Abstract
Purpose: :
To investigate the relationship between RNFL thickness measurements and disc morphology in corresponding eyes obtained with laser-scanning-tomography (LST) and spectral-domain-OCT (sd) in ocular hypertensives (OHT) and preperimetric glaucomas (pPOAG).
Methods: :
The study included 586 eyes of 295 patients and controls. 115 controls (N), 149 OHT, 132 pPOAG and 174 advanced glaucoma (POAG) patients were recruited from the Erlangen Glaucoma Registry.Methods: Controls and patients underwent a standard ophthalmic examination including slit-lamp inspection, funduscopy, gonioscopy, perimetry and papillometry. In addition, a 24-hour intraocular pressure phasing (applanation tonometry) was performed in all patients. Optic disk evaluations were based on 15° color photographs and disc appearance (rim notching, vertical elongation of cup, RNFL loss) determined the diagnostic groups. The participants were scanned with the HRT I, II , III device and a commercially available sd-OCT (Spectralis HRA+OCT; both Heidelberg Engineering, Germany). 25 consecutive circular B-scans (3.4 mm diameter, 768 A-scans) centered at the optic disc were automatically averaged. HRT III’s rim area and volume (ra/rv), retinal thickness (r/t) and the GPS score were chosen to describe the 3-D disc morphology. Parametric and non-parametric tests were applied as appropriate for comparison between groups.
Results: :
There was no significant difference in disc area between the four diagnostic groups (N 2.3 ± 0.7mm², OHT 2.3 ± 0.5mm², pPOAG 2.5 ± 0.6mm², POAG 2.4 ± 0.5mm²). Mean RFNL thickness with sd-OCT was in N 96.2±8.7µm, OHT 92.9±11.6µm (p=0.007), pPOAG 81.6±12.9µm (p=0.0001) and in POAG 63.56±14.5µm (p<0.0001). There was no significant difference for HRT’s ra, rv, rt or gps-classification between N (1.5±0.3mm², 0.4±0.2mm³, 0.3±0.07mm, 0.4±0.3) and OHT (1.5±0.4mm², 0.4±0.2mm³, 0.3±0.06mm, 0.4±0.3). PPOAG discs showed significantly different values (1.4±0.4mm² (p=0.05); 0.3±0.2mm³, 0.2±0.07mm, 0.6±0.3 (p<0.0001). Mean RNFL loss of -16% in pPOAG was correlated to a -7% loss of ra and -25% of rv respectively. OHT discs with a healthy appearance showed a mean RNFL loss of 4%.
Conclusions: :
OHT eyes tend to show a RNFL loss, although disc appearance and stereometric parameters of the disc seem to be unchanged to normals. Glaucoma discs without perimetric defects already show a significant loss of RNFL and rim volume in correlation to disc appearance on photographs. These findings may support early glaucoma detection.
Clinical Trial: :
www.clinicaltrials.gov NCT00494923
Keywords: optic disc • nerve fiber layer • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)