Evaluation of Average Retinal Nerve Fiber Layer Measurement in Eyes with Refractive Errors

Optical coherence tomography (OCT) measurements of peripapillary retinal nerve fiber layer (pRNFL) play an important role in the diagnosis of glaucoma and optic atrophy. However, the interpretation of these measurements in patients with refractive errors, especially of a high degree, presents great difficulties. Optical coherence tomography instruments from most manufacturers do not take into account the effect of refractive errors, especially of a high degree, on quantitative measurements of pRNFL.

The aim of this study was to develop a simple and easy method for evaluation of average pRNFL in eyes with refractive errors.

Average pRNFL was measured by Cirrus HD-OCT (Carl Zeiss Meditec Inc., Dublin, CA) in 183 healthy White subjects (183 eyes) older than 40 years, with an axial length of the eye from 22.5 to 24.5 mm and spherical equivalent of refraction from -1.63 to 2.0 D.

For an average pRNFL, normative database of eyes with refraction close to emmetropia was constructed. The calculated first and fifth percentiles for age groups 41 to 50, 51 to 60, 61 to 70, and 71 to 85 years were 81 and 83, 79 and 81, 78 and 80, and 76 and 79 μm, respectively. Littmann-Bennett formula was modified to calculate a table containing first and fifth percentiles for eyes with axial lengths of 19 to 30 mm in the same age groups.

For the correct interpretation of the measurements of pRNFL in patients with refractive errors, an original table was proposed, which provides a quick assessment of the results obtained on the Cirrus HD-OCT device. The proposed new formulas make it easy to calculate a similar table for any optical coherence tomography device using existing databases or after collecting a normative database of eyes with refraction close to emmetropia.