A study of orbit development and its relationship to eye size in myopia using magnetic resonance imaging

Abstract

This study covers three aspects: the first is a calibration study performed on phantoms simulating the orbit and eyeball to evaluate the accuracy of volumetric determination using MRI DICOM (Digital Imaging and Communication in Medicine) images; the second is a study on the orbit development in Hong Kong Chinese and the third is a study to demonstrate the relationship between eye size and the volume of the orbit in adult subjects with varying degrees of myopia. Calibration was conducted using ten tailor-made spherical silicon balls ranging from 5 to 14 cm3 and 10 silicon moulds of orbits from 10 human dry skulls. These were used to simulate the eyes and orbits respectively. The phantoms were subjected to MRI scanning. A T2-weighted sequence was used. The volume of each phantom was computed and compared with the known physical volumes. The computed and physical volumes were highly correlated for both eyeball and the orbit phantoms. Coefficient of variations of the computed and physical volumes were low. Consequently, it is possible to apply a calibration value to the computed volume to estimate the physical volume with a high level of confidence. The study on orbit development involved a cross-sectional MRI study of 81 Hong Kong Chinese subjects aged from 1 to 42 years. A linear growth rate was found in the first 15 years of life. The orbit grew from around 11.56 cm3 to 25.50 cm3 in 42 years. The orbit reached maturity at around the age of 16 years. To study the relationship between eye size and the volume of the orbit 33 adult subjects with varying degrees of ametropia (+1.00D to -12.75D) underwent MRI of the orbit. Results show that the larger myopic eye was not associated with a larger orbit.