Can choroid layer thickness predict future myopia for children?

Paper title: Axial length change and its relationship with baseline choroidal thickness - a five-year longitudinal study in Danish adolescents: the CCC2000 eye study

Authors: Mathias Hvidtfelt Hansen (1,2), Line Kessel (1,2), Xiao Qiang Li (1,2), Anne Mette Skovgaard (3), Michael Larsen (1,2), Inger Christine Munch (2,4)

1. Department of Ophthalmology, Rigshospitalet, Valdemar Hansens Vej 1-23, afsnit 37, 2600 Glostrup, Denmark.
2. Department of Clinical Medicine, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
3. National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
4. Department of Ophthalmology, Zealand University Hospital, Roskilde, Denmark.

Date: Sep 2019

Reference:   Hansen MH, Kessel L, Li XQ, Skovgaard AM, Larsen M, Munch IC. Axial length change and its relationship with baseline choroidal thickness - a five-year longitudinal study in Danish adolescents: the CCC2000 eye study. BMC Ophthalmol. 2020 Apr 15;20(1):152 [Link to open access paper]

Animal studies have suggested the choroid plays an active role in eye growth regulation, where fluctuations in choroidal thickness may depend on visual inputs to the retina.^1,2 Myopia is primarily thought to be caused by an abnormal elongation of the eye. Eyes that elongate excessively also have thinner choroid layers.^3,4

This longitudinal, population-based study investigated whether thinner sub-foveal choroid values at age 11 were predictive of axial eye elongation and myopia in adolescence.

The Copenhagen Child Cohort 2000 observational study followed 6090 children born in 2000 across 16 districts in Copenhagen, Denmark to study their mental health and physical growth. The children had eye examinations in 2011-12. Those eligible to participate in this study were invited for further examinations in 2016-17.

These eye examinations consisted of non-cycloplegic auto-refraction with subjective confirmation.  Myopia was defined as -0.50D or worse and only right eyes were measured. Axial length was measured, and sub-foveal choroidal thickness imaging was performed. Previous medical health information was provided by parents/guardians.

The 714 children who participated had a median age of 11.5yrs at baseline and 16.6yrs at follow-up. They showed a median increase in axial length of 248µm over this time.

The median spherical equivalent refraction was -0.75D for myopes and 0.0D for non-myopes, with no difference found due to the age or sex of the participants.

• For eyes without myopia at baseline, the axial length increased by 243µm with girls showing a 34µm higher increase in 5yr axial length compared to boys. However, axial length increased less for all children who were taller at baseline. In these children, a thicker choroid value at baseline was associated with 5yr axial length changes.
• For eyes with myopia at baseline, the axial length increased by 454µm and there was no difference in axial length changes between girls and boys. Being taller at baseline and having a thicker choroid layer at baseline were not associated with 5-year axial length change.

Longer baseline axial lengths were associated with a greater increase of axial change over the 5yr period for both myopic and non-myopic eyes.

There were 120 children who were not myopic at baseline but who had developed myopia by the follow-up time. The odds for incident myopia were found to increase 1.57 per each mm longer axial length at baseline.

The sub-foveal choroidal thickness at age 11yrs was not predictive of future myopia at age 16yrs.

Having a longer eye at age 11 was associated with longer eye lengths and future myopia by age 16 for myopes and non-myopes, and the odds for myopia increased with the axial length. Interestingly, baseline choroidal thickness in myopes did not predict future myopia progression, but baseline axial length did.

• Children with long eyes aged 11 may be at risk of myopia into adolescence, even if they are not yet myopic. 
• This may be particularly true if they are female, due to girls reaching puberty at an earlier age than boys. However, boys will be expected to experience eye growth too, albeit at a slightly later stage.

Eye care practitioners should consider monitoring children's axial eye growth where possible, as it can hold clues to their ocular development. Suggesting or reinforcing lifestyle advice may be appropriate for younger children with longer eyes.

Axial eye growth had increased along with choroidal thickness in non-myopic eyes. However, it had no effect for myopic eyes or on the incidence of myopia, suggesting that a thin choroid has no impact on future myopia development.

• Further studies can explore the association between thicker choroid layers and axial elongation for non-myopes.

Limitations to this study included:

• Non-cycloplegic auto-refraction, where there may be a risk of over-estimating myopia correction and prevalence
• The study was representative of the Danish population but may not be representative of myopia prevalence or rate of eye growth for other ethnicities
• There were only 2 time points in this study, meaning any short-term effect on axial length from choroid thickness may have been missed
• There was a small number of myopes relative to the study population, which may limit the significance of the findings.

Title: Axial length change and its relationship with baseline choroidal thickness - a five-year longitudinal study in Danish adolescents: the CCC2000 eye study

Authors: Mathias Hvidtfelt Hansen, Line Kessel, Xiao Qiang Li, Anne Mette Skovgaard, Michael Larsen, Inger Christine Munch

Purpose: Myopic eyes are longer than nonmyopic eyes and have thinner choroids. The purpose of present study was to investigate whether a thinner subfoveal choroid at 11 years of age predicted axial eye elongation and myopia during adolescence.

Methods: Longitudinal, population-based observational study. Axial length was measured using an interferometric device and choroidal thickness was measured by spectral-domain optical coherence tomography. Myopia was defined as non-cycloplegic subjective spherical equivalent refraction ≤ −0.50 diopters

Results: Right eyes of 714 children (317 boys) were examined at age (median (IQR)) 11.5 (0.6) years and 16.6 (0.3) years during which axial length (median (IQR)) increased by 243 (202) μm in eyes without myopia (n = 630) at baseline compared with 454 (549) μm in eyes with myopia (n = 84) at baseline, p < 0.0001. A thicker baseline subfoveal choroid was associated with increased five-year axial elongation after adjustment for baseline axial length in nonmyopic eyes (β = 27 μm/100 μm, 95%CI 6 to 48, p = 0.011) but not in myopic eyes (p = 0.34). Subfoveal choroidal thickness at 11 years of age did not predict incident myopia at 16 years of age (p = 0.11). Longer baseline axial length was associated with greater five-year axial elongation in both myopic (β = 196 μm/mm, 95%CI 127 to 265, p < 0.0001) and nonmyopic eyes (β = 28 μm/mm, 95%CI 7 to 49, p = 0.0085) and the odds for incident myopia increased with 1.57 (95%CI 1.18 to 2.09, p = 0.0020) per mm longer axial length at baseline.

Conclusions: A thin subfoveal choroid at age 11 years did not predict axial eye elongation and incident myopia from age 11 to 16 years. A longer eye at age 11 years was associated with greater subsequent axial eye elongation and with increased risk of incident myopia at age 16 years.

[Link to open access paper]