An Analysis of Normal Variations in Retinal Nerve Fiber Layer Thickness Profiles Measured With Optical Coherence Tomography

Abstract

Purpose-To assess the normal variations in retinal nerve fiber layer (RNFL) thickness measured with optical coherence tomography (OCT).Subjects and Methods-Both eyes of 48 individuals (age 56.4±9.5 y) with normal vision and refractive errors between ±6.0D were tested with the fast RNFL scan protocol of the OCT3 (Zeiss Meditech). Their 256-point RNFL profiles were exported for analysis. The location and peak amplitude of the maxima of the RNFL profiles were measured. Intersubject and interocular variations were assessed with a coefficient of determination, R 2 . An R 2 of 1.0 indicated that the average profile from all 48 individuals (or of the 2 eyes) accounted for 100% of the variation of an individual eye's profile.Results-The R 2 for the interocular comparison was good, with averages of 0.91±0.07 (right eye) and 0.92±0.05 (left eye). The R 2 for the comparison of the individual's profile to the mean group profile was only 0.61±0.29 (right eye) and 0.65±0.24 (left eye), with 27% of the R 2 values below 0.5. Even after normalizing each individual's profile by its mean, R 2 was only 0.75±0.16 (0.75±0.16) for the right (left) eye. The location of the peaks for the right (left) eye ranged over 91 degrees (88 degrees) for the superior peak and over 64 degrees (66 degrees) for the inferior peak. The range of peak amplitudes for the right (left) eye spanned a factor of 1.7 (1.8) and 2.0 (1.7) for the superior and inferior peaks, respectively.Conclusions-There was a wide variation in the amplitude and shape of the individual RNFL profiles. However, the RNFL profiles of the 2 eyes of an individual were extremely similar. Adding an interocular comparison with OCT RNFL tests should help identify some false positives.

Position of retinal blood vessels correlates with retinal nerve fibre layer thickness profiles as measured with GDx VCC and ECC

“…The RNFL thickness profiles measured with OCT vary across individuals, even when refractive error and scan quality are taken into consideration 6. This variation in RNFL profiles is large, relative to that found owing to measurement error,14–16 age17 18 or the size of the optic disc 17 19.…”

“…Considerable interindividual variability in RNFL thickness values among normal subjects as measured with optical coherence tomography (OCT),6 and some overlap in thickness values between normal subjects and patients with glaucoma have been reported in several studies conducted by scanning laser polarimetry (SLP) 2–4 7 8…”

Variance Reduction in a Dataset of Normal Macular Ganglion Cell Plus Inner Plexiform Layer Thickness Maps with Application to Glaucoma Diagnosis

“…In addition, the bundles can gather into inferior or superior bifurcations to produce local variations that are particularly evident on peripapillary thickness profiles. 9 Neither the ONH nor RNFL can be described by a simple spatial template.…”

Relationship between visual field changes and optical coherence tomography measurements in advanced open-angle glaucoma

“…The peripapillary and macular areas corresponds to very specifi c areas of the perimetric test. [12][13][14][15][16][17][18][19] A discrepancy has been found by some researchers between perimetric losses and OCT changes as glaucoma progresses. The two approaches to assess the glaucoma process do not run parallel.…”

“…4,10,11 However, many factors affect the relationship and limit direct comparison of the sensitivity of SAP (refl ecting the functional losses) and OCT measurements (RNFL thickness and the inner macula thickness) (refl ecting structural changes). Firstly, the computed perimeter and optical coherence tomography have different scales of measurement: SAP measures visual sensitivity in log units (range 4 log units) 12 , while OCT measures the thickness of RNFL and macula inner layers in microns (in the linear range from 25 to 200 microns in normal subjects [13][14][15] ). Secondly, when SAP macular threshold is compared with local defects in RNFL / inner retina an adaptation is required to the so-called topographic map.…”