EFFECT OF OPTIC DISK-FOVEA DISTANCE ON MEASUREMENTS OF INDIVIDUAL MACULAR INTRARETINAL LAYERS IN NORMAL SUBJECTS

Relationships between distance from the fovea to the disc and macular retinal layer thickness differ between normal and glaucomatous eyes

A multicenter cross-sectional study was conducted to investigate the magnification-corrected association between fovea-disc distance (FDD) and optical coherence tomography (OCT)-measured macular retinal layer thickness in eyes with and without primary open-angle glaucoma (POAG). A 12.0 × 9.0-mm-wide swept-source OCT scan, which includes both the macula and optic disc, was performed in 190 eyes from 124 healthy subjects (normal group) and 149 eyes from 117 POAG patients (POAG group). The FDD and thickness of the macular retinal nerve fiber layer (mRNFL), ganglion cell inner plexiform layer (GCIPL), and outer retina (OR, total retina minus (mRNFL plus GCIPL)) were measured and corrected for magnification effects. The mixed-effects models, accounting for potential confounding factors, revealed two significant associations between a longer FDD and retinal layer thickness: thinner mRNFL in the normal group (coefficients, -3.14, 95% confidence intervals (CI), -4.75 to -1.53; p = 0.0001) and thinner GCIPL in the POAG group (coefficients, -4.26; 95% CI, -6.85 to -1.67; p = 0.0013). The association between FDD and macular retinal layer thickness varies by retinal layer and the presence of POAG. FDD can significantly affect OCT-determined macular retinal layer thickness, especially GCIPL in POAG eyes and mRNFL in normal eyes.

Macular outer nuclear layer, ellipsoid zone and outer photoreceptor segment band thickness, axial length and other determinants

The study aims to assess the thickness of the retinal outer nuclear layer (ONL), ellipsoid zone (EZ) and photoreceptor outer segment (POS) band in various macular regions and its associations with axial length and other parameters. Participants of the Beijing Eye Study 2011 underwent a series of examinations including spectral-domain optical coherence tomography of the macula. The current study included 2213 participants without retinal or optic nerve diseases (age: 61.7 ± 8.4 years; range 50-93 years); axial length: 23.15 ± 0.95 mm; range 18.96-29.15 mm). The ONL (fovea: 98.9 ± 8.8 µm), EZ (fovea: 24.1 ± 0.5 µm) and POS band (fovea: 24.3 ± 3.5 µm) were the thickest (P < 0.001) in the fovea (defined as the thinnest central point), followed by the temporal inner, nasal inner, inferior inner, superior inner, inferior outer, temporal outer, nasal outer, and superior outer region. In multivariable analysis, a thicker retinal ONL was associated (correlation coefficient r: 0.40) with shorter axial length (beta: - 0.14; P < 0.001) and shorter disc-fovea distance (beta: - 0.10; P = 0.001), after adjusting for younger age (beta: - 0.26; P < 0.001), male sex (beta: 0.24; P < 0.001), lower serum cholesterol concentration (beta: - 0.05; P = 0.04), and thicker subfoveal choroidal thickness (beta: 0.08; P < 0.001). The POS thickness increased with shorter axial length (beta: - 0.06; P < 0.001) and shorter optic disc-fovea distance (beta: - 0.05; P = 0.03), after adjusting for younger age (beta: - 0.34; P < 0.001), male sex (beta: 0.15; P < 0.001), and thicker subfoveal choroidal thickness (beta: 0.24; P < 0.001). As a conclusion, the photoreceptor ONL, EZ and POS band vary in thickness between different macular regions and differ in their correlations with axial length, disc-fovea distance, age, sex, and subfoveal choroidal thickness. The ONL thickness decrease with longer axial length and longer disc-fovea distance may point to an axial elongation-associated retinal stretching in the macula.

Retinal nerve fibre layer thickness in association with gamma zone width and disc-fovea distance

PURPOSE

Previous studies have shown that the retinal nerve fibre layer (RNFL) thickness as surrogate of the optic nerve decreases with longer axial length. We explored which explanatory parameters might explain that association.

METHODS

Participants of the population-based Beijing Eye Study 2011 without any retinal or optic nerve disease were selected based on a refractive error-based stratified randomization.

