide the reference for clinical.Methods: Study300patients who did the sinus CT examination in TheSecond Affiliated Hospital of Hebei Medical University from March2011toOctober2011, with187cases of male and113female cases, ages from3to16years old(mean10.7years). The research is under the low dose scanningcondition. All patients in this study were free of clinical evidence or anyorbital disorder, and CT scans with abnormal orbital findings were excluded.The measurements of antero-posterior diameter(A-PD), transverse diameter(TD), anterior chamber depth(ACD), lens thickness(LT), vitreous cavity diameter(VCD) of eyeball, optic nerve sheaths width(ONSW), rectusdiameter(RD), bizygomatic width(BW) were obtained, and calculated the ratioof the sum of unilateral rectus diameters to the bizygomatic width.Statisticsprocessing: The SPSS13.0statistics software, The t test was used to comparedata obtained from the right and left orbits, male and female patients. TheANOVA was used to compare data obtained from different age groups.Statistical significance was designated at P<0.05. The correlations betweenA-PD and VCD, LT and age were estimated. We analysed the growth rule ofrectus thickness and the clinical significance of the ratio of the sum of rectusdiameters to the bizygomatic width.Results:1When the tube current was50mA, the CTDIvolwas2.75mGy, When it was80mA, the CTDIvolwas3.91mGy. Low dose CT scanning images displayedthe eye and the surrounding structures clearly and could be used in the orbitalmeasurement though there were some noises. Paranasal sinus displayed welland had no effect to the diagnosis.2No statistically significant difference was found between data for the rightand left orbits. There were differences between male and female in13-16years old group on A-PD, and the rest of the differences between male andfemale were no statistical significant.3-4years old group the A-PD, TD, ACD,LT, VCD of eyeball and ONSW were (23.78±0.08) mm,(23.97±0.10) mm,(3.23±0.08) mm,(3.34±0.09) mm,(15.21±0.07) mm,(4.69±0.06) mm,5-6years old group were (23.88±0.18) mm,(24.10±0.18) mm,(3.26±0.16) mm,(3.38±0.16) mm,(15.26±0.14) mm,(4.73±0.09) mm,7-8years old group were(24.02±0.12) mm,(24.31±0.10) mm,(3.27±0.27) mm,(3.43±0.17) mm,(15.33±0.21) mm,(4.71±0.14) mm,9-12years old group were (24.21±0.13)mm,(24.48±0.16) mm,(3.29±0.18) mm,(3.46±0.08) mm,(15.45±0.15) mm,(4.70±0.09) mm, male of13-16years old group the A-PD was (24.48±0.15)mm,female was (24.38±0.09) mm. TD, ACD, LT, VCD and ONSW were(24.73±0.17) mm,(3.30±0.18) mm,(3.50±0.09) mm,(15.62±0.15) mm,(4.71±0.09) mm. The differences between age groups on A-PD and TD were significant, ACD and ONSW were of no statistical significance. There haddifferences on LT, but in the adjacent the difference was no statisticalsignificant. There had no significant difference between3-4years old groupand5-6years old group on VCD. The A-PD was positively correlated withVCD (r=0.924, P<0.05).3Male of3-4years old the MRD, LRD, SRD, IRD and BW were (3.41±0.08)mm,(2.44±0.10) mm,(3.45±0.11) mm,(3.46±0.10) mm,(81.93±0.07) mm,5-6years old were (3.49±0.10) mm,(2.51±0.11) mm,(3.53±0.12) mm,(3.54±0.12) mm,(83.74±0.10) mm,7-8years old were (3.57±0.07) mm,(2.57±0.10) mm,(3.59±0.08) mm,(3.64±0.06) mm,(85.57±0.18) mm,9-12years old were (3.67±0.20) mm,(2.63±0.19) mm,(3.67±0.20) mm,(3.76±0.17)mm,(87.41±0.14) mm,13-16years old were (3.78±0.14) mm,(2.70±0.13)mm,(3.76±0.12) mm,(3.84±0.15) mm,(89.27±0.16) mm. There hadsignificant differences on MRD, IRD and BW in different age groups and nosignificant differences between5-6years old group and7-8years old group onLRD and SRD.Female of3-4years old the MRD, LRD, SRD, IRD and BW were(3.40±0.04) mm,(2.43±0.03) mm,(3.45±0.05) mm,(3.46±0.03) mm,(81.93±0.05) mm,5-6years old were (3.49±0.03) mm,(2.50±0.06) mm,(3.53±0.06) mm,(3.55±0.05) mm,(83.75±0.05) mm,7-8years old were(3.54±0.04) mm,(2.54±0.07) mm,(3.57±0.05) mm,(3.60±0.07) mm,(84.93±0.11) mm,9-12years old were (3.62±0.09) mm,(2.60±0.09) mm,(3.64±0.09) mm,(3.69±0.11) mm,(86.86±0.13) mm,13-16years old were(3.69±0.09) mm,(2.67±0.14) mm,(3.71±0.12) mm,(3.76±0.13) mm,(88.64±0.14) mm. There had significant differences on MRD and BW indifferent age groups and no differences between5-6years old group and7-8years old group on LRD,SRD and IRD.RD and BW had no significant differences between male and female in3-4years old group and5-6years old group.The differences between male andfemale on MRD, IRD and BW in7-8years old group,9-12years old groupand13-16years old group were significant. The differences between male and female on SRD in13-16years old group were significant.The ratio of the sumof rectus diameters to the bizygomatic width was0.16, there had no significantdifference in different age groups and different gender.Conclusions:1Low dose CT scanning of children orbital structures worthes to extensiveapplication, which reduces the radiation dose, protects the important organ,extends the life of the tube and saves much cost. Biological measurements ofeyeball and extraocular muscles by CT can ensure the image quality and thereliability of the data.2For most normal children, the sizes of both eyes are the same and thethicknesses of symmetric extraocular muscles are indiscriminate.3During the period of3-16years old the A-PD, TD and VCD are increasingclose to adult level untill16years old. There are positive linear correlationsbetween A-PD and VCD. The lens is still continuously incrassated after3years old, but very slowly. There are no significant changes on ACD andONSW in3-16years old. During the age of3to12, there are no differencesbetween male and female on the eye diameter. The length of male A-PD isgreater than female during the age of13-16years old. Other indexes are of nosignificant difference.4During the age of3-16the RD and BW are increasing continually, IRD isthe most thickest, LRD the thinnest. The thickening speeds of each rectus aregenerally consistent from3to6years old and there are no differences betweenmale and female. During the age of7-16the thickening speeds of IRD andMRD are greater than LRD and SRD. The MRD and IRD of male are greaterthan female. During the age of13-16the SRD of male is greater than female,but there are no differences between male and female on the LRD.5The ratio of the sum of rectus diameters to the bizygomatic width has norelevance with age and gender. The value is close to0.16, which can providesome help for the clinical earlier to diagnose the eye extrinsic thickening.