Study Suggests Fovea-Disc Distance Length Factors into Scans for Glaucoma

A recent multicenter cross-sectional study indicated that fovea-disc distance (FDD) can significantly impact macular retinal layer thickness in eyes with and without primary open-angle glaucoma (POAG).

The use of optical coherence tomography (OCT) is well known to be a crucial aspect of diagnosis and monitoring of glaucoma. In fact, OCT has become the imaging tool of choice, given its quick acquisition speed, high resolution, and great reproductibility.2 However, few studies have utilized the tool to analyze the connection between the inner retinal layer thickness and glaucoma incidence.1

“Although measuring the thickness of the inner retinal layer using OCT is crucial for diagnosing and monitoring glaucoma progress, few studies have addressed the association between FDD and inner retinal layer thickness in the macula; these studies have been limited to healthy subjects and have not provided any findings in patients with glaucoma,” wrote Tomomi Higashide, MD, PhD, department of ophthalmology, Kanazawa University Graduate School of Medical Sciences, and colleagues. “Furthermore, previous studies did not consider the magnification effects on OCT scan areas, which can lead to artificial thinning of the measured thickness of macular inner retinal layers.”1

The study was conducted at eight study sites. Five were in Japan and one each in the US, Korea, and China. It was made up of 241 individuals, divided into a “healthy” group of 124 participants and a “POAG” group with 117 participants. There were no significant differences in age between the two groups; however, FDD was substantially longer in POAG eyes than in normal eyes. (4.95 +/- 0.39 mm vs 4.78 +/- 0.38 mm, P =.0005).1

Three OCT scans were conducted on each participant; investigators took the scan with the best quality and measured the thickness of three retinal layers – macular retinal nerve fiber layer (mRNFL), GCIPL, and total retina. The relationship between FDD and each of the three layers was examined with multivariate models for both normal and POAG groups, adjusting for all possible confounders, including age, sex, corneal radius, disc area, ovality index, and so on.1

After analysis, Higashide and colleagues indicated that a longer FDD was significantly associated with thinner mRNFL (coefficients, -3.14; 95% CI, -4.75 to -1.53; P =.0001) and thinner GCIPL (coefficients, -4.26; 95% CI, -6.85 to -1.67; P =.0013) in the POAG group. The GCIPL in eyes with POAG were thinner by 4.26 μm. The difference in the coefficient of FDD between the two cohorts was significant for GCIPL thickness (P =.005), but not for mRNFL or outer retina (OR) (P =.70 and .53 respectively).1

Higashide and colleagues indicated that these results proved a connection between FDD’s effects on macular retinal layer thickness in eyes with and without POAG. Longer FDD was associated with thinner mRNFL in normal eyes, while longer FDD was associated with thinner GCIPL in POAG eyes. The relationship between FDD and GCIPL was substantially different between normal and POAG groups. Therefore, the team indicates that a connection between thinner GCIPL and longer FDD may be a specific finding related to glaucoma.1

“Given that GCIPL thickness is a representative OCT parameter for glaucoma diagnosis, further investigation is needed to determine if adjusting with FDD improves the diagnostic accuracy of magnification-corrected GCIPL thickness,” Higashide and colleagues wrote. “FDD should be considered a confounding factor to be adjusted for OCT measurements of macular retinal layer thickness, especially for GCIPL in eyes with glaucoma.”1

References

1. Higashide T, Udagawa S, Araie M, et al. Relationships between distance from the fovea to the disc and macular retinal layer thickness differ between normal and glaucomatous eyes. Sci Rep. 2025;15(1):11554. Published 2025 Apr 4. doi:10.1038/s41598-025-96741-w

2. Song WK, Lee SC, Lee ES, Kim CY, Kim SS. Macular thickness variations with sex, age, and axial length in healthy subjects: a spectral domain-optical coherence tomography study. Invest Ophthalmol Vis Sci. 2010;51(8):3913-3918. doi:10.1167/iovs.09-4189