Choroidal Thickness: A Biomarker for Monitoring Myopia Intervention Effectiveness

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March 16, 2026

By John Nguyen, BOptom

How quickly can we tell if a myopia treatment is working? For practitioners relying on refractive changes alone, the answer may be a year or more. Even those measuring axial length face a familiar challenge: a 0.05mm increase sits within measurement variability and normal physiological growth, making it difficult to confidently change course. For the high risk child, the rapid progressor with early onset myopia and strong family history, that uncertainty costs valuable time. What if we had a faster signal, one that could tell us within weeks whether the eye is responding to treatment, using the OCT sitting in your practice?

Emerging evidence suggests the choroid may be that signal. This vascular, metabolically active tissue sits between the retina and sclera and responds to visual and pharmacological inputs far more rapidly than axial length.¹ It is not a new discovery, but it remains underutilized in clinical practice.

This article examines what we know and how clinicians can apply choroidal thickness (CT) monitoring thoughtfully.

Why the Choroid Matters

The choroid is the eye’s most vascularized tissue, supplying oxygen and nutrients to the outer retina and playing a critical role in emmetropization. Unlike axial length, which reflects cumulative growth over time, CT responds dynamically to visual signals, often within hours to days. This makes it a potentially valuable early indicator of whether an eye is in a pro-elongation or stabilizing state.

Research has consistently demonstrated that choroidal thickening is associated with signals that inhibit eye growth, while thinning is linked to myopia progression. In animal models, optical defocus that slows eye growth also thickens the choroid, whereas signals promoting elongation cause choroidal thinning. This bidirectional response suggests the choroid acts as an intermediary between visual input and scleral remodeling.

For clinicians, this offers a practical advantage: if we can detect choroidal changes early, we may be able to assess treatment response before waiting months to observe axial length trends.

Choroidal Thickness as a Risk Stratification Tool

Why does baseline CT matter? Longitudinal studies have shown that a thin choroid is a better predictor of myopic maculopathy progression than axial length or refraction alone.² Even in the absence of existing macular changes, children with thinner choroids appear more likely to develop vision threatening complications as they age. This makes CT a potentially valuable addition to risk assessment at baseline.

The challenge has been interpreting what counts as “thin.” CT varies with age, sex, refraction and axial length, so comparing a measurement to a simple age-based reference does not work. Published studies report mean CT values for various populations, but this data has not been translated into usable clinical tools.³ This lack of accessible reference data has been a barrier to clinicians adopting CT for risk stratification.

Flitcroft, Lingham and colleagues (2025) addressed this by pooling over 2,000 measurements to develop a nomogram that calculates expected CT based on these factors. The nomogram was derived from populations predominantly of European descent  in Australia and Ireland (76% white, 13% Asian), so it may need adjustments for other ethnic groups. The key concept is CT mismatch: measured CT minus expected CT. A negative mismatch means the choroid is thinner than expected, suggesting higher risk. Even after accounting for age, sex, refraction and axial length, about 44% of children have CT more than 50µm different from expected, reflecting natural anatomical variation between individuals.

To use this approach, clinicians need both axial length and access to the nomogram as the normative data is built into the model. 

Without axial length, baseline risk stratification is not practical. CT is heavily influenced by axial length, as longer eyes have thinner choroids, so the nomogram requires AL to calculate what CT should be for a given child. Without this, it is not possible to determine whether a measured CT is thinner than expected. However, CT remains valuable for trend monitoring, which does not require population reference data or axial length. The clinician is simply comparing a child’s own baseline CT to follow up measurements to assess treatment response.

Monitoring Treatment Response

Beyond risk stratification, CT becomes particularly valuable as an early indicator of treatment response. The evidence for CT as a prognostic marker is clear.

• For OrthoK, a prospective study found CT increases after short-term wear, with early choroidal thickening at one month associated with less axial elongation over the following year.⁴ For soft multifocal contact lenses, the BLINK study found that choroidal thickening after two weeks of wear was associated with less axial elongation over three years.⁵ 
• For spectacle-based optical interventions, a two year randomized trial of DIMS lenses showed significant choroidal thickening from one week of wear, sustained over two years, with CT changes at three months predicting axial length changes at 12 months.⁶
• For RLRL therapy, a secondary analysis of a multicenter RCT found that CT changes at three months predicted 12 month myopia control efficacy with reasonable accuracy.⁷
• For atropine, the prognostic data comes from high-concentration studies. Research on 1% atropine found that short-term CT increase was negatively associated with long-term axial elongation: children who showed more choroidal thickening had less eye growth.⁸ For lower concentrations, we know that 0.01% atropine causes measurable choroidal thickening within one month,⁹ but whether early CT changes are associated with treatment response at these doses has not been established.

What might this mean in practice?

If a clinician initiates a myopia control treatment and observes choroidal thickening at early follow up, this could indicate a positive biological response, even before axial length trends become clear. Conversely, persistent thinning or failure to thicken from the outset might warrant closer attention. The goal is not to detect precise, micron-level changes, but to identify direction—thickening or thinning—interpreted alongside baseline risk factors and family history.

Practical Measurement Considerations

CT can be measured on most modern OCT devices, though technique and consistency matter more than absolute precision.

