[Magnetic resonance imaging study of effects of accommodation on human lens morphological characters].

OBJECTIVE: To evaluate the effects of accommodation on lens morphological characters. METHODS: From January 2011 to June 2011, magnetic resonance images of eyes were acquired from 30 subjects aged 20 to 24 years during accommodation and at rest. The optimal images were analyzed by Autocad 2010 to obtain the total lens cross-sectional area (CSA) and CSA of anterior and posterior portions of lens, anterior chamber depth, lens thickness, lens diameter, vitreous chamber depth and axial length during accommodation and at rest. Paired-t test was performed. RESULTS: The anterior curvature radius (mm), posterior curvature radius (mm), CSA of anterior portion (mm(2)), CSA of posterior portion (mm(2)), total lens CSA (mm(2)) was (8.7 ± 0.8), (6.2 ± 0.5), (7.5 ± 2.1), (12.0 ± 2.6), (20 ± 4) during relaxed accommodation; anterior curvature radius (mm), posterior curvature radius (mm), CSA of anterior portion (mm(2)), CSA of posterior portion (mm(2)), total lens CSA (mm(2)) was (7.1 ± 1.3), (5.6 ± 0.5), (14.7 ± 2.9), (12.2 ± 2.1) and (27 ± 4) during accommodation. The total lens CSA (t = -11.556, P < 0.01) and CSA of anterior portion (t = -15.653, P < 0.01) both increased in accommodative states. The CSA of posterior portion of lens (t = -0.437, P > 0.05) under a statistically independent accommodative state. There was significant difference in the anterior chamber depth (t = 4.366, P < 0.01), lens thickness (t = -5.456, P < 0.01) and lens diameter (t = 4.597, P < 0.01) in accommodative states. There were insignificant differences both in vitreous chamber depth (t = 0.428, P > 0.05) and axial length (t = 0.418, P > 0.05) under accommodative states. CONCLUSION: During accommodation, the anterior chamber depth decreases, lens thickness increases and diameter of lens decreases while anterior portions and total lens CSA increase. There are insignificant changes in posterior portions of lens CSA, vitreous chamber depth and axial length. The accommodative changes in CSA indicate that the anterior portion of lens may be related with the properties of anterior capsule and lens material, the position of zonular attachments and the location of fetal nucleus. Helmholtz theory is supported.

[Exploration of three-dimensional biometric measurement of emmetropic adult eye-ball by using magnetic resonance imaging technology].

OBJECTIVE: To study biometric measurements of emmetropic adult eyes with magnetic resonance imaging technology (MRI). METHOD: MRI technology, with super-resolution, hyper-speed imaging and the integration of the thin-scanning layer, is applied to measure the three-dimensional biometric parameters of the eyeball. From January to December, 2003, emmetropic eyes from 31 normal Chinese adults (16 males and 15 females) aged from 18 to 32 years old (23.32 +/- 3.32) were successfully measured to obtain the volume of the eyeball and vitreous cavity; inner dimensions of the eye, including the anterior-posterior, vertical and horizontal diameters. The length of ocular axis was measured by A-echo too. Data was analyzed by SPSS 11.0 statistical software. RESULTS: The volume of the eyeball, anterior chamber, lens and the vitreous cavity is (6.013 +/- 0.449) ml, (0.348 +/- 0.020) ml, (0.183 +/- 0.015) ml, and (5.482 +/- 0.440) ml, respectively. The length of anterior-posterior diameter of the vitreous cavity is (16.008 +/- 0.707) mm. The ocular inner dimensions of horizontal, vertical and anterior-posterior planes were (22.455 +/- 0.983) mm, (23.290 +/- 0.815) mm and (22.619 +/- 0.912) mm, respectively. The length of the ocular axis is (23.10 +/- 0.92) mm (with MRI & Orbscan II) and (23.67 +/- 0.82) mm (with A-echo). CONCLUSIONS: The value of the ocular length in emmetropic eye measured with both MRI + Orbscan II and the (A-echo) in the present study is very close to the value of the Bennett-Rabbitts schematic eye (24.09 mm). MRI technology is valuable for obtaining more reliable and precise data in the study of ocular physiology and clinical ophthalmology.

[The volume and dimensions of eyeball analyzed by MRI following encircling scleral buckles].

OBJECTIVE: To assess the changes of the volume and dimensions of the eyeball and the vitreous following encircling scleral buckle. METHODS: 26 eyes from 26 patients received successful broad-band encircling scleral buckles for rhegmatogenous retinal detachment from July 2002 to December 2003. The examinations, A-scan ultrasonography (SONOMED A-5500, USA), Corneal topography and MRI, were performed preoperatively and at the first week postoperatively. The volume of the eyeballs and the dimensions along the three cardinal axes from 13 eyeballs were measured with Gyroscan MR imaging system. RESULTS: The measurement of MRI for the 13 eyes operated with the encircling scleral buckling revealed that the volume of the eyeball was decreased (1.72 +/- 0.49) ml, and volume of vitreous was decreased (1.73 +/- 0.46) ml in the comparison with volume before surgery. Horizontal and vertical dimensions of eyeball were decreased (7.84 +/- 1.86) mm, (7.70 +/- 2.79) mm respectively. The length of circumference was decreased to (24.42 +/- 6.68) mm, the percentage of the decrease was (33.11 +/- 8.69)%. The average high of the buckle indentions was (3.80 +/- 0.58) mm with the average width of (3.82 +/- 0.60) mm in the temperal part and (3.51 +/- 0.76) mm in the nasal part. CONCLUSIONS: The length of the circumference at the site of buckling is shorted, and the volume of the vitreous was decreased after the surgery. The technique of MRI has an important role in the measurement and analysis of the volume and the dimension of the eyeball.