Influence of artificially elevating intraocular pressure on axial length in healthy adults

Abstract

Purpose : To investigate the impact of artificially elevated intraocular pressure (IOP) on clinical measures of axial length (AL) and a range of ocular biometric measures in a cohort of healthy adults.

Methods : Twenty-eight eyes of fourteen young adult participants (7 myopes and 7 emmetropes, median age 20 (range, 18–22) years) had their blood pressure, height, weight, and ocular measurements (spherical equivalent refraction (SER), AL, IOP, central corneal thickness, corneal curvatures) recorded at sitting position. AL, IOP and corneal curvature measurements were repeated with participants inverted by 40° in the Trendelenburg position (TLP) for 2 min. A custom-built rig allowed the positioning of the IOLMaster perpendicular to the corneal surface, while IOP was measured with a hand-held Perkins tonometer. The change in ocular parameters (sitting versus inverted) were determined (mean ± SD) and their association with SER was analyzed using linear mixed model (LMM) fitted by restricted maximum likelihood with eyes nested within subjects as random intercept.

Results : TLP led to a significant increase in IOP (mean change, 10.9 ± 3.5 mmHg, P <0.001) and AL elongation (mean change, 26.0 ± 18.5 µm, P <0.001), but neither corneal steep (-0.08 ± 0.5 D) nor flat (0.03 ± 0.15 D) meridians. A significant positive association was found between the changes in IOP and AL (r = 0.577, P =0.001, Fig. 1). LMM adjusted for corneal curvature and thickness demonstrated a differential response in AL elongation of 2.91 µm (P =0.003), 4.22 µm (P < 0.001) and 0.51 µm (P =0.773) for every 1-mmHg rise in IOP for all, myopes (SER ≥-0.50 D) and emmetropes (SER <-0.50 D), respectively. Large IOP change (≥10 mmHg) remained to have a greater impact on the AL change for myopes (4.29 µm per mmHg, P =0.003) than in emmetropes (1.34 µm per mmHg, P =0.60) (Fig. 2).

Conclusions : IOP increase induced by TLP is associated with a small, but significant, AL elongation. An equivalent increase in IOP generated a greater increase of AL for myopic eyes compared to emmetropic eyes, especially with larger changes in IOP.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Fig. 1. Change in AL as a function of the change in IOP. Difference in mean IOP plotted against the difference in mean AL from each participant’s sitting and inverted positions.

 

Fig. 2. Distribution of AL change across SER and IOP groups. Wider sections (Kernel density) on the violin plot represent higher probability distribution of AL change.