Thickness measurement of retinal nerve fiber layer with different scanning ranges in normal subjects

Objective To measure the thickness of retinal nerve fiber layer( RNFL) in normal subjects using optical coherence tomography( OCT),with 2. 4 mm and 3. 4 mm scanning diameter respectively,and to assess the difference in RNFL measured with these two scanning diameters and its clinical significance. Methods We used Poland Copernicus SOCT to scan the optic nerve head of 72 normal subjects( 118 eyes). Each subject was measured two times with the scanning diameter of 2. 4 mm and 3. 4 mm respectively. A commercial software RNFL Thickness Graph was then used to analyze RNFL thickness. Results Temporal,upper,nasal,and lower quadrants and overall average RNFL thickness measured with 2. 4 mm diameter scanning were( 73. 12 ± 12. 15)μm,( 121. 97 ± 15. 65)μm,( 70. 13 ± 10. 64)μm,( 127. 78 ±13. 90)μm,( 98. 25 ±8. 49)μm.,and 98. 25 ±8. 49 ? m,respectively. Accordingly,the RNFL thickness measured with3. 4 mm scanning diameter was( 54. 92 ± 8. 93)μm,( 96. 50 ± 11. 51)μm,( 55. 81 ± 8. 89)μm,( 97. 28 ± 9. 98)μm( 76. 13 ±6. 18)μm.. When using 2. 4 mm for the scanning diameter,RNFL thickness at upper( P =0. 024) and lower quadrants( P = 0. 035) and the average RNFL thickness( P = 0. 024) were significantly different between ages,while this difference by age was only found at upper quadrants( P = 0. 012) when using 3. 5 mm as the scanning diameter.There was no difference in RNFL thickness by gender or ocular side when using either scanning diameter. In addition,when using 2. 4 mm scanning diameter,RNFL thickness was different between upper and lower quadrants but not between nasal and temporal quadrants. In contrast,when using 3. 5 mm scanning diameter,no difference in RNFL thickness was found between any of two quadrants. Conclusion OCT measurement for RNFL thickness in normal subjects showed excellent repeatability. Different scanning diameters help to provide different RNFL thickness values,and contribute to clinical diagnosis.