Reference Database of Inner Retinal Layer Thickness and Thickness Asymmetry in Healthy Thai Adults as Measured by the Spectralis Spectral-Domain Optical Coherence Tomography

Abstract

Purpose: To determine a reference database of the thickness and intraocular thickness asymmetry of total retina, retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), and inner plexiform layer (IPL) in healthy Thai subjects measured by the Spectralis spectral-domain optical coherence tomography Methods: This cross-sectional study recruited the healthy subjects age ≥18 years, having spherical refraction within ±6 diopters and cylindrical refraction ±3 diopters, from a hospital’s personnel and the people accompanying patients visiting the ophthalmology department. If the eligibility criteria were met for both eyes, only 1 eye of each subject was randomly selected for an analysis. Macular images were obtained using posterior pole thickness scan protocol over a 24x24 degree area at the center of the fovea. The automated retinal thickness segmentation values of total retina and three inner retinal layers were calculated for the mean and the mean intraocular thickness difference between superior and inferior retinal hemispheres. The influence of age, gender, and axial length on thickness and thickness asymmetry of individualized retinal layer were evaluated. Results: Two hundred and fifty-two subjects were included in study with a mean (SD) age of 46.7 (15.8) years and 120 (47.6%) were males. According to the Early Treatment Diabetic Retinopathy Study map, the inner ring area was the thickest location of the total retina (range; 326.0 to 341.5 µm), ganglion cell layer (range; 47.7 to 52.7 µm), and inner plexiform layer (range; 39.9 to 42.1 µm); whereas the thickest location of RNFL was at the outer ring area (range; 18.8 to 47.5 µm). For posterior pole intraocular thickness asymmetry, the greatest mean ± SD difference was observed for total retina (9.0 ± 2.2 µm), followed by RNFL (9.9 ± 3.2 µm), and GCL (2.7 ± 0.6 µm) and the lowest mean difference was noted for IPL (2.4 ± 0.5 µm). The thickness and thickness asymmetry of each retinal layer were variably influenced by age, gender, and axial length; however, these factors had a minimal influence on the thickness asymmetry maps of GCL and RNFL. Conclusion: The reference database of the macular thickness and thickness asymmetry from this study would be beneficial in determining physiologic variations of the OCT parameters in the healthy Thai population.

Evaluation of Retinal Nerve Fiber Layer and Macular Ganglion Cell Layer Thickness in Relation to Optic Disc Size

“…Similar to our study, Invernizzi et al investigated retinal layer thickness in 200 Caucasian patients [ 32 ]. Studies that investigated patients of Asian descent [ 40 , 41 , 42 ] also report absolute values for mGCLT, which are comparable to the median values presented here. While some of these studies have analyzed correlations between systemic parameters, such as gender and age, and thickness of different retinal layers, they do not report on the correlation between retinal layer thickness and optic disc size.…”

Normative Database of the Superior–Inferior Thickness Asymmetry for All Inner and Outer Macular Layers of Adults for the Posterior Pole Algorithm of the Spectralis SD-OCT

“…Research works into the presence of intraocular physiological macular thickness asymmetry are limited [17][18][19][20][21]. According to previous studies [17][18][19][20][21], the results of the present study showed that the thickness asymmetries between the superior and inferior hemispheres of the macula are present in healthy eyes.…”

“…Research works into the presence of intraocular physiological macular thickness asymmetry are limited [17][18][19][20][21]. According to previous studies [17][18][19][20][21], the results of the present study showed that the thickness asymmetries between the superior and inferior hemispheres of the macula are present in healthy eyes. This finding highlights the need to develop a normative database that allows improvements to be made to the interpretation of tomography images and to identify incipient pathological asymmetries of macular thicknesses secondary to glaucoma [8] or to other retinal or neuropsychiatric diseases [1][2][3][4][5][6].…”

“…We found larger significant intraocular thickness asymmetries on RNFL and ONL, while the RPE displayed a minimal significant thickness asymmetry between hemispheres. Other authors [21] also indicate more intraocular variations in RNFL thickness than on GCL and IPL when analyzing the physiological intraocular thickness asymmetries of the inner retinal layers. Conversely to all these findings, a previous study [17] did not show any significant asymmetries thickness on GCL, likely because these authors analyzed grouped cells instead of individual ones.…”

“…Therefore, the analysis of the thickness asymmetry for each couple of corresponding cells of the different macular layers could constitute a more sensitive test than those that analyze sectors, like the peripapillary retinal nerve layer thickness analysis or the macular ganglion cell layer analysis [15]. Furthermore, a previous study [21] demonstrated that age, gender and axial length have less impact on the intraocular retinal thickness asymmetry than on the quantitative retinal thickness values.…”