Large cup-to-disc ratios in myopic children and OCT findings

Paper title: Optical coherence tomography characteristics in myopic children with large cup-disc ratios

Authors: Mark Kit Lim (1), Rachel Shujuan Chong (2,3), Muna Al Ajmi (4), Hla Myint Htoon (3), Audrey Chia (5,6)

1. MOH Holdings, Singapore, Singapore.
2. Singapore National Eye Centre, Singapore, Singapore.
3. Singapore Eye Research Institute, Singapore, Singapore.
4. Medical City for Military and Security Services, Muscat, Oman.
5. Singapore National Eye Centre, Singapore, Singapore.
6. Singapore Eye Research Institute, Singapore, Singapore. 

Date: April 2025

References: Lim MK, Chong RS, Al Ajmi M, Htoon HM, Chia A. Optical coherence tomography characteristics in myopic children with large cup-disc ratios. Graefes Arch Clin Exp Ophthalmol. 2026 Apr 25

[Link to abstract]

In myopic children, distinguishing physiologically large optic cups from early glaucomatous changes presents a clinical challenge. Optic disc tilting, peripapillary atrophy, and axial length-related magnification effects complicate both clinical cup-to-disc ratio (CDR) assessment and optical coherence tomography (OCT) interpretation of retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) thickness.

This prospective cohort study investigated OCT characteristics of large CDRs in myopic children aged 7-16 years. They were grouped by OCT-assessed vertical CDR into three groups: 0.00-0.39, 0.40-0.59, and 0.60-0.90.

Annual ocular examinations included measuring intraocular pressure, cycloplegic refraction, axial length, fundus photographs, and OCT imaging with magnification correction. The study examined associations between CDR and ocular parameters, RNFL thickness, and GCC thickness.

Key findings were as follows

• Large vertical CDR of ≥0.60 occurred in 18.2% of myopic children and associated with non-Chinese ethnicity, larger optic disc area, and flatter corneas
• Among eyes with ≥ 0.60 CDR, 76.8% had disc area exceeding 2.0mm², compared to 46.2% in the 0.40-0.59 group and 32.7% in the less than 0.40 group
• RNFL and GCC thickness remained stable across all CDR groups over two years with no progressive thinning
• OCT-assessed vertical CDR exceeded clinical assessment by more than 0.1 in 20.8% of eyes, particularly those with smaller CDRs

These findings suggest that approximately one in five myopic Asian children aged 7-16 years presents with vertical CDR of 0.60 or greater, with higher prevalence in non-Chinese populations. Practitioners could consider optic disc area measurements when evaluating large CDRs, where three-quarters of children with CDR of 0.60 or greater had disc areas exceeding 2.0mm². The association between larger CDR and flatter corneas may reflect differences in ocular biomechanics, although the clinical relevance of this finding is currently uncertain.

Retinal nerve fibre layer and ganglion cell complex measurements remained stable over 2 years, which provides short-term reassurance when assessing children with larger cup-to-disc ratios..

The study found statistically greater myopic progression in children with larger baseline CDRs, though the authors describe these differences as clinically small, limiting their relevance for clinical decision-making based on CDR alone.

OCT-assessed vertical CDR measurements were higher than clinical estimates in approximately one-fifth of eyes, particularly those with smaller cups. This highlights potential variability between clinical and image-based assessment of optic disc cupping, which may be relevant when interpreting images in clinical practice. RNFL patterns differed in larger CDRs, although average RNFL thickness differences across CDR groups were minimal, limiting the diagnostic application of these patterns.

The two-year follow-up period, while valuable, may be insufficient to reliably differentiate physiological from early glaucomatous cupping in all children with large CDRs. The study excluded children with overt glaucomatous changes, and some with larger CDRs may harbor undetected glaucoma that would only become apparent with longer follow-up. Stability over two years provides reassurance but does not exclude future glaucoma risk.

No visual field testing was performed, which limits understanding of whether functional deficits were present, alongside structural findings, and of the relationship between structural change and functional vision in myopic children with larger CDR ratios.

If OCT and clinical CDR measurements disagree, there is no clear evidence as to which method is more reliable. The study demonstrates that OCT tends to yield larger values, particularly in smaller cups, but does not establish which method provides more accurate or clinically useful.

The association between larger CDRs and flatter corneas suggests possible biomechanical factors linking corneal curvature, optic disc characteristics, and tissue "stretchiness," but the underlying mechanisms and clinical relevance remain speculative. Understanding these relationships could inform risk stratification but requires further investigation.

Purpose: This study aims to evaluate the association of optic cup-to-disc ratio (CDR) with magnification-adjusted optical coherence tomography (OCT) peripapillary retinal nerve fibre layer (RNFL) and macula ganglion cell complex (GCC) thickness in Asian myopic children, to help clinicians better evaluate glaucoma risk in myopic children with increased CDR.

Methods: In a prospective clinical cohort study, myopic children aged 7–16 years were assessed annually over 2 years, excluding children with overt glaucomatous changes. Right eye data including visual acuity, intraocular pressure, cycloplegic autorefraction, axial length, fundus photographs and magnification-adjusted OCT of the optic disc and macula were collected. Children were divided into three OCT-assessed vertical CDR (vCDR) subgroups (0.00-0.39, 0.40–0.59, and 0.60–0.90) for analyses.

Results: Among 901 eyes, 162 (18.2%) eyes had a vCDR ≥ 0.6. Multivariate analysis found that larger vCDR was associated with non-Chinese race, younger age, flatter corneas, decreased optic disc tilt, larger disc area with smaller disc rim, increased AL, sectoral RNFL thinning with nasal RNFL thickening, and reduced use of combined atropine-optical treatment. In 452 eyes with two-year follow-up data of sufficient quality, no change in OCT RNFL and GCC were noted over time. Interestingly, increased vCDR was associated with greater myopia progression.

Conclusion: In eyes with larger CDR, the presence of flatter corneas, larger optic disc area (e.g. >2mm2), and stable OCT RNFL and GCC thickness over time are reassuring for a non-glaucomatous state. However, given the increased risk of myopia progression, closer myopia monitoring and management may be necessary.

[Link to abstract]