Measurement of human eye volume in vivo with MRI and its clinical value

Abstract

Background The quantitative analysis of the relationship between the vitreous volume with diopter and axial length in high myopic eye can offer a valuable basis for relevant clinical research. However, how to measure the ocular volume in vivo is a problem. Objective This study was to measure the eyeball volumes with magnetic resonance imaging ( MRI) and compare the difference of ocular volume between emmetropic and high-myopic eyes in order to explore the influent factors of changes of eyeball volumes. Methods The volumes of ocular anterior segment,lens and vitreous were measured using MRI( 1.5-T) in 60 emmetropic eyes and 60 high-myopic eyes. The ocular axial lengths of the subjects were measured by A-scan ultrasonography. The alterations of vitreous volumes with the changes of axial lengths and diopters were evaluated by linear regression analysis. Written informed consent was obtained from each patient before any medical examination. Results The mean diopters of high myopic eyes was ( - 15. 62 ± 8. 27 ) D and the mean axial lengths were ( 28. 68 ± 2. 68 ) mm, showing a significantly positive correlation between them(R2=0. 830,P = 0. 000). The mean total ocular volumes were(7.46±0. 89)ml3 and those of vitreous were ( 6. 90 ± 0. 8 ) ml3 in the high-myopic eyes with a significant increase in comparison with emmetropic eyes [ ( 6. 00 ± 0. 35 ) ml3 and ( 5. 41 ±0. 32 ) ml3 ] ( t = - 11. 846, P = 0. 000; t = - 12. 1, P = 0. 000 ). However,no significant differences were found in the anterior segment volumes and lens volumes between high myopic eyes and emmetropic eyes (t = 1. 23, P = 0. 220; t = -0. 483 , P = 0. 630 ). The vitreous volumes of high myopic eyes were significantly correlated with the diopters and the axial lengths (R2 =0. 75 ,P = 0. 000 ;R2 =0. 85 ,P = 0. 000) ,and so were the total ocular volumes (R2 = 0. 7543, P = 0. 000; R2 = 0. 8413, P = 0. 000). Conclusion The alteration of vitreous volumes is a mainly cause of difference of total ocular volume in ammetropic eyes. In high myopic eye, vitreous volume has a good linear correlation with refractive error and axial length, which may offer valuable information for vitrectomy. Key words: Eyeball/vitreous volume/measurement; Magnetic resonance imaging; High myopia; Axial length; A-scan ultrasonography