AIMS

To assess peripapillary retinal nerve fibre layer (RNFL) thickness distribution in a group of non-glaucomatous Caucasian subjects with a high degree of myopia and to evaluate the relationship between RNFL thickness, both global and sectoral, and other variables including axial length and optic disc size.

METHOD

31 eyes of 31 healthy Caucasian subjects with spherical equivalent >or=-6 dioptres (D) were recruited from a community optometric practice. RNFL thickness was measured using the Stratus optical coherence tomography (OCT) Fast RNFL 3.4 mm scan protocol. Optic disc area was measured using the Heidelberg Retinal Tomograph II and axial length using the IOL Master. Associations between RNFL measurements and axial length, spherical equivalent and optic disc area were evaluated by linear regression analysis.

RESULTS

The sample had a mean age of 48.1 years, mean spherical equivalent of -7.7 D, and mean axial length of 26.5 mm. The mean (SD) RNFL thickness was 81.4 (13.7) microm. In comparison with the Status OCT normative database, the distribution of RNFL thickness was substantially lower in the study group. The greatest disparity was around 7 clock hours centred on the nasal meridian in which 26/31 (83.9%) had one or more clock hours in which RNFL thickness was below normal at the 5% probability level in comparison with the Stratus normative database. No statistically significant associations between mean RNFL thickness and age (p = 0.12), gender (p = 0.76), spherical equivalent (p = 0.80), cup:disc area ratio (p = 0.88), optic disc area (p = 0.14) or axial length (p = 0.18) were identified in this group. However, RNFL thickness from vertical quadrants and in particular the superior sector correlated strongly with axial length, age and optic disc area.

CONCLUSIONS

The Stratus OCT normative database may be misleading in highly myopic eyes from Caucasians resulting in a substantial proportion of false positive errors. Particular caution is needed when the RNFL appears to be below the normative database normal limit at the upper or lower poles or on the nasal side of the disc. Stratified normal databases are required for accurate diagnosis of conditions resulting in nerve fibre loss such as chronic glaucoma.