RESULTS

The study included of 632 participants (age: 59.1 ± 7.3 years; axial length: 23.5 ± 1.2 mm; range: 20.88-28.68 mm). Thicker RNFL (mean: 101.0 ± 10.0 μm) was associated (multivariable analysis) with smaller parapapillary gamma zone (defined as Bruch's membrane-free parapapillary region) (standardized regression coefficient beta: -0.13; non-stadardized regression coefficient B: -0.008; 95% confidence interval (CI): -0.014, -0.003; p = 0.005) and shorter disc-fovea distance (beta: -0.15; B: -3.91; 95% CI: -6.60; -1.22; p = 0.004), after adjusting for age (beta: -0.22; B: -030; 95% CI: -0.41, -0.19; p < 0.001), gender (beta: 0.12; B: 2.37; 95% CI 0.77, 3.97; p = 0.004) and larger optic disc area (beta: 0.12; B: 0.12; 95% CI: 2.14; 95% CI: 0.54, 3.73; p = 0.009). RNFL thickness decreased by 8 μm (95% CI: 3, 14) for each mm increase in gamma zone width, and by 3.91 μm (95% CI: 1.22, 6.60) for each mm elongation of the disc-fovea distance. If disc-fovea distance and gamma zone width were replaced by axial length, the latter was correlated with RNFL thickness (beta: -0.37; B: -3.12; 95% CI: -3.88, -2.35; p < 0.001). Longer disc-fovea distance was directly associated with larger gamma zone (beta: 0.50; B: p < 0.001).

CONCLUSIONS

The RNFL thickness decrease with longer axial length is associated with a longer optic disc-fovea distance and larger parapapillary gamma zone. Longer disc-fovea distance and larger gamma zone lead to an elongation and stretching of the retinal nerve fibres, potentially causing a thinning or loss of the nerve fibres. It may explain the occurrence of visual field defects in some non-glaucomatous highly myopic eyes without macular correlates of the perimetric defects.

Factors Associated with Changes in Peripapillary Retinal Nerve Fibre Layer Thickness in Healthy Myopic Eyes

Myopic people face an elevated risk of primary open angle glaucoma. Changes in the fundus in people with high myopia often lead to misdiagnosis of glaucoma, as this condition has many clinical signs in common with myopia, making the diagnosis of glaucoma more challenging. Compared to reduction of the visual field, a decrease in retinal nerve fibre layer (RNFL) thickness occurs earlier in glaucoma, which is widely considered useful for distinguishing between these conditions. With the development of optical coherence tomography (OCT), RNFL thickness can be measured with good reproducibility. According to previous studies, this variable is not only affected by axial length but also related to the patient's age, gender, ethnicity, optic disc area, and retinal blood flow in myopia. Herein, we intend to summarize the factors relevant to the RNFL in myopia to reduce the false-positive rate of glaucoma diagnosis and facilitate early prevention of myopia.

Axial length-related inter-individual variability in the posterior pole morphology of healthy eyes

AIM

To evaluate morphological characteristics of optic nerve head (ONH) and fovea (F) related to axial length (AL) in healthy eyes.

METHODS

This is an observational study. A consecutive series of healthy subjects was enrolled. Demographic and clinical parameters were age, gender, eye, intraocular pressure, spherical equivalent, AL. Tomographic parameters were ONH-F distance, ONH-F angle, horizontal and vertical ONH diameters, retinal nerve fiber layer (RNFL) thickness and foveal profile patterns.

RESULTS

One hundred six eyes (56 patients) were recruited. A correlation between AL and ONH-F distance was demonstrated (p = 0.0342). Horizontal diameter decreased with increasing AL (p = 0.0003), conferring to ONH a more oval shape. A significant decrease in RNFL thickness was correlated with AL, except for temporal quadrant. Two foveal profile patterns were described: concave and straight patterns. Eyes with concave pattern were longer than eyes with straight pattern.

CONCLUSION

Eye elongation affects the morphology of the ONH, the fovea and the distribution of retinal nerve fibers.

Effect of optic disc-fovea distance on the normative classifications of macular inner retinal layers as assessed with OCT in healthy subjects

Purpose

To determine the influence of the optic disc–fovea distance (DFD) on the normative classifications based on thickness measurements of macular inner retinal layers with spectral-domain optical coherence tomography (OCT) in healthy subjects.

Methods

A total of 182 eyes from 182 healthy subjects were included (mean (SD) spherical equivalent −0.8 (1.9) dioptres). We performed macula and optic disc imaging with the Topcon 3D OCT 2000. The thickness of the macular inner retinal layers (macular retinal nerve fibre layer (mRNFL), ganglion cell-inner plexiform layer (GCIPL) and both combined (ganglion cell complex; GCC)) and the corresponding classifications based on the built-in normative database were recorded. The occurrence of an abnormal normative classification (occurrence of any thickness variable below the fifth percentile) was related to the DFD and other factors (axial length/refraction, optic disc area, fovea–disc angle, age, gender, image quality, visual field mean deviation and peripapillary retinal nerve fibre layer thickness), using logistic regression.

Results

The mean (SD) DFD was 4.90 (0.29) mm. A greater DFD was associated with a higher percentage of abnormal normative classification in the OCT parameters describing the thickness of the mRNFL (OR (95%CI) per 0.1 mm increase in DFD: 1.30 (1.13 to 1.50), p<0.001), GCIPL (1.18 (1.02 to 1.38), p=0.023) and GCC measurement (1.29 (1.08 to 1.55), p=0.006).

Conclusions

Eyes with a greater DFD are prone to false-positive classifications in the thickness assessment of the macular inner retinal layers. The thicknesses should always be interpreted in the context of DFD.