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.
ABSTRACT
Objective To discuss the expansion model of the eyeball and investigate the morphologic characteristics of high-my- opic eyeball through the dimensional measurement in high-myopia and emmetropia by MRI. Design Case controll study. Participants Thirty-two emmetropes (60 eyes) and 33 high myopes (60 eyes) were enrolled, without eye diseases and history of ocular surgery or in- jury. Methods 60 high-myopic eyes and 60 emmetropic eyes were measured with MRI (I.5T,PHILIPS) to get the data of three inner ocular dimensions, intraocular volume and the volume of different parts. Main Outcome Measures Three dimensions and volumes of eyeballs. Results The average value of axial (28.16?2.80 mm), horizontal (22.87+1.23 mm) and vertical length (23.40?0.99 ram) of high-myopic eyes were much bigger than those of emmetropic eyes(P=0.000), especially the axial length( with difference of 5.38 mm); The axial length was correlated with refractive error (0.36 mm/D,r~2=0.88, P=0.000). The average value of the whole ocular volume (7. 46?0.89 ml) and vitreous volume(6.90?0.8 ml) of the high myopic eyes were bigger than those of emmetropic eyes(P=0.000), while ante- rior segment volume and lens volume were about the same as that of emmetropic eyes (P=0.220, P=0.630). Conclusions The three di- mensions of high-myopic eyes were significantly longer than that of emmetropic eyes. In high myopes, the increased vitreous volume lead to the increase of the whole ocular volume. There may be two models in the ocular expansion of high myopia: global expansion and axial elongation expansion. More serious refractive error cause more obvious expansion in axial elongation.