[Measuring nerve fiber thickness with laser scanning polarimetry in aging]

In glaucoma, visual field defects are a late sign of retinal nerve fiber layer damage. Scanning laser polarimetry directly quantifies nerve fiber layer thickness (NFLT) and may allow early detection of defects and progression during follow-up.

The NFLT of 54 healthy eyes of 54 subjects (age range from 14 to 83 years) was measured with a scanning laser polarimeter (Nerve Fiber Analyzer II). Measurements were performed along an ellipse 1.75 disc diameters away from the disc margin. For each subject an average image was calculated from three measurements. The ellipse was divided into four sectors by the internal software. All measurements were performed by the same examiner. All examined eyes had a normal ophthalmological examination, normal eye pressure and a normal computerized perimetry.

The mean NFLT was thicker in the superior (91.3 microns +/- 16.7 microns) and inferior sector (90.8 microns +/- 15.6 microns) as compared to the temporal (53.7 microns +/- 15.4 microns) and nasal sector (60.0 microns +/- 14.8 microns). There was an inverse linear correlation between age and NFLT (Pearson's correlation-coefficient r = -0.30, p < 0.025). On the average, the mean NFLT decreased by 2.5 microns for each decade of age. The interindividual variation of the NFLT (mean standard deviation (s) = 16.1 microns) was, even after correction for age, much larger than the intraindividual variation (s = 6.6 microns).

In normal subjects the NFLT decreases with age. The interindividual NFLT variation is, even after correction for age, much larger than the intraindividual. Therefore, scanning laser polarymetry might be especially useful for follow-up of NFLT.