1. Ultrasound Imaging of Optic Nerve in Healthy Subjects
Effects of Power Output and Refractive Errors
Tz. Dimitrova1, S. Karakaneva1, E. Titianova1,2
1Clinic of Functional Diagnostics of Nervous System, Military Medical Academy – Sofia
2Medical Faculty, Sofia University “St. Kl. Ohridski” – Sofia
AIM
SUBJECTS
INTRODUCTION
To evaluate the ultrasound para-meters of the optic nerve in healthy subjects in relation to different power output and refractive errors.
The study was performed in 31 healthy volunteers without history of ophthalmic disorders or neuro-ophthalmic syndromes. In comparison to women men had significantly higher growth rate and body weight (table 1). Three subjects (9.7%) had congenital myopia and ten of them (32.2%) were with hypermetropia.
Table 1. Characteristics of the subjects
In the last decade ultrasound methods have been used for differentiation the ophthalmic diseases from neuro-ophthalmic symptoms and syndromes [4, 8].
Subjects n
Age (y)
Height (m)
Weight (kg)  
Body Mass Index (kg/m2)
Men 17
55±25
1.75±0.08***
78±12*
25.3±2.8
Women 14
47±12
1.65±0.06
67±15
24.3±3.6
Total 31
51±20
1.70±0.09
73±14
25.2±4.1
METHODS
CLINICAL EXAMINATION
NEURO-OPHTHALMIC STATUS
MULTIMODAL 2D/3D/4D ULTRASOUND
Measurement of the diameters of optic nerve/sheath complex (cm) and their ratio at different Power Output.
Testing the effect of refractive error by using of two hydrophilic aspheric contact lenses (+6 and -10 diopters) on the same eye.
STATISTICAL METHODS
Variation and correlation analysis.
*p<0.05; ***p<0.001—significant differences
EXPERIMENTAL TESTS
In a healthy man without refractive error the diameters of the optic nerve/sheath complex were measured at different power output ranged from 50 to 100%.
Hydrophilic aspherical lenses with +6 and -10 diopters were placed on the right eye of a healthy woman with a congenital myopia of -2 diopters.
The optic nerve causes a hypoechoic shadow away from the globe and a typical 4D ultrasound image – the optic disc had a sharp contour without swelling into the vitreous and the optic nerves were with relatively symmetrical sheath diameters on both sides [2, 6, 9].
RESULTS
Table 1. Sonographic optic nerve parameters in relation to sex
Subjects n
Complex optic nerve/sheath diameter (cm)
Optic nerve diameter
(cm)
Index
optic nerve/sheath
Left
Right
Men 17
0.54±0.06
0.54±0.07
0.33±0.09
0.33±0.10
0.61±0.13
0.60±0.13
Women 14
0.53±0.08
0.53±0.07
0.33±0.08
0.34±0.08
0.62±0.10
0.63±0.11
Total 31
0.61±0.11
0.61±0.12
There was no significant difference in survey indicators of both optic nerves. No significant correlations between sonographic parameters, gender, age and height of clinically healthy persons were also disclosed.
No significant differences were found between sonographic parameters of our myopic and hypermetropic subjects although a tendency for lower optic nerve/sheath index was seen in cases with myopia.
EFFECT OF POWER OUTPUT
EFFECT OF REFRACTIVE ERRORS BY LENSES A B C A B C
B-mode real time imaging of the optic nerve (2) and complex optic nerve/sheath (3) diameters by standard measurement in 3 mm behind the globe in power output of 50% (А), 70% (В) и 100% (С).
Ultrasound imaging of the baseline optic nerve (2) and complex optic nerve/sheath (3) diameters on the right eye (A), ultrasound patterns after applying hydrophilic aspheric contact lens with -10 diopters (B) and -6 diopters (C) on the same eye.
Table 2. Sonographic optic disc parameters in relation to power output
Table 3. Optic nerve parameters in relation to refraction by lenses.
Power Output (%) n
Complex optic nerve/sheath diameter (cm)
Optic nerve diameter (cm)
Index
optic nerve/sheath
Left
Right
100% 9
0.61±0.01
0.39±0.01
0.38±0.01
0.64±0.01
0.62±0.02
70%
0.60±0.01
0.40±0.01
0.66±0.01
50%
0.40±0.02
0.65±0.02
Diopters n
Complex optic nerve/sheath
diameter (cm)
Optic nerve diameter (cm) 
Index
optic nerve/sheath 
Baseline - 2D 9
0.61±0.01
0.37±0.02
0.61±0.03
Test D
0.38±0.01
0.62±0.02
Test D
0.37±0.01
0.61±0.02
The change of ultrasound power output from 50% to 100% was not associated with significant alteration in the ultrasound pattern of the optic nerve/sheath complex.
The ultrasound parameters of the complex optic nerve/sheath and their ratio were independent of the induced refractive error with two different contact lenses of -10 and +6 diopters.
DISCUSSION
REFERENCES
Our study is limited due to the small number of subjects. However it confirms that in healthy subjects a high symmetry in sonographic parameters of both optic nerves exist regardless of their age, gender, height and weight [4]. Our results are similar to those reported by Bäuerle et al. [2] although the normal optic nerve diameters, measured by ultrasound, ranged from 0.39 cm [1] to 0.58 cm [5].
As shown in previous studies [3, 7] the optic nerve ultrasound pattern in our small group of healthy subjects was not associated with the variations in power output and refractive errors. Further studies are needed to evaluate the impact of eye refraction on ultrasound optic nerve parameters in normal and pathological conditions in larger population.
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