The Feasibility Analysis Of Calculating Proptosis By Heron’s Formula

Objective: Exophthalmos is a common clinical manifestation of orbital diseases.The degree of exophthalmos is an important index to assess the condition.It is well-known that Hertel exophthalmometer and orbital computed tomography are widely used to measure proptosis at present,but there are advantages and disadvantages in each method.Therefore,we propose a new method to measure proptosis.We try to calculate proptosis based on the Helen formula.Methods: It was a none-inferiority trial.The registration number was Chi CTR1900026490.In this study,we chose patients who were admitted to the Department of Ophthalmology of Peking University Shenzhen hospital from January2019 to December 2019.The patients were suspected suffering from eye diseases or orbital diseases.The included 60 subjects were without orbital dysplasia,ocular trauma or ocular fracture.The absolute values of proptosis of 120 eyes were measured by orbital computed tomography and Heron’s formula.We did regression analysis and analyzed the differences between the two methods with Medcalc software version19.0.4.The result was showed by Passing-Bablok regression analysis diagram and Bland and Altman plot.Results: The Passing-Bablok showed that the result of proptosis measured by computed tomography and Heron’s formula showed good positive correlation.A 95%limit of agreement in proptosis between computed tomography and Heron’s formula method was-0.46 to 0.54 mm in right eye and-0.45 to 0.46 mm in left eye.1.66%(1/60)point was outside 95% Lo A in both eyes.Moreover,a 95% limit of agreement between computed tomography and Heron’s formula method was-0.42 to 0.56 mm in difference of both eyes.3.33%(2/60)points were outside 95% Lo A.The points in all Bland and Altman plots were lower than 5%.It means that the results of comparison between the two methods had a good consistency in the measurement of proptosis.Conclusions: Heron’s formula could be applied to calculate proptosis and had a good consistency compared with orbital computed tomography.This method is a practical method in proptosis assessment because of its reliability and simplicity.