Evaluation of the effect of aging on the retinal nerve fiber layer thickness using scanning laser polarimetry

The scanning laser polarimeter is a new diagnostic scanning laser instrument that uses the polarizing properties of the retinal nerve fiber layer to measure its thickness in vivo. We first ascertained the measurement reproducibility of this instrument and then evaluated the effects of aging on the retinal nerve fiber layer.

We performed three consecutive measurements in six glaucomatous and six age-matched normal healthy eyes to evaluate the instrumentation. The mean thickness of the peripapillary retinal nerve fiber layer within the rings 1. 0, 1. 5, and 2. 0 disk diameters from the center of the optic nerve head was calculated. We then evaluated aging effects on the retinal nerve fiber layer thickness in 75 eyes of 75 normal volunteers 20-66 years of age.

The mean coefficients of variation of the measurements of the 1. 0, 1. 5, and 2. 0 disk diameters were 3. 64, 3. 59, and 4. 10, respectively, for the normal subjects, and 10. 20, 5. 65, 6. 08, respectively, for the patients with glaucoma. We found a significant, inverse linear correlation between age and the retinal nerve fiber layer thickness when measured along the 1. 5 disk diameter ring (R = 0. 16, p = 0. 0004). Significant decreases with aging also were observed in the nasal (R = 0. 17, p = 0. 0003) and inferior (R = 0. 09, p = 0. 0091) retinal nerve fiber layer thickness.

Our results indicate that scanning laser polarimetry is sufficiently reliable to assess the retinal nerve fiber layer thickness in vivo. The retinal nerve fiber layer thickness decreases with age in the normal healthy eye.