Manual vs Automated Measurement

Manual caliper measurement of subfoveal CT works on any OCT with adequate choroidal visualization. The measurement is taken from the outer border of the RPE to the choroid scleral interface. Swept source OCTs with enhanced depth imaging provide better choroidal visualization.

AI-powered tools already exist that can automate choroidal segmentation, map thickness across multiple points and track changes over time. These tools work with common OCT platforms and may make CT monitoring more practical in busy clinical settings.

Consistency is Key

Given natural variability, the trend matters more than any single measurement. Standardizing measurement time (CT shows diurnal variation, being thickest in the morning), measurement location (subfoveal is standard) and technique will improve the reliability of longitudinal comparisons. CT measurement, particularly on older machines, is limited by image resolution and manual measurement introduces operator bias. We understand these limitations, but they should not lead us to discount CT as a valuable clinical tool. Used thoughtfully, it gives us earlier insight into biological changes before they manifest in axial length or refraction.

Diurnal Variation and Other Variables

CT fluctuates throughout the day, typically by 20 to 30µm. The choroid is thickest in the morning and thinner in the afternoon. Other factors in children that can affect CT include hydration status, recent prolonged near work and time spent outdoors prior to measurement. A child who comes in after school having spent an hour on their tablet will have a different CT reading than one measured at 8am on a weekend. This is where the art of CT interpretation comes in. For serial monitoring, note the time of day and aim to measure under similar conditions where possible. When making any clinical judgement calls based on CT trends, frame them around the overall context rather than relying on a single measurement in isolation. A one-off thin reading after a long day of near work is different from a consistent thinning trend across multiple visits.

Clinical Integration

For practitioners looking to incorporate CT into myopia management:

1. Establish baseline CT at the initial myopia assessment, alongside axial length and refraction where available.
2. Identify patients with thin choroids using a nomogram or calculator to find those who may benefit from earlier or more aggressive intervention.
3. Monitor CT at follow up visits to assess early treatment response, as choroidal thickening may precede axial length stabilization.
4. Use CT to support parent communication because visual representations of choroidal changes can help families understand treatment effects.

Key Takeaways

• Evidence supports two specific clinical applications for CT: risk stratification and early treatment response monitoring. Use it alongside axial length and refraction.
• Children with CT substantially thinner than expected for their age, sex, refraction and axial length may represent a higher-risk group. Even after accounting for these factors, about 44% of children have CT more than 50µm different from expected, highlighting the value of comparing measured CT to an individualized expected value rather than a population average.
• CT responds to treatment faster than axial length, offering higher temporal resolution as a biological marker. By understanding its relevance, clinicians can potentially make treatment decisions within a one- to three-month window instead of waiting six to 12 months for axial length trends to become clear.
• For optical myopia control interventions, early CT changes in the first one to three months have shown prognostic value for longer-term treatment efficacy. For low-dose atropine, prognostic data exists for high concentrations but not for clinically-used doses.
• When monitoring treatment response, the trend matters more than any single measurement, and direction (thickening or thinning) matters more than precise micron changes. Always interpret within the overall clinical context.
• Consistency in measurement technique and timing is essential for meaningful longitudinal comparisons.

 

John Nguyen, BOptom, is a Sydney based optometrist and founder of Luxi Health. A free choroidal thickness calculator implementing the Flitcroft and Lingham nomogram is available at clinical.luxihealth.com.au/ct-calculator.

 

References

1. Nickla DL, Wallman J. The multifunctional choroid. Prog Retin Eye Res. 2010;29(2):144-168.
2. Fang Y, Du R, Nagaoka N, et al. Choroidal thickness predicts progression of myopic maculopathy in high myopes: a 2-year longitudinal study. Br J Ophthalmol. 2021;105:1744-1750.
3. Flitcroft I, Lingham G, Kerin E, et al. Clinical nomogram for determining expected choroidal thickness in children with myopia. Am J Ophthalmol. 2025;278:346-355.
4. Li Z, Cui D, Hu Y, et al. Choroidal thickness and axial length changes in myopic children treated with orthokeratology. Cont Lens Anterior Eye. 2017;40(6):417-423.
5. Walker MK, Berntsen DA, Robich ML, et al. Three-year change in subfoveal choroidal thickness and area with multifocal contact lens wear in the Bifocal Lenses in Nearsighted Kids (BLINK) study. Invest Ophthalmol Vis Sci. 2025;66(5):5.
6. Chun RKM, Zhang H, Liu Z, et al. Defocus incorporated multiple segments (DIMS) spectacle lenses increase the choroidal thickness: a two-year randomized clinical trial. Eye Vis (Lond). 2023;10(1):39.
7. Xiong R, Zhu Z, Jiang Y, et al. Longitudinal changes and predictive value of choroidal thickness for myopia control after repeated low-level red-light therapy. Ophthalmology. 2023;130(3):286-296.
8. Ye L, Shi Y, Yin Y, et al. Effects of atropine treatment on choroidal thickness in myopic children. Invest Ophthalmol Vis Sci. 2020;61(14):15.
9. Yam JC, Jiang Y, Tang SM, et al. Low-concentration atropine for myopia progression (LAMP) study. Ophthalmology. 2019;126(1):113-124.