Accommodative Ocular Changes Include Choroidal Thinning, Eye Length Elongation

Choroidal thinning accounts for the majority of observed eye length increase in eyes with emmetropia or myopia during accommodation, according to research published in Ophthalmic and Physiological Optics. Individuals with myopia demonstrate greater accommodation-induced choroidal thinning compared with individuals with emmetropia, according to the report.  

Researchers enrolled 53 participants with myopia or emmetropia (age range, 18-27 years; 55% women) in the investigation, but included 37 (myopia, n=21; emmetropia, n=16) in the eye length assessment and 47 (myopia, n=30; emmetropia, n=17) in the choroidal thickness assessment. Participants underwent autorefraction and aberrometry, in addition to ciliary muscle dimension, choroidal thickness, and eye length measurements. The team assessed accommodative changes in participants’ right eyes at 0 diopters (D) and 6 D stimulation using 10° steps for 30° horizontal visual field and retinal locations. The study objective was to examine peripheral choroidal thinning occurring with accommodation and assess associations with eye length occurring at the same location.

“It is not known whether choroidal changes with accommodation also contribute to the changes in eye length that are measured in the periphery, and if this would also average 30%–50%,” the study authors note. “Characterizing the physiological ocular mechanisms activated during near work may increase the understanding of why near work is linked to myopia and subsequently the management of this refractive error.”

Overall, eye length increased by a mean 33 μm during accommodation (F_[1,200], 31.10; P <.001) and changes in eye length during accommodation depended on position (F_[6,200], 3.82; P =.001). The greatest increases occurred at the center (41 μm), while the smallest increases were noted at 20° nasally (26 μm). The investigators noted no significant differences between individuals with myopia and participants with emmetropia.

Conversely, overall choroidal thickness decreased by a mean 21 μm during accommodation (F_[1,276], 23.85; P <.001). Individuals with myopia demonstrated greater choroidal thinning compared with individuals with emmetropia (-23 vs -17 μm; P =.02).  Choroidal thinning accounted for approximately 60% of the eye length increases across the horizontal 30°, according to the report. 

“The physiological mechanisms responsible for the increased eye length during accommodation are not known, except that choroidal thinning contributes,” according to the researchers. “Since previous research and the current study both show that choroidal change does not account for all of the eye length change, it is possible that both choroidal thinning and stretching of the globe contribute to the eye length changes with accommodation.”

Study limitations include a small sample size and single center design. 

Disclosure: This research was supported by Carl Zeiss Vision. Please see the original reference for a full list of disclosures.