Choroidal thickening is thought to occur as a physiological response to orthokeratology and atropine eye drops, contributing to apparent reductions in axial length (AL). (As a brief reminder, longer ALs often correlate with higher levels of myopia.) Two recent studies have brought into question the significance of choroidal thickening as it relates to long-term treatment success.

This month’s column explores these studies and their clinical implications.

Studies
The two studies indicate that the extent of choroidal thickening does not always correlate directly with the magnitude of AL reduction, suggesting that other factors may contribute to these changes.^1,2

This implies that AL shortening due to choroidal thickening may not signify a true halt in myopia progression, but rather a temporary treatment response. 

Consequently, choroidal thickening can create an impression of treatment success that may not be sustained.

Additionally, several factors, such as fluctuations in systemic blood pressure, physical activity, lighting conditions, and hormonal changes, can induce temporary, yet clinically significant variations in choroidal thickness, muddying the treatment efficacy waters even more.

Moreover, limited studies have validated the methodological agreement between choroidal thickness measurements obtained from optical coherence tomography B-scan images and axial dimensions from A-scan optical biometry, making direct comparisons between these measures potentially unreliable.

Clinical implications
These studies indicate that early AL reduction due to choroidal thickening may be transient, with the choroid gradually returning to baseline thickness, while the eye continues to elongate.

As a result, clinicians must be cautious when interpreting AL measurements during the initial treatment period. Additionally, they must monitor their myopia patients over multiple visits, alongside other factors that can determine treatment effectiveness, such as refractive error stability.

Further, AL reduction should be assessed in the context of diurnal variations (which can change IOP and choroidal volume), patient positioning (head tilt or eye alignment^3,4), and equipment calibration. All influence measurement accuracy.

Take home
In summary, choroidal thickening can produce a temporary effect that may not equate to long-term benefits, so the clinician should practice caution and assess AL reduction in the context of other influencing factors.

References: 

1. Chen Z, Xue Feng, Zhou J, Qu X, Zhou X. Effects of Orthokeratology on Choroidal Thickness and Axial Length. Optom Vis Sci. 2016;93(9):1064-71. doi: 10.1097/OPX.0000000000000894.

2. Zhu, Q., Zhao, Q. Short-term effect of orthokeratology lens wear on choroidal blood flow in children with low and moderate myopia. Sci Rep. 2022;12(1):17653. doi: 10.1038/s41598-022-21594-6.

3. Zhao W, Li Z, Hu Y, et al. Short-term effects of atropine combined with orthokeratology (ACO) on choroidal thickness. Cont Lens Anterior Eye. 2021;44(3):101348. doi: 10.1016/j.clae.2020.06.006. 

4. Sikorski, BL, Suchon P. OCT Biometry
(B-OCT): A New Method for Measuring Ocular Axial Dimensions, J Ophthalmol. 2019:9192456. doi: 10.1155/2019/9192456. 

Maria Liu, OD, is an associate professor at Herbert Wertheim School of Optometry and Vision Science, University of California Berkeley. She is also the founder of the Myopia Control Clinic, UC Berkeley Eye Center. She received her bachelor’s degree in clinical medicine from Peking University, her OD from Pacific University, and her PhD and MPH from UC Berkeley. She is a world-recognized clinical researcher in myopia. Dr. Liu is a consultant for Coopervision, Essilor, and Zeiss Vision China.