Significance of RNFL thickness measured by SD-OCT in the early diagnosis of primary glaucoma

Objective To measure RNFL thickness by Frequency-domain optical coherence tomography (OCT) in patients with different stages of primary glaucoma (CACG and POAG),to evaluate the correlation between RNFL thickness and visual field mean defect (MD),to detect RNFL thickness change of early stage primary glaucoma,and to discuss the clinical significance in the early diagnosis of primary glaucoma objectively. Methods Ninety-two subjects of 40 normal and 52 with different stages of primary glaucoma were enrolled in this study.RNFL thickness was measured by Zeiss Cirru HD-OCT,and visual field was tested by Zeiss Humphrey-750.The association between visual field MD and RNFL thickness was evaluated with Pearson correlation coefficients. Results In the normal group,mean RNFL thickness was 112.91±9.36μm; the early period glaucoma group 94.43±7.67μm; the middle period glaucoma group 80.82±10.36μm; the later period glaucoma group 67.86±8.01μm.Visual field MD in each group was-0.88±1.53dB,-4.26±1.83dB,-7.43±2.64dB and -17.06±5.85dB.The differences in mean RNFL thickness and visual field MD between normal and each stage glaucoma group were significant (P ＜0.05) by independent sample t-test.In each stages of glaucoma group,mean RNFL thickness and visual field MD (early period:r =-0.537,middle period:r =-0.615,later period:r=-0.804) correlated significantly (P ＜0.05).In the early period glaucoma group,superior RNFL thickness was 116.32±11.65μm,inferior RNFL thickness 105.58±9.73μm,nasal RNFL thickness 75.40±10.91μm,and temporal RNFL thickness 70.28±13.08μm.In group B,superior RNFL thickness was 140.15±8.79μm,inferior RNFL thickness 137.29±10.07μm,nasal RNFL thickness 90.20±14.19μm,and temporal RNFL thickness 88.43±10.85μm.The difference of superior and inferior RNFL thickness between group A1 and group B had statistical significance tested by independent sample t-test,P ＜0.05; nasal and temporal RNFL thickness between group A1 and group B was tested by independent sample t-test,P ＞0.05,there was no statistical significance difference. Conclusions Frequency-domain OCT detected that the average of RNFL thickness become thinning with the progression of disease in the primary glaucoma patients,have negative correlation with vision MD,it is able to objectively reflect the degree of glaucomatous optic nerve damage.Frequency-domain OCT can show significantly decreased superior and inferior RNFL thickness of the early period primary glaucoma,which shows good ability in distinguishing normal from early period primary glaucomatous eyes. Key words: Optical coherence tomography (OCT); Retinal nerve fiber layer (RNFL); Mean defect (MD); Early diagnosis primary glaucoma