Abstract
Purpose :
It has previously been shown that imposed positive defocus induces significant changes in axial length and choroidal thickness after only 30 minutes. We investigated in young adult subjects whether these changes result from changes in ocular blood flow.
Methods :
Sixteen young adult subjects (average age: 28±3 years, average refraction: -0.75±1.65D withing the range: +1.7 to -6D) watched a movie from a large screen (LG OLED65C9, 65 inch, 2019) at 2 m distance. Fifteen minutes wash-out period (watching a movie in a dark room with habitual refractive error correction) was followed by 30 minutes of watching a movie with a monocular positive defocus (+2.5D) in the right eye and a habitual correction in the left eye. Changes in axial length and blood flow were measured in both eyes before and after the defocus. Eye biometry was measured by using low-coherent interferometer (LS 900 with autopositioning system; Haag-Streit, Switzerland). Blood flow was measured by using a laser speckle flowgraphy (LSFG) RetFlow unit (Nidek Co., LTD, Japan). Two regions were analyzed: (1) the macular area, where choroidal blood flow can be measured, and (2) the optic nerve head.
Results :
All subjects responded to imposed positive defocus as previously found: hyperopes and emmetropes displayed eye shortening while myopes showed axial elongation (Pearson’s correlation coefficient between axial length change and refractive state: R2 = 0.50, p<0.01, Figure 1A). Control eyes did not show any significant changes in axial length after 30 minutes of watching a movie. Changes in axial length were significantly correlated with changes in choroidal blood flow in the macular region (R2 = 0.43, p<0.01, Figure 1B) and in the optic nerve head (R2 = 0.27, p<0.05, Figure 1C).
Conclusions :
Transient changes in axial length induced by positive defocus appear to be linked to changes in choroidal blood flow which may affect the thickness of the choroid. Blood flow in the macular region showed better correlation to the axial length changes than blood flow in the optic nerve probably because the macular LSFG measurement is less affected by the retinal circulation.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.