Imaging Measurement And Application Of Extraocular Muscle In Patients With Thyroid-associated Ophthalmopathy (TAO)

Part One Correlation Between Extraocular Muscle measurement value and Motility Restriction in Thyroid-associated OphthalmopathyPurpose Evaluate the relationship between the maximum cross-sectional area(MCA)of the extraocular muscle(EOM),measured by computed tomography,and the ocular motility restriction in moderate to severe Thyroid-associated Ophthalmopathy(TAO).In order to provide reference to evaluate the EOM involvement in clinical.Methods This investigate is based on a retrospective review of the records of 40 moderate to severe TAO patients(80 orbits)with ocular motility restriction.Main outcome measures included EOM size and degree of motility restriction.According to the clinical activity score(CAS)and the European Group On Graves’ Orbitopathy(EUGOGO)protocol,the study cohort(n=80 orbits)was divided in two subpopulations(active TAO and stable TAO).Three-dimensional reconstruction and section plane reslicing are performed on the patients’ orbit CT image.The MCA of the inferior rectus(IR),medial rectus(MR),superior muscle group(SRLPS,superior rectus and levator palpebrae superioris)and lateral rectus(LR)are measured with the use of a manual segmentation technique on redefined CT scans with commercially available software Mimics 18.0(materialise company,Belgium).The measured data of the two patient groups were compared,and the correlation of the MCA of the EOMs with the ocular motility restriction,and with CAS, exophthalmos,corrected visual acuity and levator palpebrae superioris muscle function were analyzed.Results 1.The MCA of the EOMs of moderate to severe TAO patients,in descending order was IR,MR,SRLPS and LR.Only the MCA of MR were significantly different between the active phase group and the stable phase group(p<0.05).The position of IR,MR,SRLPS and LR largest areas were located in the mid part of the orbit.2.The MCA of IR,MR and SRLPS were negatively correlated with corrected visual acuity(p<0.05),the MCA of SRLPS negatively correlates with levator palpebrae superioris muscle function(p<0.01).No correlation was found between the MCA of EOMs and CAS(p>0.05).3.The percentage of the motility restriction was higher in the Active subpopulation when compared with the Stable subpopulation in a statistically significant manner(supraduction restriction: p=0.040,infraduction restriction: p=0.004,adduction restriction: p<0.001,abduction restriction: p=0.030).The adduction restriction showed the highest percentage of 78.75%,and the lowest was the infraduction restriction with 27.5% in the cohort.4.Correlation between motility restriction and the MCA of EOMs: there was a significantly positive correlation between the increase in motility restriction and the increased muscle area for the IR(p<0.01),SRLPS(p<0.01)and MR(p<0.05).The LR showed no such correlation(p>0.05).Conclusion The results of this study demonstrate that maximum cross-sectional area of each rectus muscle except for lateral rectus are correlated with the restriction of eye movement.Measurement of muscle area from the largest portion of eye muscle on orbit CT is asimple and reliable method for clinical evaluation and prediction of limitation of eye movement.Part Two Comparison between Ultrasound and CT measurements of extraocular muscle thickness in thyroid-associated ophthalmopathyPurpose Compared ultrasound(US)and Computed Tomography(CT)measurements of extraocular muscle thickness in patients with Thyroid-associated Ophthalmopathy(TAO),in order to discuss whether ultrasound could be used as a tool to mesuare the extraocular muscle thickness of follow-up patients.Methods A total of 30 orbits of 15 adult patients with TAO who have been examined by both ultrasound and CT were investigated.The US measurement was taken at the point of the greatest enlargement of the muscle,perpendicular to the muscle axis.The thickness of inferior rectus(IR),medial rectus(MR),superior muscle group(SRLPS,superior rectus and levator palpebrae superioris)and lateral rectus(LR)were measured respectively.CT measurement value included maximum cross-sectional area(MCA),thickness and width of the IR,MR,SRLPS and LR,using a manual segmentation technique on redefined CT scans with commercially available software Mimics 18.0(materialise company,Belgium).Comparison between values obtained by US and CT were determined for different subgroups according to disease activity(active,stable).Results 1.There was no significant difference between ultrasound and CT measurement for the thickness of MR and SRLPS(p>0.05).But for LR and IR,statistically significant differences(p<0.05)were found.2.A positive correlation between US and CT measurement values was found in the entire study group.The correlation coefficient for the MR thickness was r = 0.712(p<0.001),for the LR was r = 0.625(p<0.001),for the SRLPS was r = 0.425(p<0.05)and for the IR was r = 0.522(p<0.01)Conclusion For measuring the thicknesses of EOM,considering the cheapness and radiation free of ultrasound,it is feasible to make follow-up examination with ultrasound.However,the clinical experience of the operator still need to be considered,and US is not recommended in the assessment of the orbital apex EOMs,optic nerve compression and the accurate measurement.